update copyright years

doc: update FAQ on improving accuracy
doc: mention dependency of net corrections on HW timestamping
2025-12-03 17:45:07 -05:00 · 2023-12-05 14:22:10 +01:00 · 2023-12-05 14:22:10 +01:00 · 2023-12-05 14:22:08 +01:00 · 2023-12-04 16:50:51 +01:00 · 2023-11-28 12:21:23 +01:00
136 changed files with 5816 additions and 1522 deletions
--- a/Makefile.in
+++ b/Makefile.in
@@ -33,9 +33,11 @@ CFLAGS = @CFLAGS@
 CPPFLAGS = @CPPFLAGS@
 LDFLAGS = @LDFLAGS@

+GETDATE_CFLAGS = @GETDATE_CFLAGS@
+
 EXTRA_OBJS = @EXTRA_OBJS@

-OBJS = array.o cmdparse.o conf.o local.o logging.o main.o memory.o \
+OBJS = array.o cmdparse.o conf.o local.o logging.o main.o memory.o quantiles.o \
       reference.o regress.o rtc.o samplefilt.o sched.o socket.o sources.o sourcestats.o \
       stubs.o smooth.o sys.o sys_null.o tempcomp.o util.o $(EXTRA_OBJS)

@@ -61,6 +63,8 @@ chronyd : $(OBJS)
 chronyc : $(CLI_OBJS)
 	$(CC) $(CFLAGS) -o chronyc $(CLI_OBJS) $(LDFLAGS) $(LIBS) $(EXTRA_CLI_LIBS)

+getdate.o: CFLAGS += $(GETDATE_CFLAGS)
+
 distclean : clean
 	$(MAKE) -C doc distclean
 	$(MAKE) -C test/unit distclean
--- a/61
+++ b/61
@@ -1,3 +1,64 @@
+New in version 4.5
+==================
+
+Enhancements
+------------
+* Add support for AES-GCM-SIV in GnuTLS
+* Add support for corrections from PTP transparent clocks
+* Add support for systemd socket activation
+
+Bug fixes
+---------
+* Fix presend in interleaved mode
+* Fix reloading of modified sources from sourcedir
+
+New in version 4.4
+==================
+
+Enhancements
+------------
+* Add support for AES-GCM-SIV with Nettle >= 3.9 to shorten NTS
+  cookies to avoid some length-specific blocking of NTP on Internet
+* Add support for multiple refclocks using extpps option on one PHC
+* Add maxpoll option to hwtimestamp directive to improve PHC tracking
+  with low packet rates
+* Add hwtstimeout directive to configure timeout for late timestamps
+* Handle late hardware transmit timestamps of NTP requests on all sockets
+* Handle mismatched 32/64-bit time_t in SOCK refclock samples
+* Improve source replacement
+* Log important changes made by command requests (chronyc)
+* Refresh address of NTP sources periodically
+* Request nanosecond kernel RX timestamping on FreeBSD
+* Set DSCP for IPv6 packets
+* Shorten NTS-KE retry interval when network is down
+* Update seccomp filter for musl
+* Warn if loading keys from file with unexpected permissions
+* Warn if source selection fails or falseticker is detected
+* Add selectopts command to modify source-specific selection options
+* Add timestamp sources to serverstats report and make its fields 64-bit
+* Add -e option to chronyc to indicate end of response
+
+New in version 4.3
+==================
+
+Enhancements
+------------
+* Add local option to refclock directive to stabilise system clock
+  with more stable free-running clock (e.g. TCXO, OCXO)
+* Add maxdelayquant option to server/pool/peer directive to replace
+  maxdelaydevratio filter with long-term quantile-based filtering
+* Add selection option to log directive
+* Allow external PPS in PHC refclock without configurable pin
+* Don't accept first interleaved response to minimise error in delay
+* Don't use arc4random on Linux to avoid server performance loss
+* Improve filter option to better handle missing NTP samples
+* Improve stability with hardware timestamping and PHC refclock
+* Update seccomp filter
+
+Bug fixes
+---------
+* Fix waitsync command to reconnect when not getting response
+
 New in version 4.2
 ==================

--- a/33
+++ b/33
@@ -47,32 +47,7 @@ Frequently Asked Questions (FAQ).
 The documentation is also available on the chrony web pages, accessible
 through the URL 

-    https://chrony.tuxfamily.org/
-
-Where are new versions announced?
-=================================
-
-There is a low volume mailing list where new versions and other
-important news relating to chrony are announced.  You can join this list
-by sending mail with the subject "subscribe" to
-
-chrony-announce-request@chrony.tuxfamily.org
-
-How can I get support for chrony?
-=================================
-
-There are two other mailing lists relating to chrony.  chrony-users is a
-discussion list for users, e.g. for questions about chrony configuration
-and bug reports.  chrony-dev is a more technical list for developers,
-e.g. for submitting patches and discussing how new features should be
-implemented.  To subscribe to either of these lists, send a message with
-the subject "subscribe" to
-
-chrony-users-request@chrony.tuxfamily.org
-or
-chrony-dev-request@chrony.tuxfamily.org
-
-as applicable.
+    https://chrony-project.org/

 License
 =======
@@ -108,6 +83,7 @@ Erik Bryer <ebryer@spots.ab.ca>
 Jonathan Cameron <jic23@cam.ac.uk>
 Bryan Christianson <bryan@whatroute.net>
 Juliusz Chroboczek <jch@pps.jussieu.fr>
+Dan Drown <dan-ntp@drown.org>
 Kamil Dudka <kdudka@redhat.com>
 Christian Ehrhardt <christian.ehrhardt@canonical.com>
 Paul Elliott <pelliott@io.com>
@@ -121,6 +97,7 @@ Juergen Hannken-Illjes <hannken@eis.cs.tu-bs.de>
 John Hasler <john@dhh.gt.org>
 Tjalling Hattink <t.hattink@fugro.nl>
 Liam Hatton <me@liamhatton.com>
+Holger Hoffstätte <holger@applied-asynchrony.com>
 Jachym Holecek <jakym@volny.cz>
 Håkan Johansson <f96hajo@chalmers.se>
 Jim Knoble <jmknoble@pobox.com>
@@ -136,15 +113,19 @@ Victor Moroz <vim@prv.adlum.ru>
 Kalle Olavi Niemitalo  <tosi@stekt.oulu.fi>
 Frank Otto <sandwichmacher@web.de>
 Denny Page <dennypage@me.com>
+Rupesh Patel <rupatel@redhat.com>
 Chris Perl <cperl@janestreet.com>
 Gautier PHILIPPON <gautier.philippon@ensimag.grenoble-inp.fr>
 Andreas Piesk <apiesk@virbus.de>
+Mike Ryan <msr@hsilop.net>
 Baruch Siach <baruch@tkos.co.il>
+Josef 'Jeff' Sipek <jeffpc@josefsipek.net>
 Foster Snowhill <forst@forstwoof.ru>
 Andreas Steinmetz <ast@domdv.de>
 NAKAMURA Takumi <takumi@ps.sakura.ne.jp>
 Timo Teras <timo.teras@iki.fi>
 Bill Unruh <unruh@physics.ubc.ca>
+Luke Valenta <lvalenta@cloudflare.com>
 Stephen Wadeley <swadeley@redhat.com>
 Bernhard Weiss <lisnablagh@web.de>
 Wolfgang Weisselberg <weissel@netcologne.de>
--- a/array.c
+++ b/array.c
@@ -116,6 +116,21 @@ ARR_AppendElement(ARR_Instance array, void *element)
  memcpy(e, element, array->elem_size);
 }

+void
+ARR_RemoveElement(ARR_Instance array, unsigned int index)
+{
+  void *e, *l;
+
+  e = ARR_GetElement(array, index);
+  l = ARR_GetElement(array, array->used - 1);
+
+  if (e < l)
+    memmove(e, (char *)e + array->elem_size, (char *)l - (char *)e);
+  array->used--;
+
+  realloc_array(array, array->used);
+}
+
 void
 ARR_SetSize(ARR_Instance array, unsigned int size)
 {
--- a/array.h
+++ b/array.h
@@ -47,6 +47,9 @@ extern void *ARR_GetElements(ARR_Instance array);
 /* Add a new element to the end of the array */
 extern void ARR_AppendElement(ARR_Instance array, void *element);

+/* Remove element with given index */
+extern void ARR_RemoveElement(ARR_Instance array, unsigned int index);
+
 /* Set the size of the array */
 extern void ARR_SetSize(ARR_Instance array, unsigned int size);

--- a/candm.h
+++ b/candm.h
@@ -109,7 +109,8 @@
 #define REQ_SELECT_DATA 69
 #define REQ_RELOAD_SOURCES 70
 #define REQ_DOFFSET2 71
-#define N_REQUEST_TYPES 72
+#define REQ_MODIFY_SELECTOPTS 72
+#define N_REQUEST_TYPES 73

 /* Structure used to exchange timespecs independent of time_t size */
 typedef struct {
@@ -121,6 +122,12 @@ typedef struct {
 /* This is used in tv_sec_high for 32-bit timestamps */
 #define TV_NOHIGHSEC 0x7fffffff

+/* Structure for 64-bit integers (not requiring 64-bit alignment) */
+typedef struct {
+  uint32_t high;
+  uint32_t low;
+} Integer64;
+
 /* 32-bit floating-point format consisting of 7-bit signed exponent
   and 25-bit signed coefficient without hidden bit.
   The result is calculated as: 2^(exp - 25) * coef */
@@ -270,7 +277,8 @@ typedef struct {
 #define REQ_ADDSRC_BURST 0x100
 #define REQ_ADDSRC_NTS 0x200
 #define REQ_ADDSRC_COPY 0x400
-#define REQ_ADDSRC_EF_EXP1 0x800
+#define REQ_ADDSRC_EF_EXP_MONO_ROOT 0x800
+#define REQ_ADDSRC_EF_EXP_NET_CORRECTION 0x1000

 typedef struct {
  uint32_t type;
@@ -296,7 +304,8 @@ typedef struct {
  uint32_t flags;
  int32_t filter_length;
  uint32_t cert_set;
-  uint32_t reserved[2];
+  Float max_delay_quant;
+  uint32_t reserved[1];
  int32_t EOR;
 } REQ_NTP_Source;

@@ -370,6 +379,15 @@ typedef struct {
  int32_t EOR;
 } REQ_SelectData;

+/* Mask and options reuse the REQ_ADDSRC flags */
+typedef struct {
+  IPAddr address;
+  uint32_t ref_id;
+  uint32_t mask;
+  uint32_t options;
+  int32_t EOR;
+} REQ_Modify_SelectOpts;
+
 /* ================================================== */

 #define PKT_TYPE_CMD_REQUEST 1
@@ -476,6 +494,7 @@ typedef struct {
    REQ_NTPSourceName ntp_source_name;
    REQ_AuthData auth_data;
    REQ_SelectData select_data;
+    REQ_Modify_SelectOpts modify_select_opts;
  } data; /* Command specific parameters */

  /* Padding used to prevent traffic amplification.  It only defines the
@@ -518,7 +537,8 @@ typedef struct {
 #define RPY_SERVER_STATS2 22
 #define RPY_SELECT_DATA 23
 #define RPY_SERVER_STATS3 24
-#define N_REPLY_TYPES 25
+#define RPY_SERVER_STATS4 25
+#define N_REPLY_TYPES 26

 /* Status codes */
 #define STT_SUCCESS 0
@@ -653,17 +673,24 @@ typedef struct {
 } RPY_ClientAccessesByIndex;

 typedef struct {
-  uint32_t ntp_hits;
-  uint32_t nke_hits;
-  uint32_t cmd_hits;
-  uint32_t ntp_drops;
-  uint32_t nke_drops;
-  uint32_t cmd_drops;
-  uint32_t log_drops;
-  uint32_t ntp_auth_hits;
-  uint32_t ntp_interleaved_hits;
-  uint32_t ntp_timestamps;
-  uint32_t ntp_span_seconds;
+  Integer64 ntp_hits;
+  Integer64 nke_hits;
+  Integer64 cmd_hits;
+  Integer64 ntp_drops;
+  Integer64 nke_drops;
+  Integer64 cmd_drops;
+  Integer64 log_drops;
+  Integer64 ntp_auth_hits;
+  Integer64 ntp_interleaved_hits;
+  Integer64 ntp_timestamps;
+  Integer64 ntp_span_seconds;
+  Integer64 ntp_daemon_rx_timestamps;
+  Integer64 ntp_daemon_tx_timestamps;
+  Integer64 ntp_kernel_rx_timestamps;
+  Integer64 ntp_kernel_tx_timestamps;
+  Integer64 ntp_hw_rx_timestamps;
+  Integer64 ntp_hw_tx_timestamps;
+  Integer64 reserved[4];
  int32_t EOR;
 } RPY_ServerStats;

@@ -733,7 +760,8 @@ typedef struct {
  uint32_t total_tx_count;
  uint32_t total_rx_count;
  uint32_t total_valid_count;
-  uint32_t reserved[4];
+  uint32_t total_good_count;
+  uint32_t reserved[3];
  int32_t EOR;
 } RPY_NTPData;

--- a/client.c
+++ b/client.c
@@ -4,7 +4,7 @@
 **********************************************************************
 * Copyright (C) Richard P. Curnow  1997-2003
 * Copyright (C) Lonnie Abelbeck  2016, 2018
- * Copyright (C) Miroslav Lichvar  2009-2021
+ * Copyright (C) Miroslav Lichvar  2009-2023
 * 
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of version 2 of the GNU General Public License as
@@ -71,6 +71,8 @@ static int source_names = 0;

 static int csv_mode = 0;

+static int end_dot = 0;
+
 /* ================================================== */
 /* Log a message. This is a minimalistic replacement of the logging.c
   implementation to avoid linking with it and other modules. */
@@ -283,6 +285,9 @@ open_io(void)
    close_io();
  }

+  /* Start from the first address if called again */
+  address_index = 0;
+
  return 0;
 }

@@ -866,6 +871,17 @@ process_cmd_doffset(CMD_Request *msg, char *line)

 /* ================================================== */

+static int
+convert_addsrc_sel_options(int options)
+{
+  return (options & SRC_SELECT_PREFER ? REQ_ADDSRC_PREFER : 0) |
+         (options & SRC_SELECT_NOSELECT ? REQ_ADDSRC_NOSELECT : 0) |
+         (options & SRC_SELECT_TRUST ? REQ_ADDSRC_TRUST : 0) |
+         (options & SRC_SELECT_REQUIRE ? REQ_ADDSRC_REQUIRE : 0);
+}
+
+/* ================================================== */
+
 static int
 process_cmd_add_source(CMD_Request *msg, char *line)
 {
@@ -942,13 +958,15 @@ process_cmd_add_source(CMD_Request *msg, char *line)
          (data.params.burst ? REQ_ADDSRC_BURST : 0) |
          (data.params.nts ? REQ_ADDSRC_NTS : 0) |
          (data.params.copy ? REQ_ADDSRC_COPY : 0) |
-          (data.params.ext_fields & NTP_EF_FLAG_EXP1 ? REQ_ADDSRC_EF_EXP1 : 0) |
-          (data.params.sel_options & SRC_SELECT_PREFER ? REQ_ADDSRC_PREFER : 0) |
-          (data.params.sel_options & SRC_SELECT_NOSELECT ? REQ_ADDSRC_NOSELECT : 0) |
-          (data.params.sel_options & SRC_SELECT_TRUST ? REQ_ADDSRC_TRUST : 0) |
-          (data.params.sel_options & SRC_SELECT_REQUIRE ? REQ_ADDSRC_REQUIRE : 0));
+          (data.params.ext_fields & NTP_EF_FLAG_EXP_MONO_ROOT ?
+           REQ_ADDSRC_EF_EXP_MONO_ROOT : 0) |
+          (data.params.ext_fields & NTP_EF_FLAG_EXP_NET_CORRECTION ?
+           REQ_ADDSRC_EF_EXP_NET_CORRECTION : 0) |
+          convert_addsrc_sel_options(data.params.sel_options));
      msg->data.ntp_source.filter_length = htonl(data.params.filter_length);
      msg->data.ntp_source.cert_set = htonl(data.params.cert_set);
+      msg->data.ntp_source.max_delay_quant =
+        UTI_FloatHostToNetwork(data.params.max_delay_quant);
      memset(msg->data.ntp_source.reserved, 0, sizeof (msg->data.ntp_source.reserved));

      result = 1;
@@ -1008,6 +1026,7 @@ give_help(void)
    "sources [-a] [-v]\0Display information about current sources\0"
    "sourcestats [-a] [-v]\0Display statistics about collected measurements\0"
    "selectdata [-a] [-v]\0Display information about source selection\0"
+    "selectopts <address|refid> <+|-options>\0Modify selection options\0"
    "reselect\0Force reselecting synchronisation source\0"
    "reselectdist <dist>\0Modify reselection distance\0"
    "\0\0"
@@ -1122,8 +1141,8 @@ command_name_generator(const char *text, int state)
    "manual", "maxdelay", "maxdelaydevratio", "maxdelayratio", "maxpoll",
    "maxupdateskew", "minpoll", "minstratum", "ntpdata", "offline", "online", "onoffline",
    "polltarget", "quit", "refresh", "rekey", "reload", "reselect", "reselectdist", "reset",
-    "retries", "rtcdata", "selectdata", "serverstats", "settime", "shutdown", "smoothing",
-    "smoothtime", "sourcename", "sources", "sourcestats",
+    "retries", "rtcdata", "selectdata", "selectopts", "serverstats", "settime",
+    "shutdown", "smoothing", "smoothtime", "sourcename", "sources", "sourcestats",
    "timeout", "tracking", "trimrtc", "waitsync", "writertc",
    NULL
  };
@@ -1151,7 +1170,7 @@ command_name_generator(const char *text, int state)

  while ((name = names[tab_complete_index][list_index++])) {
    if (strncmp(name, text, len) == 0) {
-      return strdup(name);
+      return Strdup(name);
    }
  }

@@ -1457,24 +1476,24 @@ request_reply(CMD_Request *request, CMD_Reply *reply, int requested_reply, int v
 /* ================================================== */

 static void
-print_seconds(unsigned long s)
+print_seconds(uint32_t s)
 {
-  unsigned long d;
+  uint32_t d;

  if (s == (uint32_t)-1) {
    printf("   -");
  } else if (s < 1200) {
-    printf("%4lu", s);
+    printf("%4"PRIu32, s);
  } else if (s < 36000) {
-    printf("%3lum", s / 60);
+    printf("%3"PRIu32"m", s / 60);
  } else if (s < 345600) {
-    printf("%3luh", s / 3600);
+    printf("%3"PRIu32"h", s / 3600);
  } else {
    d = s / 86400;
    if (d > 999) {
-      printf("%3luy", d / 365);
+      printf("%3"PRIu32"y", d / 365);
    } else {
-      printf("%3lud", d);
+      printf("%3"PRIu32"d", d);
    }
  }
 }
@@ -1605,8 +1624,9 @@ print_report(const char *format, ...)
  va_list ap;
  int i, field, sign, width, prec, spec;
  const char *string;
-  unsigned long long_uinteger;
  unsigned int uinteger;
+  uint64_t uinteger64;
+  uint32_t uinteger32;
  int integer;
  struct timespec *ts;
  struct tm *tm;
@@ -1704,9 +1724,9 @@ print_report(const char *format, ...)
               spec == 'O' ? "seconds" : "ppm",
               (dbl > 0.0) ^ (spec != 'O') ? "slow" : "fast");
        break;
-      case 'I': /* interval with unit */
-        long_uinteger = va_arg(ap, unsigned long);
-        print_seconds(long_uinteger);
+      case 'I': /* uint32_t interval with unit */
+        uinteger32 = va_arg(ap, uint32_t);
+        print_seconds(uinteger32);
        break;
      case 'L': /* leap status */
        integer = va_arg(ap, int);
@@ -1773,8 +1793,8 @@ print_report(const char *format, ...)
          print_freq_ppm(dbl);
        break;
      case 'R': /* reference ID in hexdecimal */
-        long_uinteger = va_arg(ap, unsigned long);
-        printf("%08lX", long_uinteger);
+        uinteger32 = va_arg(ap, uint32_t);
+        printf("%08"PRIX32, uinteger32);
        break;
      case 'S': /* offset with unit */
        dbl = va_arg(ap, double);
@@ -1791,14 +1811,18 @@ print_report(const char *format, ...)
        strftime(buf, sizeof (buf), "%a %b %d %T %Y", tm);
        printf("%s", buf);
        break;
-      case 'U': /* unsigned long in decimal */
-        long_uinteger = va_arg(ap, unsigned long);
-        printf("%*lu", width, long_uinteger);
+      case 'U': /* uint32_t in decimal */
+        uinteger32 = va_arg(ap, uint32_t);
+        printf("%*"PRIu32, width, uinteger32);
        break;
      case 'V': /* timespec as seconds since epoch */
        ts = va_arg(ap, struct timespec *);
        printf("%s", UTI_TimespecToString(ts));
        break;
+      case 'Q': /* uint64_t in decimal */
+        uinteger64 = va_arg(ap, uint64_t);
+        printf("%*"PRIu64, width, uinteger64);
+        break;
      case 'b': /* unsigned int in binary */
        uinteger = va_arg(ap, unsigned int);
        for (i = prec - 1; i >= 0; i--)
@@ -1958,7 +1982,7 @@ process_cmd_sources(char *line)
  IPAddr ip_addr;
  uint32_t i, mode, n_sources;
  char name[256], mode_ch, state_ch;
-  int all, verbose;
+  int all, verbose, ref;

  parse_sources_options(line, &all, &verbose);
  
@@ -1995,9 +2019,8 @@ process_cmd_sources(char *line)
    if (!all && ip_addr.family == IPADDR_ID)
      continue;

-    format_name(name, sizeof (name), 25,
-                mode == RPY_SD_MD_REF && ip_addr.family == IPADDR_INET4,
-                ip_addr.addr.in4, 1, &ip_addr);
+    ref = mode == RPY_SD_MD_REF && ip_addr.family == IPADDR_INET4;
+    format_name(name, sizeof (name), 25, ref, ref ? ip_addr.addr.in4 : 0, 1, &ip_addr);

    switch (mode) {
      case RPY_SD_MD_CLIENT:
@@ -2046,7 +2069,7 @@ process_cmd_sources(char *line)
                 ntohs(reply.data.source_data.stratum),
                 (int16_t)ntohs(reply.data.source_data.poll),
                 ntohs(reply.data.source_data.reachability),
-                 (unsigned long)ntohl(reply.data.source_data.since_sample),
+                 ntohl(reply.data.source_data.since_sample),
                 UTI_FloatNetworkToHost(reply.data.source_data.latest_meas),
                 UTI_FloatNetworkToHost(reply.data.source_data.orig_latest_meas),
                 UTI_FloatNetworkToHost(reply.data.source_data.latest_meas_err),
@@ -2107,9 +2130,9 @@ process_cmd_sourcestats(char *line)

    print_report("%-25s %3U %3U  %I %+P %P  %+S  %S\n",
                 name,
-                 (unsigned long)ntohl(reply.data.sourcestats.n_samples),
-                 (unsigned long)ntohl(reply.data.sourcestats.n_runs),
-                 (unsigned long)ntohl(reply.data.sourcestats.span_seconds),
+                 ntohl(reply.data.sourcestats.n_samples),
+                 ntohl(reply.data.sourcestats.n_runs),
+                 ntohl(reply.data.sourcestats.span_seconds),
                 UTI_FloatNetworkToHost(reply.data.sourcestats.resid_freq_ppm),
                 UTI_FloatNetworkToHost(reply.data.sourcestats.skew_ppm),
                 UTI_FloatNetworkToHost(reply.data.sourcestats.est_offset),
@@ -2157,7 +2180,7 @@ process_cmd_tracking(char *line)
               "Root dispersion : %.9f seconds\n"
               "Update interval : %.1f seconds\n"
               "Leap status     : %L\n",
-               (unsigned long)ref_id, name,
+               ref_id, name,
               ntohs(reply.data.tracking.stratum),
               &ref_time,
               UTI_FloatNetworkToHost(reply.data.tracking.current_correction),
@@ -2245,10 +2268,10 @@ process_cmd_authdata(char *line)

    print_report("%-27s %4s %5U %4d %4d %I %4d %4d %4d %4d\n",
                 name, mode_str,
-                 (unsigned long)ntohl(reply.data.auth_data.key_id),
+                 ntohl(reply.data.auth_data.key_id),
                 ntohs(reply.data.auth_data.key_type),
                 ntohs(reply.data.auth_data.key_length),
-                 (unsigned long)ntohl(reply.data.auth_data.last_ke_ago),
+                 ntohl(reply.data.auth_data.last_ke_ago),
                 ntohs(reply.data.auth_data.ke_attempts),
                 ntohs(reply.data.auth_data.nak),
                 ntohs(reply.data.auth_data.cookies),
@@ -2341,18 +2364,18 @@ process_cmd_ntpdata(char *line)
                 "RX timestamping : %N\n"
                 "Total TX        : %U\n"
                 "Total RX        : %U\n"
-                 "Total valid RX  : %U\n",
-                 UTI_IPToString(&remote_addr), (unsigned long)UTI_IPToRefid(&remote_addr),
+                 "Total valid RX  : %U\n"
+                 "Total good RX   : %U\n",
+                 UTI_IPToString(&remote_addr), UTI_IPToRefid(&remote_addr),
                 ntohs(reply.data.ntp_data.remote_port),
-                 UTI_IPToString(&local_addr), (unsigned long)UTI_IPToRefid(&local_addr),
+                 UTI_IPToString(&local_addr), UTI_IPToRefid(&local_addr),
                 reply.data.ntp_data.leap, reply.data.ntp_data.version,
                 reply.data.ntp_data.mode, reply.data.ntp_data.stratum,
                 reply.data.ntp_data.poll, UTI_Log2ToDouble(reply.data.ntp_data.poll),
                 reply.data.ntp_data.precision, UTI_Log2ToDouble(reply.data.ntp_data.precision),
                 UTI_FloatNetworkToHost(reply.data.ntp_data.root_delay),
                 UTI_FloatNetworkToHost(reply.data.ntp_data.root_dispersion),
-                 (unsigned long)ntohl(reply.data.ntp_data.ref_id),
-                 reply.data.ntp_data.stratum <= 1 ?
+                 ntohl(reply.data.ntp_data.ref_id), reply.data.ntp_data.stratum <= 1 ?
                   UTI_RefidToString(ntohl(reply.data.ntp_data.ref_id)) : "",
                 &ref_time,
                 UTI_FloatNetworkToHost(reply.data.ntp_data.offset),
@@ -2366,9 +2389,10 @@ process_cmd_ntpdata(char *line)
                 ntohs(reply.data.ntp_data.flags) & RPY_NTP_FLAG_INTERLEAVED,
                 ntohs(reply.data.ntp_data.flags) & RPY_NTP_FLAG_AUTHENTICATED,
                 reply.data.ntp_data.tx_tss_char, reply.data.ntp_data.rx_tss_char,
-                 (unsigned long)ntohl(reply.data.ntp_data.total_tx_count),
-                 (unsigned long)ntohl(reply.data.ntp_data.total_rx_count),
-                 (unsigned long)ntohl(reply.data.ntp_data.total_valid_count),
+                 ntohl(reply.data.ntp_data.total_tx_count),
+                 ntohl(reply.data.ntp_data.total_rx_count),
+                 ntohl(reply.data.ntp_data.total_valid_count),
+                 ntohl(reply.data.ntp_data.total_good_count),
                 REPORT_END);
  }

@@ -2396,12 +2420,12 @@ process_cmd_selectdata(char *line)
  n_sources = ntohl(reply.data.n_sources.n_sources);

  if (verbose) {
-    printf(    "  .-- State: N - noselect, M - missing samples, d/D - large distance,\n");
-    printf(    " /           ~ - jittery, w/W - waits for others, T - not trusted,\n");
-    printf(    "|            x - falseticker, P - not preferred, U - waits for update,\n");
-    printf(    "|            S - stale, O - orphan, + - combined, * - best.\n");
-    printf(    "|        Effective options ------.  (N - noselect, P - prefer\n");
-    printf(    "|       Configured options -.     \\  T - trust, R - require)\n");
+    printf(    "  . State: N - noselect, s - unsynchronised, M - missing samples,\n");
+    printf(    " /         d/D - large distance, ~ - jittery, w/W - waits for others,\n");
+    printf(    "|          S - stale, O - orphan, T - not trusted, P - not preferred,\n");
+    printf(    "|          U - waits for update,, x - falseticker, + - combined, * - best.\n");
+    printf(    "|   Effective options   ---------.  (N - noselect, P - prefer\n");
+    printf(    "|   Configured options  ----.     \\  T - trust, R - require)\n");
    printf(    "|   Auth. enabled (Y/N) -.   \\     \\     Offset interval --.\n");
    printf(    "|                        |    |     |                       |\n");
  }
@@ -2440,7 +2464,7 @@ process_cmd_selectdata(char *line)
                 eff_options & RPY_SD_OPTION_TRUST ? 'T' : '-',
                 eff_options & RPY_SD_OPTION_REQUIRE ? 'R' : '-',
                 '-',
-                 (unsigned long)ntohl(reply.data.select_data.last_sample_ago),
+                 ntohl(reply.data.select_data.last_sample_ago),
                 UTI_FloatNetworkToHost(reply.data.select_data.score),
                 UTI_FloatNetworkToHost(reply.data.select_data.lo_limit),
                 UTI_FloatNetworkToHost(reply.data.select_data.hi_limit),
@@ -2460,31 +2484,43 @@ process_cmd_serverstats(char *line)
  CMD_Reply reply;

  request.command = htons(REQ_SERVER_STATS);
-  if (!request_reply(&request, &reply, RPY_SERVER_STATS3, 0))
+  if (!request_reply(&request, &reply, RPY_SERVER_STATS4, 0))
    return 0;

-  print_report("NTP packets received       : %U\n"
-               "NTP packets dropped        : %U\n"
-               "Command packets received   : %U\n"
-               "Command packets dropped    : %U\n"
-               "Client log records dropped : %U\n"
-               "NTS-KE connections accepted: %U\n"
-               "NTS-KE connections dropped : %U\n"
-               "Authenticated NTP packets  : %U\n"
-               "Interleaved NTP packets    : %U\n"
-               "NTP timestamps held        : %U\n"
-               "NTP timestamp span         : %U\n",
-               (unsigned long)ntohl(reply.data.server_stats.ntp_hits),
-               (unsigned long)ntohl(reply.data.server_stats.ntp_drops),
-               (unsigned long)ntohl(reply.data.server_stats.cmd_hits),
-               (unsigned long)ntohl(reply.data.server_stats.cmd_drops),
-               (unsigned long)ntohl(reply.data.server_stats.log_drops),
-               (unsigned long)ntohl(reply.data.server_stats.nke_hits),
-               (unsigned long)ntohl(reply.data.server_stats.nke_drops),
-               (unsigned long)ntohl(reply.data.server_stats.ntp_auth_hits),
-               (unsigned long)ntohl(reply.data.server_stats.ntp_interleaved_hits),
-               (unsigned long)ntohl(reply.data.server_stats.ntp_timestamps),
-               (unsigned long)ntohl(reply.data.server_stats.ntp_span_seconds),
+  print_report("NTP packets received       : %Q\n"
+               "NTP packets dropped        : %Q\n"
+               "Command packets received   : %Q\n"
+               "Command packets dropped    : %Q\n"
+               "Client log records dropped : %Q\n"
+               "NTS-KE connections accepted: %Q\n"
+               "NTS-KE connections dropped : %Q\n"
+               "Authenticated NTP packets  : %Q\n"
+               "Interleaved NTP packets    : %Q\n"
+               "NTP timestamps held        : %Q\n"
+               "NTP timestamp span         : %Q\n"
+               "NTP daemon RX timestamps   : %Q\n"
+               "NTP daemon TX timestamps   : %Q\n"
+               "NTP kernel RX timestamps   : %Q\n"
+               "NTP kernel TX timestamps   : %Q\n"
+               "NTP hardware RX timestamps : %Q\n"
+               "NTP hardware TX timestamps : %Q\n",
+               UTI_Integer64NetworkToHost(reply.data.server_stats.ntp_hits),
+               UTI_Integer64NetworkToHost(reply.data.server_stats.ntp_drops),
+               UTI_Integer64NetworkToHost(reply.data.server_stats.cmd_hits),
+               UTI_Integer64NetworkToHost(reply.data.server_stats.cmd_drops),
+               UTI_Integer64NetworkToHost(reply.data.server_stats.log_drops),
+               UTI_Integer64NetworkToHost(reply.data.server_stats.nke_hits),
+               UTI_Integer64NetworkToHost(reply.data.server_stats.nke_drops),
+               UTI_Integer64NetworkToHost(reply.data.server_stats.ntp_auth_hits),
+               UTI_Integer64NetworkToHost(reply.data.server_stats.ntp_interleaved_hits),
+               UTI_Integer64NetworkToHost(reply.data.server_stats.ntp_timestamps),
+               UTI_Integer64NetworkToHost(reply.data.server_stats.ntp_span_seconds),
+               UTI_Integer64NetworkToHost(reply.data.server_stats.ntp_daemon_rx_timestamps),
+               UTI_Integer64NetworkToHost(reply.data.server_stats.ntp_daemon_tx_timestamps),
+               UTI_Integer64NetworkToHost(reply.data.server_stats.ntp_kernel_rx_timestamps),
+               UTI_Integer64NetworkToHost(reply.data.server_stats.ntp_kernel_tx_timestamps),
+               UTI_Integer64NetworkToHost(reply.data.server_stats.ntp_hw_rx_timestamps),
+               UTI_Integer64NetworkToHost(reply.data.server_stats.ntp_hw_tx_timestamps),
               REPORT_END);

  return 1;
@@ -2566,7 +2602,7 @@ process_cmd_rtcreport(char *line)
               &ref_time,
               ntohs(reply.data.rtc.n_samples),
               ntohs(reply.data.rtc.n_runs),
-               (unsigned long)ntohl(reply.data.rtc.span_seconds),
+               ntohl(reply.data.rtc.span_seconds),
               UTI_FloatNetworkToHost(reply.data.rtc.rtc_seconds_fast),
               UTI_FloatNetworkToHost(reply.data.rtc.rtc_gain_rate_ppm),
               REPORT_END);
@@ -2641,16 +2677,15 @@ process_cmd_clients(char *line)

      print_report("%-25s  %6U  %5U  %C  %C  %I  %6U  %5U  %C  %I\n",
                   name,
-                   (unsigned long)ntohl(client->ntp_hits),
-                   (unsigned long)ntohl(client->ntp_drops),
+                   ntohl(client->ntp_hits),
+                   ntohl(client->ntp_drops),
                   client->ntp_interval,
                   client->ntp_timeout_interval,
-                   (unsigned long)ntohl(client->last_ntp_hit_ago),
-                   (unsigned long)ntohl(nke ? client->nke_hits : client->cmd_hits),
-                   (unsigned long)ntohl(nke ? client->nke_drops : client->cmd_drops),
+                   ntohl(client->last_ntp_hit_ago),
+                   ntohl(nke ? client->nke_hits : client->cmd_hits),
+                   ntohl(nke ? client->nke_drops : client->cmd_drops),
                   nke ? client->nke_interval : client->cmd_interval,
-                   (unsigned long)ntohl(nke ? client->last_nke_hit_ago :
-                                              client->last_cmd_hit_ago),
+                   ntohl(nke ? client->last_nke_hit_ago : client->last_cmd_hit_ago),
                   REPORT_END);
    }

@@ -2681,7 +2716,7 @@ process_cmd_manual_list(const char *line)
    return 0;

  n_samples = ntohl(reply.data.manual_list.n_samples);
-  print_info_field("210 n_samples = %lu\n", (unsigned long)n_samples);
+  print_info_field("210 n_samples = %"PRIu32"\n", n_samples);

  print_header("#    Date     Time(UTC)    Slewed   Original   Residual");

@@ -2801,11 +2836,11 @@ process_cmd_activity(const char *line)
               "%U sources doing burst (return to online)\n"
               "%U sources doing burst (return to offline)\n"
               "%U sources with unknown address\n",
-               (unsigned long)ntohl(reply.data.activity.online),
-               (unsigned long)ntohl(reply.data.activity.offline),
-               (unsigned long)ntohl(reply.data.activity.burst_online),
-               (unsigned long)ntohl(reply.data.activity.burst_offline),
-               (unsigned long)ntohl(reply.data.activity.unresolved),
+               ntohl(reply.data.activity.online),
+               ntohl(reply.data.activity.offline),
+               ntohl(reply.data.activity.burst_online),
+               ntohl(reply.data.activity.burst_offline),
+               ntohl(reply.data.activity.unresolved),
               REPORT_END);

  return 1;
@@ -2884,6 +2919,55 @@ process_cmd_reset(CMD_Request *msg, char *line)

 /* ================================================== */

+static int
+process_cmd_selectopts(CMD_Request *msg, char *line)
+{
+  int mask, options, option;
+  uint32_t ref_id;
+  IPAddr ip_addr;
+  char *src, *opt;
+
+  src = line;
+  line = CPS_SplitWord(line);
+  ref_id = 0;
+
+  /* Don't allow hostnames to avoid conflicts with reference IDs */
+  if (!UTI_StringToIdIP(src, &ip_addr) && !UTI_StringToIP(src, &ip_addr)) {
+    ip_addr.family = IPADDR_UNSPEC;
+    if (CPS_ParseRefid(src, &ref_id) == 0) {
+      LOG(LOGS_ERR, "Invalid syntax for selectopts command");
+      return 0;
+    }
+  }
+
+  mask = options = 0;
+
+  while (*line != '\0') {
+    opt = line;
+    line = CPS_SplitWord(line);
+
+    if ((opt[0] != '+' && opt[0] != '-') || (option = CPS_GetSelectOption(opt + 1)) == 0) {
+      LOG(LOGS_ERR, "Invalid syntax for selectopts command");
+      return 0;
+    }
+
+    mask |= option;
+    if (opt[0] == '+')
+      options |= option;
+  }
+
+  UTI_IPHostToNetwork(&ip_addr, &msg->data.modify_select_opts.address);
+  msg->data.modify_select_opts.ref_id = htonl(ref_id);
+  msg->data.modify_select_opts.mask = htonl(mask);
+  msg->data.modify_select_opts.options = htonl(convert_addsrc_sel_options(options));
+
+  msg->command = htons(REQ_MODIFY_SELECTOPTS);
+
+  return 1;
+}
+
+/* ================================================== */
+
 static int
 process_cmd_waitsync(char *line)
 {
@@ -2919,7 +3003,7 @@ process_cmd_waitsync(char *line)
      skew_ppm = UTI_FloatNetworkToHost(reply.data.tracking.skew_ppm);

      print_report("try: %d, refid: %R, correction: %.9f, skew: %.3f\n",
-                   i, (unsigned long)ref_id, correction, skew_ppm, REPORT_END);
+                   i, ref_id, correction, skew_ppm, REPORT_END);

      if ((ip_addr.family != IPADDR_UNSPEC ||
           (ref_id != 0 && ref_id != 0x7f7f0101L /* LOCAL refid */)) &&
@@ -3186,6 +3270,8 @@ process_line(char *line)
  } else if (!strcmp(command, "selectdata")) {
    do_normal_submit = 0;
    ret = process_cmd_selectdata(line);
+  } else if (!strcmp(command, "selectopts")) {
+    do_normal_submit = process_cmd_selectopts(&tx_message, line);
  } else if (!strcmp(command, "serverstats")) {
    do_normal_submit = 0;
    ret = process_cmd_serverstats(line);
@@ -3235,44 +3321,50 @@ process_line(char *line)
  if (do_normal_submit) {
    ret = request_reply(&tx_message, &rx_message, RPY_NULL, 1);
  }
+
+  if (end_dot) {
+    printf(".\n");
+  }
+
  fflush(stderr);
-  fflush(stdout);
+
+  if (fflush(stdout) != 0 || ferror(stdout) != 0) {
+    LOG(LOGS_ERR, "Could not write to stdout");
+
+    /* Return error for commands that print data */
+    if (!do_normal_submit)
+      return 0;
+  }
+
  return ret;
 }

 /* ================================================== */

+#define MAX_LINE_LENGTH 2048
+
 static int
 process_args(int argc, char **argv, int multi)
 {
-  int total_length, i, ret = 0;
-  char *line;
+  char line[MAX_LINE_LENGTH];
+  int i, l, ret = 0;

-  total_length = 0;
-  for(i=0; i<argc; i++) {
-    total_length += strlen(argv[i]) + 1;
-  }
-
-  line = (char *) Malloc((2 + total_length) * sizeof(char));
-
-  for (i = 0; i < argc; i++) {
-    line[0] = '\0';
-    if (multi) {
-      strcat(line, argv[i]);
-    } else {
-      for (; i < argc; i++) {
-        strcat(line, argv[i]);
-        if (i + 1 < argc)
-          strcat(line, " ");
-      }
+  for (i = l = 0; i < argc; i++) {
+    l += snprintf(line + l, sizeof (line) - l, "%s ", argv[i]);
+    if (l >= sizeof (line)) {
+      LOG(LOGS_ERR, "Command too long");
+      return 0;
    }

+    if (!multi && i + 1 < argc)
+      continue;
+
    ret = process_line(line);
    if (!ret || quit)
      break;
-  }

-  Free(line);
+    l = 0;
+  }

  return ret;
 }
@@ -3291,7 +3383,7 @@ static void
 display_gpl(void)
 {
    printf("chrony version %s\n"
-           "Copyright (C) 1997-2003, 2007, 2009-2021 Richard P. Curnow and others\n"
+           "Copyright (C) 1997-2003, 2007, 2009-2023 Richard P. Curnow and others\n"
           "chrony comes with ABSOLUTELY NO WARRANTY.  This is free software, and\n"
           "you are welcome to redistribute it under certain conditions.  See the\n"
           "GNU General Public License version 2 for details.\n\n",
@@ -3310,6 +3402,7 @@ print_help(const char *progname)
             "  -n\t\tDon't resolve hostnames\n"
             "  -N\t\tPrint original source names\n"
             "  -c\t\tEnable CSV format\n"
+             "  -e\t\tEnd responses with dot\n"
 #if DEBUG > 0
             "  -d\t\tEnable debug messages\n"
 #endif
@@ -3354,7 +3447,7 @@ main(int argc, char **argv)
  optind = 1;

  /* Parse short command-line options */
-  while ((opt = getopt(argc, argv, "+46acdf:h:mnNp:v")) != -1) {
+  while ((opt = getopt(argc, argv, "+46acdef:h:mnNp:v")) != -1) {
    switch (opt) {
      case '4':
      case '6':
@@ -3372,6 +3465,9 @@ main(int argc, char **argv)
        log_min_severity = LOGS_DEBUG;
 #endif
        break;
+      case 'e':
+        end_dot = 1;
+        break;
      case 'h':
        hostnames = optarg;
        break;
--- a/clientlog.c
+++ b/clientlog.c
@@ -126,7 +126,8 @@ static int active;
 /* RX and TX timestamp saved for clients using interleaved mode */
 typedef struct {
  uint64_t rx_ts;
-  uint16_t flags;
+  uint8_t flags;
+  uint8_t tx_ts_source;
  uint16_t slew_epoch;
  int32_t tx_ts_offset;
 } NtpTimestamps;
@@ -155,12 +156,17 @@ static NtpTimestampMap ntp_ts_map;
 /* Maximum number of timestamps moved in the array to insert a new timestamp */
 #define NTPTS_INSERT_LIMIT 64

+/* Maximum expected value of the timestamp source */
+#define MAX_NTP_TS NTP_TS_HARDWARE
+
 /* Global statistics */
-static uint32_t total_hits[MAX_SERVICES];
-static uint32_t total_drops[MAX_SERVICES];
-static uint32_t total_ntp_auth_hits;
-static uint32_t total_ntp_interleaved_hits;
-static uint32_t total_record_drops;
+static uint64_t total_hits[MAX_SERVICES];
+static uint64_t total_drops[MAX_SERVICES];
+static uint64_t total_ntp_auth_hits;
+static uint64_t total_ntp_interleaved_hits;
+static uint64_t total_record_drops;
+static uint64_t total_ntp_rx_timestamps[MAX_NTP_TS + 1];
+static uint64_t total_ntp_tx_timestamps[MAX_NTP_TS + 1];

 #define NSEC_PER_SEC 1000000000U

@@ -639,9 +645,14 @@ CLG_LimitServiceRate(CLG_Service service, int index)
 /* ================================================== */

 void
-CLG_LogAuthNtpRequest(void)
+CLG_UpdateNtpStats(int auth, NTP_Timestamp_Source rx_ts_src, NTP_Timestamp_Source tx_ts_src)
 {
-  total_ntp_auth_hits++;
+  if (auth)
+    total_ntp_auth_hits++;
+  if (rx_ts_src >= 0 && rx_ts_src <= MAX_NTP_TS)
+    total_ntp_rx_timestamps[rx_ts_src]++;
+  if (tx_ts_src >= 0 && tx_ts_src <= MAX_NTP_TS)
+    total_ntp_tx_timestamps[tx_ts_src]++;
 }

 /* ================================================== */
@@ -773,7 +784,8 @@ push_ntp_tss(uint32_t index)
 /* ================================================== */

 static void
-set_ntp_tx_offset(NtpTimestamps *tss, NTP_int64 *rx_ts, struct timespec *tx_ts)
+set_ntp_tx(NtpTimestamps *tss, NTP_int64 *rx_ts, struct timespec *tx_ts,
+           NTP_Timestamp_Source tx_src)
 {
  struct timespec ts;

@@ -792,12 +804,13 @@ set_ntp_tx_offset(NtpTimestamps *tss, NTP_int64 *rx_ts, struct timespec *tx_ts)

  tss->tx_ts_offset = (int32_t)ts.tv_nsec + (int32_t)ts.tv_sec * (int32_t)NSEC_PER_SEC;
  tss->flags |= NTPTS_VALID_TX;
+  tss->tx_ts_source = tx_src;
 }

 /* ================================================== */

 static void
-get_ntp_tx(NtpTimestamps *tss, struct timespec *tx_ts)
+get_ntp_tx(NtpTimestamps *tss, struct timespec *tx_ts, NTP_Timestamp_Source *tx_src)
 {
  int32_t offset = tss->tx_ts_offset;
  NTP_int64 ntp_ts;
@@ -814,12 +827,14 @@ get_ntp_tx(NtpTimestamps *tss, struct timespec *tx_ts)
  } else {
    UTI_ZeroTimespec(tx_ts);
  }
+
+  *tx_src = tss->tx_ts_source;
 }

 /* ================================================== */

 void
-CLG_SaveNtpTimestamps(NTP_int64 *rx_ts, struct timespec *tx_ts)
+CLG_SaveNtpTimestamps(NTP_int64 *rx_ts, struct timespec *tx_ts, NTP_Timestamp_Source tx_src)
 {
  NtpTimestamps *tss;
  uint32_t i, index;
@@ -877,7 +892,7 @@ CLG_SaveNtpTimestamps(NTP_int64 *rx_ts, struct timespec *tx_ts)
  tss->rx_ts = rx;
  tss->flags = 0;
  tss->slew_epoch = ntp_ts_map.slew_epoch;
-  set_ntp_tx_offset(tss, rx_ts, tx_ts);
+  set_ntp_tx(tss, rx_ts, tx_ts, tx_src);

  DEBUG_LOG("Saved RX+TX index=%"PRIu32" first=%"PRIu32" size=%"PRIu32,
            index, ntp_ts_map.first, ntp_ts_map.size);
@@ -921,7 +936,8 @@ CLG_UndoNtpTxTimestampSlew(NTP_int64 *rx_ts, struct timespec *tx_ts)
 /* ================================================== */

 void
-CLG_UpdateNtpTxTimestamp(NTP_int64 *rx_ts, struct timespec *tx_ts)
+CLG_UpdateNtpTxTimestamp(NTP_int64 *rx_ts, struct timespec *tx_ts,
+                         NTP_Timestamp_Source tx_src)
 {
  uint32_t index;

@@ -931,13 +947,14 @@ CLG_UpdateNtpTxTimestamp(NTP_int64 *rx_ts, struct timespec *tx_ts)
  if (!find_ntp_rx_ts(ntp64_to_int64(rx_ts), &index))
    return;

-  set_ntp_tx_offset(get_ntp_tss(index), rx_ts, tx_ts);
+  set_ntp_tx(get_ntp_tss(index), rx_ts, tx_ts, tx_src);
 }

 /* ================================================== */

 int
-CLG_GetNtpTxTimestamp(NTP_int64 *rx_ts, struct timespec *tx_ts)
+CLG_GetNtpTxTimestamp(NTP_int64 *rx_ts, struct timespec *tx_ts,
+                      NTP_Timestamp_Source *tx_src)
 {
  NtpTimestamps *tss;
  uint32_t index;
@@ -953,7 +970,7 @@ CLG_GetNtpTxTimestamp(NTP_int64 *rx_ts, struct timespec *tx_ts)
  if (tss->flags & NTPTS_DISABLED)
    return 0;

-  get_ntp_tx(tss, tx_ts);
+  get_ntp_tx(tss, tx_ts, tx_src);

  return 1;
 }
@@ -1085,4 +1102,10 @@ CLG_GetServerStatsReport(RPT_ServerStatsReport *report)
  report->ntp_span_seconds = ntp_ts_map.size > 1 ?
                             (get_ntp_tss(ntp_ts_map.size - 1)->rx_ts -
                              get_ntp_tss(0)->rx_ts) >> 32 : 0;
+  report->ntp_daemon_rx_timestamps = total_ntp_rx_timestamps[NTP_TS_DAEMON];
+  report->ntp_daemon_tx_timestamps = total_ntp_tx_timestamps[NTP_TS_DAEMON];
+  report->ntp_kernel_rx_timestamps = total_ntp_rx_timestamps[NTP_TS_KERNEL];
+  report->ntp_kernel_tx_timestamps = total_ntp_tx_timestamps[NTP_TS_KERNEL];
+  report->ntp_hw_rx_timestamps = total_ntp_rx_timestamps[NTP_TS_HARDWARE];
+  report->ntp_hw_tx_timestamps = total_ntp_tx_timestamps[NTP_TS_HARDWARE];
 }
--- a/clientlog.h
+++ b/clientlog.h
@@ -42,14 +42,18 @@ extern void CLG_Finalise(void);
 extern int CLG_GetClientIndex(IPAddr *client);
 extern int CLG_LogServiceAccess(CLG_Service service, IPAddr *client, struct timespec *now);
 extern int CLG_LimitServiceRate(CLG_Service service, int index);
-extern void CLG_LogAuthNtpRequest(void);
+extern void CLG_UpdateNtpStats(int auth, NTP_Timestamp_Source rx_ts_src,
+                               NTP_Timestamp_Source tx_ts_src);
 extern int CLG_GetNtpMinPoll(void);

 /* Functions to save and retrieve timestamps for server interleaved mode */
-extern void CLG_SaveNtpTimestamps(NTP_int64 *rx_ts, struct timespec *tx_ts);
+extern void CLG_SaveNtpTimestamps(NTP_int64 *rx_ts, struct timespec *tx_ts,
+                                  NTP_Timestamp_Source tx_src);
 extern void CLG_UndoNtpTxTimestampSlew(NTP_int64 *rx_ts, struct timespec *tx_ts);
-extern void CLG_UpdateNtpTxTimestamp(NTP_int64 *rx_ts, struct timespec *tx_ts);
-extern int CLG_GetNtpTxTimestamp(NTP_int64 *rx_ts, struct timespec *tx_ts);
+extern void CLG_UpdateNtpTxTimestamp(NTP_int64 *rx_ts, struct timespec *tx_ts,
+                                     NTP_Timestamp_Source tx_src);
+extern int CLG_GetNtpTxTimestamp(NTP_int64 *rx_ts, struct timespec *tx_ts,
+                                 NTP_Timestamp_Source *tx_src);
 extern void CLG_DisableNtpTimestamps(NTP_int64 *rx_ts);

 /* And some reporting functions, for use by chronyc. */
--- a/cmdmon.c
+++ b/cmdmon.c
@@ -3,7 +3,7 @@

 **********************************************************************
 * Copyright (C) Richard P. Curnow  1997-2003
- * Copyright (C) Miroslav Lichvar  2009-2016, 2018-2021
+ * Copyright (C) Miroslav Lichvar  2009-2016, 2018-2023
 * 
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of version 2 of the GNU General Public License as
@@ -144,6 +144,7 @@ static const char permissions[] = {
  PERMIT_AUTH, /* SELECT_DATA */
  PERMIT_AUTH, /* RELOAD_SOURCES */
  PERMIT_AUTH, /* DOFFSET2 */
+  PERMIT_AUTH, /* MODIFY_SELECTOPTS */
 };

 /* ================================================== */
@@ -703,6 +704,17 @@ handle_cmdaccheck(CMD_Request *rx_message, CMD_Reply *tx_message)

 /* ================================================== */

+static int
+convert_addsrc_select_options(int flags)
+{
+    return (flags & REQ_ADDSRC_PREFER ? SRC_SELECT_PREFER : 0) |
+           (flags & REQ_ADDSRC_NOSELECT ? SRC_SELECT_NOSELECT : 0) |
+           (flags & REQ_ADDSRC_TRUST ? SRC_SELECT_TRUST : 0) |
+           (flags & REQ_ADDSRC_REQUIRE ? SRC_SELECT_REQUIRE : 0);
+}
+
+/* ================================================== */
+
 static void
 handle_add_source(CMD_Request *rx_message, CMD_Reply *tx_message)
 {
@@ -757,6 +769,8 @@ handle_add_source(CMD_Request *rx_message, CMD_Reply *tx_message)
    UTI_FloatNetworkToHost(rx_message->data.ntp_source.max_delay_ratio);
  params.max_delay_dev_ratio =
    UTI_FloatNetworkToHost(rx_message->data.ntp_source.max_delay_dev_ratio);
+  params.max_delay_quant =
+    UTI_FloatNetworkToHost(rx_message->data.ntp_source.max_delay_quant);
  params.min_delay = UTI_FloatNetworkToHost(rx_message->data.ntp_source.min_delay);
  params.asymmetry = UTI_FloatNetworkToHost(rx_message->data.ntp_source.asymmetry);
  params.offset = UTI_FloatNetworkToHost(rx_message->data.ntp_source.offset);
@@ -769,13 +783,11 @@ handle_add_source(CMD_Request *rx_message, CMD_Reply *tx_message)
  params.burst = ntohl(rx_message->data.ntp_source.flags) & REQ_ADDSRC_BURST ? 1 : 0;
  params.nts = ntohl(rx_message->data.ntp_source.flags) & REQ_ADDSRC_NTS ? 1 : 0;
  params.copy = ntohl(rx_message->data.ntp_source.flags) & REQ_ADDSRC_COPY ? 1 : 0;
-  params.ext_fields =
-    ntohl(rx_message->data.ntp_source.flags) & REQ_ADDSRC_EF_EXP1 ? NTP_EF_FLAG_EXP1 : 0;
-  params.sel_options =
-    (ntohl(rx_message->data.ntp_source.flags) & REQ_ADDSRC_PREFER ? SRC_SELECT_PREFER : 0) |
-    (ntohl(rx_message->data.ntp_source.flags) & REQ_ADDSRC_NOSELECT ? SRC_SELECT_NOSELECT : 0) |
-    (ntohl(rx_message->data.ntp_source.flags) & REQ_ADDSRC_TRUST ? SRC_SELECT_TRUST : 0) |
-    (ntohl(rx_message->data.ntp_source.flags) & REQ_ADDSRC_REQUIRE ? SRC_SELECT_REQUIRE : 0);
+  params.ext_fields = (ntohl(rx_message->data.ntp_source.flags) & REQ_ADDSRC_EF_EXP_MONO_ROOT ?
+                      NTP_EF_FLAG_EXP_MONO_ROOT : 0) |
+                      (ntohl(rx_message->data.ntp_source.flags) & REQ_ADDSRC_EF_EXP_NET_CORRECTION ?
+                      NTP_EF_FLAG_EXP_NET_CORRECTION : 0);
+  params.sel_options = convert_addsrc_select_options(ntohl(rx_message->data.ntp_source.flags));

  status = NSR_AddSourceByName(name, port, pool, type, &params, NULL);
  switch (status) {
@@ -1167,18 +1179,36 @@ handle_server_stats(CMD_Request *rx_message, CMD_Reply *tx_message)
  RPT_ServerStatsReport report;

  CLG_GetServerStatsReport(&report);
-  tx_message->reply = htons(RPY_SERVER_STATS3);
-  tx_message->data.server_stats.ntp_hits = htonl(report.ntp_hits);
-  tx_message->data.server_stats.nke_hits = htonl(report.nke_hits);
-  tx_message->data.server_stats.cmd_hits = htonl(report.cmd_hits);
-  tx_message->data.server_stats.ntp_drops = htonl(report.ntp_drops);
-  tx_message->data.server_stats.nke_drops = htonl(report.nke_drops);
-  tx_message->data.server_stats.cmd_drops = htonl(report.cmd_drops);
-  tx_message->data.server_stats.log_drops = htonl(report.log_drops);
-  tx_message->data.server_stats.ntp_auth_hits = htonl(report.ntp_auth_hits);
-  tx_message->data.server_stats.ntp_interleaved_hits = htonl(report.ntp_interleaved_hits);
-  tx_message->data.server_stats.ntp_timestamps = htonl(report.ntp_timestamps);
-  tx_message->data.server_stats.ntp_span_seconds = htonl(report.ntp_span_seconds);
+  tx_message->reply = htons(RPY_SERVER_STATS4);
+  tx_message->data.server_stats.ntp_hits = UTI_Integer64HostToNetwork(report.ntp_hits);
+  tx_message->data.server_stats.nke_hits = UTI_Integer64HostToNetwork(report.nke_hits);
+  tx_message->data.server_stats.cmd_hits = UTI_Integer64HostToNetwork(report.cmd_hits);
+  tx_message->data.server_stats.ntp_drops = UTI_Integer64HostToNetwork(report.ntp_drops);
+  tx_message->data.server_stats.nke_drops = UTI_Integer64HostToNetwork(report.nke_drops);
+  tx_message->data.server_stats.cmd_drops = UTI_Integer64HostToNetwork(report.cmd_drops);
+  tx_message->data.server_stats.log_drops = UTI_Integer64HostToNetwork(report.log_drops);
+  tx_message->data.server_stats.ntp_auth_hits =
+    UTI_Integer64HostToNetwork(report.ntp_auth_hits);
+  tx_message->data.server_stats.ntp_interleaved_hits =
+    UTI_Integer64HostToNetwork(report.ntp_interleaved_hits);
+  tx_message->data.server_stats.ntp_timestamps =
+    UTI_Integer64HostToNetwork(report.ntp_timestamps);
+  tx_message->data.server_stats.ntp_span_seconds =
+    UTI_Integer64HostToNetwork(report.ntp_span_seconds);
+  tx_message->data.server_stats.ntp_daemon_rx_timestamps =
+    UTI_Integer64HostToNetwork(report.ntp_daemon_rx_timestamps);
+  tx_message->data.server_stats.ntp_daemon_tx_timestamps =
+    UTI_Integer64HostToNetwork(report.ntp_daemon_tx_timestamps);
+  tx_message->data.server_stats.ntp_kernel_rx_timestamps =
+    UTI_Integer64HostToNetwork(report.ntp_kernel_rx_timestamps);
+  tx_message->data.server_stats.ntp_kernel_tx_timestamps =
+    UTI_Integer64HostToNetwork(report.ntp_kernel_tx_timestamps);
+  tx_message->data.server_stats.ntp_hw_rx_timestamps =
+    UTI_Integer64HostToNetwork(report.ntp_hw_rx_timestamps);
+  tx_message->data.server_stats.ntp_hw_tx_timestamps =
+    UTI_Integer64HostToNetwork(report.ntp_hw_tx_timestamps);
+  memset(tx_message->data.server_stats.reserved, 0xff,
+         sizeof (tx_message->data.server_stats.reserved));
 }

 /* ================================================== */
@@ -1222,6 +1252,7 @@ handle_ntp_data(CMD_Request *rx_message, CMD_Reply *tx_message)
  tx_message->data.ntp_data.total_tx_count = htonl(report.total_tx_count);
  tx_message->data.ntp_data.total_rx_count = htonl(report.total_rx_count);
  tx_message->data.ntp_data.total_valid_count = htonl(report.total_valid_count);
+  tx_message->data.ntp_data.total_good_count = htonl(report.total_good_count);
  memset(tx_message->data.ntp_data.reserved, 0xff, sizeof (tx_message->data.ntp_data.reserved));
 }

@@ -1325,7 +1356,7 @@ handle_auth_data(CMD_Request *rx_message, CMD_Reply *tx_message)
 /* ================================================== */

 static uint16_t
-convert_select_options(int options)
+convert_sd_sel_options(int options)
 {
  return (options & SRC_SELECT_PREFER ? RPY_SD_OPTION_PREFER : 0) |
         (options & SRC_SELECT_NOSELECT ? RPY_SD_OPTION_NOSELECT : 0) |
@@ -1352,14 +1383,32 @@ handle_select_data(CMD_Request *rx_message, CMD_Reply *tx_message)
  tx_message->data.select_data.state_char = report.state_char;
  tx_message->data.select_data.authentication = report.authentication;
  tx_message->data.select_data.leap = report.leap;
-  tx_message->data.select_data.conf_options = htons(convert_select_options(report.conf_options));
-  tx_message->data.select_data.eff_options = htons(convert_select_options(report.eff_options));
+  tx_message->data.select_data.conf_options = htons(convert_sd_sel_options(report.conf_options));
+  tx_message->data.select_data.eff_options = htons(convert_sd_sel_options(report.eff_options));
  tx_message->data.select_data.last_sample_ago = htonl(report.last_sample_ago);
  tx_message->data.select_data.score = UTI_FloatHostToNetwork(report.score);
  tx_message->data.select_data.hi_limit = UTI_FloatHostToNetwork(report.hi_limit);
  tx_message->data.select_data.lo_limit = UTI_FloatHostToNetwork(report.lo_limit);
 }

+/* ================================================== */
+
+static void
+handle_modify_selectopts(CMD_Request *rx_message, CMD_Reply *tx_message)
+{
+  int mask, options;
+  uint32_t ref_id;
+  IPAddr ip_addr;
+
+  UTI_IPNetworkToHost(&rx_message->data.modify_select_opts.address, &ip_addr);
+  ref_id = ntohl(rx_message->data.modify_select_opts.ref_id);
+  mask = ntohl(rx_message->data.modify_select_opts.mask);
+  options = convert_addsrc_select_options(ntohl(rx_message->data.modify_select_opts.options));
+
+  if (!SRC_ModifySelectOptions(&ip_addr, ref_id, options, mask))
+    tx_message->status = htons(STT_NOSUCHSOURCE);
+}
+
 /* ================================================== */
 /* Read a packet and process it */

@@ -1512,6 +1561,8 @@ read_from_cmd_socket(int sock_fd, int event, void *anything)
    }

    if (allowed) {
+      LOG_SetContext(LOGC_Command);
+
      switch(rx_command) {
        case REQ_NULL:
          /* Do nothing */
@@ -1754,11 +1805,17 @@ read_from_cmd_socket(int sock_fd, int event, void *anything)
          handle_reload_sources(&rx_message, &tx_message);
          break;

+        case REQ_MODIFY_SELECTOPTS:
+          handle_modify_selectopts(&rx_message, &tx_message);
+          break;
+
        default:
          DEBUG_LOG("Unhandled command %d", rx_command);
          tx_message.status = htons(STT_FAILED);
          break;
      }
+
+      LOG_UnsetContext(LOGC_Command);
    } else {
      tx_message.status = htons(STT_UNAUTH);
    }
@@ -1792,6 +1849,9 @@ CAM_AddAccessRestriction(IPAddr *ip_addr, int subnet_bits, int allow, int all)
  if (status == ADF_BADSUBNET) {
    return 0;
  } else if (status == ADF_SUCCESS) {
+    LOG(LOG_GetContextSeverity(LOGC_Command), "%s%s %s access from %s",
+        allow ? "Allowed" : "Denied", all ? " all" : "", "command",
+        UTI_IPSubnetToString(ip_addr, subnet_bits));
    return 1;
  } else {
    return 0;
--- a/cmdparse.c
+++ b/cmdparse.c
@@ -44,7 +44,7 @@ CPS_ParseNTPSourceAdd(char *line, CPS_NTP_Source *src)
 {
  char *hostname, *cmd;
  uint32_t ef_type;
-  int n;
+  int n, sel_option;
  
  src->port = SRC_DEFAULT_PORT;
  src->params.minpoll = SRC_DEFAULT_MINPOLL;
@@ -72,6 +72,7 @@ CPS_ParseNTPSourceAdd(char *line, CPS_NTP_Source *src)
  src->params.max_delay = SRC_DEFAULT_MAXDELAY;
  src->params.max_delay_ratio = SRC_DEFAULT_MAXDELAYRATIO;
  src->params.max_delay_dev_ratio = SRC_DEFAULT_MAXDELAYDEVRATIO;
+  src->params.max_delay_quant = 0.0;
  src->params.min_delay = 0.0;
  src->params.asymmetry = SRC_DEFAULT_ASYMMETRY;
  src->params.offset = 0.0;
@@ -100,14 +101,6 @@ CPS_ParseNTPSourceAdd(char *line, CPS_NTP_Source *src)
      src->params.iburst = 1;
    } else if (!strcasecmp(cmd, "offline")) {
      src->params.connectivity = SRC_OFFLINE;
-    } else if (!strcasecmp(cmd, "noselect")) {
-      src->params.sel_options |= SRC_SELECT_NOSELECT;
-    } else if (!strcasecmp(cmd, "prefer")) {
-      src->params.sel_options |= SRC_SELECT_PREFER;
-    } else if (!strcasecmp(cmd, "require")) {
-      src->params.sel_options |= SRC_SELECT_REQUIRE;
-    } else if (!strcasecmp(cmd, "trust")) {
-      src->params.sel_options |= SRC_SELECT_TRUST;
    } else if (!strcasecmp(cmd, "certset")) {
      if (sscanf(line, "%"SCNu32"%n", &src->params.cert_set, &n) != 1)
        return 0;
@@ -122,8 +115,11 @@ CPS_ParseNTPSourceAdd(char *line, CPS_NTP_Source *src)
      if (sscanf(line, "%"SCNx32"%n", &ef_type, &n) != 1)
        return 0;
      switch (ef_type) {
-        case NTP_EF_EXP1:
-          src->params.ext_fields |= NTP_EF_FLAG_EXP1;
+        case NTP_EF_EXP_MONO_ROOT:
+          src->params.ext_fields |= NTP_EF_FLAG_EXP_MONO_ROOT;
+          break;
+        case NTP_EF_EXP_NET_CORRECTION:
+          src->params.ext_fields |= NTP_EF_FLAG_EXP_NET_CORRECTION;
          break;
        default:
          return 0;
@@ -140,6 +136,9 @@ CPS_ParseNTPSourceAdd(char *line, CPS_NTP_Source *src)
    } else if (!strcasecmp(cmd, "maxdelaydevratio")) {
      if (sscanf(line, "%lf%n", &src->params.max_delay_dev_ratio, &n) != 1)
        return 0;
+    } else if (!strcasecmp(cmd, "maxdelayquant")) {
+      if (sscanf(line, "%lf%n", &src->params.max_delay_quant, &n) != 1)
+        return 0;
    } else if (!strcasecmp(cmd, "maxpoll")) {
      if (sscanf(line, "%d%n", &src->params.maxpoll, &n) != 1)
        return 0;
@@ -183,6 +182,8 @@ CPS_ParseNTPSourceAdd(char *line, CPS_NTP_Source *src)
        return 0;
    } else if (!strcasecmp(cmd, "xleave")) {
      src->params.interleaved = 1;
+    } else if ((sel_option = CPS_GetSelectOption(cmd)) != 0) {
+      src->params.sel_options |= sel_option;
    } else {
      return 0;
    }
@@ -193,6 +194,23 @@ CPS_ParseNTPSourceAdd(char *line, CPS_NTP_Source *src)

 /* ================================================== */

+int
+CPS_GetSelectOption(char *option)
+{
+  if (!strcasecmp(option, "noselect")) {
+    return SRC_SELECT_NOSELECT;
+  } else if (!strcasecmp(option, "prefer")) {
+    return SRC_SELECT_PREFER;
+  } else if (!strcasecmp(option, "require")) {
+    return SRC_SELECT_REQUIRE;
+  } else if (!strcasecmp(option, "trust")) {
+    return SRC_SELECT_TRUST;
+  }
+  return 0;
+}
+
+/* ================================================== */
+
 int
 CPS_ParseAllowDeny(char *line, int *all, IPAddr *ip, int *subnet_bits)
 {
@@ -392,3 +410,19 @@ CPS_ParseKey(char *line, uint32_t *id, const char **type, char **key)

  return 1;
 }
+
+/* ================================================== */
+
+int
+CPS_ParseRefid(char *line, uint32_t *ref_id)
+{
+  int i;
+
+  for (i = *ref_id = 0; line[i] && !isspace((unsigned char)line[i]); i++) {
+    if (i >= 4)
+      return 0;
+    *ref_id |= (uint32_t)line[i] << (24 - i * 8);
+  }
+
+  return i;
+}
--- a/cmdparse.h
+++ b/cmdparse.h
@@ -39,6 +39,9 @@ typedef struct {
 /* Parse a command to add an NTP server or peer */
 extern int CPS_ParseNTPSourceAdd(char *line, CPS_NTP_Source *src);
  
+/* Get an NTP/refclock select option */
+extern int CPS_GetSelectOption(char *option);
+
 /* Parse a command to allow/deny access */
 extern int CPS_ParseAllowDeny(char *line, int *all, IPAddr *ip, int *subnet_bits);

@@ -54,4 +57,7 @@ extern char *CPS_SplitWord(char *line);
 /* Parse a key from keyfile */
 extern int CPS_ParseKey(char *line, uint32_t *id, const char **type, char **key);

+/* Parse a refclock reference ID (returns number of characters) */
+extern int CPS_ParseRefid(char *line, uint32_t *ref_id);
+
 #endif /* GOT_CMDPARSE_H */
--- a/conf.c
+++ b/conf.c
@@ -115,6 +115,7 @@ static int cmd_port = DEFAULT_CANDM_PORT;

 static int raw_measurements = 0;
 static int do_log_measurements = 0;
+static int do_log_selection = 0;
 static int do_log_statistics = 0;
 static int do_log_tracking = 0;
 static int do_log_rtc = 0;
@@ -251,6 +252,9 @@ static char *leapsec_tz = NULL;
 /* Name of the user to which will be dropped root privileges. */
 static char *user;

+/* Address refresh interval */
+static int refresh = 1209600; /* 2 weeks */
+
 /* NTS server and client configuration */
 static char *nts_dump_dir = NULL;
 static char *nts_ntp_server = NULL;
@@ -273,6 +277,9 @@ static int no_system_cert = 0;
 /* Array of CNF_HwTsInterface */
 static ARR_Instance hwts_interfaces;

+/* Timeout for resuming reading from sockets waiting for HW TX timestamp */
+static double hwts_timeout = 0.001;
+
 /* PTP event port (disabled by default) */
 static int ptp_port = 0;

@@ -601,6 +608,8 @@ CNF_ParseLine(const char *filename, int number, char *line)
    parse_string(p, &hwclock_file);
  } else if (!strcasecmp(command, "hwtimestamp")) {
    parse_hwtimestamp(p);
+  } else if (!strcasecmp(command, "hwtstimeout")) {
+    parse_double(p, &hwts_timeout);
  } else if (!strcasecmp(command, "include")) {
    parse_include(p);
  } else if (!strcasecmp(command, "initstepslew")) {
@@ -696,6 +705,8 @@ CNF_ParseLine(const char *filename, int number, char *line)
                    &ntp_ratelimit_burst, &ntp_ratelimit_leak);
  } else if (!strcasecmp(command, "refclock")) {
    parse_refclock(p);
+  } else if (!strcasecmp(command, "refresh")) {
+    parse_int(p, &refresh);
  } else if (!strcasecmp(command, "reselectdist")) {
    parse_double(p, &reselect_distance);
  } else if (!strcasecmp(command, "rtcautotrim")) {
@@ -861,16 +872,16 @@ static void
 parse_refclock(char *line)
 {
  int n, poll, dpoll, filter_length, pps_rate, min_samples, max_samples, sel_options;
-  int max_lock_age, pps_forced, stratum, tai;
+  int local, max_lock_age, pps_forced, sel_option, stratum, tai;
  uint32_t ref_id, lock_ref_id;
  double offset, delay, precision, max_dispersion, pulse_width;
  char *p, *cmd, *name, *param;
-  unsigned char ref[5];
  RefclockParameters *refclock;

  poll = 4;
  dpoll = 0;
  filter_length = 64;
+  local = 0;
  pps_forced = 0;
  pps_rate = 0;
  min_samples = SRC_DEFAULT_MINSAMPLES;
@@ -910,13 +921,11 @@ parse_refclock(char *line)
    line = CPS_SplitWord(line);

    if (!strcasecmp(cmd, "refid")) {
-      if (sscanf(line, "%4s%n", (char *)ref, &n) != 1)
+      if ((n = CPS_ParseRefid(line, &ref_id)) == 0)
        break;
-      ref_id = (uint32_t)ref[0] << 24 | ref[1] << 16 | ref[2] << 8 | ref[3];
    } else if (!strcasecmp(cmd, "lock")) {
-      if (sscanf(line, "%4s%n", (char *)ref, &n) != 1)
+      if ((n = CPS_ParseRefid(line, &lock_ref_id)) == 0)
        break;
-      lock_ref_id = (uint32_t)ref[0] << 24 | ref[1] << 16 | ref[2] << 8 | ref[3];
    } else if (!strcasecmp(cmd, "poll")) {
      if (sscanf(line, "%d%n", &poll, &n) != 1) {
        break;
@@ -929,6 +938,9 @@ parse_refclock(char *line)
      if (sscanf(line, "%d%n", &filter_length, &n) != 1) {
        break;
      }
+    } else if (!strcasecmp(cmd, "local")) {
+      n = 0;
+      local = 1;
    } else if (!strcasecmp(cmd, "rate")) {
      if (sscanf(line, "%d%n", &pps_rate, &n) != 1)
        break;
@@ -966,18 +978,9 @@ parse_refclock(char *line)
    } else if (!strcasecmp(cmd, "width")) {
      if (sscanf(line, "%lf%n", &pulse_width, &n) != 1)
        break;
-    } else if (!strcasecmp(cmd, "noselect")) {
+    } else if ((sel_option = CPS_GetSelectOption(cmd)) != 0) {
      n = 0;
-      sel_options |= SRC_SELECT_NOSELECT;
-    } else if (!strcasecmp(cmd, "prefer")) {
-      n = 0;
-      sel_options |= SRC_SELECT_PREFER;
-    } else if (!strcasecmp(cmd, "trust")) {
-      n = 0;
-      sel_options |= SRC_SELECT_TRUST;
-    } else if (!strcasecmp(cmd, "require")) {
-      n = 0;
-      sel_options |= SRC_SELECT_REQUIRE;
+      sel_options |= sel_option;
    } else {
      other_parse_error("Invalid refclock option");
      return;
@@ -995,6 +998,7 @@ parse_refclock(char *line)
  refclock->driver_poll = dpoll;
  refclock->poll = poll;
  refclock->filter_length = filter_length;
+  refclock->local = local;
  refclock->pps_forced = pps_forced;
  refclock->pps_rate = pps_rate;
  refclock->min_samples = min_samples;
@@ -1027,6 +1031,8 @@ parse_log(char *line)
        raw_measurements = 1;
      } else if (!strcmp(log_name, "measurements")) {
        do_log_measurements = 1;
+      } else if (!strcmp(log_name, "selection")) {
+        do_log_selection = 1;
      } else if (!strcmp(log_name, "statistics")) {
        do_log_statistics = 1;
      } else if (!strcmp(log_name, "tracking")) {
@@ -1429,8 +1435,8 @@ static void
 parse_hwtimestamp(char *line)
 {
  CNF_HwTsInterface *iface;
+  int n, maxpoll_set = 0;
  char *p, filter[5];
-  int n;

  if (!*line) {
    command_parse_error();
@@ -1460,6 +1466,10 @@ parse_hwtimestamp(char *line)
    } else if (!strcasecmp(p, "minpoll")) {
      if (sscanf(line, "%d%n", &iface->minpoll, &n) != 1)
        break;
+    } else if (!strcasecmp(p, "maxpoll")) {
+      if (sscanf(line, "%d%n", &iface->maxpoll, &n) != 1)
+        break;
+      maxpoll_set = 1;
    } else if (!strcasecmp(p, "minsamples")) {
      if (sscanf(line, "%d%n", &iface->min_samples, &n) != 1)
        break;
@@ -1495,6 +1505,9 @@ parse_hwtimestamp(char *line)

  if (*p)
    command_parse_error();
+
+  if (!maxpoll_set)
+    iface->maxpoll = iface->minpoll + 1;
 }

 /* ================================================== */
@@ -1647,11 +1660,11 @@ compare_sources(const void *a, const void *b)
    return 1;
  if ((d = strcmp(sa->params.name, sb->params.name)) != 0)
    return d;
-  if ((d = (int)(sa->type) - (int)(sb->type)) != 0)
+  if ((d = (int)sa->type - (int)sb->type) != 0)
    return d;
-  if ((d = sa->pool - sb->pool) != 0)
+  if ((d = (int)sa->pool - (int)sb->pool) != 0)
    return d;
-  if ((d = sa->params.port - sb->params.port) != 0)
+  if ((d = (int)sa->params.port - (int)sb->params.port) != 0)
    return d;
  return memcmp(&sa->params.params, &sb->params.params, sizeof (sa->params.params));
 }
@@ -1666,7 +1679,7 @@ reload_source_dirs(void)
  uint32_t *prev_ids, *new_ids;
  char buf[MAX_LINE_LENGTH];
  NSR_Status s;
-  int d;
+  int d, pass;

  prev_size = ARR_GetSize(ntp_source_ids);
  if (prev_size > 0 && ARR_GetSize(ntp_sources) != prev_size)
@@ -1696,41 +1709,47 @@ reload_source_dirs(void)
  new_ids = ARR_GetElements(ntp_source_ids);
  unresolved = 0;

+  LOG_SetContext(LOGC_SourceFile);
+
  qsort(new_sources, new_size, sizeof (new_sources[0]), compare_sources);

-  for (i = j = 0; i < prev_size || j < new_size; ) {
-    if (i < prev_size && j < new_size)
-      d = compare_sources(&prev_sources[i], &new_sources[j]);
-    else
-      d = i < prev_size ? -1 : 1;
+  for (pass = 0; pass < 2; pass++) {
+    for (i = j = 0; i < prev_size || j < new_size; i += d <= 0, j += d >= 0) {
+      if (i < prev_size && j < new_size)
+        d = compare_sources(&prev_sources[i], &new_sources[j]);
+      else
+        d = i < prev_size ? -1 : 1;

-    if (d < 0) {
-      /* Remove the missing source */
-      if (prev_sources[i].params.name[0] != '\0')
+      /* Remove missing sources before adding others to avoid conflicts */
+      if (pass == 0 && d < 0 && prev_sources[i].params.name[0] != '\0') {
        NSR_RemoveSourcesById(prev_ids[i]);
-      i++;
-    } else if (d > 0) {
-      /* Add a newly configured source */
-      source = &new_sources[j];
-      s = NSR_AddSourceByName(source->params.name, source->params.port, source->pool,
-                              source->type, &source->params.params, &new_ids[j]);
-
-      if (s == NSR_UnresolvedName) {
-        unresolved++;
-      } else if (s != NSR_Success) {
-        LOG(LOGS_ERR, "Could not add source %s", source->params.name);
-
-        /* Mark the source as not present */
-        source->params.name[0] = '\0';
      }
-      j++;
-    } else {
-      /* Keep the existing source */
-      new_ids[j] = prev_ids[i];
-      i++, j++;
+
+      /* Add new sources */
+      if (pass == 1 && d > 0) {
+        source = &new_sources[j];
+        s = NSR_AddSourceByName(source->params.name, source->params.port, source->pool,
+                                source->type, &source->params.params, &new_ids[j]);
+
+        if (s == NSR_UnresolvedName) {
+          unresolved++;
+        } else if (s != NSR_Success) {
+          LOG(LOGS_ERR, "Could not add source %s : %s",
+              source->params.name, NSR_StatusToString(s));
+
+          /* Mark the source as not present */
+          source->params.name[0] = '\0';
+        }
+      }
+
+      /* Keep unchanged sources */
+      if (pass == 1 && d == 0)
+        new_ids[j] = prev_ids[i];
    }
  }

+  LOG_UnsetContext(LOGC_SourceFile);
+
  for (i = 0; i < prev_size; i++)
    Free(prev_sources[i].params.name);
  Free(prev_sources);
@@ -1774,6 +1793,19 @@ CNF_CreateDirs(uid_t uid, gid_t gid)

 /* ================================================== */

+void
+CNF_CheckReadOnlyAccess(void)
+{
+  unsigned int i;
+
+  if (keys_file)
+    UTI_CheckReadOnlyAccess(keys_file);
+  for (i = 0; i < ARR_GetSize(nts_server_key_files); i++)
+    UTI_CheckReadOnlyAccess(*(char **)ARR_GetElement(nts_server_key_files, i));
+}
+
+/* ================================================== */
+
 void
 CNF_AddInitSources(void)
 {
@@ -1924,6 +1956,14 @@ CNF_GetLogMeasurements(int *raw)

 /* ================================================== */

+int
+CNF_GetLogSelection(void)
+{
+  return do_log_selection;
+}
+
+/* ================================================== */
+
 int
 CNF_GetLogStatistics(void)
 {
@@ -2484,6 +2524,14 @@ CNF_GetHwTsInterface(unsigned int index, CNF_HwTsInterface **iface)

 /* ================================================== */

+double
+CNF_GetHwTsTimeout(void)
+{
+  return hwts_timeout;
+}
+
+/* ================================================== */
+
 int
 CNF_GetPtpPort(void)
 {
@@ -2492,6 +2540,14 @@ CNF_GetPtpPort(void)

 /* ================================================== */

+int
+CNF_GetRefresh(void)
+{
+  return refresh;
+}
+
+/* ================================================== */
+
 char *
 CNF_GetNtsDumpDir(void)
 {
--- a/conf.h
+++ b/conf.h
@@ -44,6 +44,8 @@ extern void CNF_ParseLine(const char *filename, int number, char *line);

 extern void CNF_CreateDirs(uid_t uid, gid_t gid);

+extern void CNF_CheckReadOnlyAccess(void);
+
 extern void CNF_AddInitSources(void);
 extern void CNF_AddSources(void);
 extern void CNF_AddBroadcasts(void);
@@ -58,6 +60,7 @@ extern char *CNF_GetLogDir(void);
 extern char *CNF_GetDumpDir(void);
 extern int CNF_GetLogBanner(void);
 extern int CNF_GetLogMeasurements(int *raw);
+extern int CNF_GetLogSelection(void);
 extern int CNF_GetLogStatistics(void);
 extern int CNF_GetLogTracking(void);
 extern int CNF_GetLogRtc(void);
@@ -141,6 +144,7 @@ typedef enum {
 typedef struct {
  char *name;
  int minpoll;
+  int maxpoll;
  int min_samples;
  int max_samples;
  int nocrossts;
@@ -151,9 +155,12 @@ typedef struct {
 } CNF_HwTsInterface;

 extern int CNF_GetHwTsInterface(unsigned int index, CNF_HwTsInterface **iface);
+extern double CNF_GetHwTsTimeout(void);

 extern int CNF_GetPtpPort(void);

+extern int CNF_GetRefresh(void);
+
 extern char *CNF_GetNtsDumpDir(void);
 extern char *CNF_GetNtsNtpServer(void);
 extern int CNF_GetNtsServerCertAndKeyFiles(const char ***certs, const char ***keys);
--- a/114
+++ b/114
@@ -5,7 +5,7 @@
 #
 # Copyright (C) Richard P. Curnow  1997-2003
 # Copyright (C) Bryan Christianson  2016
-# Copyright (C) Miroslav Lichvar  2009, 2012-2021
+# Copyright (C) Miroslav Lichvar  2009, 2012-2022
 # Copyright (C) Stefan R. Filipek  2019
 #
 # =======================================================================
@@ -111,10 +111,10 @@ For better control, use the options below.
  --without-editline     Don't use editline even if it is available
  --disable-sechash      Disable support for hashes other than MD5
  --without-nettle       Don't use nettle even if it is available
+  --without-gnutls       Don't use gnutls even if it is available
  --without-nss          Don't use NSS even if it is available
  --without-tomcrypt     Don't use libtomcrypt even if it is available
  --disable-nts          Disable NTS support
-  --without-gnutls       Don't use gnutls even if it is available
  --disable-cmdmon       Disable command and monitoring support
  --disable-ntp          Disable NTP support
  --disable-refclock     Disable reference clock support
@@ -128,6 +128,7 @@ For better control, use the options below.
  --without-seccomp      Don't use seccomp even if it is available
  --disable-asyncdns     Disable asynchronous name resolving
  --disable-forcednsretry Don't retry on permanent DNS error
+  --without-aes-gcm-siv  Don't use AES-GCM-SIV for NTS even if it is available
  --without-clock-gettime Don't use clock_gettime() even if it is available
  --disable-timestamping Disable support for SW/HW timestamping
  --enable-ntp-signd     Enable support for MS-SNTP authentication in Samba
@@ -244,7 +245,9 @@ try_setsched=0
 try_lockmem=0
 feat_asyncdns=1
 feat_forcednsretry=1
+try_aes_gcm_siv=1
 try_clock_gettime=1
+try_arc4random=1
 try_recvmmsg=1
 feat_timestamping=1
 try_timestamping=0
@@ -344,6 +347,9 @@ do
    --disable-forcednsretry)
      feat_forcednsretry=0
    ;;
+    --without-aes-gcm-siv)
+      try_aes_gcm_siv=0
+    ;;
    --without-clock-gettime)
      try_clock_gettime=0
    ;;
@@ -421,6 +427,7 @@ case $OPERATINGSYSTEM in
        try_setsched=1
        try_lockmem=1
        try_phc=1
+        try_arc4random=0
        add_def LINUX
        echo "Configuring for " $SYSTEM
    ;;
@@ -563,6 +570,13 @@ if [ "x$MYCFLAGS" = "x" ]; then
  fi
 fi

+TESTCFLAGS="-fwrapv"
+if test_code '-fwrapv' '' "$TESTCFLAGS" '' ''; then
+  GETDATE_CFLAGS="-fwrapv"
+else
+  GETDATE_CFLAGS=""
+fi
+
 if [ "x$MYCC" = "xgcc" ] || [ "x$MYCC" = "xclang" ]; then
  MYCFLAGS="$MYCFLAGS -Wmissing-prototypes -Wall"
 fi
@@ -671,12 +685,12 @@ fi

 if [ $try_clock_gettime = "1" ]; then
  if test_code 'clock_gettime()' 'time.h' '' '' \
-    'clock_gettime(CLOCK_REALTIME, NULL);'
+    'clock_gettime(CLOCK_REALTIME, (void *)1);'
  then
    add_def HAVE_CLOCK_GETTIME
  else
    if test_code 'clock_gettime() in -lrt' 'time.h' '' '-lrt' \
-      'clock_gettime(CLOCK_REALTIME, NULL);'
+      'clock_gettime(CLOCK_REALTIME, (void *)1);'
    then
      add_def HAVE_CLOCK_GETTIME
      EXTRA_LIBS="$EXTRA_LIBS -lrt"
@@ -702,11 +716,14 @@ then
  use_pthread=1
 fi

-if test_code 'arc4random_buf()' 'stdlib.h' '' '' 'arc4random_buf(NULL, 0);'; then
+if [ $try_arc4random = "1" ] && \
+  test_code 'arc4random_buf()' 'stdlib.h' '' '' \
+    'arc4random_buf((void *)1, 1);'
+then
  add_def HAVE_ARC4RANDOM
 else
  if test_code 'getrandom()' 'stdlib.h sys/random.h' '' '' \
-      'return getrandom(NULL, 256, 0);'; then
+      'return getrandom((void *)1, 1, 0);'; then
    add_def HAVE_GETRANDOM
  fi
 fi
@@ -900,7 +917,7 @@ if [ $feat_sechash = "1" ] && [ "x$HASH_LINK" = "x" ]  && [ $try_nettle = "1" ];
    add_def FEAT_SECHASH

    if test_code 'CMAC in nettle' 'nettle/cmac.h' "$test_cflags" "$test_link" \
-      'cmac128_update(NULL, NULL, NULL, 0, NULL);'
+      'cmac128_update((void *)1, (void *)2, (void *)3, 1, (void *)4);'
    then
      add_def HAVE_CMAC
      EXTRA_OBJECTS="$EXTRA_OBJECTS cmac_nettle.o"
@@ -909,6 +926,28 @@ if [ $feat_sechash = "1" ] && [ "x$HASH_LINK" = "x" ]  && [ $try_nettle = "1" ];
  fi
 fi

+if [ $feat_sechash = "1" ] && [ "x$HASH_LINK" = "x" ] && [ $try_gnutls = "1" ]; then
+  test_cflags="`pkg_config --cflags gnutls`"
+  test_link="`pkg_config --libs gnutls`"
+  if test_code 'gnutls' 'gnutls/crypto.h' \
+    "$test_cflags" "$test_link" '
+      return gnutls_hash((void *)1, (void *)2, 1);'
+  then
+    HASH_OBJ="hash_gnutls.o"
+    HASH_LINK="$test_link"
+    MYCPPFLAGS="$MYCPPFLAGS $test_cflags"
+    add_def FEAT_SECHASH
+
+    if test_code 'CMAC in gnutls' 'gnutls/crypto.h' "$test_cflags" "$test_link" \
+      'return gnutls_hmac_init((void *)1, GNUTLS_MAC_AES_CMAC_128, (void *)2, 0);'
+    then
+      add_def HAVE_CMAC
+      EXTRA_OBJECTS="$EXTRA_OBJECTS cmac_gnutls.o"
+      EXTRA_CLI_OBJECTS="$EXTRA_CLI_OBJECTS cmac_gnutls.o"
+    fi
+  fi
+fi
+
 if [ $feat_sechash = "1" ] && [ "x$HASH_LINK" = "x" ]  && [ $try_nss = "1" ]; then
  test_cflags="`pkg_config --cflags nss`"
  test_link="`pkg_config --libs-only-L nss` -lfreebl3 -lnssutil3"
@@ -925,7 +964,7 @@ fi

 if [ $feat_sechash = "1" ] && [ "x$HASH_LINK" = "x" ] && [ $try_tomcrypt = "1" ]; then
  if test_code 'tomcrypt' 'tomcrypt.h' '-I/usr/include/tomcrypt' '-ltomcrypt' \
-    'hash_memory_multi(find_hash("md5"), NULL, NULL, NULL, 0, NULL, 0);'
+    'hash_memory_multi(find_hash("md5"), (void *)1, (void *)2, (void *)3, 1, (void *)4, 1);'
  then
    HASH_OBJ="hash_tomcrypt.o"
    HASH_LINK="-ltomcrypt"
@@ -934,28 +973,6 @@ if [ $feat_sechash = "1" ] && [ "x$HASH_LINK" = "x" ] && [ $try_tomcrypt = "1" ]
  fi
 fi

-if [ $feat_sechash = "1" ] && [ "x$HASH_LINK" = "x" ] && [ $try_gnutls = "1" ]; then
-  test_cflags="`pkg_config --cflags gnutls`"
-  test_link="`pkg_config --libs gnutls`"
-  if test_code 'gnutls' 'gnutls/crypto.h' \
-    "$test_cflags" "$test_link" '
-      return gnutls_hash(NULL, NULL, 0);'
-  then
-    HASH_OBJ="hash_gnutls.o"
-    HASH_LINK="$test_link"
-    MYCPPFLAGS="$MYCPPFLAGS $test_cflags"
-    add_def FEAT_SECHASH
-
-    if test_code 'CMAC in gnutls' 'gnutls/crypto.h' "$test_cflags" "$test_link" \
-      'return gnutls_hmac_init(NULL, GNUTLS_MAC_AES_CMAC_128, NULL, 0);'
-    then
-      add_def HAVE_CMAC
-      EXTRA_OBJECTS="$EXTRA_OBJECTS cmac_gnutls.o"
-      EXTRA_CLI_OBJECTS="$EXTRA_CLI_OBJECTS cmac_gnutls.o"
-    fi
-  fi
-fi
-
 EXTRA_OBJECTS="$EXTRA_OBJECTS $HASH_OBJ"
 EXTRA_CLI_OBJECTS="$EXTRA_CLI_OBJECTS $HASH_OBJ"
 LIBS="$LIBS $HASH_LINK"
@@ -970,27 +987,47 @@ if [ $feat_ntp = "1" ] && [ $feat_nts = "1" ] && [ $try_gnutls = "1" ]; then
  fi
  if test_code 'TLS1.3 in gnutls' 'gnutls/gnutls.h' \
    "$test_cflags" "$test_link $LIBS" '
-      return gnutls_init(NULL, 0) + GNUTLS_TLS1_3 +
-        gnutls_priority_init2(NULL, "", NULL, GNUTLS_PRIORITY_INIT_DEF_APPEND) +
-        gnutls_prf_rfc5705(NULL, 0, "", 0, "", 16, NULL);'
+      return gnutls_init((void *)1, 0) + GNUTLS_TLS1_3 +
+        gnutls_priority_init2((void *)1, "", NULL, GNUTLS_PRIORITY_INIT_DEF_APPEND) +
+        gnutls_prf_rfc5705((void *)1, 0, "", 0, "", 16, (void *)2);'
  then
-    if test_code 'SIV in nettle' \
+    if [ $try_nettle = "1" ] && test_code 'AES-SIV-CMAC in nettle' \
      'nettle/siv-cmac.h' "" "$LIBS" \
-      'siv_cmac_aes128_set_key(NULL, NULL);'
+      'siv_cmac_aes128_set_key((void *)1, (void *)2);'
    then
      EXTRA_OBJECTS="$EXTRA_OBJECTS siv_nettle.o"
      add_def HAVE_SIV
      add_def HAVE_NETTLE_SIV_CMAC
+      if [ $try_aes_gcm_siv = "1" ] && test_code 'AES-GCM-SIV in nettle' \
+        'nettle/siv-gcm.h' "" "$LIBS" \
+        'siv_gcm_aes128_encrypt_message((void *)1, 0, NULL, 0, (void *)2, 16, (void *)3,
+                                        (void *)4);'
+      then
+        add_def HAVE_NETTLE_SIV_GCM
+      fi
    else
-      if test_code 'SIV in gnutls' 'gnutls/crypto.h' \
+      if test_code 'AES-SIV-CMAC in gnutls' 'gnutls/crypto.h' \
        "$test_cflags" "$test_link $LIBS" '
-          return gnutls_aead_cipher_init(NULL, GNUTLS_CIPHER_AES_128_SIV, NULL);'
+          return gnutls_aead_cipher_init((void *)1, GNUTLS_CIPHER_AES_128_SIV, (void *)2);'
      then
        EXTRA_OBJECTS="$EXTRA_OBJECTS siv_gnutls.o"
        add_def HAVE_SIV
+        if [ $try_aes_gcm_siv = "1" ] && test_code 'AES-GCM-SIV in gnutls' \
+          'gnutls/crypto.h' "$test_cflags" "$test_link $LIBS" '
+            return gnutls_aead_cipher_init((void *)1, GNUTLS_CIPHER_AES_128_SIV_GCM,
+                                           (void *)2);'
+        then
+          add_def HAVE_GNUTLS_SIV_GCM
+        fi
+        if test_code 'gnutls_aead_cipher_set_key()' 'gnutls/crypto.h' \
+          "$test_cflags" "$test_link $LIBS" '
+            return gnutls_aead_cipher_set_key((void *)1, (void *)2);'
+        then
+          add_def HAVE_GNUTLS_AEAD_CIPHER_SET_KEY
+        fi
      else
        if test_code 'AES128 in nettle' 'nettle/aes.h' '' "$LIBS" \
-          'aes128_set_encrypt_key(NULL, NULL);'
+          'aes128_set_encrypt_key((void *)1, (void *)2);'
        then
          EXTRA_OBJECTS="$EXTRA_OBJECTS siv_nettle.o"
          add_def HAVE_SIV
@@ -1099,6 +1136,7 @@ do
          s%@CFLAGS@%${MYCFLAGS}%;\
          s%@CPPFLAGS@%${MYCPPFLAGS}%;\
          s%@LDFLAGS@%${MYLDFLAGS}%;\
+          s%@GETDATE_CFLAGS@%${GETDATE_CFLAGS}%;\
          s%@LIBS@%${LIBS}%;\
          s%@EXTRA_LIBS@%${EXTRA_LIBS}%;\
          s%@EXTRA_CLI_LIBS@%${EXTRA_CLI_LIBS}%;\
--- a/contrib/bryan_christianson_1/README.txt
+++ b/contrib/bryan_christianson_1/README.txt
@@ -60,8 +60,8 @@ Support files
 Dates and sizes may differ
 -rw-r--r--  1 yourname  staff  2084  4 Aug 22:54 README.txt
 -rwxr-xr-x  1 yourname  staff   676  4 Aug 21:18 chronylogrotate.sh
-rw-r--r--  1 yourname  staff   543 18 Jul 20:10 org.tuxfamily.chronyc.plist
-rw-r--r--  1 yourname  staff   511 19 Jun 18:30 org.tuxfamily.chronyd.plist
+-rw-r--r--  1 yourname  staff   543 18 Jul 20:10 org.chrony-project.chronyc.plist
+-rw-r--r--  1 yourname  staff   511 19 Jun 18:30 org.chrony-project.chronyd.plist

 If you have used chrony support directories other than those suggested, you
 will need to edit each file and make the appropriate changes.
@@ -83,21 +83,21 @@ sudo chmod +x /usr/local/bin/chronylogrotate.sh
 sudo chown root:wheel /usr/local/bin/chronylogrotate.sh


-2. org.tuxfamily.chronyc.plist
+2. org.chrony-project.chronyc.plist
 This file is the launchd plist that runs logrotation each day. You may
 wish to edit this file to change the time of day at which the rotation
 will run, currently 04:05 am

-sudo cp org.tuxfamily.chronyc.plist /Library/LaunchDaemons
-sudo chown root:wheel /Library/LaunchDaemons/org.tuxfamily.chronyc.plist
-sudo chmod 0644 /Library/LaunchDaemons/org.tuxfamily.chronyc.plist
-sudo launchctl load -w /Library/LaunchDaemons/org.tuxfamily.chronyc.plist
+sudo cp org.chrony-project.chronyc.plist /Library/LaunchDaemons
+sudo chown root:wheel /Library/LaunchDaemons/org.chrony-project.chronyc.plist
+sudo chmod 0644 /Library/LaunchDaemons/org.chrony-project.chronyc.plist
+sudo launchctl load -w /Library/LaunchDaemons/org.chrony-project.chronyc.plist


-3. org.tuxfamily.chronyd.plist
+3. org.chrony-project.chronyd.plist
 This file is the launchd plist that runs chronyd when the Macintosh starts.

-sudo cp org.tuxfamily.chronyd.plist /Library/LaunchDaemons
-sudo chown root:wheel /Library/LaunchDaemons/org.tuxfamily.chronyd.plist
-sudo chmod 0644 /Library/LaunchDaemons/org.tuxfamily.chronyd.plist
-sudo launchctl load -w /Library/LaunchDaemons/org.tuxfamily.chronyd.plist
+sudo cp org.chrony-project.chronyd.plist /Library/LaunchDaemons
+sudo chown root:wheel /Library/LaunchDaemons/org.chrony-project.chronyd.plist
+sudo chmod 0644 /Library/LaunchDaemons/org.chrony-project.chronyd.plist
+sudo launchctl load -w /Library/LaunchDaemons/org.chrony-project.chronyd.plist
--- a/contrib/bryan_christianson_1/org.chrony-project.chronyc.plist
+++ b/contrib/bryan_christianson_1/org.chrony-project.chronyc.plist
@@ -3,7 +3,7 @@
 <plist version="1.0">
 <dict>
 	<key>Label</key>
-	<string>org.tuxfamily.logrotate</string>
+	<string>org.chrony-project.logrotate</string>
 	<key>KeepAlive</key>
 	<false/>
 	<key>ProgramArguments</key>
--- a/contrib/bryan_christianson_1/org.chrony-project.chronyd.plist
+++ b/contrib/bryan_christianson_1/org.chrony-project.chronyd.plist
@@ -3,7 +3,7 @@
 <plist version="1.0">
 <dict>
 	<key>Label</key>
-	<string>org.tuxfamily.chronyd</string>
+	<string>org.chrony-project.chronyd</string>
 	<key>Program</key>
 	<string>/usr/local/sbin/chronyd</string>
 	<key>ProgramArguments</key>
--- a/doc/chrony.conf.adoc
+++ b/doc/chrony.conf.adoc
@@ -3,7 +3,7 @@
 // Copyright (C) Richard P. Curnow  1997-2003
 // Copyright (C) Stephen Wadeley  2016
 // Copyright (C) Bryan Christianson  2017
-// Copyright (C) Miroslav Lichvar  2009-2021
+// Copyright (C) Miroslav Lichvar  2009-2023
 //
 // This program is free software; you can redistribute it and/or modify
 // it under the terms of version 2 of the GNU General Public License as
@@ -63,16 +63,26 @@ source. The client-server relationship is strictly hierarchical: a client might
 synchronise its system time to that of the server, but the server's system time
 will never be influenced by that of a client.
 +
+The server can be specified by its hostname or IP address. If the hostname cannot
+be resolved on start, *chronyd* will try it again in increasing intervals, and
+also when the <<chronyc.adoc#online,*online*>> command is issued in *chronyc*.
+
+The DNS record can change over time. The used address will be replaced with a
+newly resolved address when the server becomes unreachable (i.e. no valid
+response to last 8 requests), unsynchronised, a falseticker (i.e. does not
+agree with a majority of other sources), or the root distance is too large (the
+limit can be configured by the <<maxdistance,*maxdistance*>> directive). The
+automatic replacement happens at most once per 30 minutes.
+
 This directive can be used multiple times to specify multiple servers.
 +
-The directive is immediately followed by either the name of the
-server, or its IP address. It supports the following options:
+The directive supports the following options:
 +
 *minpoll* _poll_:::
 This option specifies the minimum interval between requests sent to the server
 as a power of 2 in seconds. For example, *minpoll 5* would mean that the
 polling interval should not drop below 32 seconds. The default is 6 (64
-seconds), the minimum is -6 (1/64th of a second), and the maximum is 24 (6
+seconds), the minimum is -7 (1/128th of a second), and the maximum is 24 (6
 months). Note that intervals shorter than 6 (64 seconds) should generally not
 be used with public servers on the Internet, because it might be considered
 abuse. A sub-second interval will be enabled only when the server is reachable
@@ -82,7 +92,7 @@ should be in a local network.
 This option specifies the maximum interval between requests sent to the server
 as a power of 2 in seconds. For example, *maxpoll 9* indicates that the polling
 interval should stay at or below 9 (512 seconds). The default is 10 (1024
-seconds), the minimum is -6 (1/64th of a second), and the maximum is 24 (6
+seconds), the minimum is -7 (1/128th of a second), and the maximum is 24 (6
 months).
 *iburst*:::
 With this option, *chronyd* will start with a burst of 4-8 requests in order to
@@ -138,18 +148,33 @@ behind a lot of packets related to a download of some sort).
 If the user knows that round trip delays above a certain level should cause the
 measurement to be ignored, this level can be defined with the *maxdelay*
 option. For example, *maxdelay 0.3* would indicate that measurements with a
-round-trip delay of 0.3 seconds or more should be ignored. The default value is
-3 seconds and the maximum value is 1000 seconds.
+round-trip delay greater than 0.3 seconds should be ignored. The default value
+is 3 seconds and the maximum value is 1000 seconds.
 *maxdelayratio* _ratio_:::
 This option is similar to the *maxdelay* option above. *chronyd* keeps a record
 of the minimum round-trip delay amongst the previous measurements that it has
-buffered. If a measurement has a round trip delay that is greater than the
-specified ratio times the minimum delay, it will be rejected.
+buffered. If a measurement has a round-trip delay that is greater than the
+specified ratio times the minimum delay, it will be rejected. By default, this
+test is disabled.
 *maxdelaydevratio* _ratio_:::
 If a measurement has a ratio of the increase in the round-trip delay from the
 minimum delay amongst the previous measurements to the standard deviation of
 the previous measurements that is greater than the specified ratio, it will be
 rejected. The default is 10.0.
+*maxdelayquant* _p_:::
+This option disables the *maxdelaydevratio* test and specifies the maximum
+acceptable delay as a quantile of the round-trip delay instead of a function of
+the minimum delay amongst the buffered measurements. If a measurement has a
+round-trip delay that is greater than a long-term estimate of the _p_-quantile,
+it will be rejected.
+
+The specified _p_ value should be between 0.05 and 0.95. For example,
+*maxdelayquant 0.2* would indicate that only measurements with the lowest 20
+percent of round-trip delays should be accepted. Note that it can take many
+measurements for the estimated quantile to reach the expected value. This
+option is intended for synchronisation in mostly static local networks with
+very short polling intervals and possibly combined with the *filter* option.
+By default, this test is disabled in favour of the *maxdelaydevratio* test.
 *mindelay* _delay_:::
 This option specifies a fixed minimum round-trip delay to be used instead of
 the minimum amongst the previous measurements. This can be useful in networks
@@ -176,11 +201,12 @@ Set the minimum number of samples kept for this source. This overrides the
 *maxsamples* _samples_:::
 Set the maximum number of samples kept for this source. This overrides the
 <<maxsamples,*maxsamples*>> directive.
-*filter* _samples_:::
+*filter* _polls_:::
 This option enables a median filter to reduce noise in NTP measurements. The
-filter will reduce the specified number of samples to a single sample. It is
-intended to be used with very short polling intervals in local networks where
-it is acceptable to generate a lot of NTP traffic.
+filter will process samples collected in the specified number of polls
+into a single sample. It is intended to be used with very short polling
+intervals in local networks where it is acceptable to generate a lot of NTP
+traffic.
 *offline*:::
 If the server will not be reachable when *chronyd* is started, the *offline*
 option can be specified. *chronyd* will not try to poll the server until it is
@@ -296,16 +322,27 @@ server implementations do not respond to requests containing an unknown
 extension field (*chronyd* as a server responded to such requests since
 version 2.0).
 +
-The following extension field can be enabled by this option:
+This option can be used multiple times to enable multiple extension fields.
+
+The following extension fields are supported:
 +
 _F323_::::
-This is an experimental extension field for some improvements that were
+An experimental extension field to enable several improvements that were
 proposed for the next version of the NTP protocol (NTPv5). The field contains
 root delay and dispersion in higher resolution and a monotonic receive
-timestamp, which enables a frequency transfer between the server and client. It
-can significantly improve stability of the synchronization. Generally, it
-should be expected to work only between servers and clients running the same
-version of *chronyd*.
+timestamp, which enables a frequency transfer between the server and client to
+significantly improve stability of the synchronisation. This field should be
+enabled only for servers known to be running *chronyd* version 4.2 or later.
+_F324_::::
+An experimental extension field to enable the use of the Precision Time
+Protocol (PTP) correction field in NTP-over-PTP messages updated by one-step
+end-to-end transparent clocks in network switches and routers to significantly
+improve accuracy and stability of the synchronisation. NTP-over-PTP can be
+enabled by the <<ptpport,*ptpport*>> directive and setting the *port* option to
+the PTP port. The corrections are applied only to NTP measurements with HW
+timestamps (enabled by the <<hwtimestamp,*hwtimestamp*>> directive). This
+field should be enabled only for servers known to be running *chronyd* version
+4.5 or later.
 {blank}:::

 [[pool]]*pool* _name_ [_option_]...::
@@ -325,12 +362,6 @@ This option sets the desired number of sources to be used from the pool.
 sources responding to requests. The default value is 4 and the maximum value is
 16.
 +
-{blank}::
-When an NTP source is unreachable,
-marked as a falseticker, or has a distance larger than the limit set by the
-<<maxdistance,*maxdistance*>> directive, *chronyd* will try to replace the
-source with a newly resolved address of the name.
-+
 An example of the *pool* directive is
 +
 ----
@@ -398,7 +429,7 @@ error. *chronyd* then enters its normal operating mode.
 An example of the use of the directive is:
 +
 ----
-initstepslew 30 foo.example.net bar.example.net baz.example.net
+initstepslew 30 ntp1.example.net ntp2.example.net ntp3.example.net
 ----
 +
 where 3 NTP servers are used to make the measurement. The _30_ indicates that
@@ -451,16 +482,41 @@ instead.
 Examples:
 +
 ----
-refclock PPS /dev/pps0 lock NMEA refid GPS
-refclock SHM 0 offset 0.5 delay 0.2 refid NMEA noselect
+refclock PPS /dev/pps0 lock NMEA refid GPS1
+refclock SOCK /var/run/chrony.clk.ttyS0.sock offset 0.5 delay 0.2 refid NMEA noselect
 refclock PPS /dev/pps1:clear refid GPS2
 ----
 +
+*SOCK*:::
+Unix domain socket driver. This driver uses a datagram socket to receive
+samples from another application running on the system. The parameter is the
+path to the socket, which *chronyd* will create on start. The format of the
+messages is described in the _refclock_sock.c_ file in the chrony source code.
+
+An application which supports the SOCK protocol is the *gpsd* daemon. It can
+provide accurate measurements using the receiver's PPS signal, and since
+version 3.25 also (much less accurate) measurements based on the timing of
+serial data (e.g. NMEA), which can be useful when the receiver does not provide
+a PPS signal, or it cannot be connected to the computer. The paths where *gpsd*
+expects the sockets to be created by *chronyd* are described in the *gpsd(8)*
+man page. Note that *gpsd* needs to be started after *chronyd* in order to
+connect to the socket.
+
+Examples:
+
+----
+refclock SOCK /var/run/chrony.ttyS0.sock refid GPS1 poll 2 filter 4
+refclock SOCK /var/run/chrony.clk.ttyUSB0.sock refid GPS2 offset 0.2 delay 0.1
+----
+
 *SHM*:::
-NTP shared memory driver. This driver uses a shared memory segment to receive
-samples from another process (e.g. *gpsd*). The parameter is the number of the
-shared memory segment, typically a small number like 0, 1, 2, or 3. The driver
-supports the following option:
+NTP shared memory driver. This driver implements the protocol of the *ntpd*
+driver type 28. It is functionally similar to the SOCK driver, but uses a
+shared memory segment instead of a socket. The parameter is the unit number,
+typically a small number like 0, 1, 2, or 3, from which is derived the key of
+the memory segment as 0x4e545030 + unit.
+
+The driver supports the following option:
 +
 *perm*=_mode_::::
 This option specifies the permissions of the shared memory segment created by
@@ -468,6 +524,16 @@ This option specifies the permissions of the shared memory segment created by
 (read-write access for owner only).
 {blank}:::
 +
+Unlike with the SOCK driver, there is no prescribed order of starting *chronyd*
+and the program providing measurements. Both are expected to create the memory
+segment if it does not exist. *chronyd* will attach to an existing segment even
+if it has a different owner than root or different permissions than the
+permissions specified by the *perm* option. The segment needs to be created
+before untrusted applications or users can execute code to prevent an attacker
+from feeding *chronyd* with false measurements. The owner and permissions of
+the segment can be verified with the *ipcs -m* command. For this reason, the
+SHM driver is deprecated in favor of SOCK.
+
 Examples:
 +
 ----
@@ -475,23 +541,6 @@ refclock SHM 0 poll 3 refid GPS1
 refclock SHM 1:perm=0644 refid GPS2
 ----
 +
-*SOCK*:::
-Unix domain socket driver. It is similar to the SHM driver, but samples are
-received from a Unix domain socket instead of shared memory and the messages
-have a different format. The parameter is the path to the socket, which
-*chronyd* creates on start. An advantage over the SHM driver is that SOCK does
-not require polling and it can receive PPS samples with incomplete time. The
-format of the messages is described in the _refclock_sock.c_ file in the chrony
-source code.
-+
-An application which supports the SOCK protocol is the *gpsd* daemon. The path
-where *gpsd* expects the socket to be created is described in the *gpsd(8)* man
-page. For example:
-+
----
-refclock SOCK /var/run/chrony.ttyS0.sock
----
-+
 *PHC*:::
 PTP hardware clock (PHC) driver. The parameter is the path to the device of
 the PTP clock which should be used as a time source. If the clock is kept in
@@ -511,8 +560,10 @@ Note that some PTP clocks cannot be configured to timestamp only assert or
 clear events, and it is necessary to use the *width* option to filter wrong
 PPS samples.
 *pin*=_index_::::
-This option specifies the index of the pin to which is connected the PPS
-signal. The default value is 0.
+This option specifies the index of the pin which should be enabled for the
+PPS timestamping. If the PHC does not have configurable pins (i.e. the channel
+function is fixed), the index needs to be set to -1 to disable the pin
+configuration. The default value is 0.
 *channel*=_index_::::
 This option specifies the index of the channel for the PPS mode. The default
 value is 0.
@@ -600,7 +651,9 @@ noise in the measurements. With each poll about 40 percent of the stored
 samples are discarded and one final sample is calculated as an average of the
 remaining samples. If the length is 4 or more, at least 4 samples have to be
 collected between polls. For lengths below 4, the filter has to be full. The
-default is 64.
+default is 64. With drivers that perform their own polling (PPS, PHC, SHM), the
+maximum value is adjusted to the number of driver polls per source poll, i.e.
+2^(_poll_ - _dpoll_).
 *prefer*:::
 Prefer this source over sources without the prefer option.
 *noselect*:::
@@ -624,6 +677,13 @@ and that *chronyd* should correct its offset by the current TAI-UTC offset. The
 <<leapsectz,*leapsectz*>> directive must be used with this option and the
 database must be kept up to date in order for this correction to work as
 expected. This option does not make sense with PPS refclocks.
+*local*:::
+This option specifies that the reference clock is an unsynchronised clock which
+is more stable than the system clock (e.g. TCXO, OCXO, or atomic clock) and
+it should be used as a local standard to stabilise the system clock. The
+refclock will bypass the source selection. There should be at most one refclock
+specified with this option and it should have the shortest polling interval
+among all configured sources.
 *minsamples* _samples_:::
 Set the minimum number of samples kept for this source. This overrides the
 <<minsamples,*minsamples*>> directive.
@@ -778,11 +838,16 @@ This directory is used also by the <<ntsdumpdir2,NTS server>> to save keys.
 This directive specifies the maximum interval between NTS-KE handshakes (in
 seconds) in order to refresh the keys authenticating NTP packets. The default
 value is 2419200 (4 weeks) and the maximum value is 2^31-1 (68 years).
+
+The interval must be longer than polling intervals of all configured NTP
+sources using NTS, otherwise the source with a longer polling interval will
+refresh the keys on each poll and no NTP packets will be exchanged.

 [[ntstrustedcerts]]*ntstrustedcerts* [_set-ID_] _file_|_directory_::
-This directive specifies a file or directory containing certificates (in the
-PEM format) of trusted certificate authorities (CA) which can be used to
-verify certificates of NTS servers.
+This directive specifies a file or directory containing trusted certificates
+(in the PEM format) which are needed to verify certificates of NTS-KE servers,
+e.g. certificates of trusted certificate authorities (CA) or self-signed
+certificates of the servers.
 +
 The optional _set-ID_ argument is a number in the range 0 through 2^32-1, which
 selects the set of certificates where certificates from the specified file
@@ -802,10 +867,10 @@ they change (e.g. after a renewal).
 An example is:
 +
 ----
-ntstrustedcerts /etc/pki/nts/foo.crt
-ntstrustedcerts 1 /etc/pki/nts/bar.crt
-ntstrustedcerts 1 /etc/pki/nts/baz.crt
-ntstrustedcerts 2 /etc/pki/nts/qux.crt
+ntstrustedcerts /etc/pki/nts/ca1.example.net.crt
+ntstrustedcerts 1 /etc/pki/nts/ca2.example.net.crt
+ntstrustedcerts 1 /etc/pki/nts/ca3.example.net.crt
+ntstrustedcerts 2 /etc/pki/nts/ntp2.example.net.crt
 ----

 [[nosystemcert]]*nosystemcert*::
@@ -831,6 +896,19 @@ This would disable the time checks until the clock is updated for the first
 time, assuming the first update corrects the clock and later checks can work
 with correct time.

+[[refresh]]*refresh* _interval_::
+This directive specifies the interval (in seconds) between refreshing IP
+addresses of NTP sources specified by hostname. If the hostname no longer
+resolves to the currently used address, it will be replaced with one of the new
+addresses to avoid using a server which is no longer intended for service, even
+if it is still responding correctly and would not be replaced as unreachable.
+Only one source is refreshed at a time. The default value is 1209600 (2 weeks)
+and the maximum value is 2^31-1 (68 years). A value of 0 disables the periodic
+refreshment.
+
+The <<chronyc.adoc#refresh,*refresh*>> command can be used to refresh all
+sources immediately.
+
 === Source selection

 [[authselectmode]]*authselectmode* _mode_::
@@ -889,20 +967,20 @@ before 4.0.
 As an example, the following configuration using the default *mix* mode:
 +
 ----
-server foo.example.net nts
-server bar.example.net nts
-server baz.example.net
-refclock SHM 0
+server ntp1.example.net nts
+server ntp2.example.net nts
+server ntp3.example.net
+refclock SOCK /var/run/chrony.ttyS0.sock
 ----
 +
 is equivalent to the following configuration using the *ignore* mode:
 +
 ----
 authselectmode ignore
-server foo.example.net nts require trust
-server bar.example.net nts require trust
-server baz.example.net
-refclock SHM 0 require trust
+server ntp1.example.net nts require trust
+server ntp2.example.net nts require trust
+server ntp3.example.net
+refclock /var/run/chrony.ttyS0.sock require trust
 ----

 [[combinelimit]]*combinelimit* _limit_::
@@ -1210,12 +1288,16 @@ This would step the system clock if the adjustment is larger than 0.1 seconds, b
 only in the first three clock updates.

 [[maxchange]]*maxchange* _offset_ _start_ _ignore_::
-This directive sets the maximum allowed offset corrected on a clock update. The
-check is performed only after the specified number of updates to allow a large
-initial adjustment of the system clock. When an offset larger than the
-specified maximum occurs, it will be ignored for the specified number of times
-and then *chronyd* will give up and exit (a negative value can be used to never
-exit). In both cases a message is sent to syslog.
+This directive sets the maximum offset to be accepted on a clock update. The
+offset is measured relative to the current estimate of the true time, which is
+different from the system time if a previous slew did not finish.
+
+The check is enabled after the specified number of clock updates to allow a
+large initial offset to be corrected on start. Offsets larger than the
+specified maximum will be ignored for the specified number of times. Another
+large offset will cause *chronyd* to give up and exit. A negative value
+can be used to disable the limit to ignore all large offsets. A syslog message
+will be generated when an offset is ignored or it causes the exit.
 +
 An example of the use of this directive is:
 +
@@ -1267,10 +1349,9 @@ It should be noted that this is not the only means of protection against using
 unreliable estimates. At all times, *chronyd* keeps track of both the estimated
 gain or loss rate, and the error bound on the estimate. When a new estimate is
 generated following another measurement from one of the sources, a weighted
-combination algorithm is used to update the master estimate. So if *chronyd*
-has an existing highly-reliable master estimate and a new estimate is generated
-which has large error bounds, the existing master estimate will dominate in the
-new master estimate.
+combination algorithm is used to update the existing estimate. If it has
+significantly smaller error bounds than the new estimate, the existing estimate
+will dominate in the new combined value.

 [[maxslewrate]]*maxslewrate* _rate-in-ppm_::
 The *maxslewrate* directive sets the maximum rate at which *chronyd* is allowed
@@ -1700,7 +1781,10 @@ save the keys to the _ntskeys_ file and will reload the keys from the file when
 the <<chronyc.adoc#rekey,*rekey*>> command is issued in *chronyc*. The file can
 be periodically copied from another server running *chronyd* (which does
 not have *ntsrotate* set to 0) in order to have one or more servers dedicated
-to NTS-KE. The NTS-KE servers need to be configured with the
+to NTS-KE. The file includes the subsequent key to which the NTS-KE server will
+switch on the next rotation, i.e. the process copying and reloading the file
+does not need to be timed precisely (it can be delayed by up to one rotation
+interval). The NTS-KE servers need to be configured with the
 <<ntsntpserver,*ntsntpserver*>> directive to point the clients to the right NTP
 server.
 +
@@ -1904,8 +1988,9 @@ all* directive.
 [[cmdport]]*cmdport* _port_::
 The *cmdport* directive allows the port that is used for run-time monitoring
 (via the *chronyc* program) to be altered from its default (323). If set to 0,
-*chronyd* will not open the port, this is useful to disable *chronyc*
-access from the Internet. (It does not disable the Unix domain command socket.)
+*chronyd* will not open the port, which disables remote *chronyc* access (with
+a non-default *bindcmdaddress*) and local access for unprivileged users. It
+does not disable the Unix domain command socket.
 +
 An example shows the syntax:
 +
@@ -1914,7 +1999,7 @@ cmdport 257
 ----
 +
 This would make *chronyd* use UDP 257 as its command port. (*chronyc* would
-need to be run with the *-p 257* switch to inter-operate correctly.)
+need to be run with the *-p 257* option to inter-operate correctly.)

 [[cmdratelimit]]*cmdratelimit* [_option_]...::
 This directive enables response rate limiting for command packets. It is
@@ -2055,9 +2140,11 @@ from the example line above):
 . Stratum of remote computer. [2]
 . RFC 5905 tests 1 through 3 (1=pass, 0=fail) [111]
 . RFC 5905 tests 5 through 7 (1=pass, 0=fail) [111]
-. Tests for maximum delay, maximum delay ratio and maximum delay dev ratio,
-  against defined parameters, and a test for synchronisation loop (1=pass,
-  0=fail) [1111]
+. Results of the *maxdelay*, *maxdelayratio*, and *maxdelaydevratio* (or
+  *maxdelayquant*) tests, and a test for synchronisation loop (1=pass,
+  0=fail). The first test from these four also checks the server precision,
+  response time, and whether an interleaved response is acceptable for
+  synchronisation. [1111]
 . Local poll [10]
 . Remote poll [10]
 . '`Score`' (an internal score within each polling level used to decide when to
@@ -2131,6 +2218,78 @@ from the example line above):
  the source is more variable than the delay of packets sent from the source
  back. [0.00, i.e. no correction for asymmetry]
 +
+*selection*:::
+This option logs information about selection of sources for synchronisation to
+a file called _selection.log_. Note that the rate of entries written to this
+file grows quadratically with the number of specified sources (each measurement
+triggers the selection for all sources). An example line (which actually
+appears as a single line in the file) from the log file is shown below.
+
+----
+2022-05-01 02:01:20 203.0.113.15    * -----  377  1.00  \
+     4.228e+01 -1.575e-04  1.239e-04
+----
+
+The columns are as follows (the quantities in square brackets are the values
+from the example line above):
+
+. Date [2022-05-01]
+. Hour:Minute:Second. Note that the date-time pair is expressed in
+  UTC, not the local time zone. [02:01:20]
+. IP address or reference ID of the source. [203.0.113.15]
+. State of the source indicated with one of the following symbols. [*]
+{blank}::::
+Not considered selectable for synchronisation:
+* _N_ - has the *noselect* option.
+* _s_ - is not synchronised.
+* _M_ - does not have enough measurements.
+* _d_ - has a root distance larger than the maximum distance (configured by the
+        <<maxdistance,*maxdistance*>> directive).
+* _~_ - has a jitter larger than the maximum jitter (configured by the
+        <<maxjitter,*maxjitter*>> directive).
+* _w_ - waits for other sources to get out of the _M_ state.
+* _S_ - has older measurements than other sources.
+* _O_ - has a stratum equal or larger than the orphan stratum (configured by
+        the <<local,*local*>> directive).
+* _T_ - does not fully agree with sources that have the *trust* option.
+* _x_ - does not agree with other sources (falseticker).
+{blank}::::
+Considered selectable for synchronisation, but not currently used:
+* _W_ - waits for other sources to be selectable (required by the
+        <<minsources,*minsources*>> directive, or the *require* option of
+        another source).
+* _P_ - another selectable source is preferred due to the *prefer* option.
+* _U_ - waits for a new measurement (after selecting a different best source).
+* _D_ - has, or recently had, a root distance which is too large to be combined
+        with other sources (configured by the <<combinelimit,*combinelimit*>>
+        directive).
+{blank}::::
+Used for synchronisation of the local clock:
+* _+_ - combined with the best source.
+* _*_ - selected as the best source to update the reference data (e.g. root
+        delay, root dispersion).
+. Current effective selection options of the source. which can be different
+  from the configured options due to the authentication selection mode
+  (configured by the <<authselectmode,*authselectmode*>> directive). [-----]
+* _N_ indicates the *noselect* option.
+* _P_ indicates the *prefer* option.
+* _T_ indicates the *trust* option.
+* _R_ indicates the *require* option.
+. Reachability register printed as an octal number. The register has 8 bits and
+  is updated on every received or missed packet from the source. A value of 377
+  indicates that a valid reply was received for all from the last eight
+  transmissions. [377]
+. Current score against the source in the _*_ state. The scoring system avoids
+  frequent reselection when multiple sources have a similar root distance. A
+  value larger than 1 indicates this source was better than the _*_ source in
+  recent selections. If the score reaches 10, the best source will be reselected
+  and the scores will be reset to 1. [1.00]
+. Interval since the last measurement of the source in seconds. [4.228e+01]
+. Lower endpoint of the interval which was expected to contain the true offset
+  of the local clock determined by the root distance of the source. [-1.575e-04]
+. Upper endpoint of the interval which was expected to contain the true offset
+  of the local clock determined by the root distance of the source. [1.239e-04]
+
 *tracking*:::
 This option logs changes to the estimate of the system's gain or loss rate, and
 any slews made, to a file called _tracking.log_. An example line (which
@@ -2385,19 +2544,29 @@ be enabled by the *xleave* option in the <<server,*server*>> or the
 +
 This directive is supported on Linux 3.19 and newer. The NIC must support HW
 timestamping, which can be verified with the *ethtool -T* command. The list of
-capabilities should include _SOF_TIMESTAMPING_RAW_HARDWARE_,
-_SOF_TIMESTAMPING_TX_HARDWARE_, and _SOF_TIMESTAMPING_RX_HARDWARE_. Receive
-filter _HWTSTAMP_FILTER_ALL_, or _HWTSTAMP_FILTER_NTP_ALL_, is necessary for
-timestamping of received NTP packets. Timestamping of packets received on bridged
-and bonded interfaces is supported on Linux 4.13 and newer. When *chronyd* is
-running, no other process (e.g. a PTP daemon) should be working with the NIC
-clock.
+capabilities should include _hardware-raw-clock_, _hardware-transmit_, and
+_hardware-receive_. The receive filter _all_, or _ntp_, is necessary for
+timestamping of received NTP packets. Timestamping of packets received on
+bridged and bonded interfaces is supported on Linux 4.13 and newer. If HW
+timestamping does not work for received packets, *chronyd* will use kernel
+receive timestamps instead. Transmit-only HW timestamping can still be useful
+to improve stability of the synchronisation.
+
+*chronyd* does not synchronise the NIC clock. It assumes the clock is running
+free. Multiple instances of *chronyd* can use the same interface with enabled
+HW timestamping. Applications which need HW timestamping with a synchronised
+clock (e.g. a PTP daemon) should use a virtual clock running on top of the
+physical clock created by writing to _/sys/class/ptp/ptpX/n_vclocks_. This
+feature is available on Linux 5.14 and newer.
 +
 If the kernel supports software timestamping, it will be enabled for all
-interfaces. The source of timestamps (i.e. hardware, kernel, or daemon) is
-indicated in the _measurements.log_ file if enabled by the <<log,*log
-measurements*>> directive, and the <<chronyc.adoc#ntpdata,*ntpdata*>> report in
-*chronyc*.
+interfaces automatically.
+
+The source of timestamps (i.e. hardware, kernel, or daemon) is indicated on the
+client side in the _measurements.log_ file (if enabled by the <<log,*log*>>
+directive) and the <<chronyc.adoc#ntpdata,*ntpdata*>> report. On the server
+side, the number of served timestamps from each source is provided in the
+<<chronyc.adoc#serverstats,*serverstats*>> report.
 +
 This directive can be used multiple times to enable HW timestamping on multiple
 interfaces. If the specified interface is _*_, *chronyd* will try to enable HW
@@ -2407,10 +2576,15 @@ The *hwtimestamp* directive has the following options:
 +
 *minpoll* _poll_:::
 This option specifies the minimum interval between readings of the NIC clock.
-It's defined as a power of two. It should correspond to the minimum polling
+It's defined as a power of 2. It should correspond to the minimum polling
 interval of all NTP sources and the minimum expected polling interval of NTP
-clients. The default value is 0 (1 second) and the minimum value is -6 (1/64th
-of a second).
+clients. The default value is 0 (1 second), the minimum value is -6 (1/64th
+of a second), and the maximum value is 20 (about 12 days).
+*maxpoll* _poll_:::
+This option specifies the maximum interval between readings of the NIC clock,
+as a power of 2. The default value is *minpoll* + 1, i.e. 1 (2 seconds) with
+the default *minpoll* of 0. The minimum and maximum values are the same as with
+the *minpoll* option.
 *minsamples* _samples_:::
 This option specifies the minimum number of readings kept for tracking of the
 NIC clock. The default value is 2.
@@ -2449,7 +2623,8 @@ is selected by default. Some NICs can timestamp PTP packets only. By default,
 they will be configured with the _none_ filter and expected to provide hardware
 timestamps for transmitted packets only. Timestamping of PTP packets is useful
 with NTP-over-PTP enabled by the <<chrony.conf.adoc#ptpport,*ptpport*>>
-directive. Forcing timestamping of all packets with the _all_ filter could be
+directive, or when another application is receiving PTP packets on the
+interface. Forcing timestamping of all packets with the _all_ filter could be
 useful if the NIC supported both the _all_ and _ntp_ filters, and it should
 timestamp both NTP and PTP packets, or NTP packets on a different UDP port.
 {blank}::
@@ -2462,6 +2637,27 @@ hwtimestamp eth1 txcomp 300e-9 rxcomp 645e-9
 hwtimestamp *
 ----

+[[hwtstimeout]]*hwtstimeout* _timeout_::
+If hardware timestamping is used with a close NTP server, or the NIC or its
+driver is slow in providing the transmit timestamp of NTP requests, a response
+from the server can be received before the transmit timestamp of the request.
+To avoid calculating the offset with a less accurate transmit timestamp,
+*chronyd* can save the response for later processing and wait for the hardware
+transmit timestamp. There is no guarantee that the timestamp will be provided
+(NICs typically have a limited rate of transmit timestamping). This directive
+configures how long should *chronyd* wait for the timestamp after receiving a
+valid response from the server. If a second valid response is received from the
+server while waiting for the timestamp, they will be both processed
+immediately.
+
+The default value is 0.001 seconds, which should be sufficient with most
+hardware. If you frequently see kernel transmit timestamps in the
+_measurements.log_ file or <<chronyc.adoc#ntpdata,*ntpdata*>> report, and it is
+not a server handling a high rate of requests in the interleaved mode on the
+same interface (which would compete with timestamping of the server's own
+requests), increasing the timeout to 0.01 or possibly even longer might help.
+Note that the maximum timeout is limited by the NTP polling interval.
+
 [[keyfile]]*keyfile* _file_::
 This directive is used to specify the location of the file containing symmetric
 keys which are shared between NTP servers and clients, or peers, in order to
@@ -2495,7 +2691,7 @@ The type is a name of a cryptographic hash function or cipher which is used to
 generate and verify the MAC. The default type is *MD5*, which is always
 supported.
 If *chronyd* was built with enabled support for hashing using a crypto library
-(nettle, nss, or libtomcrypt), the following functions are available: *MD5*,
+(Nettle, GnuTLS, NSS, or LibTomCrypt), the following functions are available: *MD5*,
 *SHA1*, *SHA256*, *SHA384*, *SHA512*. Depending on which library and version is
 *chronyd* using, some of the following hash functions and ciphers may
 also be available:
@@ -2545,24 +2741,27 @@ pidfile /run/chronyd.pid
 The *ptpport* directive enables *chronyd* to send and receive NTP messages
 contained in PTP event messages (NTP-over-PTP) to enable hardware timestamping
 on NICs which cannot timestamp NTP packets, but can timestamp unicast PTP
-packets. The port recognized by the NICs is 319 (PTP event port). The default
-value is 0 (disabled).
+packets, and also use corrections provided by PTP one-step end-to-end
+transparent clocks in network switches and routers. The port recognized by the
+NICs and PTP transparent clocks is 319 (PTP event port). The default value is 0
+(disabled).
 +
 The NTP-over-PTP support is experimental. The protocol and configuration can
-change in future. It should be used only in local networks and expected to work
-only between servers and clients running the same version of *chronyd*.
+change in future. It should be used only in local networks.
 +
 The PTP port will be open even if *chronyd* is not configured to operate as a
 server or client. The directive does not change the default protocol of
 specified NTP sources. Each NTP source that should use NTP-over-PTP needs to
 be specified with the *port* option set to the PTP port. To actually enable
 hardware timestamping on NICs which can timestamp PTP packets only, the
-*rxfilter* option of the *hwtimestamp* directive needs to be set to _ptp_.
+*rxfilter* option of the *hwtimestamp* directive needs to be set to _ptp_. The
+extension field _F324_ needs to be enabled to use the corrections provided by
+the PTP transparent clocks.
 +
 An example of client configuration is:
 +
 ----
-server foo.example.net minpoll 0 maxpoll 0 xleave port 319
+server ntp1.example.net minpoll 0 maxpoll 0 xleave port 319 extfield F324
 hwtimestamp * rxfilter ptp
 ptpport 319
 ----
@@ -2623,13 +2822,13 @@ the following methods:
  facilities.
 * Use public servers from the https://www.pool.ntp.org/[pool.ntp.org] project.

-Assuming that your NTP servers are called _foo.example.net_, _bar.example.net_
-and _baz.example.net_, your _chrony.conf_ file could contain as a minimum:
+Assuming that your NTP servers are called _ntp1.example.net_, _ntp2.example.net_
+and _ntp3.example.net_, your _chrony.conf_ file could contain as a minimum:

 ----
-server foo.example.net
-server bar.example.net
-server baz.example.net
+server ntp1.example.net
+server ntp2.example.net
+server ntp3.example.net
 ----

 However, you will probably want to include some of the other directives. The
@@ -2640,9 +2839,9 @@ synchronisation. The smallest useful configuration file would look something
 like:

 ----
-server foo.example.net iburst
-server bar.example.net iburst
-server baz.example.net iburst
+server ntp1.example.net iburst
+server ntp2.example.net iburst
+server ntp3.example.net iburst
 driftfile @CHRONYVARDIR@/drift
 makestep 1.0 3
 rtcsync
@@ -2666,9 +2865,9 @@ option will enable a secure synchronisation to the servers. The configuration
 file could look like:

 ----
-server foo.example.net iburst nts
-server bar.example.net iburst nts
-server baz.example.net iburst nts
+server ntp1.example.net iburst nts
+server ntp2.example.net iburst nts
+server ntp3.example.net iburst nts
 driftfile @CHRONYVARDIR@/drift
 makestep 1.0 3
 rtcsync
@@ -2682,14 +2881,14 @@ additional configuration to tell *chronyd* when the connection goes up and
 down. This saves the program from continuously trying to poll the servers when
 they are inaccessible.

-Again, assuming that your NTP servers are called _foo.example.net_,
-_bar.example.net_ and _baz.example.net_, your _chrony.conf_ file would now
+Again, assuming that your NTP servers are called _ntp1.example.net_,
+_ntp2.example.net_ and _ntp3.example.net_, your _chrony.conf_ file would now
 contain:

 ----
-server foo.example.net offline
-server bar.example.net offline
-server baz.example.net offline
+server ntp1.example.net offline
+server ntp2.example.net offline
+server ntp3.example.net offline
 driftfile @CHRONYVARDIR@/drift
 makestep 1.0 3
 rtcsync
@@ -2873,9 +3072,9 @@ configuration files are shown.
 For the _chrony.conf_ file, the following can be used as an example.

 ----
-server foo.example.net maxdelay 0.4 offline
-server bar.example.net maxdelay 0.4 offline
-server baz.example.net maxdelay 0.4 offline
+server ntp1.example.net maxdelay 0.4 offline
+server ntp2.example.net maxdelay 0.4 offline
+server ntp3.example.net maxdelay 0.4 offline
 logdir /var/log/chrony
 log statistics measurements tracking
 driftfile @CHRONYVARDIR@/drift
@@ -2934,10 +3133,10 @@ configuration).
 The configuration file could look like:

 ----
-server foo.example.net iburst
-server bar.example.net iburst
-server baz.example.net iburst
-server qux.example.net iburst
+server ntp1.example.net iburst
+server ntp2.example.net iburst
+server ntp3.example.net iburst
+server ntp4.example.net iburst
 makestep 1.0 3
 rtcsync
 allow
@@ -2954,7 +3153,7 @@ dumpdir @CHRONYRUNDIR@
 == BUGS

 For instructions on how to report bugs, please visit
-https://chrony.tuxfamily.org/.
+https://chrony-project.org/.

 == AUTHORS

--- a/doc/chronyc.adoc
+++ b/doc/chronyc.adoc
@@ -2,7 +2,7 @@
 //
 // Copyright (C) Richard P. Curnow  1997-2003
 // Copyright (C) Stephen Wadeley  2016
-// Copyright (C) Miroslav Lichvar  2009-2017, 2019-2020
+// Copyright (C) Miroslav Lichvar  2009-2017, 2019-2023
 //
 // This program is free software; you can redistribute it and/or modify
 // it under the terms of version 2 of the GNU General Public License as
@@ -89,6 +89,10 @@ format. Reverse DNS lookups will be disabled, time will be printed as number of
 seconds since the epoch, and values in seconds will not be converted to other
 units.

+*-e*::
+With this option each *chronyc* response will end with a line containing a
+single dot.
+
 *-d*::
 This option enables printing of debugging messages if *chronyc* was compiled
 with debugging support.
@@ -99,12 +103,15 @@ With this option multiple commands can be specified. Each argument will be
 interpreted as a whole command.

 *-h* _host_::
-This option allows the user to specify which host (or comma-separated list of
-addresses) running the *chronyd* program is to be contacted. This allows for
-remote monitoring, without having to connect over SSH to the other host first.
+This option specifies the host to be contacted by *chronyc*. It can be
+specified with a hostname, IP address, or path to the local Unix domain socket.
+Multiple values can be specified as a comma-separated list to provide a
+fallback.
 +
-The default is to contact *chronyd* running on the same host where
-*chronyc* is being run.
+The default value is _@CHRONYRUNDIR@/chronyd.sock,127.0.0.1,::1_, i.e. the host
+where *chronyc* is being run. First, it tries to connect to the Unix domain
+socket and if that fails (e.g. due to running under a non-root user), it
+will try to connect to 127.0.0.1 and then ::1.

 *-p* _port_::
 This option allows the user to specify the UDP port number which the target
@@ -137,7 +144,7 @@ The *tracking* command displays parameters about the system's clock
 performance. An example of the output is shown below.
 +
 ----
-Reference ID    : CB00710F (foo.example.net)
+Reference ID    : CB00710F (ntp1.example.net)
 Stratum         : 3
 Ref time (UTC)  : Fri Jan 27 09:49:17 2017
 System time     : 0.000006523 seconds slow of NTP time
@@ -171,21 +178,25 @@ with an IPv4 address.
 *Stratum*:::
 The stratum indicates how many hops away from a computer with an attached
 reference clock we are. Such a computer is a stratum-1 computer, so the
-computer in the example is two hops away (i.e. _foo.example.net_ is a
+computer in the example is two hops away (i.e. _ntp1.example.net_ is a
 stratum-2 and is synchronised from a stratum-1).
 *Ref time*:::
 This is the time (UTC) at which the last measurement from the reference
 source was processed.
 *System time*:::
-In normal operation, *chronyd* by default never steps the system clock, because
-any jump in the time can have adverse consequences for certain application
-programs. Instead, any error in the system clock is corrected by slightly
-speeding up or slowing down the system clock until the error has been removed,
-and then returning to the system clock's normal speed. A consequence of this is
-that there will be a period when the system clock (as read by other programs)
-will be different from *chronyd*'s estimate of the current true time (which it
-reports to NTP clients when it is operating as a server). The value reported
-on this line is the difference due to this effect.
+This is the current offset between the NTP clock and system clock. The NTP
+clock is a software (virtual) clock maintained by *chronyd*, which is
+synchronised to the configured time sources and provides time to NTP clients.
+The system clock is synchronised to the NTP clock. To avoid steps in the
+system time, which might have adverse consequences for certain applications,
+the system clock is normally corrected only by speeding up or slowing down (up
+to the rate configured by the <<chrony.conf.adoc#maxslewrate,*maxslewrate*>>
+directive). If the offset is too large, this correction will take a very long
+time. A step can be forced by the <<makestep,*makestep*>> command, or the
+<<chrony.conf.adoc#makestep,*makestep*>> directive in the configuration file.
+
+Note that all other offsets reported by *chronyc* and most offsets in the log
+files are relative to the NTP clock, not the system clock.
 *Last offset*:::
 This is the estimated local offset on the last clock update. A positive value
 indicates the local time (as previously estimated true time) was ahead of the
@@ -310,8 +321,8 @@ extra caption lines are shown as a reminder of the meanings of the columns.
 MS Name/IP address         Stratum Poll Reach LastRx Last sample
 ===============================================================================
 #* GPS0                          0   4   377    11   -479ns[ -621ns] +/-  134ns
-^? foo.example.net               2   6   377    23   -923us[ -924us] +/-   43ms
-^+ bar.example.net               1   6   377    21  -2629us[-2619us] +/-   86ms
+^? ntp1.example.net              2   6   377    23   -923us[ -924us] +/-   43ms
+^+ ntp2.example.net              1   6   377    21  -2629us[-2619us] +/-   86ms
 ----
 +
 The columns are as follows:
@@ -368,9 +379,9 @@ offset. This can be suffixed by _ns_ (indicating nanoseconds), _us_
 (indicating microseconds), _ms_ (indicating milliseconds), or _s_ (indicating
 seconds). The number to the left of the square brackets shows the original
 measurement, adjusted to allow for any slews applied to the local clock
-since. The number following the _+/-_ indicator shows the margin of error in
-the measurement. Positive offsets indicate that the local clock is ahead of
-the source.
+since. Positive offsets indicate that the local clock is ahead of the source.
+The number following the _+/-_ indicator shows the margin of error in the
+measurement (NTP root distance).

 [[sourcestats]]*sourcestats* [*-a*] [*-v*]::
 The *sourcestats* command displays information about the drift rate and offset
@@ -389,7 +400,7 @@ An example report is:
 ----
 Name/IP Address            NP  NR  Span  Frequency  Freq Skew  Offset  Std Dev
 ===============================================================================
-foo.example.net            11   5   46m     -0.001      0.045      1us    25us
+ntp1.example.net           11   5   46m     -0.001      0.045      1us    25us
 ----
 +
 The columns are as follows:
@@ -433,9 +444,9 @@ An example of the output is shown below.
 ----
 S Name/IP Address        Auth COpts EOpts Last Score     Interval  Leap
 =======================================================================
-D foo.example.net           Y ----- --TR-    4   1.0   -61ms   +62ms  N
-* bar.example.net           N ----- -----    0   1.0 -6846us +7305us  N
-+ baz.example.net           N ----- -----   10   1.0 -7381us +7355us  N
+D ntp1.example.net          Y ----- --TR-    4   1.0   -61ms   +62ms  N
+* ntp2.example.net          N ----- -----    0   1.0 -6846us +7305us  N
+ ntp3.example.net          N ----- -----   10   1.0 -7381us +7355us  N
 ----
 +
 The columns are as follows:
@@ -448,6 +459,7 @@ states are reported.
 The following states indicate the source is not considered selectable for
 synchronisation:
 * _N_ - has the *noselect* option.
+* _s_ - is not synchronised.
 * _M_ - does not have enough measurements.
 * _d_ - has a root distance larger than the maximum distance (configured by the
        <<chrony.conf.adoc#maxdistance,*maxdistance*>> directive).
@@ -492,8 +504,8 @@ This column displays the configured selection options of the source.
 This column displays the current effective selection options of the source,
 which can be different from the configured options due to the authentication
 selection mode (configured by the
-<<chrony.conf.adoc#authselmode,*authselmode*>> directive). The symbols are the
-same as in the *COpts* column.
+<<chrony.conf.adoc#authselectmode,*authselectmode*>> directive). The symbols
+are the same as in the *COpts* column.
 *Last*:::
 This column displays how long ago was the last measurement of the source made
 when the selection was performed.
@@ -514,6 +526,23 @@ This column displays the current leap status of the source.
 * _-_ indicates that a leap second will be deleted at the end of the month.
 * _?_ indicates the unknown status (i.e. no valid measurement was made).

+[[selectopts]]*selectopts* _address|refid_ [_+|-option_]...::
+The *selectopts* command modifies the configured selection options of an NTP
+source specified by IP address (or the _ID#XXXXXXXXXX_ identifier used for
+unknown addresses), or a reference clock specified by reference ID as a string.
+
+The selection options can be added with the *+* symbol or removed with the *-*
+symbol. The *selectdata* command can be used to verify the configuration. The
+modified options will be applied in the next source selection, e.g. when a new
+measurement is made, or the *reselect* command is executed.
+
+An example of using this command is shown below.
+
+----
+selectopts 1.2.3.4 -noselect +prefer
+selectopts GPS +trust
+----
+
 [[reselect]]*reselect*::
 To avoid excessive switching between sources, *chronyd* can stay synchronised
 to a source even when it is not currently the best one among the available
@@ -563,9 +592,9 @@ shown below.
 ----
 Name/IP address             Mode KeyID Type KLen Last Atmp  NAK Cook CLen
 =========================================================================
-foo.example.net              NTS     1   15  256 135m    0    0    8  100
-bar.example.net               SK    30   13  128    -    0    0    0    0
-baz.example.net                -     0    0    0    -    0    0    0    0
+ntp1.example.net             NTS     1   15  256 135m    0    0    8  100
+ntp2.example.net              SK    30   13  128    -    0    0    0    0
+ntp3.example.net               -     0    0    0    -    0    0    0    0
 ----
 +
 The columns are as follows:
@@ -602,6 +631,7 @@ be reported:
 * 13: AES128
 * 14: AES256
 * 15: AEAD-AES-SIV-CMAC-256
+* 30: AEAD-AES-128-GCM-SIV
 *KLen*:::
 This column shows the length of the key in bits.
 *Last*:::
@@ -658,6 +688,7 @@ RX timestamping : Kernel
 Total TX        : 24
 Total RX        : 24
 Total valid RX  : 24
+Total good RX   : 22
 ----
 +
 The fields are explained as follows:
@@ -695,7 +726,8 @@ packets sent to the source is more variable than the delay of packets sent
 from the source back.
 *NTP tests*:::
 Results of RFC 5905 tests 1 through 3, 5 through 7, and tests for maximum
-delay, delay ratio, delay dev ratio, and synchronisation loop.
+delay, delay ratio, delay dev ratio (or delay quantile), and synchronisation
+loop.
 *Interleaved*:::
 This shows if the response was in the interleaved mode.
 *Authenticated*:::
@@ -710,7 +742,10 @@ The number of packets sent to the source.
 *Total RX*:::
 The number of all packets received from the source.
 *Total valid RX*:::
-The number of valid packets received from the source.
+The number of packets which passed the first two groups of NTP tests.
+*Total good RX*:::
+The number of packets which passed all three groups of NTP tests, i.e. the NTP
+measurement was accepted.

 [[add_peer]]*add peer* _name_ [_option_]...::
 The *add peer* command allows a new NTP peer to be added whilst
@@ -723,7 +758,7 @@ parameters and options is identical to that for the
 An example of using this command is shown below.
 +
 ----
-add peer foo.example.net minpoll 6 maxpoll 10 key 25
+add peer ntp1.example.net minpoll 6 maxpoll 10 key 25
 ----

 [[add_pool]]*add pool* _name_ [_option_]...::
@@ -737,7 +772,7 @@ directive in the configuration file.
 An example of using this command is shown below:
 +
 ----
-add pool foo.example.net maxsources 3 iburst
+add pool ntp1.example.net maxsources 3 iburst
 ----

 [[add_server]]*add server* _name_ [_option_]...::
@@ -751,7 +786,7 @@ directive in the configuration file.
 An example of using this command is shown below:
 +
 ----
-add server foo.example.net minpoll 6 maxpoll 10 key 25
+add server ntp1.example.net minpoll 6 maxpoll 10 key 25
 ----

 [[delete]]*delete* _address_::
@@ -827,7 +862,7 @@ IPv6 addresses have first 48 bits equal to _2001:db8:789a_.
 Example of the three-argument form of the command is:
 +
 ----
-burst 2/10 foo.example.net
+burst 2/10 ntp1.example.net
 ----

 [[maxdelay]]*maxdelay* _address_ _delay_::
@@ -893,7 +928,7 @@ uses an IP address or a hostname. These forms are illustrated below.
 offline
 offline 255.255.255.0/1.2.3.0
 offline 2001:db8:789a::/48
-offline foo.example.net
+offline ntp1.example.net
 ----
 +
 The second form means that the *offline* command is to be applied to any source
@@ -935,17 +970,26 @@ current set of sources. It is equivalent to the *polltarget* option in the

 [[refresh]]*refresh*::
 The *refresh* command can be used to force *chronyd* to resolve the names of
-configured sources to IP addresses again, e.g. after suspending and resuming
-the machine in a different network.
+configured NTP sources to IP addresses again and replace any addresses missing
+in the list of resolved addresses.
 +
-Sources that stop responding will be replaced with newly resolved addresses
-automatically after 8 polling intervals, but this command can still be useful
-to replace them immediately and not wait until they are marked as unreachable.
+Sources that stop responding are replaced with newly resolved addresses
+automatically after 8 polling intervals. This command can be used to replace
+them immediately, e.g. after suspending and resuming the machine in a different
+network.
+
+Note that with pools which have more than 16 addresses, or not all IPv4 or IPv6
+addresses are included in a single DNS response (e.g. pool.ntp.org), this
+command might replace the addresses even if they are still in the pool.

 [[reload]]*reload* *sources*::
 The *reload sources* command causes *chronyd* to re-read all _*.sources_ files
 from the directories specified by the
 <<chrony.conf.adoc#sourcedir,*sourcedir*>> directive.
+
+Note that modified sources (e.g. specified with a new option) are not modified
+in memory. They are removed and added again, which causes them to lose old
+measurements and reset the selection state.

 [[sourcename]]*sourcename* _address_::
 The *sourcename* command prints the original hostname or address that was
@@ -1054,7 +1098,7 @@ particular host.
 Examples of use, showing a named host and a numeric IP address, are as follows:
 +
 ----
-accheck foo.example.net
+accheck ntp1.example.net
 accheck 1.2.3.4
 accheck 2001:db8::1
 ----
@@ -1081,7 +1125,7 @@ An example of the output is:
 Hostname                      NTP   Drop Int IntL Last     Cmd   Drop Int  Last
 ===============================================================================
 localhost                       2      0   2   -   133      15      0  -1     7
-foo.example.net                12      0   6   -    23       0      0   -     -
+ntp1.example.net               12      0   6   -    23       0      0   -     -
 ----
 +
 Each row shows the data for a single host. Only hosts that have passed the host
@@ -1123,6 +1167,12 @@ Authenticated NTP packets  : 189
 Interleaved NTP packets    : 43
 NTP timestamps held        : 44
 NTP timestamp span         : 120
+NTP daemon RX timestamps   : 0
+NTP daemon TX timestamps   : 1537
+NTP kernel RX timestamps   : 1590
+NTP kernel TX timestamps   : 43
+NTP hardware RX timestamps : 0
+NTP hardware TX timestamps : 0
 ----
 +
 The fields have the following meaning:
@@ -1157,10 +1207,24 @@ The number of pairs of receive and transmit timestamps that the server is
 currently holding in memory for clients using the interleaved mode.
 *NTP timestamp span*:::
 The interval (in seconds) covered by the currently held NTP timestamps.
-{blank}::
-+
-Note that the numbers reported by this overflow to zero after 4294967295
-(32-bit values).
+*NTP daemon RX timestamps*:::
+The number of NTP responses which included a receive timestamp captured by the
+daemon.
+*NTP daemon TX timestamps*:::
+The number of NTP responses which included a transmit timestamp captured by the
+daemon.
+*NTP kernel RX timestamps*:::
+The number of NTP responses which included a receive timestamp captured by the
+kernel.
+*NTP kernel TX timestamps*:::
+The number of NTP responses (in the interleaved mode) which included a transmit
+timestamp captured by the kernel.
+*NTP hardware RX timestamps*:::
+The number of NTP responses which included a receive timestamp captured by the
+NIC.
+*NTP hardware TX timestamps*:::
+The number of NTP responses (in the interleaved mode) which included a transmit
+timestamp captured by the NIC.

 [[allow]]*allow* [*all*] [_subnet_]::
 The effect of the allow command is identical to the
@@ -1199,8 +1263,8 @@ deny all
 *local* *off*::
 The *local* command allows *chronyd* to be told that it is to appear as a
 reference source, even if it is not itself properly synchronised to an external
-source. (This can be used on isolated networks, to allow one computer to be a
-master time server with the other computers slaving to it.)
+source. This can be used on isolated networks, to allow a computer to be the
+primary time server for other computers.
 +
 The first form enables the local reference mode on the host. The syntax is
 identical to the <<chrony.conf.adoc#local,*local*>> directive in the
@@ -1261,7 +1325,7 @@ used to check whether monitoring access is permitted from a named host.
 Examples of use are as follows:
 +
 ----
-cmdaccheck foo.example.net
+cmdaccheck ntp1.example.net
 cmdaccheck 1.2.3.4
 cmdaccheck 2001:db8::1
 ----
@@ -1488,7 +1552,7 @@ The *help* command displays a summary of the commands and their arguments.
 == BUGS

 For instructions on how to report bugs, please visit
-https://chrony.tuxfamily.org/.
+https://chrony-project.org/.

 == AUTHORS

--- a/doc/chronyd.adoc
+++ b/doc/chronyd.adoc
@@ -72,9 +72,9 @@ terminal.

 *-L* _level_::
 This option specifies the minimum severity level of messages to be written to
-the log file, syslog, or terminal. The following levels can be specified:
-0 (informational), 1 (warning), 2 (non-fatal error), and 3 (fatal error). The
-default value is 0.
+the log file, syslog, or terminal. The following levels can be specified: -1
+(debug, if compiled with enabled support for debugging), 0 (informational), 1
+(warning), 2 (non-fatal error), and 3 (fatal error). The default value is 0.

 *-p*::
 When run in this mode, *chronyd* will print the configuration and exit. It will
@@ -88,8 +88,10 @@ will not detach from the terminal.

 *-Q*::
 This option is similar to the *-q* option, except it only prints the offset
-without making any corrections of the clock and it allows *chronyd* to be
-started without root privileges.
+without making any corrections of the clock and disables server ports to allow
+*chronyd* to be started without root privileges, assuming the configuration
+does not have any directives which would require them (e.g. *refclock*,
+*hwtimestamp*, *rtcfile*, etc).

 *-r*::
 This option will try to reload and then delete files containing sample
@@ -204,6 +206,17 @@ With this option *chronyd* will print version number to the terminal and exit.
 *-h*, *--help*::
 With this option *chronyd* will print a help message to the terminal and exit.

+== ENVIRONMENT VARIABLES
+
+*LISTEN_FDS*::
+On Linux systems, the systemd service manager may pass file descriptors for
+pre-initialised sockets to *chronyd*. The service manager allocates and binds
+the file descriptors, and passes a copy to each spawned instance of the
+service. This allows for zero-downtime service restarts as the sockets buffer
+client requests until the service is able to handle them. The service manager
+sets the LISTEN_FDS environment variable to the number of passed file
+descriptors.
+
 == FILES

 _@SYSCONFDIR@/chrony.conf_
@@ -215,7 +228,7 @@ _@SYSCONFDIR@/chrony.conf_
 == BUGS

 For instructions on how to report bugs, please visit
-https://chrony.tuxfamily.org/.
+https://chrony-project.org/.

 == AUTHORS

--- a/doc/faq.adoc
+++ b/doc/faq.adoc
@@ -1,7 +1,8 @@
 // This file is part of chrony
 //
 // Copyright (C) Richard P. Curnow  1997-2003
-// Copyright (C) Miroslav Lichvar  2014-2016, 2020-2021
+// Copyright (C) Luke Valenta  2023
+// Copyright (C) Miroslav Lichvar  2014-2016, 2020-2023
 //
 // This program is free software; you can redistribute it and/or modify
 // it under the terms of version 2 of the GNU General Public License as
@@ -40,9 +41,36 @@ on an isolated network with no hardware reference clocks in sight, `chrony`
 will probably work better for you.

 For a more detailed comparison of features and performance, see the
-https://chrony.tuxfamily.org/comparison.html[comparison page] on the `chrony`
+https://chrony-project.org/comparison.html[comparison page] on the `chrony`
 website.

+=== Should I prefer `chrony` over `timesyncd` if I do not need to run a server?
+
+Generally, yes.
+
+`systemd-timesyncd` is a very simple NTP client included in the `systemd`
+suite. It lacks almost all features of `chrony` and other advanced client
+implementations listed on the
+https://chrony-project.org/comparison.html[comparison page]. One of its main
+limitations is that it cannot poll multiple servers at the same time and detect
+servers having incorrect time (falsetickers in the NTP terminology). It should
+be used only with trusted reliable servers, ideally in local network.
+
+Using `timesyncd` with `pool.ntp.org` is problematic. The pool is very
+robust as a whole, but the individual servers run by volunteers cannot be
+relied on. Occasionally, servers drift away or make a step to distant past or
+future due to misconfiguration, problematic implementation, and other bugs
+(e.g. in firmware of a GPS receiver). The pool monitoring system detects such
+servers and quickly removes them from the pool DNS, but clients like
+`timesyncd` cannot recover from that. They follow the server as long as it
+claims to be synchronised. They need to be restarted in order to get a new
+address from the pool DNS.
+
+Note that the complexity of NTP and clock synchronisation is on the client
+side. The amount of code in `chrony` specific to NTP server is very small and
+it is disabled by default. If it was removed, it would not significantly reduce
+the amount of memory or storage needed.
+
 == Configuration issues

 === What is the minimum recommended configuration for an NTP client?
@@ -232,17 +260,17 @@ authenticated servers should be configured as trusted and required to not allow
 the unauthenticated servers to override the authenticated servers in the source
 selection. Since `chrony` version 4.0, the selection options are enabled in
 such a case automatically. This behaviour can be disabled or modified by the
-`authselmode` directive.
+`authselectmode` directive.

 An example of a client configuration limiting the impact of the attacks could
 be

 ----
-server foo.example.net iburst nts maxdelay 0.1
-server bar.example.net iburst nts maxdelay 0.2
-server baz.example.net iburst nts maxdelay 0.05
-server qux.example.net iburst nts maxdelay 0.1
-server quux.example.net iburst nts maxdelay 0.1
+server ntp1.example.net iburst nts maxdelay 0.1
+server ntp2.example.net iburst nts maxdelay 0.2
+server ntp3.example.net iburst nts maxdelay 0.05
+server ntp4.example.net iburst nts maxdelay 0.1
+server ntp5.example.net iburst nts maxdelay 0.1
 minsources 3
 maxchange 100 0 0
 makestep 0.001 1
@@ -291,7 +319,7 @@ An example of the directive for an NTP server on the Internet that you are
 allowed to poll frequently could be

 ----
-server foo.example.net minpoll 4 maxpoll 6 polltarget 16
+server ntp.example.net minpoll 4 maxpoll 6 polltarget 16
 ----

 An example using shorter polling intervals with a server located in the same
@@ -345,7 +373,16 @@ server ntp.local minpoll -6 maxpoll -6 filter 15 xleave
 hwtimestamp eth0 minpoll -6
 ----

-As an experimental feature added in version 4.2, `chronyd` supports an NTPv4
+Since `chrony` version 4.3, the minimum `minpoll` is -7 and a filter using a
+long-term estimate of a delay quantile can be enabled by the `maxdelayquant`
+option to replace the default `maxdelaydevratio` filter, which is sensitive to
+outliers corrupting the minimum delay. For example:
+
+----
+server ntp.local minpoll -7 maxpoll -7 filter 31 maxdelayquant 0.3 xleave
+----
+
+Since version 4.2, `chronyd` supports an NTPv4
 extension field containing an additional timestamp to enable frequency transfer
 and significantly improve stability of synchronisation. It can be enabled by
 the `extfield F323` option. For example:
@@ -354,6 +391,18 @@ the `extfield F323` option. For example:
 server ntp.local minpoll 0 maxpoll 0 xleave extfield F323
 ----

+Since version 4.5, `chronyd` can apply corrections from PTP one-step end-to-end
+transparent clocks (e.g. network switches) to significantly improve accuracy of
+synchronisation in local networks. It requires the PTP transport to be enabled
+by the `ptpport` directive, HW timestamping, and the `extfield F324` option.
+For example:
+
+----
+server ntp.local minpoll -4 maxpoll -4 xleave extfield F323 extfield F324 port 319
+ptpport 319
+hwtimestamp eth0 minpoll -4
+----
+
 === Does `chronyd` have an ntpdate mode?

 Yes. With the `-q` option `chronyd` will set the system clock once and exit.
@@ -461,6 +510,59 @@ pidfile /var/run/chronyd-server1.pid
 driftfile /var/lib/chrony/drift-server1
 ----

+=== How can `chronyd` be configured to minimise downtime during restarts?
+
+The `dumpdir` directive in _chrony.conf_ provides `chronyd` a location to save
+a measurement history of the sources it uses when the service exits. The `-r`
+option then enables `chronyd` to load state from the dump files, reducing the
+synchronisation time after a restart.
+
+Similarly, the `ntsdumpdir` directive provides a location for `chronyd` to save
+NTS cookies received from the server to avoid making a NTS-KE request when
+`chronyd` is started. When operating as an NTS server, `chronyd` also saves
+cookies keys to this directory to allow clients to continue to use the old keys
+after a server restart for a more seamless experience.
+
+On Linux systems,
+https://www.freedesktop.org/software/systemd/man/latest/sd_listen_fds.html[systemd
+socket activation] provides a mechanism to reuse server sockets across
+`chronyd` restarts, so that client requests will be buffered until the service
+is again able to handle the requests. This allows for zero-downtime service
+restarts, simplified dependency logic at boot, and on-demand service spawning
+(for instance, for separated server `chronyd` instances run with the `-x`
+flag).
+
+Socket activation is supported since `chrony` version 4.5.
+The service manager (systemd) creates sockets and
+passes file descriptors to them to the process via the `LISTEN_FDS` environment
+variable. Before opening new sockets, `chronyd` first checks for and attempts
+to reuse matching sockets passed from the service manager. For instance, if an
+IPv4 datagram socket bound on `bindaddress` and `port` is available, it will be
+used by the NTP server to accept incoming IPv4 requests.
+
+An example systemd socket unit is below, where `chronyd` is configured with
+`bindaddress 0.0.0.0`, `bindaddress ::`, `port 123`, and `ntsport 4460`.
+
+----
+[Unit]
+Description=chronyd server sockets
+
+[Socket]
+Service=chronyd.service
+# IPv4 NTP server
+ListenDatagram=0.0.0.0:123
+# IPv6 NTP server
+ListenDatagram=[::]:123
+# IPv4 NTS-KE server
+ListenStream=0.0.0.0:4460
+# IPv6 NTS-KE server
+ListenStream=[::]:4460
+BindIPv6Only=ipv6-only
+
+[Install]
+WantedBy=sockets.target
+----
+
 === Should be a leap smear enabled on NTP server?

 With the `smoothtime` and `leapsecmode` directives it is possible to enable a
@@ -475,6 +577,72 @@ identically configured leap-smearing servers. Note that some clients can get
 leap seconds from other sources (e.g. with the `leapsectz` directive in
 `chrony`) and they will not work correctly with a leap smearing server.

+=== How should `chronyd` be configured with `gpsd`?
+
+A GPS or other GNSS receiver can be used as a reference clock with `gpsd`. It
+can work as one or two separate time sources for each connected receiver. The
+first time source is based on timestamping of messages sent by the receiver.
+Typically, it is accurate to milliseconds. The other source is much more
+accurate. It is timestamping a pulse-per-second (PPS) signal, usually connected
+to a serial port (e.g. DCD pin) or GPIO pin.
+
+If the PPS signal is connected to the serial port which is receiving messages
+from the GPS/GNSS receiver, `gpsd` should detect and use it automatically. If
+it is connected to a GPIO pin, or another serial port, the PPS device needs to
+be specified on the command line as an additional data source. On Linux, the
+`ldattach` utility can be used to create a PPS device for a serial device.
+
+The PPS-based time source provided by `gpsd` is available as a `SHM 1`
+refclock, or other odd number if `gpsd` is configured with multiple receivers,
+and also as `SOCK /var/run/chrony.DEV.sock` where `DEV` is the name of the
+serial device (e.g. ttyS0).
+
+The message-based time source is available as a `SHM 0` refclock (or other even
+number) and since `gpsd` version 3.25 also as
+`SOCK /var/run/chrony.clk.DEV.sock` where `DEV` is the name of the serial
+device.
+
+The SOCK refclocks should be preferred over SHM for better security
+(the shared memory segment needs to be created by `chronyd` or `gpsd` with an
+expected owner and permissions before an untrusted application or user has a
+chance to create its own in order to feed `chronyd` with false measurements).
+`gpsd` needs to be started after `chronyd` in order to connect to the socket.
+
+With `chronyd` and `gpsd` both supporting PPS, there are two different
+recommended configurations:
+
+----
+# First option
+refclock SOCK /var/run/chrony.ttyS0.sock refid GPS
+
+# Second option
+refclock PPS /dev/pps0 lock NMEA refid GPS
+refclock SOCK /var/run/chrony.clk.ttyS0.sock offset 0.5 delay 0.1 refid NMEA noselect
+----
+
+They both have some advantages:
+
+* `SOCK` can be more accurate than `PPS` if `gpsd` corrects for the
+  sawtooth error provided by the receiver in serial data
+* `PPS` can be used with higher PPS rates (specified by the `rate` option),
+  but it requires a second refclock or another time source to pair pulses
+  with seconds, and the `SOCK` offset needs to be specified
+  <<using-pps-refclock,correctly>> to compensate for the message delay, while
+  `gpsd` can apply HW-specific information
+
+If the PPS signal is not available, or cannot be used for some reason, the only
+option is the message-based timing
+
+----
+refclock SOCK /var/run/chrony.clk.ttyS0.sock offset 0.5 delay 0.1 refid GPS
+----
+
+or the SHM equivalent if using `gpsd` version before 3.25
+
+----
+refclock SHM 0 offset 0.5 delay 0.1 refid GPS
+----
+
 === Does `chrony` support PTP?

 No, the Precision Time Protocol (PTP) is not supported as a protocol for
@@ -496,7 +664,49 @@ The `ethtool -T` command can be used to verify the timestamping support.
 As an experimental feature added in version 4.2, `chrony` can use PTP as a
 transport for NTP messages (NTP over PTP) to enable hardware timestamping on
 hardware which can timestamp PTP packets only. It can be enabled by the
-`ptpport` directive.
+`ptpport` directive. Since version 4.5, `chrony` can also apply corrections
+provided by PTP one-step end-to-end transparent clocks to reach the accuracy of
+ordinary PTP clocks. The application of PTP corrections can be enabled by the
+`extfield F324` option.
+
+=== How can I avoid using wrong PHC refclock?
+
+If your system has multiple PHC devices, normally named by `udev` as
+_/dev/ptp0_, _/dev/ptp1_, and so on, their order can change randomly across
+reboots depending on the order of initialisation of their drivers. If a PHC
+refclock is specified by this name, `chronyd` could be using a wrong refclock
+after reboot. To prevent that, you can configure `udev` to create a stable
+symlink for `chronyd` with a rule like this (e.g. written to
+_/etc/udev/rules.d/80-phc.rules_):
+
+----
+KERNEL=="ptp[0-9]*", DEVPATH=="/devices/pci0000:00/0000:00:01.2/0000:02:00.0/ptp/*", SYMLINK+="ptp-i350-1"
+----
+
+You can get the full _DEVPATH_ of an existing PHC device with the `udevadm
+info` command. You will need to execute the `udevadm trigger` command, or
+reboot the system, for these changes to take effect.
+
+=== Why are client log records dropped before reaching `clientloglimit`?
+
+The number of dropped client log records reported by the `serverstats` command
+can be increasing before the number of clients reported by the `clients` command
+reaches the maximum value corresponding to the memory limit set by the
+`clientloglimit` directive.
+
+This is due to the design of the data structure keeping the client records. It
+is a hash table which can store only up to 16 colliding addresses per slot. If
+a slot has more collisions and the table already has the maximum size, the
+oldest record will be dropped and replaced by the new client.
+
+Note that the size of the table is always a power of two and it can only grow.
+The limit set by the `clientloglimit` directive takes into account that two
+copies of the table exist when it is being resized. This means the actual
+memory usage reported by `top` and other utilities can be significantly smaller
+than the limit even when the maximum number of records is used.
+
+The absolute maximum number of client records kept at the same time is
+16777216.

 === What happened to the `commandkey` and `generatecommandkey` directives?

@@ -517,8 +727,9 @@ following questions.
 Check the `Reach` value printed by the ``chronyc``'s `sources` command. If it
 is zero, it means `chronyd` did not get any valid responses from the NTP server
 you are trying to use. If there is a firewall between you and the server, the
-packets might be blocked. Try using a tool like `wireshark` or `tcpdump` to see
-if you are getting any responses from the server.
+requests sent to the UDP port 123 of the server or responses sent back from
+the port might be blocked. Try using a tool like `wireshark` or `tcpdump` to
+see if you are getting any responses from the server.

 When `chronyd` is receiving responses from the servers, the output of the
 `sources` command issued few minutes after `chronyd` start might look like
@@ -527,9 +738,9 @@ this:
 ----
 MS Name/IP address         Stratum Poll Reach LastRx Last sample
 ===============================================================================
-^* foo.example.net               2   6   377    34   +484us[ -157us] +/-   30ms
-^- bar.example.net               2   6   377    34    +33ms[  +32ms] +/-   47ms
-^+ baz.example.net               3   6   377    35  -1397us[-2033us] +/-   60ms
+^* ntp1.example.net              2   6   377    34   +484us[ -157us] +/-   30ms
+^- ntp2.example.net              2   6   377    34    +33ms[  +32ms] +/-   47ms
+^+ ntp3.example.net              3   6   377    35  -1397us[-2033us] +/-   60ms
 ----

 === Are NTP servers specified with the `offline` option?
@@ -599,9 +810,9 @@ successful:
 # chronyc -N authdata
 Name/IP address             Mode KeyID Type KLen Last Atmp  NAK Cook CLen
 =========================================================================
-foo.example.net              NTS     1   15  256  33m    0    0    8  100
-bar.example.net              NTS     1   15  256  33m    0    0    8  100
-baz.example.net              NTS     1   15  256  33m    0    0    8  100
+ntp1.example.net             NTS     1   15  256  33m    0    0    8  100
+ntp2.example.net             NTS     1   15  256  33m    0    0    8  100
+ntp3.example.net             NTS     1   15  256  33m    0    0    8  100
 ----

 The KeyID, Type, and KLen columns should have non-zero values. If they are
@@ -624,6 +835,18 @@ was not shut down for too long and the server's certificate was not renewed too
 close to its expiration, it should be sufficient for the time checks to
 succeed.

+If you run your own server, you can use a self-signed certificate covering
+all dates where the client can start (e.g. years 1970-2100). The certificate
+needs to be installed on the client and specified with the `ntstrustedcerts`
+directive. The server can have multiple names and certificates. To avoid
+trusting a certificate for too long, a new certificate can be added to the
+server periodically (e.g. once per year) and the client can have the server
+name and trusted certificate updated automatically (e.g. using a package
+repository, or a cron script downloading the files directly from the server
+over HTTPS). A client that was shut down for years will still be able to
+synchronise its clock and perform the update as long as the server keeps
+the old certificate.
+
 As a last resort, you can disable the time checks by the `nocerttimecheck`
 directive. This has some important security implications. To reduce the
 security risk, you can use the `nosystemcert` and `ntstrustedcerts` directives
@@ -692,12 +915,14 @@ frequently, you can effectively disable the test by setting the
 `maxdelaydevratio` option to a very large value (e.g. 1000000), or speed up the
 recovery by increasing the clock error rate with the `maxclockerror` directive.

+[[using-pps-refclock]]
 === Using a PPS reference clock?

 A pulse-per-second (PPS) reference clock requires a non-PPS time source to
 determine which second of UTC corresponds to each pulse. If it is another
 reference clock specified with the `lock` option in the `refclock` directive,
-the offset between the two reference clocks must be smaller than 0.2 seconds in
+the offset between the two reference clocks must be smaller than 0.4 seconds
+(0.2 seconds with `chrony` versions before 4.1) in
 order for the PPS reference clock to work. With NMEA reference clocks it is
 common to have a larger offset. It needs to be corrected with the `offset`
 option.
@@ -711,12 +936,12 @@ Name/IP Address            NP  NR  Span  Frequency  Freq Skew  Offset  Std Dev
 ==============================================================================
 PPS0                        0   0     0     +0.000   2000.000     +0ns  4000ms
 NMEA                       58  30   231    -96.494     38.406   +504ms  6080us
-foo.example.net             7   3   200     -2.991     16.141   -107us   492us
+ntp1.example.net            7   3   200     -2.991     16.141   -107us   492us
 ----

 the offset of the NMEA source would need to be increased by about 0.504
 seconds. It does not have to be very accurate. As long as the offset of the
-NMEA reference clock stays below 0.2 seconds, the PPS reference clock should be
+NMEA reference clock stays below the limit, the PPS reference clock should be
 able to determine the seconds corresponding to the pulses and allow the samples
 to be used for synchronisation.

@@ -772,6 +997,10 @@ in parentheses) on the `Reference ID` line.
 Only by the source code. See _cmdmon.c_ (`chronyd` side) and _client.c_
 (`chronyc` side).

+Note that this protocol is not compatible with the mode 6 or mode 7 protocol
+supported by `ntpd`, i.e. the `ntpq` or `ntpdc` utility cannot be used to
+monitor `chronyd`, and `chronyc` cannot be used to monitor `ntpd`.
+
 == Real-time clock issues

 === What is the real-time clock (RTC)?
@@ -898,6 +1127,34 @@ timestamps (e.g. daemon timestamp vs kernel timestamp) for serving time and
 synchronisation of its own clock, which will cause the other computer to
 measure a significant offset.

+== Operation
+
+=== What clocks does `chronyd` use?
+
+There are several different clocks used by `chronyd`:
+
+* *System clock:* software clock maintained by the kernel. It is the main clock
+  used by applications running on the computer. It is synchronised by `chronyd`
+  to its NTP clock, unless started with the *-x* option.
+* *NTP clock:* software clock (virtual) based on the system clock and internal
+  to `chronyd`. It keeps the best estimate of the true time according to the
+  configured time sources, which is served to NTP clients unless time smoothing
+  is enabled by the *smoothtime* directive. The *System time* value in the
+  `tracking` report is the current offset between the system and NTP clock.
+* *Real-time clock (RTC):* hardware clock keeping time even when the
+  computer is turned off. It is used by the kernel to initialise the system
+  clock on boot and also by `chronyd` to compensate for its measured drift if
+  configured with the `rtcfile` directive and started with the `-s` option.
+  The clock can be kept accurate only by stepping enabled by the `rtcsync` or
+  `rtcautotrim` directive.
+* *Reference clock:* hardware clock used as a time source. It is specified by
+  the `refclock` directive.
+* *NIC clock (also known as PTP hardware clock):* hardware clock timestamping
+  packets received and transmitted by a network device specified by the
+  *hwtimestamp* directive. The clock is expected to be running free. It is not
+  synchronised by `chronyd`. Its offset is tracked relative to the NTP clock in
+  order to convert the hardware timestamps.
+
 == Operating systems

 === Does `chrony` support Windows?
--- a/doc/installation.adoc
+++ b/doc/installation.adoc
@@ -27,7 +27,7 @@ The following libraries with their development files, and programs, are needed
 to enable optional features:

 * pkg-config: detection of development libraries
-* Nettle, NSS, or LibTomCrypt: secure hash functions (`SECHASH`)
+* Nettle, GnuTLS, NSS, or LibTomCrypt: secure hash functions (`SECHASH`)
 * libcap: dropping root privileges on Linux (`DROPROOT`)
 * libseccomp: system call filter on Linux (`SCFILTER`)
 * GnuTLS and Nettle: Network Time Security (`NTS`)
--- a/examples/chrony-wait.service
+++ b/examples/chrony-wait.service
@@ -25,7 +25,6 @@ LockPersonality=yes
 MemoryDenyWriteExecute=yes
 PrivateDevices=yes
 PrivateUsers=yes
-ProcSubset=pid
 ProtectClock=yes
 ProtectControlGroups=yes
 ProtectHome=yes
--- a/examples/chrony.conf.example3
+++ b/examples/chrony.conf.example3
@@ -27,9 +27,9 @@
 # you can access at http://support.ntp.org/bin/view/Servers/WebHome or
 # you can use servers from the pool.ntp.org project.

-! server foo.example.net iburst
-! server bar.example.net iburst
-! server baz.example.net iburst
+! server ntp1.example.net iburst
+! server ntp2.example.net iburst
+! server ntp3.example.net iburst

 ! pool pool.ntp.org iburst
 
@@ -99,8 +99,8 @@ ntsdumpdir /var/lib/chrony
 # and edit the following lines to specify the locations of the certificate and
 # key.

-! ntsservercert /etc/.../foo.example.net.crt
-! ntsserverkey /etc/.../foo.example.net.key
+! ntsservercert /etc/.../nts-server.crt
+! ntsserverkey /etc/.../nts-server.key

 # chronyd can save the measurement history for the servers to files when
 # it exits.  This is useful in 2 situations:
@@ -238,7 +238,7 @@ ntsdumpdir /var/lib/chrony
 # several people, you need to set up a mailing list or sendmail alias
 # for them and use the address of that.)

-! mailonchange wibble@foo.example.net 0.5
+! mailonchange wibble@example.net 0.5

 #######################################################################
 ### COMMAND ACCESS
--- a/examples/chrony.keys.example
+++ b/examples/chrony.keys.example
@@ -11,3 +11,5 @@
 #1 MD5 AVeryLongAndRandomPassword
 #2 MD5 HEX:12114855C7931009B4049EF3EFC48A139C3F989F
 #3 SHA1 HEX:B2159C05D6A219673A3B7E896B6DE07F6A440995
+#4 AES128 HEX:2DA837C4B6573748CA692B8C828E4891
+#5 AES256 HEX:2666B8099BFF2D5BA20876121788ED24D2BE59111B8FFB562F0F56AE6EC7246E
--- a/examples/chrony.nm-dispatcher.dhcp
+++ b/examples/chrony.nm-dispatcher.dhcp
@@ -1,8 +1,7 @@
 #!/bin/sh
 # This is a NetworkManager dispatcher script for chronyd to update
-# its NTP sources passed from DHCP options. Note that this script is
-# specific to NetworkManager-dispatcher due to use of the
-# DHCP4_NTP_SERVERS environment variable.
+# its NTP sources with servers from DHCP options passed by NetworkManager
+# in the DHCP4_NTP_SERVERS and DHCP6_DHCP6_NTP_SERVERS environment variables.

 export LC_ALL=C

@@ -10,17 +9,23 @@ interface=$1
 action=$2

 chronyc=/usr/bin/chronyc
-default_server_options=iburst
+server_options=iburst
 server_dir=/var/run/chrony-dhcp

 dhcp_server_file=$server_dir/$interface.sources
-# DHCP4_NTP_SERVERS is passed from DHCP options by NetworkManager.
-nm_dhcp_servers=$DHCP4_NTP_SERVERS
+dhcp_ntp_servers="$DHCP4_NTP_SERVERS $DHCP6_DHCP6_NTP_SERVERS"

 add_servers_from_dhcp() {
    rm -f "$dhcp_server_file"
-    for server in $nm_dhcp_servers; do
-        echo "server $server $default_server_options" >> "$dhcp_server_file"
+    for server in $dhcp_ntp_servers; do
+        # Check for invalid characters (from the DHCPv6 NTP FQDN suboption)
+        len1=$(printf '%s' "$server" | wc -c)
+        len2=$(printf '%s' "$server" | tr -d -c 'A-Za-z0-9:.-' | wc -c)
+        if [ "$len1" -ne "$len2" ] || [ "$len2" -lt 1 ] || [ "$len2" -gt 255 ]; then
+          continue
+        fi
+
+        printf 'server %s %s\n' "$server" "$server_options" >> "$dhcp_server_file"
    done
    $chronyc reload sources > /dev/null 2>&1 || :
 }
@@ -34,10 +39,11 @@ clear_servers_from_dhcp() {

 mkdir -p $server_dir

-if [ "$action" = "up" ] || [ "$action" = "dhcp4-change" ]; then
-    add_servers_from_dhcp
-elif [ "$action" = "down" ]; then
-    clear_servers_from_dhcp
-fi
+case "$action" in
+    up|dhcp4-change|dhcp6-change)
+        add_servers_from_dhcp;;
+    down)
+        clear_servers_from_dhcp;;
+esac

 exit 0
--- a/examples/chrony.nm-dispatcher.onoffline
+++ b/examples/chrony.nm-dispatcher.onoffline
@@ -7,8 +7,20 @@ export LC_ALL=C

 chronyc=/usr/bin/chronyc

-# For NetworkManager consider only up/down events
-[ $# -ge 2 ] && [ "$2" != "up" ] && [ "$2" != "down" ] && exit 0
+# For NetworkManager consider only selected events
+if [ $# -ge 2 ]; then
+    case "$2" in
+        up|down|connectivity-change)
+            ;;
+        dhcp4-change|dhcp6-change)
+            # Actions "up" and "connectivity-change" in some cases do not
+            # guarantee that the interface has a route (e.g. a bond).
+            # dhcp(x)-change handles at least cases that use DHCP.
+            ;;
+        *)
+            exit 0;;
+    esac
+fi

 # Note: for networkd-dispatcher routable.d ~= on and off.d ~= off

--- a/examples/chronyd-restricted.service
+++ b/examples/chronyd-restricted.service
@@ -0,0 +1,58 @@
+# This is a more restricted version of the chronyd service intended for
+# minimal NTP/NTS client configurations. The daemon is started without root
+# privileges and is allowed to write only to its own runtime, state, and log
+# directories. It cannot bind to privileged ports in order to operate as an
+# NTP server, or provide monitoring access over IPv4/IPv6. It cannot use
+# reference clocks, HW timestamping, RTC tracking, and other features.
+[Unit]
+Description=NTP client (restricted)
+Documentation=man:chronyd(8) man:chrony.conf(5)
+After=chronyd.service ntpdate.service sntp.service ntpd.service
+Conflicts=chronyd.service ntpd.service systemd-timesyncd.service
+ConditionCapability=CAP_SYS_TIME
+
+[Service]
+Type=forking
+PIDFile=/run/chrony/chronyd.pid
+EnvironmentFile=-/etc/sysconfig/chronyd
+ExecStart=/usr/sbin/chronyd -U $OPTIONS
+
+User=chrony
+LogsDirectory=chrony
+LogsDirectoryMode=0750
+RuntimeDirectory=chrony
+RuntimeDirectoryMode=0750
+RuntimeDirectoryPreserve=restart
+StateDirectory=chrony
+StateDirectoryMode=0750
+
+AmbientCapabilities=CAP_SYS_TIME
+CapabilityBoundingSet=CAP_SYS_TIME
+DevicePolicy=closed
+LockPersonality=yes
+MemoryDenyWriteExecute=yes
+NoNewPrivileges=yes
+PrivateDevices=yes
+PrivateTmp=yes
+# This breaks adjtimex()
+#PrivateUsers=yes
+ProtectControlGroups=yes
+ProtectHome=yes
+ProtectHostname=yes
+ProtectKernelLogs=yes
+ProtectKernelModules=yes
+ProtectKernelTunables=yes
+ProtectProc=invisible
+ProtectSystem=strict
+RemoveIPC=yes
+RestrictAddressFamilies=AF_INET AF_INET6 AF_UNIX
+RestrictNamespaces=yes
+RestrictRealtime=yes
+RestrictSUIDSGID=yes
+SystemCallArchitectures=native
+SystemCallFilter=~@cpu-emulation @debug @module @mount @obsolete @raw-io
+SystemCallFilter=~@reboot @resources @swap
+UMask=0077
+
+[Install]
+WantedBy=multi-user.target
--- a/examples/chronyd.service
+++ b/examples/chronyd.service
@@ -24,7 +24,6 @@ LockPersonality=yes
 MemoryDenyWriteExecute=yes
 NoNewPrivileges=yes
 PrivateTmp=yes
-ProcSubset=pid
 ProtectControlGroups=yes
 ProtectHome=yes
 ProtectHostname=yes
--- a/getdate.y
+++ b/getdate.y
@@ -448,9 +448,9 @@ o_merid	: /* NULL */
   the same signature as the function definition does. */
 #include "getdate.h"

-extern struct tm	*gmtime ();
-extern struct tm	*localtime ();
-extern time_t		mktime ();
+extern struct tm	*gmtime (const time_t *timep);
+extern struct tm	*localtime (const time_t *timep);
+extern time_t		mktime (struct tm *tm);

 /* Month and day table. */
 static TABLE const MonthDayTable[] = {
@@ -641,16 +641,13 @@ static TABLE const MilitaryTable[] = {

 /* ARGSUSED */
 static int
-yyerror (s)
-     char *s ATTRIBUTE_UNUSED;
+yyerror (char *s ATTRIBUTE_UNUSED)
 {
  return 0;
 }

 static int
-ToHour (Hours, Meridian)
-     int Hours;
-     MERIDIAN Meridian;
+ToHour (int Hours, MERIDIAN Meridian)
 {
  switch (Meridian)
    {
@@ -677,8 +674,7 @@ ToHour (Hours, Meridian)
 }

 static int
-ToYear (Year)
-     int Year;
+ToYear (int Year)
 {
  if (Year < 0)
    Year = -Year;
@@ -694,8 +690,7 @@ ToYear (Year)
 }

 static int
-LookupWord (buff)
-     char *buff;
+LookupWord (char *buff)
 {
  register char *p;
  register char *q;
--- a/hwclock.c
+++ b/hwclock.c
@@ -2,7 +2,7 @@
  chronyd/chronyc - Programs for keeping computer clocks accurate.

 **********************************************************************
- * Copyright (C) Miroslav Lichvar  2016-2018
+ * Copyright (C) Miroslav Lichvar  2016-2018, 2022
 * 
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of version 2 of the GNU General Public License as
@@ -33,6 +33,7 @@
 #include "local.h"
 #include "logging.h"
 #include "memory.h"
+#include "quantiles.h"
 #include "regress.h"
 #include "util.h"

@@ -43,6 +44,13 @@
 /* Maximum acceptable frequency offset of the clock */
 #define MAX_FREQ_OFFSET (2.0 / 3.0)

+/* Quantiles for filtering readings by delay */
+#define DELAY_QUANT_MIN_K 1
+#define DELAY_QUANT_MAX_K 2
+#define DELAY_QUANT_Q 10
+#define DELAY_QUANT_REPEAT 7
+#define DELAY_QUANT_MIN_STEP 1.0e-9
+
 struct HCL_Instance_Record {
  /* HW and local reference timestamp */
  struct timespec hw_ref;
@@ -64,12 +72,18 @@ struct HCL_Instance_Record {
  /* Minimum interval between samples */
  double min_separation;

+  /* Expected precision of readings */
+  double precision;
+
  /* Flag indicating the offset and frequency values are valid */
  int valid_coefs;

  /* Estimated offset and frequency of HW clock relative to local clock */
  double offset;
  double frequency;
+
+  /* Estimated quantiles of reading delay */
+  QNT_Instance delay_quants;
 };

 /* ================================================== */
@@ -92,7 +106,7 @@ handle_slew(struct timespec *raw, struct timespec *cooked, double dfreq,
 /* ================================================== */

 HCL_Instance
-HCL_CreateInstance(int min_samples, int max_samples, double min_separation)
+HCL_CreateInstance(int min_samples, int max_samples, double min_separation, double precision)
 {
  HCL_Instance clock;

@@ -110,6 +124,10 @@ HCL_CreateInstance(int min_samples, int max_samples, double min_separation)
  clock->n_samples = 0;
  clock->valid_coefs = 0;
  clock->min_separation = min_separation;
+  clock->precision = precision;
+  clock->delay_quants = QNT_CreateInstance(DELAY_QUANT_MIN_K, DELAY_QUANT_MAX_K,
+                                           DELAY_QUANT_Q, DELAY_QUANT_REPEAT,
+                                           DELAY_QUANT_MIN_STEP);

  LCL_AddParameterChangeHandler(handle_slew, clock);

@@ -121,6 +139,7 @@ HCL_CreateInstance(int min_samples, int max_samples, double min_separation)
 void HCL_DestroyInstance(HCL_Instance clock)
 {
  LCL_RemoveParameterChangeHandler(handle_slew, clock);
+  QNT_DestroyInstance(clock->delay_quants);
  Free(clock->y_data);
  Free(clock->x_data);
  Free(clock);
@@ -140,6 +159,94 @@ HCL_NeedsNewSample(HCL_Instance clock, struct timespec *now)

 /* ================================================== */

+int
+HCL_ProcessReadings(HCL_Instance clock, int n_readings, struct timespec tss[][3],
+                    struct timespec *hw_ts, struct timespec *local_ts, double *err)
+{
+  double delay, raw_delay, min_delay, low_delay, high_delay, e, pred_err;
+  double delay_sum, hw_sum, local_sum, local_prec, freq;
+  int i, min_reading, combined;
+  struct timespec ts1, ts2;
+
+  if (n_readings < 1)
+    return 0;
+
+  /* Work out the current correction multiplier needed to get cooked delays */
+  LCL_CookTime(&tss[0][0], &ts1, NULL);
+  LCL_CookTime(&tss[n_readings - 1][2], &ts2, NULL);
+  if (UTI_CompareTimespecs(&tss[0][0], &tss[n_readings - 1][2]) < 0)
+    freq = UTI_DiffTimespecsToDouble(&ts1, &ts2) /
+           UTI_DiffTimespecsToDouble(&tss[0][0], &tss[n_readings - 1][2]);
+  else
+    freq = 1.0;
+
+  for (i = 0; i < n_readings; i++) {
+    delay = freq * UTI_DiffTimespecsToDouble(&tss[i][2], &tss[i][0]);
+
+    if (delay < 0.0) {
+      /* Step in the middle of a reading? */
+      DEBUG_LOG("Bad reading delay=%e", delay);
+      return 0;
+    }
+
+    if (i == 0 || min_delay > delay) {
+      min_delay = delay;
+      min_reading = i;
+    }
+
+    QNT_Accumulate(clock->delay_quants, delay);
+  }
+
+  local_prec = LCL_GetSysPrecisionAsQuantum();
+
+  low_delay = QNT_GetQuantile(clock->delay_quants, DELAY_QUANT_MIN_K);
+  high_delay = QNT_GetQuantile(clock->delay_quants, DELAY_QUANT_MAX_K);
+  low_delay = MIN(low_delay, high_delay);
+  high_delay = MAX(high_delay, low_delay + local_prec);
+
+  /* Combine readings with delay in the expected interval */
+  for (i = combined = 0, delay_sum = hw_sum = local_sum = 0.0; i < n_readings; i++) {
+    raw_delay = UTI_DiffTimespecsToDouble(&tss[i][2], &tss[i][0]);
+    delay = freq * raw_delay;
+
+    if (delay < low_delay || delay > high_delay)
+      continue;
+
+    delay_sum += delay;
+    hw_sum += UTI_DiffTimespecsToDouble(&tss[i][1], &tss[0][1]);
+    local_sum += UTI_DiffTimespecsToDouble(&tss[i][0], &tss[0][0]) + raw_delay / 2.0;
+    combined++;
+  }
+
+  DEBUG_LOG("Combined %d readings lo=%e hi=%e", combined, low_delay, high_delay);
+
+  if (combined > 0) {
+    UTI_AddDoubleToTimespec(&tss[0][1], hw_sum / combined, hw_ts);
+    UTI_AddDoubleToTimespec(&tss[0][0], local_sum / combined, local_ts);
+    *err = MAX(delay_sum / combined / 2.0, clock->precision);
+    return 1;
+  }
+
+  /* Accept the reading with minimum delay if its interval does not contain
+     the current offset predicted from previous samples */
+
+  *hw_ts = tss[min_reading][1];
+  UTI_AddDoubleToTimespec(&tss[min_reading][0], min_delay / freq / 2.0, local_ts);
+  *err = MAX(min_delay / 2.0, clock->precision);
+
+  pred_err = 0.0;
+  LCL_CookTime(local_ts, &ts1, NULL);
+  if (!HCL_CookTime(clock, hw_ts, &ts2, &e) ||
+      ((pred_err = UTI_DiffTimespecsToDouble(&ts1, &ts2)) > *err)) {
+    DEBUG_LOG("Accepted reading err=%e prerr=%e", *err, pred_err);
+    return 1;
+  }
+
+  return 0;
+}
+
+/* ================================================== */
+
 void
 HCL_AccumulateSample(HCL_Instance clock, struct timespec *hw_ts,
                     struct timespec *local_ts, double err)
--- a/hwclock.h
+++ b/hwclock.h
@@ -30,7 +30,7 @@ typedef struct HCL_Instance_Record *HCL_Instance;

 /* Create a new HW clock instance */
 extern HCL_Instance HCL_CreateInstance(int min_samples, int max_samples,
-                                       double min_separation);
+                                       double min_separation, double precision);

 /* Destroy a HW clock instance */
 extern void HCL_DestroyInstance(HCL_Instance clock);
@@ -38,6 +38,11 @@ extern void HCL_DestroyInstance(HCL_Instance clock);
 /* Check if a new sample should be accumulated at this time */
 extern int HCL_NeedsNewSample(HCL_Instance clock, struct timespec *now);

+/* Process new readings of the HW clock in form of (sys, hw, sys) triplets and
+   produce a sample which can be accumulated */
+extern int HCL_ProcessReadings(HCL_Instance clock, int n_readings, struct timespec tss[][3],
+                               struct timespec *hw_ts, struct timespec *local_ts, double *err);
+
 /* Accumulate a new sample */
 extern void HCL_AccumulateSample(HCL_Instance clock, struct timespec *hw_ts,
                                 struct timespec *local_ts, double err);
--- a/keys.c
+++ b/keys.c
@@ -182,6 +182,9 @@ KEY_Reload(void)
  if (!key_file)
    return;

+  if (!UTI_CheckFilePermissions(key_file, 0771))
+    ;
+
  in = UTI_OpenFile(NULL, key_file, NULL, 'r', 0);
  if (!in) {
    LOG(LOGS_WARN, "Could not open keyfile %s", key_file);
@@ -255,6 +258,8 @@ KEY_Reload(void)
     more careful! */
  qsort(ARR_GetElements(keys), ARR_GetSize(keys), sizeof (Key), compare_keys_by_id);

+  LOG(LOGS_INFO, "Loaded %u symmetric keys", ARR_GetSize(keys));
+
  /* Check for duplicates */
  for (i = 1; i < ARR_GetSize(keys); i++) {
    if (get_key(i - 1)->id == get_key(i)->id)
--- a/local.c
+++ b/local.c
@@ -563,6 +563,8 @@ void
 LCL_NotifyExternalTimeStep(struct timespec *raw, struct timespec *cooked,
    double offset, double dispersion)
 {
+  LCL_CancelOffsetCorrection();
+
  /* Dispatch to all handlers */
  invoke_parameter_change_handlers(raw, cooked, 0.0, offset, LCL_ChangeUnknownStep);

@@ -628,6 +630,24 @@ LCL_AccumulateFrequencyAndOffset(double dfreq, double doffset, double corr_rate)

 /* ================================================== */

+int
+LCL_AccumulateFrequencyAndOffsetNoHandlers(double dfreq, double doffset, double corr_rate)
+{
+  ChangeListEntry *first_handler;
+  int r;
+
+  first_handler = change_list.next;
+  change_list.next = &change_list;
+
+  r = LCL_AccumulateFrequencyAndOffset(dfreq, doffset, corr_rate);
+
+  change_list.next = first_handler;
+
+  return r;
+}
+
+/* ================================================== */
+
 void
 lcl_InvokeDispersionNotifyHandlers(double dispersion)
 {
--- a/local.h
+++ b/local.h
@@ -173,6 +173,11 @@ extern void LCL_NotifyLeap(int leap);
   a slew, in one easy step */
 extern int LCL_AccumulateFrequencyAndOffset(double dfreq, double doffset, double corr_rate);

+/* Same as the routine above, except it does not call the registered
+   parameter change handlers */
+extern int LCL_AccumulateFrequencyAndOffsetNoHandlers(double dfreq, double doffset,
+                                                      double corr_rate);
+
 /* Routine to read the system precision as a log to base 2 value. */
 extern int LCL_GetSysPrecisionAsLog(void);

--- a/logging.c
+++ b/logging.c
@@ -39,6 +39,9 @@
 /* This is used by DEBUG_LOG macro */
 LOG_Severity log_min_severity = LOGS_INFO;

+/* Current logging contexts */
+static LOG_Context log_contexts;
+
 /* ================================================== */
 /* Flag indicating we have initialised */
 static int initialised = 0;
@@ -72,6 +75,8 @@ void
 LOG_Initialise(void)
 {
  debug_prefix = Strdup("");
+  log_contexts = 0;
+
  initialised = 1;
  LOG_OpenFileLog(NULL);
 }
@@ -140,6 +145,7 @@ void LOG_Message(LOG_Severity severity,
  struct tm *tm;

  assert(initialised);
+  severity = CLAMP(LOGS_DEBUG, severity, LOGS_FATAL);

  if (!system_log && file_log && severity >= log_min_severity) {
    /* Don't clutter up syslog with timestamps and internal debugging info */
@@ -150,8 +156,13 @@ void LOG_Message(LOG_Severity severity,
      fprintf(file_log, "%s ", buf);
    }
 #if DEBUG > 0
-    if (log_min_severity <= LOGS_DEBUG)
-      fprintf(file_log, "%s%s:%d:(%s) ", debug_prefix, filename, line_number, function_name);
+    if (log_min_severity <= LOGS_DEBUG) {
+      /* Log severity to character mapping (debug, info, warn, err, fatal) */
+      const char severity_chars[LOGS_FATAL - LOGS_DEBUG + 1] = {'D', 'I', 'W', 'E', 'F'};
+
+      fprintf(file_log, "%c:%s%s:%d:(%s) ", severity_chars[severity - LOGS_DEBUG],
+              debug_prefix, filename, line_number, function_name);
+    }
 #endif
  }

@@ -237,6 +248,30 @@ LOG_GetMinSeverity(void)

 /* ================================================== */

+void
+LOG_SetContext(LOG_Context context)
+{
+  log_contexts |= context;
+}
+
+/* ================================================== */
+
+void
+LOG_UnsetContext(LOG_Context context)
+{
+  log_contexts &= ~context;
+}
+
+/* ================================================== */
+
+LOG_Severity
+LOG_GetContextSeverity(LOG_Context contexts)
+{
+  return log_contexts & contexts ? LOGS_INFO : LOGS_DEBUG;
+}
+
+/* ================================================== */
+
 void
 LOG_SetDebugPrefix(const char *prefix)
 {
--- a/logging.h
+++ b/logging.h
@@ -100,6 +100,20 @@ extern void LOG_SetMinSeverity(LOG_Severity severity);
 /* Get the minimum severity */
 extern LOG_Severity LOG_GetMinSeverity(void);

+/* Flags for info messages that should be logged only in specific contexts */
+typedef enum {
+  LOGC_Command = 1,
+  LOGC_SourceFile = 2,
+} LOG_Context;
+
+/* Modify current contexts */
+extern void LOG_SetContext(LOG_Context context);
+extern void LOG_UnsetContext(LOG_Context context);
+
+/* Get severity depending on the current active contexts: INFO if they contain
+   at least one of the specified contexts, DEBUG otherwise */
+extern LOG_Severity LOG_GetContextSeverity(LOG_Context contexts);
+
 /* Set a prefix for debug messages */
 extern void LOG_SetDebugPrefix(const char *prefix);

--- a/main.c
+++ b/main.c
@@ -166,6 +166,8 @@ signal_cleanup(int x)
 static void
 quit_timeout(void *arg)
 {
+  LOG(LOGS_INFO, "Timeout reached");
+
  /* Return with non-zero status if the clock is not synchronised */
  exit_status = REF_GetOurStratum() >= NTP_MAX_STRATUM;
  SCH_QuitProgram();
@@ -329,6 +331,9 @@ go_daemon(void)
    char message[1024];
    int r;

+    /* Don't exit before the 'parent' */
+    waitpid(pid, NULL, 0);
+
    close(pipefd[1]);
    r = read(pipefd[0], message, sizeof (message));
    if (r) {
@@ -351,7 +356,9 @@ go_daemon(void)
    if (pid < 0) {
      LOG_FATAL("fork() failed : %s", strerror(errno));
    } else if (pid > 0) {
-      exit(0); /* In the 'parent' */
+      /* In the 'parent' */
+      close(pipefd[1]);
+      exit(0);
    } else {
      /* In the child we want to leave running as the daemon */

@@ -361,9 +368,9 @@ go_daemon(void)
      }

      /* Don't keep stdin/out/err from before. But don't close
-         the parent pipe yet. */
+         the parent pipe yet, or reusable file descriptors. */
      for (fd=0; fd<1024; fd++) {
-        if (fd != pipefd[1])
+        if (fd != pipefd[1] && !SCK_IsReusable(fd))
          close(fd);
      }

@@ -553,6 +560,9 @@ int main
  if (user_check && getuid() != 0)
    LOG_FATAL("Not superuser");

+  /* Initialise reusable file descriptors before fork */
+  SCK_PreInitialise();
+
  /* Turn into a daemon */
  if (!nofork) {
    go_daemon();
@@ -635,9 +645,13 @@ int main
  }

  /* Drop root privileges if the specified user has a non-zero UID */
-  if (!geteuid() && (pw->pw_uid || pw->pw_gid))
+  if (!geteuid() && (pw->pw_uid || pw->pw_gid)) {
    SYS_DropRoot(pw->pw_uid, pw->pw_gid, SYS_MAIN_PROCESS);

+    /* Warn if missing read access or having write access to keys */
+    CNF_CheckReadOnlyAccess();
+  }
+
  if (!geteuid())
    LOG(LOGS_WARN, "Running with root privileges");

--- a/md5.c
+++ b/md5.c
@@ -117,8 +117,7 @@ inline UINT4 ROTATE_LEFT(UINT4 x, int n)
 /* The routine MD5Init initializes the message-digest context
   mdContext. All fields are set to zero.
 */
-void MD5Init (mdContext)
-MD5_CTX *mdContext;
+void MD5Init (MD5_CTX *mdContext)
 {
  mdContext->i[0] = mdContext->i[1] = (UINT4)0;

@@ -134,10 +133,7 @@ MD5_CTX *mdContext;
   account for the presence of each of the characters inBuf[0..inLen-1]
   in the message whose digest is being computed.
 */
-void MD5Update (mdContext, inBuf, inLen)
-MD5_CTX *mdContext;
-unsigned const char *inBuf;
-unsigned int inLen;
+void MD5Update (MD5_CTX *mdContext, unsigned const char *inBuf, unsigned int inLen)
 {
  UINT4 in[16];
  int mdi;
@@ -173,8 +169,7 @@ unsigned int inLen;
   ends with the desired message digest in mdContext->digest[0...15].
 */

-void MD5Final (mdContext)
-MD5_CTX *mdContext;
+void MD5Final (MD5_CTX *mdContext)
 {
  UINT4 in[16];
  int mdi;
@@ -214,9 +209,7 @@ MD5_CTX *mdContext;

 /* Basic MD5 step. Transforms buf based on in.
 */
-static void Transform (buf, in)
-UINT4 *buf;
-UINT4 *in;
+static void Transform (UINT4 *buf, UINT4 *in)
 {
  UINT4 a = buf[0], b = buf[1], c = buf[2], d = buf[3];

--- a/memory.c
+++ b/memory.c
@@ -47,8 +47,13 @@ Realloc(void *ptr, size_t size)
 {
  void *r;

+  if (size == 0) {
+    Free(ptr);
+    return NULL;
+  }
+
  r = realloc(ptr, size);
-  if (!r && size)
+  if (!r)
    LOG_FATAL("Could not allocate memory");

  return r;
--- a/ntp.h
+++ b/ntp.h
@@ -115,9 +115,11 @@ typedef struct {

 /* Non-authentication extension fields and corresponding internal flags */

-#define NTP_EF_EXP1                     0xF323
+#define NTP_EF_EXP_MONO_ROOT            0xF323
+#define NTP_EF_EXP_NET_CORRECTION       0xF324

-#define NTP_EF_FLAG_EXP1                0x1
+#define NTP_EF_FLAG_EXP_MONO_ROOT       0x1
+#define NTP_EF_FLAG_EXP_NET_CORRECTION  0x2

 /* Pre-NTPv5 experimental extension field */
 typedef struct {
@@ -126,9 +128,18 @@ typedef struct {
  NTP_int32 root_dispersion;
  NTP_int64 mono_receive_ts;
  uint32_t mono_epoch;
-} NTP_ExtFieldExp1;
+} NTP_EFExpMonoRoot;

-#define NTP_EF_EXP1_MAGIC 0xF5BEDD9AU
+#define NTP_EF_EXP_MONO_ROOT_MAGIC      0xF5BEDD9AU
+
+/* Experimental extension field to provide PTP corrections */
+typedef struct {
+  uint32_t magic;
+  NTP_int64 correction;
+  uint32_t reserved[3];
+} NTP_EFExpNetCorrection;
+
+#define NTP_EF_EXP_NET_CORRECTION_MAGIC 0x07AC2CEBU

 /* Authentication extension fields */

@@ -179,4 +190,11 @@ typedef struct {
  double root_dispersion;
 } NTP_Sample;

+/* Possible sources of timestamps */
+typedef enum {
+  NTP_TS_DAEMON = 0,
+  NTP_TS_KERNEL,
+  NTP_TS_HARDWARE
+} NTP_Timestamp_Source;
+
 #endif /* GOT_NTP_H */
--- a/ntp_core.c
+++ b/ntp_core.c
--- a/ntp_core.h
+++ b/ntp_core.h
@@ -38,16 +38,12 @@ typedef enum {
  NTP_SERVER, NTP_PEER
 } NTP_Source_Type;

-typedef enum {
-  NTP_TS_DAEMON = 0,
-  NTP_TS_KERNEL,
-  NTP_TS_HARDWARE
-} NTP_Timestamp_Source;
-
 typedef struct {
  struct timespec ts;
  double err;
  NTP_Timestamp_Source source;
+  double rx_duration;
+  double net_correction;
 } NTP_Local_Timestamp;

 /* This is a private data type used for storing the instance record for
--- a/ntp_io.c
+++ b/ntp_io.c
@@ -126,8 +126,14 @@ open_socket(int family, int local_port, int client_only, IPSockAddr *remote_addr
  dscp = CNF_GetNtpDscp();
  if (dscp > 0 && dscp < 64) {
 #ifdef IP_TOS
-    if (!SCK_SetIntOption(sock_fd, IPPROTO_IP, IP_TOS, dscp << 2))
-      ;
+    if (family == IPADDR_INET4)
+      if (!SCK_SetIntOption(sock_fd, IPPROTO_IP, IP_TOS, dscp << 2))
+        ;
+#endif
+#if defined(FEAT_IPV6) && defined(IPV6_TCLASS)
+    if (family == IPADDR_INET6)
+      if (!SCK_SetIntOption(sock_fd, IPPROTO_IPV6, IPV6_TCLASS, dscp << 2))
+        ;
 #endif
  }

@@ -163,9 +169,6 @@ close_socket(int sock_fd)
  if (sock_fd == INVALID_SOCK_FD)
    return;

-#ifdef HAVE_LINUX_TIMESTAMPING
-  NIO_Linux_NotifySocketClosing(sock_fd);
-#endif
  SCH_RemoveFileHandler(sock_fd);
  SCK_CloseSocket(sock_fd);
 }
@@ -275,6 +278,18 @@ NIO_Finalise(void)

 /* ================================================== */

+int
+NIO_IsHwTsEnabled(void)
+{
+#ifdef HAVE_LINUX_TIMESTAMPING
+  return NIO_Linux_IsHwTsEnabled();
+#else
+  return 0;
+#endif
+}
+
+/* ================================================== */
+
 int
 NIO_OpenClientSocket(NTP_Remote_Address *remote_addr)
 {
@@ -416,6 +431,9 @@ process_message(SCK_Message *message, int sock_fd, int event)

  SCH_GetLastEventTime(&local_ts.ts, &local_ts.err, NULL);
  local_ts.source = NTP_TS_DAEMON;
+  local_ts.rx_duration = 0.0;
+  local_ts.net_correction = 0.0;
+
  sched_ts = local_ts.ts;

  if (message->addr_type != SCK_ADDR_IP) {
@@ -441,7 +459,7 @@ process_message(SCK_Message *message, int sock_fd, int event)
    DEBUG_LOG("Updated RX timestamp delay=%.9f tss=%u",
              UTI_DiffTimespecsToDouble(&sched_ts, &local_ts.ts), local_ts.source);

-  if (!NIO_UnwrapMessage(message, sock_fd))
+  if (!NIO_UnwrapMessage(message, sock_fd, &local_ts.net_correction))
    return;

  /* Just ignore the packet if it's not of a recognized length */
@@ -461,11 +479,6 @@ read_from_socket(int sock_fd, int event, void *anything)
  SCK_Message *messages;
  int i, received, flags = 0;

-#ifdef HAVE_LINUX_TIMESTAMPING
-  if (NIO_Linux_ProcessEvent(sock_fd, event))
-    return;
-#endif
-
  if (event == SCH_FILE_EXCEPTION) {
 #ifdef HAVE_LINUX_TIMESTAMPING
    flags |= SCK_FLAG_MSG_ERRQUEUE;
@@ -485,8 +498,9 @@ read_from_socket(int sock_fd, int event, void *anything)
 /* ================================================== */

 int
-NIO_UnwrapMessage(SCK_Message *message, int sock_fd)
+NIO_UnwrapMessage(SCK_Message *message, int sock_fd, double *net_correction)
 {
+  double ptp_correction;
  PTP_NtpMessage *msg;

  if (!is_ptp_socket(sock_fd))
@@ -512,7 +526,14 @@ NIO_UnwrapMessage(SCK_Message *message, int sock_fd)
  message->data = (char *)message->data + PTP_NTP_PREFIX_LENGTH;
  message->length -= PTP_NTP_PREFIX_LENGTH;

-  DEBUG_LOG("Unwrapped PTP->NTP len=%d", message->length);
+  ptp_correction = UTI_Integer64NetworkToHost(*(Integer64 *)msg->header.correction) /
+                   ((1 << 16) * 1.0e9);
+
+  /* Use the correction only if the RX duration is known (i.e. HW timestamp) */
+  if (*net_correction > 0.0)
+    *net_correction += ptp_correction;
+
+  DEBUG_LOG("Unwrapped PTP->NTP len=%d corr=%.9f", message->length, ptp_correction);

  return 1;
 }
@@ -522,6 +543,8 @@ NIO_UnwrapMessage(SCK_Message *message, int sock_fd)
 static int
 wrap_message(SCK_Message *message, int sock_fd)
 {
+  static uint16_t sequence_id = 0;
+
  assert(PTP_NTP_PREFIX_LENGTH == 48);

  if (!is_ptp_socket(sock_fd))
@@ -542,6 +565,7 @@ wrap_message(SCK_Message *message, int sock_fd)
  ptp_message->header.length = htons(PTP_NTP_PREFIX_LENGTH + message->length);
  ptp_message->header.domain = PTP_DOMAIN_NTP;
  ptp_message->header.flags = htons(PTP_FLAG_UNICAST);
+  ptp_message->header.sequence_id = htons(sequence_id++);
  ptp_message->tlv_header.type = htons(PTP_TLV_NTP);
  ptp_message->tlv_header.length = htons(message->length);
  memcpy((char *)ptp_message + PTP_NTP_PREFIX_LENGTH, message->data, message->length);
--- a/ntp_io.h
+++ b/ntp_io.h
@@ -39,6 +39,9 @@ extern void NIO_Initialise(void);
 /* Function to finalise the module */
 extern void NIO_Finalise(void);

+/* Function to check if HW timestamping is enabled on any interface */
+extern int NIO_IsHwTsEnabled(void);
+
 /* Function to obtain a socket for sending client packets */
 extern int NIO_OpenClientSocket(NTP_Remote_Address *remote_addr);

@@ -61,7 +64,7 @@ extern int NIO_IsServerSocketOpen(void);
 extern int NIO_IsServerConnectable(NTP_Remote_Address *remote_addr);

 /* Function to unwrap an NTP message from non-native transport (e.g. PTP) */
-extern int NIO_UnwrapMessage(SCK_Message *message, int sock_fd);
+extern int NIO_UnwrapMessage(SCK_Message *message, int sock_fd, double *net_correction);

 /* Function to transmit a packet */
 extern int NIO_SendPacket(NTP_Packet *packet, NTP_Remote_Address *remote_addr,
--- a/ntp_io_linux.c
+++ b/ntp_io_linux.c
@@ -2,7 +2,7 @@
  chronyd/chronyc - Programs for keeping computer clocks accurate.

 **********************************************************************
- * Copyright (C) Miroslav Lichvar  2016-2019
+ * Copyright (C) Miroslav Lichvar  2016-2019, 2021-2023
 * 
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of version 2 of the GNU General Public License as
@@ -39,6 +39,7 @@
 #include "hwclock.h"
 #include "local.h"
 #include "logging.h"
+#include "memory.h"
 #include "ntp_core.h"
 #include "ntp_io.h"
 #include "ntp_io_linux.h"
@@ -59,19 +60,20 @@ struct Interface {
  /* Start of UDP data at layer 2 for IPv4 and IPv6 */
  int l2_udp4_ntp_start;
  int l2_udp6_ntp_start;
-  /* Precision of PHC readings */
-  double precision;
  /* Compensation of errors in TX and RX timestamping */
  double tx_comp;
  double rx_comp;
  HCL_Instance clock;
+  int maxpoll;
+  SCH_TimeoutID poll_timeout_id;
 };

 /* Number of PHC readings per HW clock sample */
-#define PHC_READINGS 10
+#define PHC_READINGS 25

-/* Minimum interval between PHC readings */
+/* Minimum and maximum interval between PHC readings */
 #define MIN_PHC_POLL -6
+#define MAX_PHC_POLL 20

 /* Maximum acceptable offset between SW/HW and daemon timestamp */
 #define MAX_TS_DELAY 1.0
@@ -86,19 +88,6 @@ static int ts_tx_flags;
 /* Flag indicating the socket options can't be changed in control messages */
 static int permanent_ts_options;

-/* When sending client requests to a close and fast server, it is possible that
-   a response will be received before the HW transmit timestamp of the request
-   itself.  To avoid processing of the response without the HW timestamp, we
-   monitor events returned by select() and suspend reading of packets from the
-   receive queue for up to 200 microseconds.  As the requests are normally
-   separated by at least 200 milliseconds, it is sufficient to monitor and
-   suspend one socket at a time. */
-static int monitored_socket;
-static int suspended_socket;
-static SCH_TimeoutID resume_timeout_id;
-
-#define RESUME_TIMEOUT 200.0e-6
-
 /* Unbound socket keeping the kernel RX timestamping permanently enabled
   in order to avoid a race condition between receiving a server response
   and the kernel actually starting to timestamp received packets after
@@ -109,13 +98,17 @@ static int dummy_rxts_socket;

 /* ================================================== */

+static void poll_phc(struct Interface *iface, struct timespec *now);
+
+/* ================================================== */
+
 static int
 add_interface(CNF_HwTsInterface *conf_iface)
 {
+  int sock_fd, if_index, minpoll, phc_fd, req_hwts_flags, rx_filter;
  struct ethtool_ts_info ts_info;
  struct hwtstamp_config ts_config;
  struct ifreq req;
-  int sock_fd, if_index, phc_fd, req_hwts_flags, rx_filter;
  unsigned int i;
  struct Interface *iface;

@@ -244,12 +237,18 @@ add_interface(CNF_HwTsInterface *conf_iface)
  iface->l2_udp4_ntp_start = 42;
  iface->l2_udp6_ntp_start = 62;

-  iface->precision = conf_iface->precision;
  iface->tx_comp = conf_iface->tx_comp;
  iface->rx_comp = conf_iface->rx_comp;

+  minpoll = CLAMP(MIN_PHC_POLL, conf_iface->minpoll, MAX_PHC_POLL);
  iface->clock = HCL_CreateInstance(conf_iface->min_samples, conf_iface->max_samples,
-                                    UTI_Log2ToDouble(MAX(conf_iface->minpoll, MIN_PHC_POLL)));
+                                    UTI_Log2ToDouble(minpoll), conf_iface->precision);
+
+  iface->maxpoll = CLAMP(minpoll, conf_iface->maxpoll, MAX_PHC_POLL);
+
+  /* Do not schedule the first poll timeout here!  The argument (interface) can
+     move until all interfaces are added.  Wait for the first HW timestamp. */
+  iface->poll_timeout_id = 0;

  LOG(LOGS_INFO, "Enabled HW timestamping %son %s",
      ts_config.rx_filter == HWTSTAMP_FILTER_NONE ? "(TX only) " : "", iface->name);
@@ -414,8 +413,6 @@ NIO_Linux_Initialise(void)
  /* Kernels before 4.7 ignore timestamping flags set in control messages */
  permanent_ts_options = !SYS_Linux_CheckKernelVersion(4, 7);

-  monitored_socket = INVALID_SOCK_FD;
-  suspended_socket = INVALID_SOCK_FD;
  dummy_rxts_socket = INVALID_SOCK_FD;
 }

@@ -432,6 +429,7 @@ NIO_Linux_Finalise(void)

  for (i = 0; i < ARR_GetSize(interfaces); i++) {
    iface = ARR_GetElement(interfaces, i);
+    SCH_RemoveTimeout(iface->poll_timeout_id);
    HCL_DestroyInstance(iface->clock);
    close(iface->phc_fd);
  }
@@ -441,6 +439,14 @@ NIO_Linux_Finalise(void)

 /* ================================================== */

+int
+NIO_Linux_IsHwTsEnabled(void)
+{
+  return ARR_GetSize(interfaces) > 0;
+}
+
+/* ================================================== */
+
 int
 NIO_Linux_SetTimestampSocketOptions(int sock_fd, int client_only, int *events)
 {
@@ -474,73 +480,6 @@ NIO_Linux_SetTimestampSocketOptions(int sock_fd, int client_only, int *events)

 /* ================================================== */

-static void
-resume_socket(int sock_fd)
-{
-  if (monitored_socket == sock_fd)
-    monitored_socket = INVALID_SOCK_FD;
-
-  if (sock_fd == INVALID_SOCK_FD || sock_fd != suspended_socket)
-    return;
-
-  suspended_socket = INVALID_SOCK_FD;
-
-  SCH_SetFileHandlerEvent(sock_fd, SCH_FILE_INPUT, 1);
-
-  DEBUG_LOG("Resumed RX processing %s timeout fd=%d",
-            resume_timeout_id ? "before" : "on", sock_fd);
-
-  if (resume_timeout_id) {
-    SCH_RemoveTimeout(resume_timeout_id);
-    resume_timeout_id = 0;
-  }
-}
-
-/* ================================================== */
-
-static void
-resume_timeout(void *arg)
-{
-  resume_timeout_id = 0;
-  resume_socket(suspended_socket);
-}
-
-/* ================================================== */
-
-static void
-suspend_socket(int sock_fd)
-{
-  resume_socket(suspended_socket);
-
-  suspended_socket = sock_fd;
-
-  SCH_SetFileHandlerEvent(suspended_socket, SCH_FILE_INPUT, 0);
-  resume_timeout_id = SCH_AddTimeoutByDelay(RESUME_TIMEOUT, resume_timeout, NULL);
-
-  DEBUG_LOG("Suspended RX processing fd=%d", sock_fd);
-}
-
-/* ================================================== */
-
-int
-NIO_Linux_ProcessEvent(int sock_fd, int event)
-{
-  if (sock_fd != monitored_socket)
-    return 0;
-
-  if (event == SCH_FILE_INPUT) {
-    suspend_socket(monitored_socket);
-    monitored_socket = INVALID_SOCK_FD;
-
-    /* Don't process the message yet */
-    return 1;
-  }
-
-  return 0;
-}
-
-/* ================================================== */
-
 static struct Interface *
 get_interface(int if_index)
 {
@@ -560,26 +499,70 @@ get_interface(int if_index)

 /* ================================================== */

+static void
+poll_timeout(void *arg)
+{
+  struct Interface *iface = arg;
+  struct timespec now;
+
+  iface->poll_timeout_id = 0;
+
+  SCH_GetLastEventTime(&now, NULL, NULL);
+  poll_phc(iface, &now);
+}
+
+/* ================================================== */
+
+static void
+poll_phc(struct Interface *iface, struct timespec *now)
+{
+  struct timespec sample_phc_ts, sample_sys_ts, sample_local_ts;
+  struct timespec phc_readings[PHC_READINGS][3];
+  double phc_err, local_err, interval;
+  int n_readings;
+
+  if (!HCL_NeedsNewSample(iface->clock, now))
+    return;
+
+  DEBUG_LOG("Polling PHC on %s%s",
+            iface->name, iface->poll_timeout_id != 0 ? " before timeout" : "");
+
+  n_readings = SYS_Linux_GetPHCReadings(iface->phc_fd, iface->phc_nocrossts,
+                                        &iface->phc_mode, PHC_READINGS, phc_readings);
+
+  /* Add timeout for the next poll in case no HW timestamp will be captured
+     between the minpoll and maxpoll.  Separate reading of different PHCs to
+     avoid long intervals between handling I/O events. */
+  SCH_RemoveTimeout(iface->poll_timeout_id);
+  interval = UTI_Log2ToDouble(iface->maxpoll);
+  iface->poll_timeout_id = SCH_AddTimeoutInClass(interval, interval /
+                                                   ARR_GetSize(interfaces) / 4, 0.1,
+                                                 SCH_PhcPollClass, poll_timeout, iface);
+
+  if (n_readings <= 0)
+    return;
+
+  if (!HCL_ProcessReadings(iface->clock, n_readings, phc_readings,
+                           &sample_phc_ts, &sample_sys_ts, &phc_err))
+    return;
+
+  LCL_CookTime(&sample_sys_ts, &sample_local_ts, &local_err);
+  HCL_AccumulateSample(iface->clock, &sample_phc_ts, &sample_local_ts, phc_err + local_err);
+
+  update_interface_speed(iface);
+}
+
+/* ================================================== */
+
 static void
 process_hw_timestamp(struct Interface *iface, struct timespec *hw_ts,
                     NTP_Local_Timestamp *local_ts, int rx_ntp_length, int family,
                     int l2_length)
 {
-  struct timespec sample_phc_ts, sample_sys_ts, sample_local_ts, ts;
-  double rx_correction, ts_delay, phc_err, local_err;
+  double rx_correction = 0.0, ts_delay, local_err;
+  struct timespec ts;

-  if (HCL_NeedsNewSample(iface->clock, &local_ts->ts)) {
-    if (!SYS_Linux_GetPHCSample(iface->phc_fd, iface->phc_nocrossts, iface->precision,
-                                &iface->phc_mode, &sample_phc_ts, &sample_sys_ts,
-                                &phc_err))
-      return;
-
-    LCL_CookTime(&sample_sys_ts, &sample_local_ts, &local_err);
-    HCL_AccumulateSample(iface->clock, &sample_phc_ts, &sample_local_ts,
-                         phc_err + local_err);
-
-    update_interface_speed(iface);
-  }
+  poll_phc(iface, &local_ts->ts);

  /* We need to transpose RX timestamps as hardware timestamps are normally
     preamble timestamps and RX timestamps in NTP are supposed to be trailer
@@ -617,6 +600,10 @@ process_hw_timestamp(struct Interface *iface, struct timespec *hw_ts,
  local_ts->ts = ts;
  local_ts->err = local_err;
  local_ts->source = NTP_TS_HARDWARE;
+  local_ts->rx_duration = rx_correction;
+  /* Network correction needs to include the RX duration to avoid
+     asymmetric correction with asymmetric link speeds */
+  local_ts->net_correction = rx_correction;
 }

 /* ================================================== */
@@ -740,6 +727,7 @@ NIO_Linux_ProcessMessage(SCK_Message *message, NTP_Local_Address *local_addr,
 {
  struct Interface *iface;
  int is_tx, ts_if_index, l2_length;
+  double c = 0.0;

  is_tx = event == SCH_FILE_EXCEPTION;
  iface = NULL;
@@ -757,11 +745,6 @@ NIO_Linux_ProcessMessage(SCK_Message *message, NTP_Local_Address *local_addr,
    } else {
      DEBUG_LOG("HW clock not found for interface %d", ts_if_index);
    }
-
-    /* If a HW transmit timestamp was received, resume processing
-       of non-error messages on this socket */
-    if (is_tx)
-      resume_socket(local_addr->sock_fd);
  }

  if (local_ts->source == NTP_TS_DAEMON && !UTI_IsZeroTimespec(&message->timestamp.kernel) &&
@@ -805,7 +788,7 @@ NIO_Linux_ProcessMessage(SCK_Message *message, NTP_Local_Address *local_addr,
    return 1;
  }

-  if (!NIO_UnwrapMessage(message, local_addr->sock_fd))
+  if (!NIO_UnwrapMessage(message, local_addr->sock_fd, &c))
    return 1;

  if (message->length < NTP_HEADER_LENGTH || message->length > sizeof (NTP_Packet))
@@ -824,23 +807,9 @@ NIO_Linux_RequestTxTimestamp(SCK_Message *message, int sock_fd)
  if (!ts_flags)
    return;

-  /* If a HW transmit timestamp is requested on a client socket, monitor
-     events on the socket in order to avoid processing of a fast response
-     without the HW timestamp of the request */
-  if (ts_tx_flags & SOF_TIMESTAMPING_TX_HARDWARE && !NIO_IsServerSocket(sock_fd))
-    monitored_socket = sock_fd;
-
  /* Check if TX timestamping is disabled on this socket */
  if (permanent_ts_options || !NIO_IsServerSocket(sock_fd))
    return;

  message->timestamp.tx_flags = ts_tx_flags;
 }
-
-/* ================================================== */
-
-void
-NIO_Linux_NotifySocketClosing(int sock_fd)
-{
-  resume_socket(sock_fd);
-}
--- a/ntp_io_linux.h
+++ b/ntp_io_linux.h
@@ -33,15 +33,13 @@ extern void NIO_Linux_Initialise(void);

 extern void NIO_Linux_Finalise(void);

-extern int NIO_Linux_SetTimestampSocketOptions(int sock_fd, int client_only, int *events);
+extern int NIO_Linux_IsHwTsEnabled(void);

-extern int NIO_Linux_ProcessEvent(int sock_fd, int event);
+extern int NIO_Linux_SetTimestampSocketOptions(int sock_fd, int client_only, int *events);

 extern int NIO_Linux_ProcessMessage(SCK_Message *message, NTP_Local_Address *local_addr,
                                    NTP_Local_Timestamp *local_ts, int event);

 extern void NIO_Linux_RequestTxTimestamp(SCK_Message *message, int sock_fd);

-extern void NIO_Linux_NotifySocketClosing(int sock_fd);
-
 #endif
--- a/ntp_sources.c
+++ b/ntp_sources.c
@@ -3,7 +3,7 @@

 **********************************************************************
 * Copyright (C) Richard P. Curnow  1997-2003
- * Copyright (C) Miroslav Lichvar  2011-2012, 2014, 2016, 2020-2021
+ * Copyright (C) Miroslav Lichvar  2011-2012, 2014, 2016, 2020-2023
 * 
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of version 2 of the GNU General Public License as
@@ -32,6 +32,7 @@
 #include "sysincl.h"

 #include "array.h"
+#include "conf.h"
 #include "ntp_sources.h"
 #include "ntp_core.h"
 #include "ntp_io.h"
@@ -58,12 +59,15 @@ typedef struct {
  NCR_Instance data;            /* Data for the protocol engine for this source */
  char *name;                   /* Name of the source as it was specified
                                   (may be an IP address) */
+  IPAddr resolved_addr;         /* Address resolved from the name, which can be
+                                   different from remote_addr (e.g. NTS-KE) */
  int pool_id;                  /* ID of the pool from which was this source
                                   added or INVALID_POOL */
  int tentative;                /* Flag indicating there was no valid response
                                   received from the source yet */
  uint32_t conf_id;             /* Configuration ID, which can be shared with
                                   different sources in case of a pool */
+  double last_resolving;        /* Time of last name resolving (monotonic) */
 } SourceRecord;

 /* Hash table of SourceRecord, its size is a power of two and it's never
@@ -96,6 +100,9 @@ struct UnresolvedSource {
  char *name;
  /* Flag indicating addresses should be used in a random order */
  int random_order;
+  /* Flag indicating current address should be replaced only if it is
+     no longer returned by the resolver */
+  int refreshment;
  /* Next unresolved source in the list */
  struct UnresolvedSource *next;
 };
@@ -103,7 +110,7 @@ struct UnresolvedSource {
 #define RESOLVE_INTERVAL_UNIT 7
 #define MIN_RESOLVE_INTERVAL 2
 #define MAX_RESOLVE_INTERVAL 9
-#define MIN_REPLACEMENT_INTERVAL 8
+#define MAX_REPLACEMENT_INTERVAL 9

 static struct UnresolvedSource *unresolved_sources = NULL;
 static int resolving_interval = 0;
@@ -184,6 +191,7 @@ void
 NSR_Initialise(void)
 {
  n_sources = 0;
+  resolving_id = 0;
  initialised = 1;

  records = ARR_CreateInstance(sizeof (SourceRecord));
@@ -206,6 +214,7 @@ NSR_Finalise(void)
  ARR_DestroyInstance(records);
  ARR_DestroyInstance(pools);

+  SCH_RemoveTimeout(resolving_id);
  while (unresolved_sources)
    remove_unresolved_source(unresolved_sources);

@@ -317,6 +326,31 @@ rehash_records(void)

 /* ================================================== */

+static void
+log_source(SourceRecord *record, int addition, int once_per_pool)
+{
+  int pool, log_addr;
+  char *ip_str;
+
+  if (once_per_pool && record->pool_id != INVALID_POOL) {
+    if (get_pool(record->pool_id)->sources > 1)
+      return;
+    pool = 1;
+    log_addr = 0;
+  } else {
+    ip_str = UTI_IPToString(&record->remote_addr->ip_addr);
+    pool = 0;
+    log_addr = strcmp(record->name, ip_str) != 0;
+  }
+
+  LOG(LOG_GetContextSeverity(LOGC_Command | LOGC_SourceFile), "%s %s %s%s%s%s",
+      addition ? "Added" : "Removed", pool ? "pool" : "source",
+      log_addr ? ip_str : record->name,
+      log_addr ? " (" : "", log_addr ? record->name : "", log_addr ? ")" : "");
+}
+
+/* ================================================== */
+
 /* Procedure to add a new source */
 static NSR_Status
 add_source(NTP_Remote_Address *remote_addr, char *name, NTP_Source_Type type,
@@ -353,13 +387,14 @@ add_source(NTP_Remote_Address *remote_addr, char *name, NTP_Source_Type type,
      record_lock = 1;

      record = get_record(slot);
-      assert(!name || !UTI_IsStringIP(name));
      record->name = Strdup(name ? name : UTI_IPToString(&remote_addr->ip_addr));
      record->data = NCR_CreateInstance(remote_addr, type, params, record->name);
      record->remote_addr = NCR_GetRemoteAddress(record->data);
+      record->resolved_addr = remote_addr->ip_addr;
      record->pool_id = pool_id;
      record->tentative = 1;
      record->conf_id = conf_id;
+      record->last_resolving = SCH_GetLastEventMonoTime();

      record_lock = 0;

@@ -372,6 +407,8 @@ add_source(NTP_Remote_Address *remote_addr, char *name, NTP_Source_Type type,
      if (auto_start_sources && UTI_IsIPReal(&remote_addr->ip_addr))
        NCR_StartInstance(record->data);

+      log_source(record, 1, 1);
+
      /* The new instance is allowed to change its address immediately */
      handle_saved_address_update();

@@ -406,6 +443,8 @@ change_source_address(NTP_Remote_Address *old_addr, NTP_Remote_Address *new_addr

  record = get_record(slot1);
  NCR_ChangeRemoteAddress(record->data, new_addr, !replacement);
+  if (replacement)
+    record->resolved_addr = new_addr->ip_addr;

  if (record->remote_addr != NCR_GetRemoteAddress(record->data) ||
      UTI_CompareIPs(&record->remote_addr->ip_addr, &new_addr->ip_addr, NULL) != 0)
@@ -489,7 +528,21 @@ process_resolved_name(struct UnresolvedSource *us, IPAddr *ip_addrs, int n_addrs
  NTP_Remote_Address old_addr, new_addr;
  SourceRecord *record;
  unsigned short first = 0;
-  int i, j;
+  int i, j, slot;
+
+  /* Keep using the current address if it is being refreshed and it is
+     still included in the resolved addresses */
+  if (us->refreshment) {
+    assert(us->pool_id == INVALID_POOL);
+
+    for (i = 0; i < n_addrs; i++) {
+      if (find_slot2(&us->address, &slot) == 2 &&
+          UTI_CompareIPs(&get_record(slot)->resolved_addr, &ip_addrs[i], NULL) == 0) {
+        DEBUG_LOG("%s still fresh", UTI_IPToString(&us->address.ip_addr));
+        return;
+      }
+    }
+  }

  if (us->random_order)
    UTI_GetRandomBytes(&first, sizeof (first));
@@ -698,21 +751,25 @@ static int get_unused_pool_id(void)

 /* ================================================== */

+static uint32_t
+get_next_conf_id(uint32_t *conf_id)
+{
+  last_conf_id++;
+
+  if (conf_id)
+    *conf_id = last_conf_id;
+
+  return last_conf_id;
+}
+
+/* ================================================== */
+
 NSR_Status
 NSR_AddSource(NTP_Remote_Address *remote_addr, NTP_Source_Type type,
              SourceParameters *params, uint32_t *conf_id)
 {
-  NSR_Status s;
-
-  s = add_source(remote_addr, NULL, type, params, INVALID_POOL, last_conf_id + 1);
-  if (s != NSR_Success)
-    return s;
-
-  last_conf_id++;
-  if (conf_id)
-    *conf_id = last_conf_id;
-
-  return s;
+  return add_source(remote_addr, NULL, type, params, INVALID_POOL,
+                    get_next_conf_id(conf_id));
 }

 /* ================================================== */
@@ -725,11 +782,13 @@ NSR_AddSourceByName(char *name, int port, int pool, NTP_Source_Type type,
  struct SourcePool *sp;
  NTP_Remote_Address remote_addr;
  int i, new_sources, pool_id;
+  uint32_t cid;

  /* If the name is an IP address, add the source with the address directly */
  if (UTI_StringToIP(name, &remote_addr.ip_addr)) {
    remote_addr.port = port;
-    return NSR_AddSource(&remote_addr, type, params, conf_id);
+    return add_source(&remote_addr, name, type, params, INVALID_POOL,
+                      get_next_conf_id(conf_id));
  }

  /* Make sure the name is at least printable and has no spaces */
@@ -741,6 +800,7 @@ NSR_AddSourceByName(char *name, int port, int pool, NTP_Source_Type type,
  us = MallocNew(struct UnresolvedSource);
  us->name = Strdup(name);
  us->random_order = 0;
+  us->refreshment = 0;

  remote_addr.ip_addr.family = IPADDR_ID;
  remote_addr.ip_addr.addr.id = ++last_address_id;
@@ -770,14 +830,12 @@ NSR_AddSourceByName(char *name, int port, int pool, NTP_Source_Type type,

  append_unresolved_source(us);

-  last_conf_id++;
-  if (conf_id)
-    *conf_id = last_conf_id;
+  cid = get_next_conf_id(conf_id);

  for (i = 0; i < new_sources; i++) {
    if (i > 0)
      remote_addr.ip_addr.addr.id = ++last_address_id;
-    if (add_source(&remote_addr, name, type, params, us->pool_id, last_conf_id) != NSR_Success)
+    if (add_source(&remote_addr, name, type, params, us->pool_id, cid) != NSR_Success)
      return NSR_TooManySources;
  }

@@ -786,6 +844,31 @@ NSR_AddSourceByName(char *name, int port, int pool, NTP_Source_Type type,

 /* ================================================== */

+const char *
+NSR_StatusToString(NSR_Status status)
+{
+  switch (status) {
+    case NSR_Success:
+      return "Success";
+    case NSR_NoSuchSource:
+      return "No such source";
+    case NSR_AlreadyInUse:
+      return "Already in use";
+    case NSR_TooManySources:
+      return "Too many sources";
+    case NSR_InvalidAF:
+      return "Invalid address";
+    case NSR_InvalidName:
+      return "Invalid name";
+    case NSR_UnresolvedName:
+      return "Unresolved name";
+    default:
+      return "?";
+  }
+}
+
+/* ================================================== */
+
 void
 NSR_SetSourceResolvingEndHandler(NSR_SourceResolvingEndHandler handler)
 {
@@ -881,6 +964,7 @@ NSR_RemoveSource(IPAddr *address)
  if (find_slot(address, &slot) == 0)
    return NSR_NoSuchSource;

+  log_source(get_record(slot), 0, 0);
  clean_source_record(get_record(slot));

  /* Rehash the table to make sure there are no broken probe sequences.
@@ -903,6 +987,7 @@ NSR_RemoveSourcesById(uint32_t conf_id)
    record = get_record(i);
    if (!record->remote_addr || record->conf_id != conf_id)
      continue;
+    log_source(record, 0, 1);
    clean_source_record(record);
  }

@@ -930,20 +1015,23 @@ NSR_RemoveAllSources(void)
 /* ================================================== */

 static void
-resolve_source_replacement(SourceRecord *record)
+resolve_source_replacement(SourceRecord *record, int refreshment)
 {
  struct UnresolvedSource *us;

-  DEBUG_LOG("trying to replace %s (%s)",
+  DEBUG_LOG("%s %s (%s)", refreshment ? "refreshing" : "trying to replace",
            UTI_IPToString(&record->remote_addr->ip_addr), record->name);

+  record->last_resolving = SCH_GetLastEventMonoTime();
+
  us = MallocNew(struct UnresolvedSource);
  us->name = Strdup(record->name);
-  /* If there never was a valid reply from this source (e.g. it was a bad
-     replacement), ignore the order of addresses from the resolver to not get
-     stuck to a pair of addresses if the order doesn't change, or a group of
-     IPv4/IPv6 addresses if the resolver prefers inaccessible IP family */
-  us->random_order = record->tentative;
+  /* Ignore the order of addresses from the resolver to not get
+     stuck with a pair of unreachable or otherwise unusable servers
+     (e.g. falsetickers) in case the order doesn't change, or a group
+     of servers if they are ordered by IP family */
+  us->random_order = 1;
+  us->refreshment = refreshment;
  us->pool_id = INVALID_POOL;
  us->address = *record->remote_addr;

@@ -956,11 +1044,11 @@ resolve_source_replacement(SourceRecord *record)
 void
 NSR_HandleBadSource(IPAddr *address)
 {
-  static struct timespec last_replacement;
-  struct timespec now;
+  static double next_replacement = 0.0;
  SourceRecord *record;
  IPAddr ip_addr;
-  double diff;
+  uint32_t rnd;
+  double now;
  int slot;

  if (!find_slot(address, &slot))
@@ -975,15 +1063,56 @@ NSR_HandleBadSource(IPAddr *address)
    return;

  /* Don't resolve names too frequently */
-  SCH_GetLastEventTime(NULL, NULL, &now);
-  diff = UTI_DiffTimespecsToDouble(&now, &last_replacement);
-  if (fabs(diff) < RESOLVE_INTERVAL_UNIT * (1 << MIN_REPLACEMENT_INTERVAL)) {
+  now = SCH_GetLastEventMonoTime();
+  if (now < next_replacement) {
    DEBUG_LOG("replacement postponed");
    return;
  }
-  last_replacement = now;

-  resolve_source_replacement(record);
+  UTI_GetRandomBytes(&rnd, sizeof (rnd));
+  next_replacement = now + ((double)rnd / (uint32_t)-1) *
+                     (RESOLVE_INTERVAL_UNIT * (1 << MAX_REPLACEMENT_INTERVAL));
+
+  resolve_source_replacement(record, 0);
+}
+
+/* ================================================== */
+
+static void
+maybe_refresh_source(void)
+{
+  static double last_refreshment = 0.0;
+  SourceRecord *record, *oldest_record;
+  int i, min_interval;
+  double now;
+
+  min_interval = CNF_GetRefresh();
+
+  now = SCH_GetLastEventMonoTime();
+  if (min_interval <= 0 || now < last_refreshment + min_interval)
+    return;
+
+  last_refreshment = now;
+
+  for (i = 0, oldest_record = NULL; i < ARR_GetSize(records); i++) {
+    record = get_record(i);
+    if (!record->remote_addr || UTI_IsStringIP(record->name))
+      continue;
+
+    if (!oldest_record || oldest_record->last_resolving > record->last_resolving)
+      oldest_record = record;
+  }
+
+  if (!oldest_record)
+    return;
+
+  /* Check if the name wasn't already resolved in the last interval */
+  if (now < oldest_record->last_resolving + min_interval) {
+    last_refreshment = oldest_record->last_resolving;
+    return;
+  }
+
+  resolve_source_replacement(oldest_record, 1);
 }

 /* ================================================== */
@@ -999,7 +1128,7 @@ NSR_RefreshAddresses(void)
    if (!record->remote_addr)
      continue;

-    resolve_source_replacement(record);
+    resolve_source_replacement(record, 1);
  }
 }

@@ -1125,6 +1254,8 @@ NSR_ProcessRx(NTP_Remote_Address *remote_addr, NTP_Local_Address *local_addr,
          remove_pool_sources(record->pool_id, 1, 0);
      }
    }
+
+    maybe_refresh_source();
  } else {
    NCR_ProcessRxUnknown(remote_addr, local_addr, rx_ts, message, length);
  }
--- a/ntp_sources.h
+++ b/ntp_sources.h
@@ -60,6 +60,8 @@ extern NSR_Status NSR_AddSource(NTP_Remote_Address *remote_addr, NTP_Source_Type
 extern NSR_Status NSR_AddSourceByName(char *name, int port, int pool, NTP_Source_Type type,
                                      SourceParameters *params, uint32_t *conf_id);

+extern const char *NSR_StatusToString(NSR_Status status);
+
 /* Function type for handlers to be called back when an attempt
 * (possibly unsuccessful) to resolve unresolved sources ends */
 typedef void (*NSR_SourceResolvingEndHandler)(void);
--- a/nts_ke_client.c
+++ b/nts_ke_client.c
@@ -102,16 +102,22 @@ static int
 prepare_request(NKC_Instance inst)
 {
  NKSN_Instance session = inst->session;
-  uint16_t datum;
+  uint16_t data[2];
+  int length;

  NKSN_BeginMessage(session);

-  datum = htons(NKE_NEXT_PROTOCOL_NTPV4);
-  if (!NKSN_AddRecord(session, 1, NKE_RECORD_NEXT_PROTOCOL, &datum, sizeof (datum)))
+  data[0] = htons(NKE_NEXT_PROTOCOL_NTPV4);
+  if (!NKSN_AddRecord(session, 1, NKE_RECORD_NEXT_PROTOCOL, data, sizeof (data[0])))
    return 0;

-  datum = htons(AEAD_AES_SIV_CMAC_256);
-  if (!NKSN_AddRecord(session, 1, NKE_RECORD_AEAD_ALGORITHM, &datum, sizeof (datum)))
+  length = 0;
+  if (SIV_GetKeyLength(AEAD_AES_128_GCM_SIV) > 0)
+    data[length++] = htons(AEAD_AES_128_GCM_SIV);
+  if (SIV_GetKeyLength(AEAD_AES_SIV_CMAC_256) > 0)
+    data[length++] = htons(AEAD_AES_SIV_CMAC_256);
+  if (!NKSN_AddRecord(session, 1, NKE_RECORD_AEAD_ALGORITHM, data,
+                      length * sizeof (data[0])))
    return 0;

  if (!NKSN_EndMessage(session))
@@ -159,12 +165,14 @@ process_response(NKC_Instance inst)
        next_protocol = NKE_NEXT_PROTOCOL_NTPV4;
        break;
      case NKE_RECORD_AEAD_ALGORITHM:
-        if (length != 2 || ntohs(data[0]) != AEAD_AES_SIV_CMAC_256) {
+        if (length != 2 || (ntohs(data[0]) != AEAD_AES_SIV_CMAC_256 &&
+                            ntohs(data[0]) != AEAD_AES_128_GCM_SIV) ||
+            SIV_GetKeyLength(ntohs(data[0])) <= 0) {
          DEBUG_LOG("Unexpected NTS-KE AEAD algorithm");
          error = 1;
          break;
        }
-        aead_algorithm = AEAD_AES_SIV_CMAC_256;
+        aead_algorithm = ntohs(data[0]);
        inst->context.algorithm = aead_algorithm;
        break;
      case NKE_RECORD_ERROR:
@@ -236,7 +244,7 @@ process_response(NKC_Instance inst)

  if (error || inst->num_cookies == 0 ||
      next_protocol != NKE_NEXT_PROTOCOL_NTPV4 ||
-      aead_algorithm != AEAD_AES_SIV_CMAC_256)
+      aead_algorithm < 0)
    return 0;

  return 1;
@@ -370,6 +378,13 @@ NKC_Start(NKC_Instance inst)
    return 0;
  }

+  /* Don't try to connect if missing the algorithm which all servers
+     are required to support */
+  if (SIV_GetKeyLength(AEAD_AES_SIV_CMAC_256) <= 0) {
+    LOG(LOGS_ERR, "Missing AES-SIV-CMAC-256");
+    return 0;
+  }
+
  /* Follow the bindacqaddress and bindacqdevice settings */
  CNF_GetBindAcquisitionAddress(inst->address.ip_addr.family, &local_addr.ip_addr);
  local_addr.port = 0;
--- a/nts_ke_server.c
+++ b/nts_ke_server.c
@@ -2,7 +2,7 @@
  chronyd/chronyc - Programs for keeping computer clocks accurate.

 **********************************************************************
- * Copyright (C) Miroslav Lichvar  2020
+ * Copyright (C) Miroslav Lichvar  2020, 2022
 * 
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of version 2 of the GNU General Public License as
@@ -47,31 +47,33 @@

 #define SERVER_TIMEOUT 2.0

-#define SERVER_COOKIE_SIV AEAD_AES_SIV_CMAC_256
-#define SERVER_COOKIE_NONCE_LENGTH 16
+#define MAX_COOKIE_NONCE_LENGTH 16

 #define KEY_ID_INDEX_BITS 2
 #define MAX_SERVER_KEYS (1U << KEY_ID_INDEX_BITS)
 #define FUTURE_KEYS 1

 #define DUMP_FILENAME "ntskeys"
-#define DUMP_IDENTIFIER "NKS0\n"
+#define DUMP_IDENTIFIER "NKS1\n"
+#define OLD_DUMP_IDENTIFIER "NKS0\n"

 #define INVALID_SOCK_FD (-7)

 typedef struct {
  uint32_t key_id;
-  unsigned char nonce[SERVER_COOKIE_NONCE_LENGTH];
 } ServerCookieHeader;

 typedef struct {
  uint32_t id;
  unsigned char key[SIV_MAX_KEY_LENGTH];
+  SIV_Algorithm siv_algorithm;
  SIV_Instance siv;
+  int nonce_length;
 } ServerKey;

 typedef struct {
  uint32_t key_id;
+  uint32_t siv_algorithm;
  unsigned char key[SIV_MAX_KEY_LENGTH];
  IPAddr client_addr;
  uint16_t client_port;
@@ -148,12 +150,30 @@ handle_client(int sock_fd, IPSockAddr *addr)

 /* ================================================== */

+static void
+update_key_siv(ServerKey *key, SIV_Algorithm algorithm)
+{
+  if (!key->siv || key->siv_algorithm != algorithm) {
+    if (key->siv)
+      SIV_DestroyInstance(key->siv);
+    key->siv_algorithm = algorithm;
+    key->siv = SIV_CreateInstance(algorithm);
+    key->nonce_length = MIN(SIV_GetMaxNonceLength(key->siv), MAX_COOKIE_NONCE_LENGTH);
+  }
+
+  if (!key->siv || !SIV_SetKey(key->siv, key->key, SIV_GetKeyLength(key->siv_algorithm)))
+    LOG_FATAL("Could not set SIV key");
+}
+
+/* ================================================== */
+
 static void
 handle_helper_request(int fd, int event, void *arg)
 {
  SCK_Message *message;
  HelperRequest *req;
  IPSockAddr client_addr;
+  ServerKey *key;
  int sock_fd;

  /* Receive the helper request with the NTS-KE session socket.
@@ -181,16 +201,14 @@ handle_helper_request(int fd, int event, void *arg)
  req = message->data;

  /* Extract the current server key and client address from the request */
-  server_keys[current_server_key].id = ntohl(req->key_id);
-  assert(sizeof (server_keys[current_server_key].key) == sizeof (req->key));
-  memcpy(server_keys[current_server_key].key, req->key,
-         sizeof (server_keys[current_server_key].key));
+  key = &server_keys[current_server_key];
+  key->id = ntohl(req->key_id);
+  assert(sizeof (key->key) == sizeof (req->key));
+  memcpy(key->key, req->key, sizeof (key->key));
  UTI_IPNetworkToHost(&req->client_addr, &client_addr.ip_addr);
  client_addr.port = ntohs(req->client_port);

-  if (!SIV_SetKey(server_keys[current_server_key].siv, server_keys[current_server_key].key,
-                  SIV_GetKeyLength(SERVER_COOKIE_SIV)))
-    LOG_FATAL("Could not set SIV key");
+  update_key_siv(key, ntohl(req->siv_algorithm));

  if (!handle_client(sock_fd, &client_addr)) {
    SCK_CloseSocket(sock_fd);
@@ -240,6 +258,7 @@ accept_connection(int listening_fd, int event, void *arg)

    /* Include the current server key and client address in the request */
    req.key_id = htonl(server_keys[current_server_key].id);
+    req.siv_algorithm = htonl(server_keys[current_server_key].siv_algorithm);
    assert(sizeof (req.key) == sizeof (server_keys[current_server_key].key));
    memcpy(req.key, server_keys[current_server_key].key, sizeof (req.key));
    UTI_IPHostToNetwork(&addr.ip_addr, &req.client_addr);
@@ -427,8 +446,9 @@ process_request(NKSN_Instance session)

        for (i = 0; i < MIN(length, sizeof (data)) / 2; i++) {
          aead_algorithm_values++;
-          if (ntohs(data[i]) == AEAD_AES_SIV_CMAC_256)
-            aead_algorithm = AEAD_AES_SIV_CMAC_256;
+          /* Use the first supported algorithm */
+          if (aead_algorithm < 0 && SIV_GetKeyLength(ntohs(data[i])) > 0)
+            aead_algorithm = ntohs(data[i]);
        }
        break;
      case NKE_RECORD_ERROR:
@@ -470,28 +490,38 @@ handle_message(void *arg)
 static void
 generate_key(int index)
 {
+  SIV_Algorithm algorithm;
+  ServerKey *key;
  int key_length;

  if (index < 0 || index >= MAX_SERVER_KEYS)
    assert(0);

-  key_length = SIV_GetKeyLength(SERVER_COOKIE_SIV);
-  if (key_length > sizeof (server_keys[index].key))
+  /* Prefer AES-128-GCM-SIV if available.  Note that if older keys loaded
+     from ntsdumpdir use a different algorithm, responding to NTP requests
+     with cookies encrypted with those keys will not work if the new algorithm
+     produces longer cookies (i.e. response would be longer than request).
+     Switching from AES-SIV-CMAC-256 to AES-128-GCM-SIV is ok. */
+  algorithm = SIV_GetKeyLength(AEAD_AES_128_GCM_SIV) > 0 ?
+              AEAD_AES_128_GCM_SIV : AEAD_AES_SIV_CMAC_256;
+
+  key = &server_keys[index];
+
+  key_length = SIV_GetKeyLength(algorithm);
+  if (key_length > sizeof (key->key))
    assert(0);

-  UTI_GetRandomBytesUrandom(server_keys[index].key, key_length);
-
-  if (!server_keys[index].siv ||
-      !SIV_SetKey(server_keys[index].siv, server_keys[index].key, key_length))
-    LOG_FATAL("Could not set SIV key");
-
-  UTI_GetRandomBytes(&server_keys[index].id, sizeof (server_keys[index].id));
+  UTI_GetRandomBytesUrandom(key->key, key_length);
+  memset(key->key + key_length, 0, sizeof (key->key) - key_length);
+  UTI_GetRandomBytes(&key->id, sizeof (key->id));

  /* Encode the index in the lowest bits of the ID */
-  server_keys[index].id &= -1U << KEY_ID_INDEX_BITS;
-  server_keys[index].id |= index;
+  key->id &= -1U << KEY_ID_INDEX_BITS;
+  key->id |= index;

-  DEBUG_LOG("Generated server key %"PRIX32, server_keys[index].id);
+  update_key_siv(key, algorithm);
+
+  DEBUG_LOG("Generated key %08"PRIX32" (%d)", key->id, (int)key->siv_algorithm);

  last_server_key_ts = SCH_GetLastEventMonoTime();
 }
@@ -519,18 +549,19 @@ save_keys(void)
  if (!f)
    return;

-  key_length = SIV_GetKeyLength(SERVER_COOKIE_SIV);
  last_key_age = SCH_GetLastEventMonoTime() - last_server_key_ts;

-  if (fprintf(f, "%s%d %.1f\n", DUMP_IDENTIFIER, SERVER_COOKIE_SIV, last_key_age) < 0)
+  if (fprintf(f, "%s%.1f\n", DUMP_IDENTIFIER, last_key_age) < 0)
    goto error;

  for (i = 0; i < MAX_SERVER_KEYS; i++) {
    index = (current_server_key + i + 1 + FUTURE_KEYS) % MAX_SERVER_KEYS;
+    key_length = SIV_GetKeyLength(server_keys[index].siv_algorithm);

    if (key_length > sizeof (server_keys[index].key) ||
        !UTI_BytesToHex(server_keys[index].key, key_length, buf, sizeof (buf)) ||
-        fprintf(f, "%08"PRIX32" %s\n", server_keys[index].id, buf) < 0)
+        fprintf(f, "%08"PRIX32" %s %d\n", server_keys[index].id, buf,
+                (int)server_keys[index].siv_algorithm) < 0)
      goto error;
  }

@@ -545,7 +576,7 @@ save_keys(void)
  return;

 error:
-  DEBUG_LOG("Could not %s server keys", "save");
+  LOG(LOGS_ERR, "Could not %s %s", "save", "server NTS keys");
  fclose(f);

  if (!UTI_RemoveFile(dump_dir, DUMP_FILENAME, NULL))
@@ -554,17 +585,16 @@ error:

 /* ================================================== */

-#define MAX_WORDS 2
+#define MAX_WORDS 3

 static int
 load_keys(void)
 {
+  int i, index, key_length, algorithm = 0, old_ver;
  char *dump_dir, line[1024], *words[MAX_WORDS];
-  unsigned char key[SIV_MAX_KEY_LENGTH];
-  int i, index, key_length, algorithm;
+  ServerKey new_keys[MAX_SERVER_KEYS];
  double key_age;
  FILE *f;
-  uint32_t id;

  dump_dir = CNF_GetNtsDumpDir();
  if (!dump_dir)
@@ -574,43 +604,58 @@ load_keys(void)
  if (!f)
    return 0;

-  if (!fgets(line, sizeof (line), f) || strcmp(line, DUMP_IDENTIFIER) != 0 ||
-      !fgets(line, sizeof (line), f) || UTI_SplitString(line, words, MAX_WORDS) != 2 ||
-        sscanf(words[0], "%d", &algorithm) != 1 || algorithm != SERVER_COOKIE_SIV ||
-        sscanf(words[1], "%lf", &key_age) != 1)
+  if (!fgets(line, sizeof (line), f) ||
+      (strcmp(line, DUMP_IDENTIFIER) != 0 && strcmp(line, OLD_DUMP_IDENTIFIER) != 0))
    goto error;

-  key_length = SIV_GetKeyLength(SERVER_COOKIE_SIV);
-  last_server_key_ts = SCH_GetLastEventMonoTime() - MAX(key_age, 0.0);
+  old_ver = strcmp(line, DUMP_IDENTIFIER) != 0;
+
+  if (!fgets(line, sizeof (line), f) ||
+      UTI_SplitString(line, words, MAX_WORDS) != (old_ver ? 2 : 1) ||
+      (old_ver && sscanf(words[0], "%d", &algorithm) != 1) ||
+      sscanf(words[old_ver ? 1 : 0], "%lf", &key_age) != 1)
+    goto error;

  for (i = 0; i < MAX_SERVER_KEYS && fgets(line, sizeof (line), f); i++) {
-    if (UTI_SplitString(line, words, MAX_WORDS) != 2 ||
-        sscanf(words[0], "%"PRIX32, &id) != 1)
+    if (UTI_SplitString(line, words, MAX_WORDS) != (old_ver ? 2 : 3) ||
+        sscanf(words[0], "%"PRIX32, &new_keys[i].id) != 1 ||
+        (!old_ver && sscanf(words[2], "%d", &algorithm) != 1))
      goto error;

-    if (UTI_HexToBytes(words[1], key, sizeof (key)) != key_length)
+    new_keys[i].siv_algorithm = algorithm;
+    key_length = SIV_GetKeyLength(algorithm);
+
+    if ((i > 0 && (new_keys[i].id - new_keys[i - 1].id) % MAX_SERVER_KEYS != 1) ||
+        key_length <= 0 ||
+        UTI_HexToBytes(words[1], new_keys[i].key, sizeof (new_keys[i].key)) != key_length)
      goto error;
-
-    index = id % MAX_SERVER_KEYS;
-
-    server_keys[index].id = id;
-    assert(sizeof (server_keys[index].key) == sizeof (key));
-    memcpy(server_keys[index].key, key, key_length);
-
-    if (!SIV_SetKey(server_keys[index].siv, server_keys[index].key, key_length))
-      LOG_FATAL("Could not set SIV key");
-
-    DEBUG_LOG("Loaded key %"PRIX32, id);
-
-    current_server_key = (index + MAX_SERVER_KEYS - FUTURE_KEYS) % MAX_SERVER_KEYS;
+    memset(new_keys[i].key + key_length, 0, sizeof (new_keys[i].key) - key_length);
  }

+  if (i < MAX_SERVER_KEYS)
+    goto error;
+
+  for (i = 0; i < MAX_SERVER_KEYS; i++) {
+    index = new_keys[i].id % MAX_SERVER_KEYS;
+    server_keys[index].id = new_keys[i].id;
+    memcpy(server_keys[index].key, new_keys[i].key, sizeof (server_keys[index].key));
+
+    update_key_siv(&server_keys[index], new_keys[i].siv_algorithm);
+
+    DEBUG_LOG("Loaded key %08"PRIX32" (%d)",
+              server_keys[index].id, (int)server_keys[index].siv_algorithm);
+  }
+
+  current_server_key = (index + MAX_SERVER_KEYS - FUTURE_KEYS) % MAX_SERVER_KEYS;
+  last_server_key_ts = SCH_GetLastEventMonoTime() - MAX(key_age, 0.0);
+
  fclose(f);

+  LOG(LOGS_INFO, "Loaded %s", "server NTS keys");
  return 1;

 error:
-  DEBUG_LOG("Could not %s server keys", "load");
+  LOG(LOGS_ERR, "Could not %s %s", "load", "server NTS keys");
  fclose(f);

  return 0;
@@ -640,6 +685,8 @@ run_helper(uid_t uid, gid_t gid, int scfilter_level)

  DEBUG_LOG("Helper started");

+  SCK_CloseReusableSockets();
+
  /* Suppress a log message about disabled clock control */
  log_severity = LOG_GetMinSeverity();
  LOG_SetMinSeverity(LOGS_ERR);
@@ -759,7 +806,7 @@ NKS_Initialise(void)
  /* Generate random keys, even if they will be replaced by reloaded keys,
     or unused (in the helper) */
  for (i = 0; i < MAX_SERVER_KEYS; i++) {
-    server_keys[i].siv = SIV_CreateInstance(SERVER_COOKIE_SIV);
+    server_keys[i].siv = NULL;
    generate_key(i);
  }

@@ -779,6 +826,11 @@ NKS_Initialise(void)
      key_delay = key_rotation_interval - (SCH_GetLastEventMonoTime() - last_server_key_ts);
      SCH_AddTimeoutByDelay(MAX(key_delay, 0.0), key_timeout, NULL);
    }
+
+    /* Warn if keys are not saved, which can cause a flood of requests
+       after server restart */
+    if (!CNF_GetNtsDumpDir())
+      LOG(LOGS_WARN, "No ntsdumpdir to save server keys");
  }

  initialised = 1;
@@ -852,7 +904,7 @@ NKS_ReloadKeys(void)
 int
 NKS_GenerateCookie(NKE_Context *context, NKE_Cookie *cookie)
 {
-  unsigned char plaintext[2 * NKE_MAX_KEY_LENGTH], *ciphertext;
+  unsigned char *nonce, plaintext[2 * NKE_MAX_KEY_LENGTH], *ciphertext;
  int plaintext_length, tag_length;
  ServerCookieHeader *header;
  ServerKey *key;
@@ -862,14 +914,12 @@ NKS_GenerateCookie(NKE_Context *context, NKE_Cookie *cookie)
    return 0;
  }

-  /* The algorithm is hardcoded for now */
-  if (context->algorithm != AEAD_AES_SIV_CMAC_256) {
-    DEBUG_LOG("Unexpected SIV algorithm");
-    return 0;
-  }
+  /* The AEAD ID is not encoded in the cookie.  It is implied from the key
+     length (as long as only algorithms with different key lengths are
+     supported). */

  if (context->c2s.length < 0 || context->c2s.length > NKE_MAX_KEY_LENGTH ||
-      context->s2c.length < 0 || context->s2c.length > NKE_MAX_KEY_LENGTH) {
+      context->s2c.length != context->c2s.length) {
    DEBUG_LOG("Invalid key length");
    return 0;
  }
@@ -879,7 +929,11 @@ NKS_GenerateCookie(NKE_Context *context, NKE_Cookie *cookie)
  header = (ServerCookieHeader *)cookie->cookie;

  header->key_id = htonl(key->id);
-  UTI_GetRandomBytes(header->nonce, sizeof (header->nonce));
+
+  nonce = cookie->cookie + sizeof (*header);
+  if (key->nonce_length > sizeof (cookie->cookie) - sizeof (*header))
+    assert(0);
+  UTI_GetRandomBytes(nonce, key->nonce_length);

  plaintext_length = context->c2s.length + context->s2c.length;
  assert(plaintext_length <= sizeof (plaintext));
@@ -887,11 +941,11 @@ NKS_GenerateCookie(NKE_Context *context, NKE_Cookie *cookie)
  memcpy(plaintext + context->c2s.length, context->s2c.key, context->s2c.length);

  tag_length = SIV_GetTagLength(key->siv);
-  cookie->length = sizeof (*header) + plaintext_length + tag_length;
+  cookie->length = sizeof (*header) + key->nonce_length + plaintext_length + tag_length;
  assert(cookie->length <= sizeof (cookie->cookie));
-  ciphertext = cookie->cookie + sizeof (*header);
+  ciphertext = cookie->cookie + sizeof (*header) + key->nonce_length;

-  if (!SIV_Encrypt(key->siv, header->nonce, sizeof (header->nonce),
+  if (!SIV_Encrypt(key->siv, nonce, key->nonce_length,
                   "", 0,
                   plaintext, plaintext_length,
                   ciphertext, plaintext_length + tag_length)) {
@@ -907,7 +961,7 @@ NKS_GenerateCookie(NKE_Context *context, NKE_Cookie *cookie)
 int
 NKS_DecodeCookie(NKE_Cookie *cookie, NKE_Context *context)
 {
-  unsigned char plaintext[2 * NKE_MAX_KEY_LENGTH], *ciphertext;
+  unsigned char *nonce, plaintext[2 * NKE_MAX_KEY_LENGTH], *ciphertext;
  int ciphertext_length, plaintext_length, tag_length;
  ServerCookieHeader *header;
  ServerKey *key;
@@ -924,8 +978,6 @@ NKS_DecodeCookie(NKE_Cookie *cookie, NKE_Context *context)
  }

  header = (ServerCookieHeader *)cookie->cookie;
-  ciphertext = cookie->cookie + sizeof (*header);
-  ciphertext_length = cookie->length - sizeof (*header);

  key_id = ntohl(header->key_id);
  key = &server_keys[key_id % MAX_SERVER_KEYS];
@@ -935,18 +987,23 @@ NKS_DecodeCookie(NKE_Cookie *cookie, NKE_Context *context)
  }

  tag_length = SIV_GetTagLength(key->siv);
-  if (tag_length >= ciphertext_length) {
+
+  if (cookie->length <= (int)sizeof (*header) + key->nonce_length + tag_length) {
    DEBUG_LOG("Invalid cookie length");
    return 0;
  }

+  nonce = cookie->cookie + sizeof (*header);
+  ciphertext = cookie->cookie + sizeof (*header) + key->nonce_length;
+  ciphertext_length = cookie->length - sizeof (*header) - key->nonce_length;
  plaintext_length = ciphertext_length - tag_length;
+
  if (plaintext_length > sizeof (plaintext) || plaintext_length % 2 != 0) {
    DEBUG_LOG("Invalid cookie length");
    return 0;
  }

-  if (!SIV_Decrypt(key->siv, header->nonce, sizeof (header->nonce),
+  if (!SIV_Decrypt(key->siv, nonce, key->nonce_length,
                   "", 0,
                   ciphertext, ciphertext_length,
                   plaintext, plaintext_length)) {
@@ -954,7 +1011,19 @@ NKS_DecodeCookie(NKE_Cookie *cookie, NKE_Context *context)
    return 0;
  }

-  context->algorithm = AEAD_AES_SIV_CMAC_256;
+  /* Select a supported algorithm corresponding to the key length, avoiding
+     potentially slow SIV_GetKeyLength() */
+  switch (plaintext_length / 2) {
+    case 16:
+      context->algorithm = AEAD_AES_128_GCM_SIV;
+      break;
+    case 32:
+      context->algorithm = AEAD_AES_SIV_CMAC_256;
+      break;
+    default:
+      DEBUG_LOG("Unknown key length");
+      return 0;
+  }

  context->c2s.length = plaintext_length / 2;
  context->s2c.length = plaintext_length / 2;
--- a/nts_ke_session.c
+++ b/nts_ke_session.c
@@ -594,13 +594,13 @@ handle_step(struct timespec *raw, struct timespec *cooked, double dfreq,

 static int gnutls_initialised = 0;

-static void
+static int
 init_gnutls(void)
 {
  int r;

  if (gnutls_initialised)
-    return;
+    return 1;

  r = gnutls_global_init();
  if (r < 0)
@@ -611,8 +611,12 @@ init_gnutls(void)
  r = gnutls_priority_init2(&priority_cache,
                            "-VERS-SSL3.0:-VERS-TLS1.0:-VERS-TLS1.1:-VERS-TLS1.2:-VERS-DTLS-ALL",
                            NULL, GNUTLS_PRIORITY_INIT_DEF_APPEND);
-  if (r < 0)
-    LOG_FATAL("Could not initialise %s : %s", "priority cache", gnutls_strerror(r));
+  if (r < 0) {
+    LOG(LOGS_ERR, "Could not initialise %s : %s",
+        "priority cache for TLS", gnutls_strerror(r));
+    gnutls_global_deinit();
+    return 0;
+  }

  /* Use our clock instead of the system clock in certificate verification */
  gnutls_global_set_time_function(get_time);
@@ -621,6 +625,8 @@ init_gnutls(void)
  DEBUG_LOG("Initialised");

  LCL_AddParameterChangeHandler(handle_step, NULL);
+
+  return 1;
 }

 /* ================================================== */
@@ -649,7 +655,8 @@ create_credentials(const char **certs, const char **keys, int n_certs_keys,
  gnutls_certificate_credentials_t credentials = NULL;
  int i, r;

-  init_gnutls();
+  if (!init_gnutls())
+    return NULL;

  r = gnutls_certificate_allocate_credentials(&credentials);
  if (r < 0)
@@ -660,6 +667,8 @@ create_credentials(const char **certs, const char **keys, int n_certs_keys,
      assert(0);

    for (i = 0; i < n_certs_keys; i++) {
+      if (!UTI_CheckFilePermissions(keys[i], 0771))
+        ;
      r = gnutls_certificate_set_x509_key_file(credentials, certs[i], keys[i],
                                               GNUTLS_X509_FMT_PEM);
      if (r < 0)
--- a/nts_ntp_auth.c
+++ b/nts_ntp_auth.c
@@ -61,23 +61,25 @@ get_padded_length(int length)

 int
 NNA_GenerateAuthEF(NTP_Packet *packet, NTP_PacketInfo *info, SIV_Instance siv,
-                   const unsigned char *nonce, int nonce_length,
+                   const unsigned char *nonce, int max_nonce_length,
                   const unsigned char *plaintext, int plaintext_length,
                   int min_ef_length)
 {
-  int auth_length, ciphertext_length, assoc_length;
+  int auth_length, ciphertext_length, assoc_length, nonce_length, max_siv_nonce_length;
  int nonce_padding, ciphertext_padding, additional_padding;
  unsigned char *ciphertext, *body;
  struct AuthHeader *header;

  assert(sizeof (*header) == 4);

-  if (nonce_length <= 0 || plaintext_length < 0) {
+  if (max_nonce_length <= 0 || plaintext_length < 0) {
    DEBUG_LOG("Invalid nonce/plaintext length");
    return 0;
  }

  assoc_length = info->length;
+  max_siv_nonce_length = SIV_GetMaxNonceLength(siv);
+  nonce_length = MIN(max_nonce_length, max_siv_nonce_length);
  ciphertext_length = SIV_GetTagLength(siv) + plaintext_length;
  nonce_padding = get_padding_length(nonce_length);
  ciphertext_padding = get_padding_length(ciphertext_length);
@@ -86,8 +88,8 @@ NNA_GenerateAuthEF(NTP_Packet *packet, NTP_PacketInfo *info, SIV_Instance siv,
  auth_length = sizeof (*header) + nonce_length + nonce_padding +
                ciphertext_length + ciphertext_padding;
  additional_padding = MAX(min_ef_length - auth_length - 4, 0);
-  additional_padding = MAX(NTS_MIN_UNPADDED_NONCE_LENGTH - nonce_length - nonce_padding,
-                           additional_padding);
+  additional_padding = MAX(MIN(NTS_MIN_UNPADDED_NONCE_LENGTH, max_siv_nonce_length) -
+                           nonce_length - nonce_padding, additional_padding);
  auth_length += additional_padding;

  if (!NEF_AddBlankField(packet, info, NTP_EF_NTS_AUTH_AND_EEF, auth_length,
@@ -113,6 +115,7 @@ NNA_GenerateAuthEF(NTP_Packet *packet, NTP_PacketInfo *info, SIV_Instance siv,
                   plaintext, plaintext_length, ciphertext, ciphertext_length)) {
    DEBUG_LOG("SIV encrypt failed");
    info->length = assoc_length;
+    info->ext_fields--;
    return 0;
  }

@@ -127,7 +130,7 @@ int
 NNA_DecryptAuthEF(NTP_Packet *packet, NTP_PacketInfo *info, SIV_Instance siv, int ef_start,
                  unsigned char *plaintext, int buffer_length, int *plaintext_length)
 {
-  unsigned int siv_tag_length, nonce_length, ciphertext_length;
+  int siv_tag_length, max_siv_nonce_length, nonce_length, ciphertext_length;
  unsigned char *nonce, *ciphertext;
  int ef_type, ef_body_length;
  void *ef_body;
@@ -155,6 +158,7 @@ NNA_DecryptAuthEF(NTP_Packet *packet, NTP_PacketInfo *info, SIV_Instance siv, in
  nonce = (unsigned char *)(header + 1);
  ciphertext = nonce + get_padded_length(nonce_length);

+  max_siv_nonce_length = SIV_GetMaxNonceLength(siv);
  siv_tag_length = SIV_GetTagLength(siv);

  if (nonce_length < 1 ||
@@ -164,8 +168,8 @@ NNA_DecryptAuthEF(NTP_Packet *packet, NTP_PacketInfo *info, SIV_Instance siv, in
    return 0;
  }

-  if (ef_body_length < sizeof (*header) +
-        NTS_MIN_UNPADDED_NONCE_LENGTH + get_padded_length(ciphertext_length)) {
+  if (sizeof (*header) + MIN(NTS_MIN_UNPADDED_NONCE_LENGTH, max_siv_nonce_length) +
+      get_padded_length(ciphertext_length) > ef_body_length) {
    DEBUG_LOG("Missing padding");
    return 0;
  }
--- a/nts_ntp_auth.h
+++ b/nts_ntp_auth.h
@@ -32,7 +32,7 @@
 #include "siv.h"

 extern int NNA_GenerateAuthEF(NTP_Packet *packet, NTP_PacketInfo *info, SIV_Instance siv,
-                              const unsigned char *nonce, int nonce_length,
+                              const unsigned char *nonce, int max_nonce_length,
                              const unsigned char *plaintext, int plaintext_length,
                              int min_ef_length);

--- a/nts_ntp_client.c
+++ b/nts_ntp_client.c
@@ -46,6 +46,9 @@
 /* Maximum length of all cookies to avoid IP fragmentation */
 #define MAX_TOTAL_COOKIE_LENGTH (8 * 108)

+/* Retry interval for NTS-KE start (which doesn't generate network traffic) */
+#define RETRY_INTERVAL_KE_START 2.0
+
 /* Magic string of files containing keys and cookies */
 #define DUMP_IDENTIFIER "NNC0\n"

@@ -203,10 +206,15 @@ set_ntp_address(NNC_Instance inst, NTP_Remote_Address *negotiated_address)
 /* ================================================== */

 static void
-update_next_nke_attempt(NNC_Instance inst, double now)
+update_next_nke_attempt(NNC_Instance inst, int failed_start, double now)
 {
  int factor, interval;

+  if (failed_start) {
+    inst->next_nke_attempt = now + RETRY_INTERVAL_KE_START;
+    return;
+  }
+
  if (!inst->nke)
    return;

@@ -221,8 +229,8 @@ static int
 get_cookies(NNC_Instance inst)
 {
  NTP_Remote_Address ntp_address;
+  int got_data, failed_start = 0;
  double now;
-  int got_data;

  assert(inst->num_cookies == 0);

@@ -239,13 +247,12 @@ get_cookies(NNC_Instance inst)
    inst->nke = NKC_CreateInstance(&inst->nts_address, inst->name, inst->cert_set);

    inst->nke_attempts++;
-    update_next_nke_attempt(inst, now);

    if (!NKC_Start(inst->nke))
-      return 0;
+      failed_start = 1;
  }

-  update_next_nke_attempt(inst, now);
+  update_next_nke_attempt(inst, failed_start, now);

  /* Wait until the session stops */
  if (NKC_IsActive(inst->nke))
@@ -643,6 +650,7 @@ load_cookies(NNC_Instance inst)
                                            sizeof (inst->context.c2s.key));

  if (inst->context.s2c.length != SIV_GetKeyLength(algorithm) ||
+      inst->context.s2c.length <= 0 ||
      inst->context.c2s.length != inst->context.s2c.length)
    goto error;

--- a/nts_ntp_server.c
+++ b/nts_ntp_server.c
@@ -2,7 +2,7 @@
  chronyd/chronyc - Programs for keeping computer clocks accurate.

 **********************************************************************
- * Copyright (C) Miroslav Lichvar  2020
+ * Copyright (C) Miroslav Lichvar  2020, 2022
 * 
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of version 2 of the GNU General Public License as
@@ -41,13 +41,15 @@
 #include "siv.h"
 #include "util.h"

-#define SERVER_SIV AEAD_AES_SIV_CMAC_256
+#define MAX_SERVER_SIVS 2

 struct NtsServer {
-  SIV_Instance siv;
+  SIV_Instance sivs[MAX_SERVER_SIVS];
+  SIV_Algorithm siv_algorithms[MAX_SERVER_SIVS];
  unsigned char nonce[NTS_MIN_UNPADDED_NONCE_LENGTH];
  NKE_Cookie cookies[NTS_MAX_COOKIES];
  int num_cookies;
+  int siv_index;
  NTP_int64 req_tx;
 };

@@ -60,6 +62,7 @@ void
 NNS_Initialise(void)
 {
  const char **certs, **keys;
+  int i;

  /* Create an NTS-NTP server instance only if NTS-KE server is enabled */
  if (CNF_GetNtsServerCertAndKeyFiles(&certs, &keys) <= 0) {
@@ -68,9 +71,17 @@ NNS_Initialise(void)
  }

  server = Malloc(sizeof (struct NtsServer));
-  server->siv = SIV_CreateInstance(SERVER_SIV);
-  if (!server->siv)
-    LOG_FATAL("Could not initialise SIV cipher");
+
+  server->siv_algorithms[0] = AEAD_AES_SIV_CMAC_256;
+  server->siv_algorithms[1] = AEAD_AES_128_GCM_SIV;
+  assert(MAX_SERVER_SIVS == 2);
+
+  for (i = 0; i < 2; i++)
+    server->sivs[i] = SIV_CreateInstance(server->siv_algorithms[i]);
+
+  /* AES-SIV-CMAC-256 is required on servers */
+  if (!server->sivs[0])
+    LOG_FATAL("Missing AES-SIV-CMAC-256");
 }

 /* ================================================== */
@@ -78,10 +89,15 @@ NNS_Initialise(void)
 void
 NNS_Finalise(void)
 {
+  int i;
+
  if (!server)
    return;

-  SIV_DestroyInstance(server->siv);
+  for (i = 0; i < MAX_SERVER_SIVS; i++) {
+    if (server->sivs[i])
+      SIV_DestroyInstance(server->sivs[i]);
+  }
  Free(server);
  server = NULL;
 }
@@ -96,6 +112,7 @@ NNS_CheckRequestAuth(NTP_Packet *packet, NTP_PacketInfo *info, uint32_t *kod)
  unsigned char plaintext[NTP_MAX_EXTENSIONS_LENGTH];
  NKE_Context context;
  NKE_Cookie cookie;
+  SIV_Instance siv;
  void *ef_body;

  *kod = 0;
@@ -104,6 +121,7 @@ NNS_CheckRequestAuth(NTP_Packet *packet, NTP_PacketInfo *info, uint32_t *kod)
    return 0;

  server->num_cookies = 0;
+  server->siv_index = -1;
  server->req_tx = packet->transmit_ts;

  if (info->ext_fields == 0 || info->mode != MODE_CLIENT)
@@ -163,17 +181,22 @@ NNS_CheckRequestAuth(NTP_Packet *packet, NTP_PacketInfo *info, uint32_t *kod)
    return 0;
  }

-  if (context.algorithm != SERVER_SIV) {
+  /* Find the SIV instance needed for authentication */
+  for (i = 0; i < MAX_SERVER_SIVS && context.algorithm != server->siv_algorithms[i]; i++)
+    ;
+  if (i == MAX_SERVER_SIVS || !server->sivs[i]) {
    DEBUG_LOG("Unexpected SIV");
    return 0;
  }
+  server->siv_index = i;
+  siv = server->sivs[i];

-  if (!SIV_SetKey(server->siv, context.c2s.key, context.c2s.length)) {
+  if (!SIV_SetKey(siv, context.c2s.key, context.c2s.length)) {
    DEBUG_LOG("Could not set C2S key");
    return 0;
  }

-  if (!NNA_DecryptAuthEF(packet, info, server->siv, auth_start,
+  if (!NNA_DecryptAuthEF(packet, info, siv, auth_start,
                         plaintext, sizeof (plaintext), &plaintext_length)) {
    *kod = NTP_KOD_NTS_NAK;
    return 0;
@@ -199,7 +222,7 @@ NNS_CheckRequestAuth(NTP_Packet *packet, NTP_PacketInfo *info, uint32_t *kod)
    }
  }

-  if (!SIV_SetKey(server->siv, context.s2c.key, context.s2c.length)) {
+  if (!SIV_SetKey(siv, context.s2c.key, context.s2c.length)) {
    DEBUG_LOG("Could not set S2C key");
    return 0;
  }
@@ -271,9 +294,12 @@ NNS_GenerateResponseAuth(NTP_Packet *request, NTP_PacketInfo *req_info,

  server->num_cookies = 0;

+  if (server->siv_index < 0)
+    return 0;
+
  /* Generate an authenticator field which will make the length
     of the response equal to the length of the request */
-  if (!NNA_GenerateAuthEF(response, res_info, server->siv,
+  if (!NNA_GenerateAuthEF(response, res_info, server->sivs[server->siv_index],
                          server->nonce, sizeof (server->nonce),
                          plaintext, plaintext_length,
                          req_info->length - res_info->length))
--- a/pktlength.c
+++ b/pktlength.c
@@ -129,6 +129,7 @@ static const struct request_length request_lengths[] = {
  REQ_LENGTH_ENTRY(select_data, select_data),   /* SELECT_DATA */
  REQ_LENGTH_ENTRY(null, null),                 /* RELOAD_SOURCES */
  REQ_LENGTH_ENTRY(doffset, null),              /* DOFFSET2 */
+  REQ_LENGTH_ENTRY(modify_select_opts, null),   /* MODIFY_SELECTOPTS */
 };

 static const uint16_t reply_lengths[] = {
@@ -156,7 +157,8 @@ static const uint16_t reply_lengths[] = {
  RPY_LENGTH_ENTRY(client_accesses_by_index),   /* CLIENT_ACCESSES_BY_INDEX3 */
  0,                                            /* SERVER_STATS2 - not supported */
  RPY_LENGTH_ENTRY(select_data),                /* SELECT_DATA */
-  RPY_LENGTH_ENTRY(server_stats),               /* SERVER_STATS3 */
+  0,                                            /* SERVER_STATS3 - not supported */
+  RPY_LENGTH_ENTRY(server_stats),               /* SERVER_STATS4 */
 };

 /* ================================================== */
--- a/ptp.h
+++ b/ptp.h
@@ -44,7 +44,12 @@ typedef struct {
  uint8_t domain;
  uint8_t min_sdoid;
  uint16_t flags;
-  uint8_t rest[26];
+  uint8_t correction[8];
+  uint8_t msg_specific[4];
+  uint8_t port_id[10];
+  uint16_t sequence_id;
+  uint8_t control;
+  int8_t interval;
 } PTP_Header;

 typedef struct {
--- a/quantiles.c
+++ b/quantiles.c
@@ -0,0 +1,209 @@
+/*
+  chronyd/chronyc - Programs for keeping computer clocks accurate.
+
+ **********************************************************************
+ * Copyright (C) Miroslav Lichvar  2022
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of version 2 of the GNU General Public License as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ *
+ **********************************************************************
+
+  =======================================================================
+
+  Estimation of quantiles using the Frugal-2U streaming algorithm
+  (https://arxiv.org/pdf/1407.1121v1.pdf)
+  */
+
+#include "config.h"
+
+#include "logging.h"
+#include "memory.h"
+#include "quantiles.h"
+#include "regress.h"
+#include "util.h"
+
+/* Maximum number of repeated estimates for stabilisation */
+#define MAX_REPEAT 64
+
+struct Quantile {
+  double est;
+  double step;
+  int sign;
+};
+
+struct QNT_Instance_Record {
+  struct Quantile *quants;
+  int n_quants;
+  int repeat;
+  int q;
+  int min_k;
+  double min_step;
+  int n_set;
+};
+
+/* ================================================== */
+
+QNT_Instance
+QNT_CreateInstance(int min_k, int max_k, int q, int repeat, double min_step)
+{
+  QNT_Instance inst;
+  long seed;
+
+  if (q < 2 || min_k > max_k || min_k < 1 || max_k >= q ||
+      repeat < 1 || repeat > MAX_REPEAT || min_step <= 0.0)
+    assert(0);
+
+  inst = MallocNew(struct QNT_Instance_Record);
+  inst->n_quants = (max_k - min_k + 1) * repeat;
+  inst->quants = MallocArray(struct Quantile, inst->n_quants);
+  inst->repeat = repeat;
+  inst->q = q;
+  inst->min_k = min_k;
+  inst->min_step = min_step;
+
+  QNT_Reset(inst);
+
+  /* Seed the random number generator, which will not be isolated from
+     other instances and other random() users */
+  UTI_GetRandomBytes(&seed, sizeof (seed));
+  srandom(seed);
+
+  return inst;
+}
+
+/* ================================================== */
+
+void
+QNT_DestroyInstance(QNT_Instance inst)
+{
+  Free(inst->quants);
+  Free(inst);
+}
+
+/* ================================================== */
+
+void
+QNT_Reset(QNT_Instance inst)
+{
+  int i;
+
+  inst->n_set = 0;
+
+  for (i = 0; i < inst->n_quants; i++) {
+    inst->quants[i].est = 0.0;
+    inst->quants[i].step = inst->min_step;
+    inst->quants[i].sign = 1;
+  }
+}
+
+/* ================================================== */
+
+static void
+insert_initial_value(QNT_Instance inst, double value)
+{
+  int i, j, r = inst->repeat;
+
+  if (inst->n_set * r >= inst->n_quants)
+    assert(0);
+
+  /* Keep the initial estimates repeated and ordered */
+  for (i = inst->n_set; i > 0 && inst->quants[(i - 1) * r].est > value; i--) {
+    for (j = 0; j < r; j++)
+      inst->quants[i * r + j].est = inst->quants[(i - 1) * r].est;
+  }
+
+  for (j = 0; j < r; j++)
+    inst->quants[i * r + j].est = value;
+  inst->n_set++;
+
+  /* Duplicate the largest value in unset quantiles */
+  for (i = inst->n_set * r; i < inst->n_quants; i++)
+    inst->quants[i].est = inst->quants[i - 1].est;
+}
+
+/* ================================================== */
+
+static void
+update_estimate(struct Quantile *quantile, double value, double p, double rand,
+                double min_step)
+{
+  if (value > quantile->est && rand > (1.0 - p)) {
+    quantile->step += quantile->sign > 0 ? min_step : -min_step;
+    quantile->est += quantile->step > 0.0 ? fabs(quantile->step) : min_step;
+    if (quantile->est > value) {
+      quantile->step += value - quantile->est;
+      quantile->est = value;
+    }
+    if (quantile->sign < 0 && quantile->step > min_step)
+      quantile->step = min_step;
+    quantile->sign = 1;
+  } else if (value < quantile->est && rand > p) {
+    quantile->step += quantile->sign < 0 ? min_step : -min_step;
+    quantile->est -= quantile->step > 0.0 ? fabs(quantile->step) : min_step;
+    if (quantile->est < value) {
+      quantile->step += quantile->est - value;
+      quantile->est = value;
+    }
+    if (quantile->sign > 0 && quantile->step > min_step)
+      quantile->step = min_step;
+    quantile->sign = -1;
+  }
+}
+
+/* ================================================== */
+
+void
+QNT_Accumulate(QNT_Instance inst, double value)
+{
+  double p, rand;
+  int i;
+
+  /* Initialise the estimates with first received values */
+  if (inst->n_set * inst->repeat < inst->n_quants) {
+    insert_initial_value(inst, value);
+    return;
+  }
+
+  for (i = 0; i < inst->n_quants; i++) {
+    p = (double)(i / inst->repeat + inst->min_k) / inst->q;
+    rand = (double)random() / ((1U << 31) - 1);
+
+    update_estimate(&inst->quants[i], value, p, rand, inst->min_step);
+  }
+}
+
+/* ================================================== */
+
+int
+QNT_GetMinK(QNT_Instance inst)
+{
+  return inst->min_k;
+}
+
+/* ================================================== */
+
+double
+QNT_GetQuantile(QNT_Instance inst, int k)
+{
+  double estimates[MAX_REPEAT];
+  int i;
+
+  if (k < inst->min_k || k - inst->min_k >= inst->n_quants)
+    assert(0);
+
+  for (i = 0; i < inst->repeat; i++)
+    estimates[i] = inst->quants[(k - inst->min_k) * inst->repeat + i].est;
+
+  return RGR_FindMedian(estimates, inst->repeat);
+}
--- a/quantiles.h
+++ b/quantiles.h
@@ -0,0 +1,41 @@
+/*
+  chronyd/chronyc - Programs for keeping computer clocks accurate.
+
+ **********************************************************************
+ * Copyright (C) Miroslav Lichvar  2022
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of version 2 of the GNU General Public License as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ *
+ **********************************************************************
+
+  =======================================================================
+
+  Header file for estimation of quantiles.
+
+  */
+
+#ifndef GOT_QUANTILES_H
+#define GOT_QUANTILES_H
+
+typedef struct QNT_Instance_Record *QNT_Instance;
+
+extern QNT_Instance QNT_CreateInstance(int min_k, int max_k, int q, int repeat, double min_step);
+extern void QNT_DestroyInstance(QNT_Instance inst);
+
+extern void QNT_Reset(QNT_Instance inst);
+extern void QNT_Accumulate(QNT_Instance inst, double value);
+extern int QNT_GetMinK(QNT_Instance inst);
+extern double QNT_GetQuantile(QNT_Instance inst, int k);
+
+#endif
--- a/refclock.c
+++ b/refclock.c
@@ -2,7 +2,7 @@
  chronyd/chronyc - Programs for keeping computer clocks accurate.

 **********************************************************************
- * Copyright (C) Miroslav Lichvar  2009-2011, 2013-2014, 2016-2019
+ * Copyright (C) Miroslav Lichvar  2009-2011, 2013-2014, 2016-2019, 2022
 * 
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of version 2 of the GNU General Public License as
@@ -55,21 +55,6 @@ struct FilterSample {
  struct timespec sample_time;
 };

-struct MedianFilter {
-  int length;
-  int index;
-  int used;
-  int last;
-  int avg_var_n;
-  double avg_var;
-  double max_var;
-  struct FilterSample *samples;
-  int *selected;
-  double *x_data;
-  double *y_data;
-  double *w_data;
-};
-
 struct RCL_Instance_Record {
  RefclockDriver *driver;
  void *data;
@@ -79,6 +64,7 @@ struct RCL_Instance_Record {
  int driver_polled;
  int poll;
  int leap_status;
+  int local;
  int pps_forced;
  int pps_rate;
  int pps_active;
@@ -190,6 +176,7 @@ RCL_AddRefclock(RefclockParameters *params)
  inst->poll = params->poll;
  inst->driver_polled = 0;
  inst->leap_status = LEAP_Normal;
+  inst->local = params->local;
  inst->pps_forced = params->pps_forced;
  inst->pps_rate = params->pps_rate;
  inst->pps_active = 0;
@@ -231,6 +218,13 @@ RCL_AddRefclock(RefclockParameters *params)
    inst->ref_id = (uint32_t)ref[0] << 24 | ref[1] << 16 | ref[2] << 8 | ref[3];
  }

+  if (inst->local) {
+    inst->pps_forced = 1;
+    inst->lock_ref = inst->ref_id;
+    inst->leap_status = LEAP_Unsynchronised;
+    inst->max_lock_age = MAX(inst->max_lock_age, 3);
+  }
+
  if (inst->driver->poll) {
    int max_samples;

@@ -300,7 +294,7 @@ RCL_StartRefclocks(void)
        break;
      }

-      if (lock_index == -1 || lock_index == i)
+      if (lock_index == -1 || (lock_index == i && !inst->local))
        LOG(LOGS_WARN, "Invalid lock refid %s", UTI_RefidToString(inst->lock_ref));
    }

@@ -440,20 +434,24 @@ accumulate_sample(RCL_Instance instance, struct timespec *sample_time, double of
 }

 int
-RCL_AddSample(RCL_Instance instance, struct timespec *sample_time, double offset, int leap)
+RCL_AddSample(RCL_Instance instance, struct timespec *sample_time,
+              struct timespec *ref_time, int leap)
 {
-  double correction, dispersion;
+  double correction, dispersion, raw_offset, offset;
  struct timespec cooked_time;

  if (instance->pps_forced)
-    return RCL_AddPulse(instance, sample_time, -offset);
+    return RCL_AddPulse(instance, sample_time,
+                        1.0e-9 * (sample_time->tv_nsec - ref_time->tv_nsec));
+
+  raw_offset = UTI_DiffTimespecsToDouble(ref_time, sample_time);

  LCL_GetOffsetCorrection(sample_time, &correction, &dispersion);
  UTI_AddDoubleToTimespec(sample_time, correction, &cooked_time);
  dispersion += instance->precision;

  /* Make sure the timestamp and offset provided by the driver are sane */
-  if (!UTI_IsTimeOffsetSane(sample_time, offset) ||
+  if (!UTI_IsTimeOffsetSane(sample_time, raw_offset) ||
      !valid_sample_time(instance, &cooked_time))
    return 0;

@@ -468,18 +466,24 @@ RCL_AddSample(RCL_Instance instance, struct timespec *sample_time, double offset
      return 0;
  }

+  /* Calculate offset = raw_offset - correction + instance->offset
+     in parts to avoid loss of precision if there are large differences */
+  offset = ref_time->tv_sec - sample_time->tv_sec -
+           (time_t)correction + (time_t)instance->offset;
+  offset += 1.0e-9 * (ref_time->tv_nsec - sample_time->tv_nsec) -
+            (correction - (time_t)correction) + (instance->offset - (time_t)instance->offset);
+
  if (instance->tai && !convert_tai_offset(sample_time, &offset)) {
    DEBUG_LOG("refclock sample ignored unknown TAI offset");
    return 0;
  }

-  if (!accumulate_sample(instance, &cooked_time,
-                         offset - correction + instance->offset, dispersion))
+  if (!accumulate_sample(instance, &cooked_time, offset, dispersion))
    return 0;

  instance->pps_active = 0;

-  log_sample(instance, &cooked_time, 0, 0, offset, offset - correction + instance->offset, dispersion);
+  log_sample(instance, &cooked_time, 0, 0, raw_offset, offset, dispersion);

  /* for logging purposes */
  if (!instance->driver->poll)
@@ -558,16 +562,30 @@ RCL_AddCookedPulse(RCL_Instance instance, struct timespec *cooked_time,
    lock_refclock = get_refclock(instance->lock_ref);

    if (!SPF_GetLastSample(lock_refclock->filter, &ref_sample)) {
-      DEBUG_LOG("refclock pulse ignored no ref sample");
-      return 0;
+      if (instance->local) {
+        /* Make the first sample in order to lock to itself */
+        ref_sample.time = *cooked_time;
+        ref_sample.offset = offset;
+        ref_sample.peer_delay = ref_sample.peer_dispersion = 0;
+        ref_sample.root_delay = ref_sample.root_dispersion = 0;
+      } else {
+        DEBUG_LOG("refclock pulse ignored no ref sample");
+        return 0;
+      }
    }

    ref_sample.root_dispersion += SPF_GetAvgSampleDispersion(lock_refclock->filter);

    sample_diff = UTI_DiffTimespecsToDouble(cooked_time, &ref_sample.time);
    if (fabs(sample_diff) >= (double)instance->max_lock_age / rate) {
-      DEBUG_LOG("refclock pulse ignored samplediff=%.9f",
-          sample_diff);
+      DEBUG_LOG("refclock pulse ignored samplediff=%.9f", sample_diff);
+
+      /* Restart the local mode */
+      if (instance->local) {
+        LOG(LOGS_WARN, "Local refclock lost lock");
+        SPF_DropSamples(instance->filter);
+        SRC_ResetInstance(instance->source);
+      }
      return 0;
    }

@@ -693,6 +711,52 @@ pps_stratum(RCL_Instance instance, struct timespec *ts)
  return 0;
 }

+static void
+get_local_stats(RCL_Instance inst, struct timespec *ref, double *freq, double *offset)
+{
+  double offset_sd, freq_sd, skew, root_delay, root_disp;
+  SST_Stats stats = SRC_GetSourcestats(inst->source);
+
+  if (SST_Samples(stats) < SST_GetMinSamples(stats)) {
+    UTI_ZeroTimespec(ref);
+    return;
+  }
+
+  SST_GetTrackingData(stats, ref, offset, &offset_sd, freq, &freq_sd,
+                      &skew, &root_delay, &root_disp);
+}
+
+static void
+follow_local(RCL_Instance inst, struct timespec *prev_ref_time, double prev_freq,
+             double prev_offset)
+{
+  SST_Stats stats = SRC_GetSourcestats(inst->source);
+  double freq, dfreq, offset, doffset, elapsed;
+  struct timespec now, ref_time;
+
+  get_local_stats(inst, &ref_time, &freq, &offset);
+
+  if (UTI_IsZeroTimespec(prev_ref_time) || UTI_IsZeroTimespec(&ref_time))
+    return;
+
+  dfreq = (freq - prev_freq) / (1.0 - prev_freq);
+  elapsed = UTI_DiffTimespecsToDouble(&ref_time, prev_ref_time);
+  doffset = offset - elapsed * prev_freq - prev_offset;
+
+  if (!REF_AdjustReference(doffset, dfreq))
+    return;
+
+  LCL_ReadCookedTime(&now, NULL);
+  SST_SlewSamples(stats, &now, dfreq, doffset);
+  SPF_SlewSamples(inst->filter, &now, dfreq, doffset);
+
+  /* Keep the offset close to zero to not lose precision */
+  if (fabs(offset) >= 1.0) {
+    SST_CorrectOffset(stats, -round(offset));
+    SPF_CorrectOffset(inst->filter, -round(offset));
+  }
+}
+
 static void
 poll_timeout(void *arg)
 {
@@ -713,17 +777,28 @@ poll_timeout(void *arg)
    inst->driver_polled = 0;

    if (SPF_GetFilteredSample(inst->filter, &sample)) {
+      double local_freq, local_offset;
+      struct timespec local_ref_time;
+
      /* Handle special case when PPS is used with the local reference */
      if (inst->pps_active && inst->lock_ref == -1)
        stratum = pps_stratum(inst, &sample.time);
      else
        stratum = inst->stratum;

+      if (inst->local) {
+        get_local_stats(inst, &local_ref_time, &local_freq, &local_offset);
+        inst->leap_status = LEAP_Unsynchronised;
+      }
+
      SRC_UpdateReachability(inst->source, 1);
      SRC_UpdateStatus(inst->source, stratum, inst->leap_status);
      SRC_AccumulateSample(inst->source, &sample);
      SRC_SelectSource(inst->source);

+      if (inst->local)
+        follow_local(inst, &local_ref_time, local_freq, local_offset);
+
      log_sample(inst, &sample.time, 1, 0, 0.0, sample.offset, sample.peer_dispersion);
    } else {
      SRC_UpdateReachability(inst->source, 0);
--- a/refclock.h
+++ b/refclock.h
@@ -37,6 +37,7 @@ typedef struct {
  int driver_poll;
  int poll;
  int filter_length;
+  int local;
  int pps_forced;
  int pps_rate;
  int min_samples;
@@ -74,7 +75,8 @@ extern void *RCL_GetDriverData(RCL_Instance instance);
 extern char *RCL_GetDriverParameter(RCL_Instance instance);
 extern void RCL_CheckDriverOptions(RCL_Instance instance, const char **options);
 extern char *RCL_GetDriverOption(RCL_Instance instance, char *name);
-extern int RCL_AddSample(RCL_Instance instance, struct timespec *sample_time, double offset, int leap);
+extern int RCL_AddSample(RCL_Instance instance, struct timespec *sample_time,
+                         struct timespec *ref_time, int leap);
 extern int RCL_AddPulse(RCL_Instance instance, struct timespec *pulse_time, double second);
 extern int RCL_AddCookedPulse(RCL_Instance instance, struct timespec *cooked_time,
                              double second, double dispersion, double raw_correction);
--- a/refclock_phc.c
+++ b/refclock_phc.c
@@ -2,7 +2,7 @@
  chronyd/chronyc - Programs for keeping computer clocks accurate.

 **********************************************************************
- * Copyright (C) Miroslav Lichvar  2013, 2017
+ * Copyright (C) Miroslav Lichvar  2013, 2017, 2023
 * 
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of version 2 of the GNU General Public License as
@@ -33,6 +33,9 @@

 #include "sysincl.h"

+#include <sys/sysmacros.h>
+
+#include "array.h"
 #include "refclock.h"
 #include "hwclock.h"
 #include "local.h"
@@ -44,14 +47,19 @@

 struct phc_instance {
  int fd;
+  int dev_index;
  int mode;
  int nocrossts;
  int extpps;
  int pin;
  int channel;
+  struct timespec last_extts;
  HCL_Instance clock;
 };

+/* Array of RCL_Instance with enabled extpps */
+static ARR_Instance extts_phcs = NULL;
+
 static void read_ext_pulse(int sockfd, int event, void *anything);

 static int phc_initialise(RCL_Instance instance)
@@ -59,6 +67,7 @@ static int phc_initialise(RCL_Instance instance)
  const char *options[] = {"nocrossts", "extpps", "pin", "channel", "clear", NULL};
  struct phc_instance *phc;
  int phc_fd, rising_edge;
+  struct stat st;
  char *path, *s;

  RCL_CheckDriverOptions(instance, options);
@@ -71,9 +80,15 @@ static int phc_initialise(RCL_Instance instance)

  phc = MallocNew(struct phc_instance);
  phc->fd = phc_fd;
+  if (fstat(phc_fd, &st) < 0 || !S_ISCHR(st.st_mode))
+    LOG_FATAL("Could not get PHC index");
+  phc->dev_index = minor(st.st_rdev);
  phc->mode = 0;
  phc->nocrossts = RCL_GetDriverOption(instance, "nocrossts") ? 1 : 0;
  phc->extpps = RCL_GetDriverOption(instance, "extpps") ? 1 : 0;
+  UTI_ZeroTimespec(&phc->last_extts);
+  phc->clock = HCL_CreateInstance(0, 16, UTI_Log2ToDouble(RCL_GetDriverPoll(instance)),
+                                  RCL_GetPrecision(instance));

  if (phc->extpps) {
    s = RCL_GetDriverOption(instance, "pin");
@@ -81,16 +96,18 @@ static int phc_initialise(RCL_Instance instance)
    s = RCL_GetDriverOption(instance, "channel");
    phc->channel = s ? atoi(s) : 0;
    rising_edge = RCL_GetDriverOption(instance, "clear") ? 0 : 1;
-    phc->clock = HCL_CreateInstance(0, 16, UTI_Log2ToDouble(RCL_GetDriverPoll(instance)));

    if (!SYS_Linux_SetPHCExtTimestamping(phc->fd, phc->pin, phc->channel,
                                         rising_edge, !rising_edge, 1))
      LOG_FATAL("Could not enable external PHC timestamping");

    SCH_AddFileHandler(phc->fd, SCH_FILE_INPUT, read_ext_pulse, instance);
+
+    if (!extts_phcs)
+      extts_phcs = ARR_CreateInstance(sizeof (RCL_Instance));
+    ARR_AppendElement(extts_phcs, &instance);
  } else {
    phc->pin = phc->channel = 0;
-    phc->clock = NULL;
  }

  RCL_SetDriverData(instance, phc);
@@ -100,68 +117,106 @@ static int phc_initialise(RCL_Instance instance)
 static void phc_finalise(RCL_Instance instance)
 {
  struct phc_instance *phc;
+  unsigned int i;

  phc = (struct phc_instance *)RCL_GetDriverData(instance);

  if (phc->extpps) {
    SCH_RemoveFileHandler(phc->fd);
    SYS_Linux_SetPHCExtTimestamping(phc->fd, phc->pin, phc->channel, 0, 0, 0);
-    HCL_DestroyInstance(phc->clock);
+
+    for (i = 0; i < ARR_GetSize(extts_phcs); i++) {
+      if ((*(RCL_Instance *)ARR_GetElement(extts_phcs, i)) == instance)
+        ARR_RemoveElement(extts_phcs, i--);
+    }
+    if (ARR_GetSize(extts_phcs) == 0) {
+      ARR_DestroyInstance(extts_phcs);
+      extts_phcs = NULL;
+    }
  }

+  HCL_DestroyInstance(phc->clock);
  close(phc->fd);
  Free(phc);
 }

+static void process_ext_pulse(RCL_Instance instance, struct timespec *phc_ts)
+{
+  struct phc_instance *phc;
+  struct timespec local_ts;
+  double local_err;
+
+  phc = RCL_GetDriverData(instance);
+
+  if (UTI_CompareTimespecs(&phc->last_extts, phc_ts) == 0) {
+    DEBUG_LOG("Ignoring duplicated PHC timestamp");
+    return;
+  }
+  phc->last_extts = *phc_ts;
+
+  if (!HCL_CookTime(phc->clock, phc_ts, &local_ts, &local_err))
+    return;
+
+  RCL_AddCookedPulse(instance, &local_ts, 1.0e-9 * local_ts.tv_nsec, local_err,
+                     UTI_DiffTimespecsToDouble(phc_ts, &local_ts));
+}
+
 static void read_ext_pulse(int fd, int event, void *anything)
 {
  RCL_Instance instance;
-  struct phc_instance *phc;
-  struct timespec phc_ts, local_ts;
-  double local_err;
+  struct phc_instance *phc1, *phc2;
+  struct timespec phc_ts;
+  unsigned int i;
  int channel;

+  if (!SYS_Linux_ReadPHCExtTimestamp(fd, &phc_ts, &channel))
+    return;
+
  instance = anything;
-  phc = RCL_GetDriverData(instance);
+  phc1 = RCL_GetDriverData(instance);

-  if (!SYS_Linux_ReadPHCExtTimestamp(phc->fd, &phc_ts, &channel))
-    return;
+  /* The Linux kernel (as of 6.2) has one shared queue of timestamps for all
+     descriptors of the same PHC.  Search for all refclocks that expect
+     the timestamp. */

-  if (channel != phc->channel) {
-    DEBUG_LOG("Unexpected extts channel %d\n", channel);
-    return;
+  for (i = 0; i < ARR_GetSize(extts_phcs); i++) {
+    instance = *(RCL_Instance *)ARR_GetElement(extts_phcs, i);
+    phc2 = RCL_GetDriverData(instance);
+    if (!phc2->extpps || phc2->dev_index != phc1->dev_index || phc2->channel != channel)
+      continue;
+    process_ext_pulse(instance, &phc_ts);
  }
-
-  if (!HCL_CookTime(phc->clock, &phc_ts, &local_ts, &local_err))
-    return;
-
-  RCL_AddCookedPulse(instance, &local_ts, 1.0e-9 * local_ts.tv_nsec, local_err,
-                     UTI_DiffTimespecsToDouble(&phc_ts, &local_ts));
 }

+#define PHC_READINGS 25
+
 static int phc_poll(RCL_Instance instance)
 {
+  struct timespec phc_ts, sys_ts, local_ts, readings[PHC_READINGS][3];
  struct phc_instance *phc;
-  struct timespec phc_ts, sys_ts, local_ts;
-  double offset, phc_err, local_err;
+  double phc_err, local_err;
+  int n_readings;

  phc = (struct phc_instance *)RCL_GetDriverData(instance);

-  if (!SYS_Linux_GetPHCSample(phc->fd, phc->nocrossts, RCL_GetPrecision(instance),
-                              &phc->mode, &phc_ts, &sys_ts, &phc_err))
+  n_readings = SYS_Linux_GetPHCReadings(phc->fd, phc->nocrossts, &phc->mode,
+                                        PHC_READINGS, readings);
+  if (n_readings < 1)
    return 0;

-  if (phc->extpps) {
-    LCL_CookTime(&sys_ts, &local_ts, &local_err);
-    HCL_AccumulateSample(phc->clock, &phc_ts, &local_ts, phc_err + local_err);
+  if (!HCL_ProcessReadings(phc->clock, n_readings, readings, &phc_ts, &sys_ts, &phc_err))
    return 0;
-  }

-  offset = UTI_DiffTimespecsToDouble(&phc_ts, &sys_ts);
+  LCL_CookTime(&sys_ts, &local_ts, &local_err);
+  HCL_AccumulateSample(phc->clock, &phc_ts, &local_ts, phc_err + local_err);

-  DEBUG_LOG("PHC offset: %+.9f err: %.9f", offset, phc_err);
+  if (phc->extpps)
+    return 0;

-  return RCL_AddSample(instance, &sys_ts, offset, LEAP_Normal);
+  DEBUG_LOG("PHC offset: %+.9f err: %.9f",
+            UTI_DiffTimespecsToDouble(&phc_ts, &sys_ts), phc_err);
+
+  return RCL_AddSample(instance, &sys_ts, &phc_ts, LEAP_Normal);
 }

 RefclockDriver RCL_PHC_driver = {
--- a/refclock_shm.c
+++ b/refclock_shm.c
@@ -95,7 +95,6 @@ static int shm_poll(RCL_Instance instance)
 {
  struct timespec receive_ts, clock_ts;
  struct shmTime t, *shm;
-  double offset;

  shm = (struct shmTime *)RCL_GetDriverData(instance);

@@ -124,9 +123,8 @@ static int shm_poll(RCL_Instance instance)

  UTI_NormaliseTimespec(&clock_ts);
  UTI_NormaliseTimespec(&receive_ts);
-  offset = UTI_DiffTimespecsToDouble(&clock_ts, &receive_ts);

-  return RCL_AddSample(instance, &receive_ts, offset, t.leap);
+  return RCL_AddSample(instance, &receive_ts, &clock_ts, t.leap);
 }

 RefclockDriver RCL_SHM_driver = {
--- a/refclock_sock.c
+++ b/refclock_sock.c
@@ -58,23 +58,63 @@ struct sock_sample {
  int magic;
 };

+/* On 32-bit glibc-based systems enable conversion between timevals using
+   32-bit and 64-bit time_t to support SOCK clients compiled with different
+   time_t size than chrony */
+#ifdef __GLIBC_PREREQ
+#if __GLIBC_PREREQ(2, 34) && __TIMESIZE == 32
+#define CONVERT_TIMEVAL 1
+#if defined(_TIME_BITS) && _TIME_BITS == 64
+typedef int32_t alt_time_t;
+typedef int32_t alt_suseconds_t;
+#else
+typedef int64_t alt_time_t;
+typedef int64_t alt_suseconds_t;
+#endif
+struct alt_timeval {
+  alt_time_t tv_sec;
+  alt_suseconds_t tv_usec;
+};
+#endif
+#endif
+
 static void read_sample(int sockfd, int event, void *anything)
 {
+  char buf[sizeof (struct sock_sample) + 16];
+  struct timespec sys_ts, ref_ts;
  struct sock_sample sample;
-  struct timespec ts;
  RCL_Instance instance;
  int s;

  instance = (RCL_Instance)anything;

-  s = recv(sockfd, &sample, sizeof (sample), 0);
+  s = recv(sockfd, buf, sizeof (buf), 0);

  if (s < 0) {
    DEBUG_LOG("Could not read SOCK sample : %s", strerror(errno));
    return;
  }

-  if (s != sizeof (sample)) {
+  if (s == sizeof (sample)) {
+    memcpy(&sample, buf, sizeof (sample));
+#ifdef CONVERT_TIMEVAL
+  } else if (s == sizeof (sample) - sizeof (struct timeval) + sizeof (struct alt_timeval)) {
+    struct alt_timeval atv;
+    memcpy(&atv, buf, sizeof (atv));
+#ifndef HAVE_LONG_TIME_T
+    if (atv.tv_sec > INT32_MAX || atv.tv_sec < INT32_MIN ||
+        atv.tv_usec > INT32_MAX || atv.tv_usec < INT32_MIN) {
+      DEBUG_LOG("Could not convert 64-bit timeval");
+      return;
+    }
+#endif
+    sample.tv.tv_sec = atv.tv_sec;
+    sample.tv.tv_usec = atv.tv_usec;
+    DEBUG_LOG("Converted %d-bit timeval", 8 * (int)sizeof (alt_time_t));
+    memcpy((char *)&sample + sizeof (struct timeval), buf + sizeof (struct alt_timeval),
+           sizeof (sample) - sizeof (struct timeval));
+#endif
+  } else {
    DEBUG_LOG("Unexpected length of SOCK sample : %d != %ld",
              s, (long)sizeof (sample));
    return;
@@ -86,13 +126,18 @@ static void read_sample(int sockfd, int event, void *anything)
    return;
  }

-  UTI_TimevalToTimespec(&sample.tv, &ts);
-  UTI_NormaliseTimespec(&ts);
+  UTI_TimevalToTimespec(&sample.tv, &sys_ts);
+  UTI_NormaliseTimespec(&sys_ts);
+
+  if (!UTI_IsTimeOffsetSane(&sys_ts, sample.offset))
+    return;
+
+  UTI_AddDoubleToTimespec(&sys_ts, sample.offset, &ref_ts);

  if (sample.pulse) {
-    RCL_AddPulse(instance, &ts, sample.offset);
+    RCL_AddPulse(instance, &sys_ts, sample.offset);
  } else {
-    RCL_AddSample(instance, &ts, sample.offset, sample.leap);
+    RCL_AddSample(instance, &sys_ts, &ref_ts, sample.leap);
  }
 }

--- a/reference.c
+++ b/reference.c
@@ -3,7 +3,7 @@

 **********************************************************************
 * Copyright (C) Richard P. Curnow  1997-2003
- * Copyright (C) Miroslav Lichvar  2009-2018, 2020
+ * Copyright (C) Miroslav Lichvar  2009-2018, 2020, 2022
 * 
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of version 2 of the GNU General Public License as
@@ -150,6 +150,9 @@ static SCH_TimeoutID fb_drift_timeout_id;
 static double last_ref_update;
 static double last_ref_update_interval;

+static double last_ref_adjustment;
+static int ref_adjustments;
+
 /* ================================================== */

 static NTP_Leap get_tz_leap(time_t when, int *tai_offset);
@@ -286,6 +289,8 @@ REF_Initialise(void)
  UTI_ZeroTimespec(&our_ref_time);
  last_ref_update = 0.0;
  last_ref_update_interval = 0.0;
+  last_ref_adjustment = 0.0;
+  ref_adjustments = 0;

  LCL_AddParameterChangeHandler(handle_slew, NULL);

@@ -960,6 +965,27 @@ fuzz_ref_time(struct timespec *ts)

 /* ================================================== */

+static double
+get_correction_rate(double offset_sd, double update_interval)
+{
+  /* We want to correct the offset quickly, but we also want to keep the
+     frequency error caused by the correction itself low.
+
+     Define correction rate as the area of the region bounded by the graph of
+     offset corrected in time.  Set the rate so that the time needed to correct
+     an offset equal to the current sourcestats stddev will be equal to the
+     update interval multiplied by the correction time ratio (assuming linear
+     adjustment).  The offset and the time needed to make the correction are
+     inversely proportional.
+
+     This is only a suggestion and it's up to the system driver how the
+     adjustment will be executed. */
+
+  return correction_time_ratio * 0.5 * offset_sd * update_interval;
+}
+
+/* ================================================== */
+
 void
 REF_SetReference(int stratum, NTP_Leap leap, int combined_sources,
                 uint32_t ref_id, IPAddr *ref_ip, struct timespec *ref_time,
@@ -969,7 +995,7 @@ REF_SetReference(int stratum, NTP_Leap leap, int combined_sources,
 {
  double uncorrected_offset, accumulate_offset, step_offset;
  double residual_frequency, local_abs_frequency;
-  double elapsed, mono_now, update_interval, correction_rate, orig_root_distance;
+  double elapsed, mono_now, update_interval, orig_root_distance;
  struct timespec now, raw_now;
  int manual;

@@ -1024,21 +1050,6 @@ REF_SetReference(int stratum, NTP_Leap leap, int combined_sources,
  last_ref_update_interval = update_interval;
  last_offset = offset;

-  /* We want to correct the offset quickly, but we also want to keep the
-     frequency error caused by the correction itself low.
-
-     Define correction rate as the area of the region bounded by the graph of
-     offset corrected in time. Set the rate so that the time needed to correct
-     an offset equal to the current sourcestats stddev will be equal to the
-     update interval multiplied by the correction time ratio (assuming linear
-     adjustment). The offset and the time needed to make the correction are
-     inversely proportional.
-
-     This is only a suggestion and it's up to the system driver how the
-     adjustment will be executed. */
-
-  correction_rate = correction_time_ratio * 0.5 * offset_sd * update_interval;
-
  /* Check if the clock should be stepped */
  if (is_step_limit_reached(offset, uncorrected_offset)) {
    /* Cancel the uncorrected offset and correct the total offset by step */
@@ -1050,7 +1061,8 @@ REF_SetReference(int stratum, NTP_Leap leap, int combined_sources,
  }

  /* Adjust the clock */
-  LCL_AccumulateFrequencyAndOffset(frequency, accumulate_offset, correction_rate);
+  LCL_AccumulateFrequencyAndOffset(frequency, accumulate_offset,
+                                   get_correction_rate(offset_sd, update_interval));
    
  maybe_log_offset(offset, raw_now.tv_sec);

@@ -1095,6 +1107,27 @@ REF_SetReference(int stratum, NTP_Leap leap, int combined_sources,
      avg2_moving = 1;
    avg2_offset = SQUARE(offset);
  }
+
+  ref_adjustments = 0;
+}
+
+/* ================================================== */
+
+int
+REF_AdjustReference(double offset, double frequency)
+{
+  double adj_corr_rate, ref_corr_rate, mono_now;
+
+  mono_now = SCH_GetLastEventMonoTime();
+  ref_adjustments++;
+
+  adj_corr_rate = get_correction_rate(fabs(offset), mono_now - last_ref_adjustment);
+  ref_corr_rate = get_correction_rate(our_offset_sd, last_ref_update_interval) /
+                  ref_adjustments;
+  last_ref_adjustment = mono_now;
+
+  return LCL_AccumulateFrequencyAndOffsetNoHandlers(frequency, offset,
+                                                    MAX(adj_corr_rate, ref_corr_rate));
 }

 /* ================================================== */
@@ -1296,6 +1329,7 @@ void
 REF_ModifyMaxupdateskew(double new_max_update_skew)
 {
  max_update_skew = new_max_update_skew * 1.0e-6;
+  LOG(LOGS_INFO, "New maxupdateskew %f ppm", new_max_update_skew);
 }

 /* ================================================== */
@@ -1305,6 +1339,7 @@ REF_ModifyMakestep(int limit, double threshold)
 {
  make_step_limit = limit;
  make_step_threshold = threshold;
+  LOG(LOGS_INFO, "New makestep %f %d", threshold, limit);
 }

 /* ================================================== */
@@ -1316,6 +1351,7 @@ REF_EnableLocal(int stratum, double distance, int orphan)
  local_stratum = CLAMP(1, stratum, NTP_MAX_STRATUM - 1);
  local_distance = distance;
  local_orphan = !!orphan;
+  LOG(LOGS_INFO, "%s local reference mode", "Enabled");
 }

 /* ================================================== */
@@ -1324,6 +1360,7 @@ void
 REF_DisableLocal(void)
 {
  enable_local_stratum = 0;
+  LOG(LOGS_INFO, "%s local reference mode", "Disabled");
 }

 /* ================================================== */
--- a/reference.h
+++ b/reference.h
@@ -162,6 +162,10 @@ extern void REF_SetManualReference
 extern void
 REF_SetUnsynchronised(void);

+/* Make a small correction of the clock without updating the reference
+   parameters and calling the clock change handlers */
+extern int REF_AdjustReference(double offset, double frequency);
+
 /* Announce a leap second before the full reference update */
 extern void REF_UpdateLeapStatus(NTP_Leap leap);

--- a/reports.h
+++ b/reports.h
@@ -109,17 +109,23 @@ typedef struct {
 } RPT_ClientAccessByIndex_Report;

 typedef struct {
-  uint32_t ntp_hits;
-  uint32_t nke_hits;
-  uint32_t cmd_hits;
-  uint32_t ntp_drops;
-  uint32_t nke_drops;
-  uint32_t cmd_drops;
-  uint32_t log_drops;
-  uint32_t ntp_auth_hits;
-  uint32_t ntp_interleaved_hits;
-  uint32_t ntp_timestamps;
-  uint32_t ntp_span_seconds;
+  uint64_t ntp_hits;
+  uint64_t nke_hits;
+  uint64_t cmd_hits;
+  uint64_t ntp_drops;
+  uint64_t nke_drops;
+  uint64_t cmd_drops;
+  uint64_t log_drops;
+  uint64_t ntp_auth_hits;
+  uint64_t ntp_interleaved_hits;
+  uint64_t ntp_timestamps;
+  uint64_t ntp_span_seconds;
+  uint64_t ntp_daemon_rx_timestamps;
+  uint64_t ntp_daemon_tx_timestamps;
+  uint64_t ntp_kernel_rx_timestamps;
+  uint64_t ntp_kernel_tx_timestamps;
+  uint64_t ntp_hw_rx_timestamps;
+  uint64_t ntp_hw_tx_timestamps;
 } RPT_ServerStatsReport;

 typedef struct {
@@ -174,6 +180,7 @@ typedef struct {
  uint32_t total_tx_count;
  uint32_t total_rx_count;
  uint32_t total_valid_count;
+  uint32_t total_good_count;
 } RPT_NTPReport;

 typedef struct {
--- a/samplefilt.c
+++ b/samplefilt.c
@@ -162,6 +162,14 @@ SPF_GetNumberOfSamples(SPF_Instance filter)

 /* ================================================== */

+int
+SPF_GetMaxSamples(SPF_Instance filter)
+{
+  return filter->max_samples;
+}
+
+/* ================================================== */
+
 double
 SPF_GetAvgSampleDispersion(SPF_Instance filter)
 {
@@ -170,11 +178,21 @@ SPF_GetAvgSampleDispersion(SPF_Instance filter)

 /* ================================================== */

-void
-SPF_DropSamples(SPF_Instance filter)
+static void
+drop_samples(SPF_Instance filter, int keep_last)
 {
  filter->index = -1;
  filter->used = 0;
+  if (!keep_last)
+    filter->last = -1;
+}
+
+/* ================================================== */
+
+void
+SPF_DropSamples(SPF_Instance filter)
+{
+  drop_samples(filter, 0);
 }

 /* ================================================== */
@@ -399,17 +417,40 @@ SPF_GetFilteredSample(SPF_Instance filter, NTP_Sample *sample)

  n = select_samples(filter);

+  DEBUG_LOG("selected %d from %d samples", n, filter->used);
+
  if (n < 1)
    return 0;

  if (!combine_selected_samples(filter, n, sample))
    return 0;

-  SPF_DropSamples(filter);
+  drop_samples(filter, 1);

  return 1;
 }

+/* ================================================== */
+
+static int
+get_first_last(SPF_Instance filter, int *first, int *last)
+{
+  if (filter->last < 0)
+    return 0;
+
+  /* Always slew the last sample as it may be returned even if no new
+     samples were accumulated */
+  if (filter->used > 0) {
+    *first = 0;
+    *last = filter->used - 1;
+  } else {
+    *first = *last = filter->last;
+  }
+
+  return 1;
+}
+
+
 /* ================================================== */

 void
@@ -418,18 +459,9 @@ SPF_SlewSamples(SPF_Instance filter, struct timespec *when, double dfreq, double
  int i, first, last;
  double delta_time;

-  if (filter->last < 0)
+  if (!get_first_last(filter, &first, &last))
    return;

-  /* Always slew the last sample as it may be returned even if no new
-     samples were accumulated */
-  if (filter->used > 0) {
-    first = 0;
-    last = filter->used - 1;
-  } else {
-    first = last = filter->last;
-  }
-
  for (i = first; i <= last; i++) {
    UTI_AdjustTimespec(&filter->samples[i].time, when, &filter->samples[i].time,
                       &delta_time, dfreq, doffset);
@@ -439,6 +471,20 @@ SPF_SlewSamples(SPF_Instance filter, struct timespec *when, double dfreq, double

 /* ================================================== */

+void
+SPF_CorrectOffset(SPF_Instance filter, double doffset)
+{
+  int i, first, last;
+
+  if (!get_first_last(filter, &first, &last))
+    return;
+
+  for (i = first; i <= last; i++)
+    filter->samples[i].offset -= doffset;
+}
+
+/* ================================================== */
+
 void
 SPF_AddDispersion(SPF_Instance filter, double dispersion)
 {
--- a/samplefilt.h
+++ b/samplefilt.h
@@ -39,11 +39,13 @@ extern void SPF_DestroyInstance(SPF_Instance filter);
 extern int SPF_AccumulateSample(SPF_Instance filter, NTP_Sample *sample);
 extern int SPF_GetLastSample(SPF_Instance filter, NTP_Sample *sample);
 extern int SPF_GetNumberOfSamples(SPF_Instance filter);
+extern int SPF_GetMaxSamples(SPF_Instance filter);
 extern double SPF_GetAvgSampleDispersion(SPF_Instance filter);
 extern void SPF_DropSamples(SPF_Instance filter);
 extern int SPF_GetFilteredSample(SPF_Instance filter, NTP_Sample *sample);
 extern void SPF_SlewSamples(SPF_Instance filter, struct timespec *when,
                            double dfreq, double doffset);
+extern void SPF_CorrectOffset(SPF_Instance filter, double doffset);
 extern void SPF_AddDispersion(SPF_Instance filter, double dispersion);

 #endif
--- a/sched.c
+++ b/sched.c
@@ -104,7 +104,10 @@ static unsigned long n_timer_queue_entries;
 static SCH_TimeoutID next_tqe_id;

 /* Pointer to head of free list */
-static TimerQueueEntry *tqe_free_list = NULL;
+static TimerQueueEntry *tqe_free_list;
+
+/* Array of all allocated tqe blocks to be freed in finalisation */
+static ARR_Instance tqe_blocks;

 /* Timestamp when was last timeout dispatched for each class */
 static struct timespec last_class_dispatch[SCH_NumberOfClasses];
@@ -133,6 +136,8 @@ SCH_Initialise(void)

  n_timer_queue_entries = 0;
  next_tqe_id = 0;
+  tqe_free_list = NULL;
+  tqe_blocks = ARR_CreateInstance(sizeof (TimerQueueEntry *));

  timer_queue.next = &timer_queue;
  timer_queue.prev = &timer_queue;
@@ -154,8 +159,16 @@ SCH_Initialise(void)

 void
 SCH_Finalise(void) {
+  unsigned int i;
+
  ARR_DestroyInstance(file_handlers);

+  timer_queue.next = &timer_queue;
+  timer_queue.prev = &timer_queue;
+  for (i = 0; i < ARR_GetSize(tqe_blocks); i++)
+    Free(*(TimerQueueEntry **)ARR_GetElement(tqe_blocks, i));
+  ARR_DestroyInstance(tqe_blocks);
+
  LCL_RemoveParameterChangeHandler(handle_slew, NULL);

  initialised = 0;
@@ -281,6 +294,7 @@ allocate_tqe(void)
    }
    new_block[0].next = NULL;
    tqe_free_list = &(new_block[TQE_ALLOC_QUANTUM - 1]);
+    ARR_AppendElement(tqe_blocks, &new_block);
  }

  result = tqe_free_list;
--- a/sched.h
+++ b/sched.h
@@ -37,6 +37,7 @@ typedef enum {
  SCH_NtpClientClass,
  SCH_NtpPeerClass,
  SCH_NtpBroadcastClass,
+  SCH_PhcPollClass,
  SCH_NumberOfClasses /* needs to be last */
 } SCH_TimeoutClass;

--- a/siv.h
+++ b/siv.h
@@ -53,6 +53,10 @@ extern int SIV_GetKeyLength(SIV_Algorithm algorithm);

 extern int SIV_SetKey(SIV_Instance instance, const unsigned char *key, int length);

+extern int SIV_GetMinNonceLength(SIV_Instance instance);
+
+extern int SIV_GetMaxNonceLength(SIV_Instance instance);
+
 extern int SIV_GetTagLength(SIV_Instance instance);

 extern int SIV_Encrypt(SIV_Instance instance,
--- a/siv_gnutls.c
+++ b/siv_gnutls.c
@@ -2,7 +2,7 @@
  chronyd/chronyc - Programs for keeping computer clocks accurate.

 **********************************************************************
- * Copyright (C) Miroslav Lichvar  2020
+ * Copyright (C) Miroslav Lichvar  2020, 2023
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of version 2 of the GNU General Public License as
@@ -37,6 +37,8 @@
 struct SIV_Instance_Record {
  gnutls_cipher_algorithm_t algorithm;
  gnutls_aead_cipher_hd_t cipher;
+  int min_nonce_length;
+  int max_nonce_length;
 };

 /* ================================================== */
@@ -81,6 +83,10 @@ get_cipher_algorithm(SIV_Algorithm algorithm)
  switch (algorithm) {
    case AEAD_AES_SIV_CMAC_256:
      return GNUTLS_CIPHER_AES_128_SIV;
+#if HAVE_GNUTLS_SIV_GCM
+    case AEAD_AES_128_GCM_SIV:
+      return GNUTLS_CIPHER_AES_128_SIV_GCM;
+#endif
    default:
      return 0;
  }
@@ -112,6 +118,19 @@ SIV_CreateInstance(SIV_Algorithm algorithm)
  instance->algorithm = calgo;
  instance->cipher = NULL;

+  switch (algorithm) {
+    case AEAD_AES_SIV_CMAC_256:
+      instance->min_nonce_length = 1;
+      instance->max_nonce_length = INT_MAX;
+      break;
+    case AEAD_AES_128_GCM_SIV:
+      instance->min_nonce_length = 12;
+      instance->max_nonce_length = 12;
+      break;
+    default:
+      assert(0);
+  }
+
  instance_counter++;

  return instance;
@@ -143,6 +162,8 @@ SIV_GetKeyLength(SIV_Algorithm algorithm)
    return 0;

  len = gnutls_cipher_get_key_size(calgo);
+  if (len == 0)
+    return 0;

  if (len < 1 || len > SIV_MAX_KEY_LENGTH)
    LOG_FATAL("Invalid key length");
@@ -165,17 +186,29 @@ SIV_SetKey(SIV_Instance instance, const unsigned char *key, int length)
  datum.data = (unsigned char *)key;
  datum.size = length;

-  /* Initialise a new cipher with the provided key (gnutls does not seem to
-     have a function to change the key directly) */
+#ifdef HAVE_GNUTLS_AEAD_CIPHER_SET_KEY
+  if (instance->cipher) {
+    r = gnutls_aead_cipher_set_key(instance->cipher, &datum);
+    if (r < 0) {
+      DEBUG_LOG("Could not set cipher key : %s", gnutls_strerror(r));
+      return 0;
+    }
+
+    return 1;
+  }
+#endif
+
+  /* Initialise a new cipher with the provided key */
  r = gnutls_aead_cipher_init(&cipher, instance->algorithm, &datum);
  if (r < 0) {
    DEBUG_LOG("Could not initialise %s : %s", "cipher", gnutls_strerror(r));
    return 0;
  }

-  /* Replace the previous cipher */
+  /* Destroy the previous cipher (if its key could not be changed directly) */
  if (instance->cipher)
    gnutls_aead_cipher_deinit(instance->cipher);
+
  instance->cipher = cipher;

  return 1;
@@ -183,6 +216,22 @@ SIV_SetKey(SIV_Instance instance, const unsigned char *key, int length)

 /* ================================================== */

+int
+SIV_GetMinNonceLength(SIV_Instance instance)
+{
+  return instance->min_nonce_length;
+}
+
+/* ================================================== */
+
+int
+SIV_GetMaxNonceLength(SIV_Instance instance)
+{
+  return instance->max_nonce_length;
+}
+
+/* ================================================== */
+
 int
 SIV_GetTagLength(SIV_Instance instance)
 {
@@ -210,7 +259,8 @@ SIV_Encrypt(SIV_Instance instance,
  if (!instance->cipher)
    return 0;

-  if (nonce_length < 1 || assoc_length < 0 ||
+  if (nonce_length < instance->min_nonce_length ||
+      nonce_length > instance->max_nonce_length || assoc_length < 0 ||
      plaintext_length < 0 || ciphertext_length < 0)
    return 0;

@@ -241,7 +291,8 @@ SIV_Decrypt(SIV_Instance instance,
  if (!instance->cipher)
    return 0;

-  if (nonce_length < 1 || assoc_length < 0 ||
+  if (nonce_length < instance->min_nonce_length ||
+      nonce_length > instance->max_nonce_length || assoc_length < 0 ||
      plaintext_length < 0 || ciphertext_length < 0)
    return 0;

--- a/siv_nettle.c
+++ b/siv_nettle.c
@@ -2,7 +2,7 @@
  chronyd/chronyc - Programs for keeping computer clocks accurate.

 **********************************************************************
- * Copyright (C) Miroslav Lichvar  2019
+ * Copyright (C) Miroslav Lichvar  2019, 2022
 * 
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of version 2 of the GNU General Public License as
@@ -34,12 +34,25 @@
 #include "siv_nettle_int.c"
 #endif

+#ifdef HAVE_NETTLE_SIV_GCM
+#include <nettle/siv-gcm.h>
+#endif
+
 #include "memory.h"
 #include "siv.h"

 struct SIV_Instance_Record {
-  struct siv_cmac_aes128_ctx siv;
+  SIV_Algorithm algorithm;
  int key_set;
+  int min_nonce_length;
+  int max_nonce_length;
+  int tag_length;
+  union {
+    struct siv_cmac_aes128_ctx cmac_aes128;
+#ifdef HAVE_NETTLE_SIV_GCM
+    struct aes128_ctx aes128;
+#endif
+  } ctx;
 };

 /* ================================================== */
@@ -49,12 +62,30 @@ SIV_CreateInstance(SIV_Algorithm algorithm)
 {
  SIV_Instance instance;

-  if (algorithm != AEAD_AES_SIV_CMAC_256)
+  if (SIV_GetKeyLength(algorithm) <= 0)
    return NULL;

  instance = MallocNew(struct SIV_Instance_Record);
+  instance->algorithm = algorithm;
  instance->key_set = 0;

+  switch (algorithm) {
+    case AEAD_AES_SIV_CMAC_256:
+      instance->min_nonce_length = SIV_MIN_NONCE_SIZE;
+      instance->max_nonce_length = INT_MAX;
+      instance->tag_length = SIV_DIGEST_SIZE;
+      break;
+#ifdef HAVE_NETTLE_SIV_GCM
+    case AEAD_AES_128_GCM_SIV:
+      instance->min_nonce_length = SIV_GCM_NONCE_SIZE;
+      instance->max_nonce_length = SIV_GCM_NONCE_SIZE;
+      instance->tag_length = SIV_GCM_DIGEST_SIZE;
+      break;
+#endif
+    default:
+      assert(0);
+  }
+
  return instance;
 }

@@ -71,11 +102,18 @@ SIV_DestroyInstance(SIV_Instance instance)
 int
 SIV_GetKeyLength(SIV_Algorithm algorithm)
 {
-  assert(32 <= SIV_MAX_KEY_LENGTH);
+  assert(2 * AES128_KEY_SIZE <= SIV_MAX_KEY_LENGTH);

-  if (algorithm == AEAD_AES_SIV_CMAC_256)
-    return 32;
-  return 0;
+  switch (algorithm) {
+    case AEAD_AES_SIV_CMAC_256:
+      return 2 * AES128_KEY_SIZE;
+#ifdef HAVE_NETTLE_SIV_GCM
+    case AEAD_AES_128_GCM_SIV:
+      return AES128_KEY_SIZE;
+#endif
+    default:
+      return 0;
+  }
 }

 /* ================================================== */
@@ -83,10 +121,21 @@ SIV_GetKeyLength(SIV_Algorithm algorithm)
 int
 SIV_SetKey(SIV_Instance instance, const unsigned char *key, int length)
 {
-  if (length != 32)
+  if (length != SIV_GetKeyLength(instance->algorithm))
    return 0;

-  siv_cmac_aes128_set_key(&instance->siv, key);
+  switch (instance->algorithm) {
+    case AEAD_AES_SIV_CMAC_256:
+      siv_cmac_aes128_set_key(&instance->ctx.cmac_aes128, key);
+      break;
+#ifdef HAVE_NETTLE_SIV_GCM
+    case AEAD_AES_128_GCM_SIV:
+      aes128_set_encrypt_key(&instance->ctx.aes128, key);
+      break;
+#endif
+    default:
+      assert(0);
+  }

  instance->key_set = 1;

@@ -95,12 +144,28 @@ SIV_SetKey(SIV_Instance instance, const unsigned char *key, int length)

 /* ================================================== */

+int
+SIV_GetMinNonceLength(SIV_Instance instance)
+{
+  return instance->min_nonce_length;
+}
+
+/* ================================================== */
+
+int
+SIV_GetMaxNonceLength(SIV_Instance instance)
+{
+  return instance->max_nonce_length;
+}
+
+/* ================================================== */
+
 int
 SIV_GetTagLength(SIV_Instance instance)
 {
-  assert(SIV_DIGEST_SIZE <= SIV_MAX_TAG_LENGTH);
-
-  return SIV_DIGEST_SIZE;
+  if (instance->tag_length < 1 || instance->tag_length > SIV_MAX_TAG_LENGTH)
+    assert(0);
+  return instance->tag_length;
 }

 /* ================================================== */
@@ -115,16 +180,31 @@ SIV_Encrypt(SIV_Instance instance,
  if (!instance->key_set)
    return 0;

-  if (nonce_length < SIV_MIN_NONCE_SIZE || assoc_length < 0 ||
+  if (nonce_length < instance->min_nonce_length ||
+      nonce_length > instance->max_nonce_length || assoc_length < 0 ||
      plaintext_length < 0 || plaintext_length > ciphertext_length ||
-      plaintext_length + SIV_DIGEST_SIZE != ciphertext_length)
+      plaintext_length + SIV_GetTagLength(instance) != ciphertext_length)
    return 0;

  assert(assoc && plaintext);

-  siv_cmac_aes128_encrypt_message(&instance->siv, nonce_length, nonce,
-                                  assoc_length, assoc,
-                                  ciphertext_length, ciphertext, plaintext);
+  switch (instance->algorithm) {
+    case AEAD_AES_SIV_CMAC_256:
+      siv_cmac_aes128_encrypt_message(&instance->ctx.cmac_aes128,
+                                      nonce_length, nonce, assoc_length, assoc,
+                                      ciphertext_length, ciphertext, plaintext);
+      break;
+#ifdef HAVE_NETTLE_SIV_GCM
+    case AEAD_AES_128_GCM_SIV:
+      siv_gcm_aes128_encrypt_message(&instance->ctx.aes128,
+                                     nonce_length, nonce, assoc_length, assoc,
+                                     ciphertext_length, ciphertext, plaintext);
+      break;
+#endif
+    default:
+      assert(0);
+  }
+
  return 1;
 }

@@ -140,17 +220,32 @@ SIV_Decrypt(SIV_Instance instance,
  if (!instance->key_set)
    return 0;

-  if (nonce_length < SIV_MIN_NONCE_SIZE || assoc_length < 0 ||
+  if (nonce_length < instance->min_nonce_length ||
+      nonce_length > instance->max_nonce_length || assoc_length < 0 ||
      plaintext_length < 0 || plaintext_length > ciphertext_length ||
-      plaintext_length + SIV_DIGEST_SIZE != ciphertext_length)
+      plaintext_length + SIV_GetTagLength(instance) != ciphertext_length)
    return 0;

  assert(assoc && plaintext);

-  if (!siv_cmac_aes128_decrypt_message(&instance->siv, nonce_length, nonce,
-                                       assoc_length, assoc,
-                                       plaintext_length, plaintext, ciphertext))
-    return 0;
+  switch (instance->algorithm) {
+    case AEAD_AES_SIV_CMAC_256:
+      if (!siv_cmac_aes128_decrypt_message(&instance->ctx.cmac_aes128,
+                                           nonce_length, nonce, assoc_length, assoc,
+                                           plaintext_length, plaintext, ciphertext))
+        return 0;
+      break;
+#ifdef HAVE_NETTLE_SIV_GCM
+    case AEAD_AES_128_GCM_SIV:
+      if (!siv_gcm_aes128_decrypt_message(&instance->ctx.aes128,
+                                          nonce_length, nonce, assoc_length, assoc,
+                                          plaintext_length, plaintext, ciphertext))
+        return 0;
+      break;
+#endif
+    default:
+      assert(0);
+  }

  return 1;
 }
--- a/smooth.c
+++ b/smooth.c
@@ -302,7 +302,7 @@ SMT_Activate(struct timespec *now)
  if (!enabled || !locked)
    return;

-  LOG(LOGS_INFO, "Time smoothing activated%s", leap_only_mode ?
+  LOG(LOGS_INFO, "Activated %s%s", "time smoothing", leap_only_mode ?
      " (leap seconds only)" : "");
  locked = 0;
  last_update = *now;
@@ -322,6 +322,8 @@ SMT_Reset(struct timespec *now)

  for (i = 0; i < NUM_STAGES; i++)
    stages[i].wander = stages[i].length = 0.0;
+
+  LOG(LOGS_INFO, "Reset %s", "time smoothing");
 }

 void
--- a/socket.c
+++ b/socket.c
@@ -5,6 +5,7 @@
 * Copyright (C) Richard P. Curnow  1997-2003
 * Copyright (C) Timo Teras  2009
 * Copyright (C) Miroslav Lichvar  2009, 2013-2020
+ * Copyright (C) Luke Valenta  2023
 * 
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of version 2 of the GNU General Public License as
@@ -89,6 +90,9 @@ struct MessageHeader {

 static int initialised;

+static int first_reusable_fd;
+static int reusable_fds;
+
 /* Flags indicating in which IP families sockets can be requested */
 static int ip4_enabled;
 static int ip6_enabled;
@@ -155,6 +159,59 @@ domain_to_string(int domain)

 /* ================================================== */

+static int
+get_reusable_socket(int type, IPSockAddr *spec)
+{
+#ifdef LINUX
+  union sockaddr_all sa;
+  IPSockAddr ip_sa;
+  int sock_fd, opt;
+  socklen_t l;
+
+  /* Abort early if not an IPv4/IPv6 server socket */
+  if (!spec || spec->ip_addr.family == IPADDR_UNSPEC || spec->port == 0)
+    return INVALID_SOCK_FD;
+
+  /* Loop over available reusable sockets */
+  for (sock_fd = first_reusable_fd; sock_fd < first_reusable_fd + reusable_fds; sock_fd++) {
+
+    /* Check that types match */
+    l = sizeof (opt);
+    if (getsockopt(sock_fd, SOL_SOCKET, SO_TYPE, &opt, &l) < 0 ||
+        l != sizeof (opt) || opt != type)
+      continue;
+
+    /* Get sockaddr for reusable socket */
+    l = sizeof (sa);
+    if (getsockname(sock_fd, &sa.sa, &l) < 0 || l < sizeof (sa_family_t))
+      continue;
+    SCK_SockaddrToIPSockAddr(&sa.sa, l, &ip_sa);
+
+    /* Check that reusable socket matches specification */
+    if (ip_sa.port != spec->port || UTI_CompareIPs(&ip_sa.ip_addr, &spec->ip_addr, NULL) != 0)
+      continue;
+
+    /* Check that STREAM socket is listening */
+    l = sizeof (opt);
+    if (type == SOCK_STREAM && (getsockopt(sock_fd, SOL_SOCKET, SO_ACCEPTCONN, &opt, &l) < 0 ||
+                                l != sizeof (opt) || opt == 0))
+      continue;
+
+#if defined(FEAT_IPV6) && defined(IPV6_V6ONLY)
+    if (spec->ip_addr.family == IPADDR_INET6 &&
+        (!SCK_GetIntOption(sock_fd, IPPROTO_IPV6, IPV6_V6ONLY, &opt) || opt != 1))
+      LOG(LOGS_WARN, "Reusable IPv6 socket missing IPV6_V6ONLY option");
+#endif
+
+    return sock_fd;
+  }
+#endif
+
+  return INVALID_SOCK_FD;
+}
+
+/* ================================================== */
+
 #if defined(SOCK_CLOEXEC) || defined(SOCK_NONBLOCK)
 static int
 check_socket_flag(int sock_flag, int fd_flag, int fs_flag)
@@ -212,7 +269,7 @@ static int
 set_socket_flags(int sock_fd, int flags)
 {
  /* Close the socket automatically on exec */
-  if (
+  if (!SCK_IsReusable(sock_fd) &&
 #ifdef SOCK_CLOEXEC
      (supported_socket_flags & SOCK_CLOEXEC) == 0 &&
 #endif
@@ -222,7 +279,7 @@ set_socket_flags(int sock_fd, int flags)
  /* Enable non-blocking mode */
  if ((flags & SCK_FLAG_BLOCK) == 0 &&
 #ifdef SOCK_NONBLOCK
-      (supported_socket_flags & SOCK_NONBLOCK) == 0 &&
+      (SCK_IsReusable(sock_fd) || (supported_socket_flags & SOCK_NONBLOCK) == 0) &&
 #endif
      !set_socket_nonblock(sock_fd))
    return 0;
@@ -279,6 +336,32 @@ open_socket_pair(int domain, int type, int flags, int *other_fd)

 /* ================================================== */

+static int
+get_ip_socket(int domain, int type, int flags, IPSockAddr *ip_sa)
+{
+  int sock_fd;
+
+  /* Check if there is a matching reusable socket */
+  sock_fd = get_reusable_socket(type, ip_sa);
+
+  if (sock_fd < 0) {
+    sock_fd = open_socket(domain, type, flags);
+
+    /* Unexpected, but make sure the new socket is not in the reusable range */
+    if (SCK_IsReusable(sock_fd))
+      LOG_FATAL("Could not open %s socket : file descriptor in reusable range",
+                domain_to_string(domain));
+  } else {
+    /* Set socket flags on reusable socket */
+    if (!set_socket_flags(sock_fd, flags))
+      return INVALID_SOCK_FD;
+  }
+
+  return sock_fd;
+}
+
+/* ================================================== */
+
 static int
 set_socket_options(int sock_fd, int flags)
 {
@@ -295,8 +378,10 @@ static int
 set_ip_options(int sock_fd, int family, int flags)
 {
 #if defined(FEAT_IPV6) && defined(IPV6_V6ONLY)
-  /* Receive only IPv6 packets on an IPv6 socket */
-  if (family == IPADDR_INET6 && !SCK_SetIntOption(sock_fd, IPPROTO_IPV6, IPV6_V6ONLY, 1))
+  /* Receive only IPv6 packets on an IPv6 socket, but do not attempt
+     to set this option on pre-initialised reuseable sockets */
+  if (family == IPADDR_INET6 && !SCK_IsReusable(sock_fd) &&
+      !SCK_SetIntOption(sock_fd, IPPROTO_IPV6, IPV6_V6ONLY, 1))
    return 0;
 #endif

@@ -385,6 +470,10 @@ bind_ip_address(int sock_fd, IPSockAddr *addr, int flags)
    ;
 #endif

+  /* Do not attempt to bind pre-initialised reusable socket */
+  if (SCK_IsReusable(sock_fd))
+    return 1;
+
  saddr_len = SCK_IPSockAddrToSockaddr(addr, (struct sockaddr *)&saddr, sizeof (saddr));
  if (saddr_len == 0)
    return 0;
@@ -457,7 +546,7 @@ open_ip_socket(IPSockAddr *remote_addr, IPSockAddr *local_addr, const char *ifac
      return INVALID_SOCK_FD;
  }

-  sock_fd = open_socket(domain, type, flags);
+  sock_fd = get_ip_socket(domain, type, flags, local_addr);
  if (sock_fd < 0)
    return INVALID_SOCK_FD;

@@ -482,7 +571,8 @@ open_ip_socket(IPSockAddr *remote_addr, IPSockAddr *local_addr, const char *ifac
    goto error;

  if (remote_addr || local_addr)
-    DEBUG_LOG("Opened %s%s socket fd=%d%s%s%s%s",
+    DEBUG_LOG("%s %s%s socket fd=%d%s%s%s%s",
+              SCK_IsReusable(sock_fd) ? "Reusing" : "Opened",
              type == SOCK_DGRAM ? "UDP" : type == SOCK_STREAM ? "TCP" : "?",
              family == IPADDR_INET4 ? "v4" : "v6",
              sock_fd,
@@ -869,6 +959,11 @@ process_header(struct msghdr *msg, int msg_length, int sock_fd, int flags,
      memcpy(&message->timestamp.kernel, CMSG_DATA(cmsg), sizeof (message->timestamp.kernel));
    }
 #endif
+#ifdef SCM_REALTIME
+    else if (match_cmsg(cmsg, SOL_SOCKET, SCM_REALTIME, sizeof (message->timestamp.kernel))) {
+      memcpy(&message->timestamp.kernel, CMSG_DATA(cmsg), sizeof (message->timestamp.kernel));
+    }
+#endif
 #ifdef HAVE_LINUX_TIMESTAMPING
 #ifdef HAVE_LINUX_TIMESTAMPING_OPT_PKTINFO
    else if (match_cmsg(cmsg, SOL_SOCKET, SCM_TIMESTAMPING_PKTINFO,
@@ -1165,9 +1260,44 @@ send_message(int sock_fd, SCK_Message *message, int flags)

 /* ================================================== */

+void
+SCK_PreInitialise(void)
+{
+#ifdef LINUX
+  char *s, *ptr;
+
+  /* On Linux systems, the systemd service manager may pass file descriptors
+     for pre-initialised sockets to the chronyd daemon.  The service manager
+     allocates and binds the file descriptors, and passes a copy to each
+     spawned instance of the service.  This allows for zero-downtime service
+     restarts as the sockets buffer client requests until the service is able
+     to handle them.  The service manager sets the LISTEN_FDS environment
+     variable to the number of passed file descriptors, and the integer file
+     descriptors start at 3 (see SD_LISTEN_FDS_START in
+     https://www.freedesktop.org/software/systemd/man/latest/sd_listen_fds.html). */
+  first_reusable_fd = 3;
+  reusable_fds = 0;
+
+  s = getenv("LISTEN_FDS");
+  if (s) {
+    errno = 0;
+    reusable_fds = strtol(s, &ptr, 10);
+    if (errno != 0 || *ptr != '\0' || reusable_fds < 0)
+      reusable_fds = 0;
+  }
+#else
+  first_reusable_fd = 0;
+  reusable_fds = 0;
+#endif
+}
+
+/* ================================================== */
+
 void
 SCK_Initialise(int family)
 {
+  int fd;
+
  ip4_enabled = family == IPADDR_INET4 || family == IPADDR_UNSPEC;
 #ifdef FEAT_IPV6
  ip6_enabled = family == IPADDR_INET6 || family == IPADDR_UNSPEC;
@@ -1196,6 +1326,9 @@ SCK_Initialise(int family)
    supported_socket_flags |= SOCK_NONBLOCK;
 #endif

+  for (fd = first_reusable_fd; fd < first_reusable_fd + reusable_fds; fd++)
+    UTI_FdSetCloexec(fd);
+
  initialised = 1;
 }

@@ -1208,6 +1341,8 @@ SCK_Finalise(void)
  ARR_DestroyInstance(recv_headers);
  ARR_DestroyInstance(recv_messages);

+  SCK_CloseReusableSockets();
+
  initialised = 0;
 }

@@ -1348,6 +1483,27 @@ SCK_OpenUnixSocketPair(int flags, int *other_fd)

 /* ================================================== */

+int
+SCK_IsReusable(int fd)
+{
+  return fd >= first_reusable_fd && fd < first_reusable_fd + reusable_fds;
+}
+
+/* ================================================== */
+
+void
+SCK_CloseReusableSockets(void)
+{
+  int fd;
+
+  for (fd = first_reusable_fd; fd < first_reusable_fd + reusable_fds; fd++)
+    close(fd);
+  reusable_fds = 0;
+  first_reusable_fd = 0;
+}
+
+/* ================================================== */
+
 int
 SCK_SetIntOption(int sock_fd, int level, int name, int value)
 {
@@ -1386,8 +1542,15 @@ SCK_EnableKernelRxTimestamping(int sock_fd)
    return 1;
 #endif
 #ifdef SO_TIMESTAMP
-  if (SCK_SetIntOption(sock_fd, SOL_SOCKET, SO_TIMESTAMP, 1))
+  if (SCK_SetIntOption(sock_fd, SOL_SOCKET, SO_TIMESTAMP, 1)) {
+#if defined(SO_TS_CLOCK) && defined(SO_TS_REALTIME)
+    /* We don't care about the return value - we'll get either a
+       SCM_REALTIME (if we succeded) or a SCM_TIMESTAMP (if we failed) */
+    if (!SCK_SetIntOption(sock_fd, SOL_SOCKET, SO_TS_CLOCK, SO_TS_REALTIME))
+      ;
+#endif
    return 1;
+  }
 #endif

  return 0;
@@ -1398,7 +1561,7 @@ SCK_EnableKernelRxTimestamping(int sock_fd)
 int
 SCK_ListenOnSocket(int sock_fd, int backlog)
 {
-  if (listen(sock_fd, backlog) < 0) {
+  if (!SCK_IsReusable(sock_fd) && listen(sock_fd, backlog) < 0) {
    DEBUG_LOG("listen() failed : %s", strerror(errno));
    return 0;
  }
@@ -1561,6 +1724,10 @@ SCK_RemoveSocket(int sock_fd)
 void
 SCK_CloseSocket(int sock_fd)
 {
+  /* Reusable sockets are closed in finalisation */
+  if (SCK_IsReusable(sock_fd))
+    return;
+
  close(sock_fd);
 }

--- a/socket.h
+++ b/socket.h
@@ -73,6 +73,9 @@ typedef struct {
  int descriptor;
 } SCK_Message;

+/* Pre-initialisation function */
+extern void SCK_PreInitialise(void);
+
 /* Initialisation function (the specified IP family is enabled,
   or all if IPADDR_UNSPEC) */
 extern void SCK_Initialise(int family);
@@ -106,6 +109,12 @@ extern int SCK_OpenUnixStreamSocket(const char *remote_addr, const char *local_a
                                    int flags);
 extern int SCK_OpenUnixSocketPair(int flags, int *other_fd);

+/* Check if a file descriptor was passed from the service manager */
+extern int SCK_IsReusable(int sock_fd);
+
+/* Close all reusable sockets before finalisation (e.g. in a helper process) */
+extern void SCK_CloseReusableSockets(void);
+
 /* Set and get a socket option of int size */
 extern int SCK_SetIntOption(int sock_fd, int level, int name, int value);
 extern int SCK_GetIntOption(int sock_fd, int level, int name, int *value);
--- a/sources.c
+++ b/sources.c
@@ -3,7 +3,7 @@

 **********************************************************************
 * Copyright (C) Richard P. Curnow  1997-2003
- * Copyright (C) Miroslav Lichvar  2011-2016, 2018, 2020-2021
+ * Copyright (C) Miroslav Lichvar  2011-2016, 2018, 2020-2023
 * 
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of version 2 of the GNU General Public License as
@@ -68,6 +68,7 @@ struct SelectInfo {
 typedef enum {
  SRC_OK,               /* OK so far, not a final status! */
  SRC_UNSELECTABLE,     /* Has noselect option set */
+  SRC_UNSYNCHRONISED,   /* Provides samples but not unsynchronised */
  SRC_BAD_STATS,        /* Doesn't have valid stats data */
  SRC_BAD_DISTANCE,     /* Has root distance longer than allowed maximum */
  SRC_JITTERY,          /* Had std dev larger than allowed maximum */
@@ -111,6 +112,9 @@ struct SRC_Instance_Record {
  /* Updates left before allowing combining */
  int distant;

+  /* Updates with a status requiring source replacement */
+  int bad;
+
  /* Flag indicating the status of the source */
  SRC_Status status;

@@ -139,6 +143,10 @@ struct SRC_Instance_Record {

  /* Flag indicating the source has a leap second vote */
  int leap_vote;
+
+  /* Flag indicating the source was already reported as
+     a falseticker since the last selection change */
+  int reported_falseticker;
 };

 /* ================================================== */
@@ -164,6 +172,11 @@ static int max_n_sources; /* Capacity of the table */
 static int selected_source_index; /* Which source index is currently
                                     selected (set to INVALID_SOURCE
                                     if no current valid reference) */
+static int reported_no_majority;  /* Flag to avoid repeated log message
+                                     about no majority */
+static int report_selection_loss; /* Flag to force logging a message if
+                                     selection is lost in a transient state
+                                     (SRC_WAITS_STATS, SRC_WAITS_UPDATE) */

 /* Score needed to replace the currently selected source */
 #define SCORE_LIMIT 10.0
@@ -171,12 +184,19 @@ static int selected_source_index; /* Which source index is currently
 /* Number of updates needed to reset the distant status */
 #define DISTANT_PENALTY 32

+/* Number of updates needed to trigger handling of bad sources */
+#define BAD_HANDLE_THRESHOLD 4
+
 static double max_distance;
 static double max_jitter;
 static double reselect_distance;
 static double stratum_weight;
 static double combine_limit;

+static SRC_Instance last_updated_inst;
+
+static LOG_FileID logfileid;
+
 /* Identifier of the dump file */
 #define DUMP_IDENTIFIER "SRC0\n"

@@ -184,10 +204,13 @@ static double combine_limit;
 /* Forward prototype */

 static void update_sel_options(void);
+static void unselect_selected_source(LOG_Severity severity, const char *format,
+                                     const char *arg);
 static void slew_sources(struct timespec *raw, struct timespec *cooked, double dfreq,
                         double doffset, LCL_ChangeType change_type, void *anything);
 static void add_dispersion(double dispersion, void *anything);
 static char *source_to_string(SRC_Instance inst);
+static char get_status_char(SRC_Status status);

 /* ================================================== */
 /* Initialisation function */
@@ -207,6 +230,12 @@ void SRC_Initialise(void) {

  LCL_AddParameterChangeHandler(slew_sources, NULL);
  LCL_AddDispersionNotifyHandler(add_dispersion, NULL);
+
+  last_updated_inst = NULL;
+
+  logfileid = CNF_GetLogSelection() ? LOG_FileOpen("selection",
+              "   Date (UTC) Time     IP Address   S EOpts Reach Score Last sample  Low end   High end")
+              : -1;
 }

 /* ================================================== */
@@ -287,7 +316,13 @@ void SRC_DestroyInstance(SRC_Instance instance)
 {
  int dead_index, i;

+  if (last_updated_inst == instance)
+    last_updated_inst = NULL;
+
  assert(initialised);
+  if (instance->index < 0 || instance->index >= n_sources ||
+      instance != sources[instance->index])
+    assert(0);

  SST_DeleteInstance(instance->stats);
  dead_index = instance->index;
@@ -300,11 +335,12 @@ void SRC_DestroyInstance(SRC_Instance instance)

  update_sel_options();

-  /* If this was the previous reference source, we have to reselect! */
-  if (selected_source_index == dead_index)
-    SRC_ReselectSource();
-  else if (selected_source_index > dead_index)
+  if (selected_source_index > dead_index)
    --selected_source_index;
+  else if (selected_source_index == dead_index)
+    unselect_selected_source(LOGS_INFO, NULL, NULL);
+
+  SRC_SelectSource(NULL);
 }

 /* ================================================== */
@@ -316,15 +352,20 @@ SRC_ResetInstance(SRC_Instance instance)
  instance->reachability = 0;
  instance->reachability_size = 0;
  instance->distant = 0;
+  instance->bad = 0;
  instance->status = SRC_BAD_STATS;
  instance->sel_score = 1.0;
  instance->stratum = 0;
  instance->leap = LEAP_Unsynchronised;
  instance->leap_vote = 0;
+  instance->reported_falseticker = 0;

  memset(&instance->sel_info, 0, sizeof (instance->sel_info));

  SST_ResetInstance(instance->stats);
+
+  if (selected_source_index == instance->index)
+    SRC_SelectSource(NULL);
 }

 /* ================================================== */
@@ -460,6 +501,19 @@ special_mode_end(void)
    return 1;
 }

+/* ================================================== */
+
+static void
+handle_bad_source(SRC_Instance inst)
+{
+  if (inst->type == SRC_NTP) {
+    DEBUG_LOG("Bad source status=%c", get_status_char(inst->status));
+    NSR_HandleBadSource(inst->ip_addr);
+  }
+}
+
+/* ================================================== */
+
 void
 SRC_UpdateReachability(SRC_Instance inst, int reachable)
 {
@@ -480,14 +534,9 @@ SRC_UpdateReachability(SRC_Instance inst, int reachable)
    REF_SetUnsynchronised();
  }

-  /* Try to replace NTP sources that are unreachable, falsetickers, or
-     have root distance or jitter larger than the allowed maximums */
-  if (inst->type == SRC_NTP &&
-      ((!inst->reachability && inst->reachability_size == SOURCE_REACH_BITS) ||
-       inst->status == SRC_BAD_DISTANCE || inst->status == SRC_JITTERY ||
-       inst->status == SRC_FALSETICKER)) {
-    NSR_HandleBadSource(inst->ip_addr);
-  }
+  /* Try to replace unreachable NTP sources */
+  if (inst->reachability == 0 && inst->reachability_size == SOURCE_REACH_BITS)
+    handle_bad_source(inst);
 }

 /* ================================================== */
@@ -547,18 +596,17 @@ update_sel_options(void)
  for (i = 0; i < n_sources; i++) {
    options = sources[i]->conf_sel_options;

-    if (options & SRC_SELECT_NOSELECT)
-      continue;
-
-    switch (sources[i]->type) {
-      case SRC_NTP:
-        options |= sources[i]->authenticated ? auth_ntp_options : unauth_ntp_options;
-        break;
-      case SRC_REFCLOCK:
-        options |= refclk_options;
-        break;
-      default:
-        assert(0);
+    if (!(options & SRC_SELECT_NOSELECT)) {
+      switch (sources[i]->type) {
+        case SRC_NTP:
+          options |= sources[i]->authenticated ? auth_ntp_options : unauth_ntp_options;
+          break;
+        case SRC_REFCLOCK:
+          options |= refclk_options;
+          break;
+        default:
+          assert(0);
+      }
    }

    if (sources[i]->sel_options != options) {
@@ -572,17 +620,17 @@ update_sel_options(void)
 /* ================================================== */

 static void
-log_selection_message(const char *format, const char *arg)
+log_selection_message(LOG_Severity severity, const char *format, const char *arg)
 {
  if (REF_GetMode() != REF_ModeNormal)
    return;
-  LOG(LOGS_INFO, format, arg);
+  LOG(severity, format, arg);
 }

 /* ================================================== */

 static void
-log_selection_source(const char *format, SRC_Instance inst)
+log_selection_source(LOG_Severity severity, const char *format, SRC_Instance inst)
 {
  char buf[320], *name, *ntp_name;

@@ -594,7 +642,7 @@ log_selection_source(const char *format, SRC_Instance inst)
  else
    snprintf(buf, sizeof (buf), "%s", name);

-  log_selection_message(format, buf);
+  log_selection_message(severity, format, buf);
 }

 /* ================================================== */
@@ -639,13 +687,45 @@ source_to_string(SRC_Instance inst)
 static void
 mark_source(SRC_Instance inst, SRC_Status status)
 {
+  struct timespec now;
+
  inst->status = status;

-  DEBUG_LOG("%s status=%d options=%x reach=%o/%d updates=%d distant=%d leap=%d vote=%d lo=%f hi=%f",
-            source_to_string(inst), (int)inst->status, (unsigned int)inst->sel_options,
-            (unsigned int)inst->reachability, inst->reachability_size, inst->updates,
-            inst->distant, (int)inst->leap, inst->leap_vote,
+  /* Try to replace NTP sources that are falsetickers, or have a root
+     distance or jitter larger than the allowed maximums */
+  if (inst == last_updated_inst) {
+    if (inst->bad < INT_MAX &&
+        (status == SRC_FALSETICKER || status == SRC_BAD_DISTANCE || status == SRC_JITTERY))
+      inst->bad++;
+    else
+      inst->bad = 0;
+    if (inst->bad >= BAD_HANDLE_THRESHOLD)
+      handle_bad_source(inst);
+  }
+
+  DEBUG_LOG("%s status=%c options=%x reach=%o/%d updates=%d distant=%d bad=%d leap=%d vote=%d lo=%f hi=%f",
+            source_to_string(inst), get_status_char(inst->status),
+            (unsigned int)inst->sel_options, (unsigned int)inst->reachability,
+            inst->reachability_size, inst->updates,
+            inst->distant, inst->bad, (int)inst->leap, inst->leap_vote,
            inst->sel_info.lo_limit, inst->sel_info.hi_limit);
+
+  if (logfileid == -1)
+    return;
+
+  SCH_GetLastEventTime(&now, NULL, NULL);
+
+  LOG_FileWrite(logfileid,
+                "%s %-15s %c -%c%c%c%c %4o %5.2f %10.3e %10.3e %10.3e",
+                UTI_TimeToLogForm(now.tv_sec), source_to_string(inst),
+                get_status_char(inst->status),
+                inst->sel_options & SRC_SELECT_NOSELECT ? 'N' : '-',
+                inst->sel_options & SRC_SELECT_PREFER ? 'P' : '-',
+                inst->sel_options & SRC_SELECT_TRUST ? 'T' : '-',
+                inst->sel_options & SRC_SELECT_REQUIRE ? 'R' : '-',
+                (unsigned int)inst->reachability, inst->sel_score,
+                inst->sel_info.last_sample_ago,
+                inst->sel_info.lo_limit, inst->sel_info.hi_limit);
 }

 /* ================================================== */
@@ -662,6 +742,26 @@ mark_ok_sources(SRC_Status status)
  }
 }

+/* ================================================== */
+/* Reset the index of selected source and report the selection loss.  If no
+   message is provided, assume it is a transient state and wait for another
+   call providing a message or selection of another source, which resets the
+   report_selection_loss flag. */
+
+static void
+unselect_selected_source(LOG_Severity severity, const char *format, const char *arg)
+{
+  if (selected_source_index != INVALID_SOURCE) {
+    selected_source_index = INVALID_SOURCE;
+    report_selection_loss = 1;
+  }
+
+  if (report_selection_loss && format) {
+    log_selection_message(severity, format, arg);
+    report_selection_loss = 0;
+  }
+}
+
 /* ================================================== */

 static int
@@ -722,8 +822,8 @@ combine_sources(int n_sel_sources, struct timespec *ref_time, double *offset,
    offset_weight = 1.0 / sources[index]->sel_info.root_distance;
    frequency_weight = 1.0 / SQUARE(src_frequency_sd);

-    DEBUG_LOG("combining index=%d oweight=%e offset=%e osd=%e fweight=%e freq=%e fsd=%e skew=%e",
-              index, offset_weight, src_offset, src_offset_sd,
+    DEBUG_LOG("combining %s oweight=%e offset=%e osd=%e fweight=%e freq=%e fsd=%e skew=%e",
+              source_to_string(sources[index]), offset_weight, src_offset, src_offset_sd,
              frequency_weight, src_frequency, src_frequency_sd, src_skew);

    sum_offset_weight += offset_weight;
@@ -773,15 +873,13 @@ SRC_SelectSource(SRC_Instance updated_inst)
  double first_sample_ago, max_reach_sample_ago;
  NTP_Leap leap_status;

-  if (updated_inst)
+  if (updated_inst) {
    updated_inst->updates++;
+    last_updated_inst = updated_inst;
+  }

  if (n_sources == 0) {
-    /* In this case, we clearly cannot synchronise to anything */
-    if (selected_source_index != INVALID_SOURCE) {
-      log_selection_message("Can't synchronise: no sources", NULL);
-      selected_source_index = INVALID_SOURCE;
-    }
+    unselect_selected_source(LOGS_INFO, "Can't synchronise: no sources", NULL);
    return;
  }

@@ -815,6 +913,12 @@ SRC_SelectSource(SRC_Instance updated_inst)
      continue;
    }

+    /* Ignore sources which are not synchronised */
+    if (sources[i]->leap == LEAP_Unsynchronised) {
+      mark_source(sources[i], SRC_UNSYNCHRONISED);
+      continue;
+    }
+
    si = &sources[i]->sel_info;
    SST_GetSelectionData(sources[i]->stats, &now,
                         &si->lo_limit, &si->hi_limit, &si->root_distance,
@@ -960,15 +1064,13 @@ SRC_SelectSource(SRC_Instance updated_inst)
  if (n_badstats_sources && n_sel_sources && selected_source_index == INVALID_SOURCE &&
      max_sel_reach_size < SOURCE_REACH_BITS && max_sel_reach >> 1 == max_badstat_reach) {
    mark_ok_sources(SRC_WAITS_STATS);
+    unselect_selected_source(LOGS_INFO, NULL, NULL);
    return;
  }

  if (n_endpoints == 0) {
    /* No sources provided valid endpoints */
-    if (selected_source_index != INVALID_SOURCE) {
-      log_selection_message("Can't synchronise: no selectable sources", NULL);
-      selected_source_index = INVALID_SOURCE;
-    }
+    unselect_selected_source(LOGS_INFO, "Can't synchronise: no selectable sources", NULL);
    return;
  }

@@ -1046,8 +1148,13 @@ SRC_SelectSource(SRC_Instance updated_inst)
      (best_trust_depth > 0 && best_trust_depth <= n_sel_trust_sources / 2)) {
    /* Could not even get half the reachable (trusted) sources to agree */

+    if (!reported_no_majority) {
+      log_selection_message(LOGS_WARN, "Can't synchronise: no majority", NULL);
+      reported_no_majority = 1;
+      report_selection_loss = 0;
+    }
+
    if (selected_source_index != INVALID_SOURCE) {
-      log_selection_message("Can't synchronise: no majority", NULL);
      REF_SetUnsynchronised();
      selected_source_index = INVALID_SOURCE;
    }
@@ -1093,16 +1200,17 @@ SRC_SelectSource(SRC_Instance updated_inst)
        sel_req_source = 0;
    } else {
      mark_source(sources[i], SRC_FALSETICKER);
+      if (!sources[i]->reported_falseticker) {
+        log_selection_source(LOGS_WARN, "Detected falseticker %s", sources[i]);
+        sources[i]->reported_falseticker = 1;
+      }
    }
  }

  if (!n_sel_sources || sel_req_source || n_sel_sources < CNF_GetMinSources()) {
-    if (selected_source_index != INVALID_SOURCE) {
-      log_selection_message("Can't synchronise: %s selectable sources",
-                            !n_sel_sources ? "no" :
-                            sel_req_source ? "no required source in" : "not enough");
-      selected_source_index = INVALID_SOURCE;
-    }
+    unselect_selected_source(LOGS_INFO, "Can't synchronise: %s selectable sources",
+                             !n_sel_sources ? "no" :
+                             sel_req_source ? "no required source in" : "not enough");
    mark_ok_sources(SRC_WAITS_SOURCES);
    return;
  }
@@ -1209,19 +1317,23 @@ SRC_SelectSource(SRC_Instance updated_inst)
    /* Before selecting the new synchronisation source wait until the reference
       can be updated */
    if (sources[max_score_index]->updates == 0) {
-      selected_source_index = INVALID_SOURCE;
+      unselect_selected_source(LOGS_INFO, NULL, NULL);
      mark_ok_sources(SRC_WAITS_UPDATE);
      return;
    }

    selected_source_index = max_score_index;
-    log_selection_source("Selected source %s", sources[selected_source_index]);
+    log_selection_source(LOGS_INFO, "Selected source %s", sources[selected_source_index]);

    /* New source has been selected, reset all scores */
    for (i = 0; i < n_sources; i++) {
      sources[i]->sel_score = 1.0;
      sources[i]->distant = 0;
+      sources[i]->reported_falseticker = 0;
    }
+
+    reported_no_majority = 0;
+    report_selection_loss = 0;
  }

  mark_source(sources[selected_source_index], SRC_SELECTED);
@@ -1512,6 +1624,8 @@ SRC_ResetSources(void)

  for (i = 0; i < n_sources; i++)
    SRC_ResetInstance(sources[i]);
+
+  LOG(LOGS_INFO, "Reset all sources");
 }

 /* ================================================== */
@@ -1559,6 +1673,46 @@ SRC_ActiveSources(void)

 /* ================================================== */

+static SRC_Instance
+find_source(IPAddr *ip, uint32_t ref_id)
+{
+  int i;
+
+  for (i = 0; i < n_sources; i++) {
+    if ((ip->family != IPADDR_UNSPEC && sources[i]->type == SRC_NTP &&
+         UTI_CompareIPs(ip, sources[i]->ip_addr, NULL) == 0) ||
+        (ip->family == IPADDR_UNSPEC && sources[i]->type == SRC_REFCLOCK &&
+         ref_id == sources[i]->ref_id))
+      return sources[i];
+  }
+
+  return NULL;
+}
+
+/* ================================================== */
+
+int
+SRC_ModifySelectOptions(IPAddr *ip, uint32_t ref_id, int options, int mask)
+{
+  SRC_Instance inst;
+
+  inst = find_source(ip, ref_id);
+  if (!inst)
+    return 0;
+
+  if ((inst->conf_sel_options & mask) == options)
+    return 1;
+
+  inst->conf_sel_options = (inst->conf_sel_options & ~mask) | options;
+  LOG(LOGS_INFO, "Source %s selection options modified", source_to_string(inst));
+
+  update_sel_options();
+
+  return 1;
+}
+
+/* ================================================== */
+
 int
 SRC_ReportSource(int index, RPT_SourceReport *report, struct timespec *now)
 {
@@ -1642,6 +1796,8 @@ get_status_char(SRC_Status status)
  switch (status) {
    case SRC_UNSELECTABLE:
      return 'N';
+    case SRC_UNSYNCHRONISED:
+      return 's';
    case SRC_BAD_STATS:
      return 'M';
    case SRC_BAD_DISTANCE:
--- a/sources.h
+++ b/sources.h
@@ -131,6 +131,10 @@ extern int SRC_IsReachable(SRC_Instance inst);
 extern int SRC_ReadNumberOfSources(void);
 extern int SRC_ActiveSources(void);

+/* Modify selection options of an NTP source specified by address, or
+   refclock specified by its reference ID */
+extern int SRC_ModifySelectOptions(IPAddr *ip, uint32_t ref_id, int options, int mask);
+
 extern int SRC_ReportSource(int index, RPT_SourceReport *report, struct timespec *now);
 extern int SRC_ReportSourcestats(int index, RPT_SourcestatsReport *report, struct timespec *now);
 extern int SRC_GetSelectReport(int index, RPT_SelectReport *report);
--- a/sourcestats.c
+++ b/sourcestats.c
@@ -80,7 +80,7 @@ static LOG_FileID logfileid;

 struct SST_Stats_Record {

-  /* Reference ID and IP address of source, used for logging to statistics log */
+  /* Reference ID and IP address (NULL if not an NTP source) */
  uint32_t refid;
  IPAddr *ip_addr;

@@ -211,8 +211,8 @@ SST_CreateInstance(uint32_t refid, IPAddr *addr, int min_samples, int max_sample
  SST_Stats inst;
  inst = MallocNew(struct SST_Stats_Record);

-  inst->min_samples = min_samples;
-  inst->max_samples = max_samples;
+  inst->max_samples = max_samples > 0 ? CLAMP(1, max_samples, MAX_SAMPLES) : MAX_SAMPLES;
+  inst->min_samples = CLAMP(1, min_samples, inst->max_samples);
  inst->fixed_min_delay = min_delay;
  inst->fixed_asymmetry = asymmetry;

@@ -698,7 +698,8 @@ SST_GetSelectionData(SST_Stats inst, struct timespec *now,

  /* If maxsamples is too small to have a successful regression, enable the
     selection as a special case for a fast update/print-once reference mode */
-  if (!*select_ok && inst->n_samples < 3 && inst->n_samples == inst->max_samples) {
+  if (!*select_ok && inst->n_samples < MIN_SAMPLES_FOR_REGRESS &&
+      inst->n_samples == inst->max_samples) {
    *std_dev = CNF_GetMaxJitter();
    *select_ok = 1;
  }
@@ -814,7 +815,7 @@ SST_PredictOffset(SST_Stats inst, struct timespec *when)
 {
  double elapsed;
  
-  if (inst->n_samples < 3) {
+  if (inst->n_samples < MIN_SAMPLES_FOR_REGRESS) {
    /* We don't have any useful statistics, and presumably the poll
       interval is minimal.  We can't do any useful prediction other
       than use the latest sample or zero if we don't have any samples */
@@ -930,6 +931,7 @@ SST_LoadFromFile(SST_Stats inst, FILE *in)

    /* Make sure the samples are sane and they are in order */
    if (!UTI_IsTimeOffsetSane(&inst->sample_times[i], -inst->offsets[i]) ||
+        UTI_CompareTimespecs(&now, &inst->sample_times[i]) < 0 ||
        !(fabs(inst->peer_delays[i]) < 1.0e6 && fabs(inst->peer_dispersions[i]) < 1.0e6 &&
          fabs(inst->root_delays[i]) < 1.0e6 && fabs(inst->root_dispersions[i]) < 1.0e6) ||
        (i > 0 && UTI_CompareTimespecs(&inst->sample_times[i],
@@ -962,9 +964,10 @@ SST_DoSourceReport(SST_Stats inst, RPT_SourceReport *report, struct timespec *no
    report->latest_meas = inst->offsets[i];
    report->latest_meas_err = 0.5*inst->root_delays[j] + inst->root_dispersions[j];

-    /* Align the sample time to reduce the leak of the receive timestamp */
+    /* Align the sample time to reduce the leak of the NTP receive timestamp */
    last_sample_time = inst->sample_times[i];
-    last_sample_time.tv_nsec = 0;
+    if (inst->ip_addr)
+      last_sample_time.tv_nsec = 0;
    report->latest_meas_ago = UTI_DiffTimespecsToDouble(now, &last_sample_time);
  } else {
    report->latest_meas_ago = (uint32_t)-1;
@@ -985,6 +988,14 @@ SST_Samples(SST_Stats inst)

 /* ================================================== */

+int
+SST_GetMinSamples(SST_Stats inst)
+{
+  return inst->min_samples;
+}
+
+/* ================================================== */
+
 void
 SST_DoSourcestatsReport(SST_Stats inst, RPT_SourcestatsReport *report, struct timespec *now)
 {
--- a/sourcestats.h
+++ b/sourcestats.h
@@ -133,6 +133,8 @@ extern void SST_DoSourcestatsReport(SST_Stats inst, RPT_SourcestatsReport *repor

 extern int SST_Samples(SST_Stats inst);

+extern int SST_GetMinSamples(SST_Stats inst);
+
 extern double SST_GetJitterAsymmetry(SST_Stats inst);

 #endif /* GOT_SOURCESTATS_H */
--- a/srcparams.h
+++ b/srcparams.h
@@ -61,6 +61,7 @@ typedef struct {
  double max_delay;
  double max_delay_ratio;
  double max_delay_dev_ratio;
+  double max_delay_quant;
  double min_delay;
  double asymmetry;
  double offset;
--- a/stubs.c
+++ b/stubs.c
@@ -207,6 +207,12 @@ NSR_AddSourceByName(char *name, int port, int pool, NTP_Source_Type type,
  return NSR_TooManySources;
 }

+const char *
+NSR_StatusToString(NSR_Status status)
+{
+  return "NTP not supported";
+}
+
 NSR_Status
 NSR_RemoveSource(IPAddr *address)
 {
--- a/sys_generic.c
+++ b/sys_generic.c
@@ -73,13 +73,28 @@ static double slew_freq;
 /* Time (raw) of last update of slewing frequency and offset */
 static struct timespec slew_start;

-/* Limits for the slew timeout */
-#define MIN_SLEW_TIMEOUT 1.0
-#define MAX_SLEW_TIMEOUT 1.0e4
+/* Limits for the slew length */
+#define MIN_SLEW_DURATION 1.0
+#define MAX_SLEW_DURATION 1.0e4

 /* Scheduler timeout ID for ending of the currently running slew */
 static SCH_TimeoutID slew_timeout_id;

+/* Scheduled duration of the currently running slew */
+static double slew_duration;
+
+/* Expected delay in ending of the slew due to process scheduling and
+   execution time, tracked as a decaying maximum value */
+static double slew_excess_duration;
+
+/* Maximum accepted excess duration to ignore large jumps after resuming
+   suspended system and other reasons (which should be handled in the
+   scheduler), a constant to determine the minimum slew duration to avoid
+   oscillations due to the excess, and the decay constant */
+#define MAX_SLEW_EXCESS_DURATION 100.0
+#define MIN_SLEW_DURATION_EXCESS_RATIO 5.0
+#define SLEW_EXCESS_DURATION_DECAY 0.9
+
 /* Suggested offset correction rate (correction time * offset) */
 static double correction_rate;

@@ -109,12 +124,7 @@ static void
 handle_step(struct timespec *raw, struct timespec *cooked, double dfreq,
            double doffset, LCL_ChangeType change_type, void *anything)
 {
-  if (change_type == LCL_ChangeUnknownStep) {
-    /* Reset offset and slewing */
-    slew_start = *raw;
-    offset_register = 0.0;
-    update_slew();
-  } else if (change_type == LCL_ChangeStep) {
+  if (change_type == LCL_ChangeStep) {
    UTI_AddDoubleToTimespec(&slew_start, -doffset, &slew_start);
  }
 }
@@ -169,8 +179,8 @@ clamp_freq(double freq)
 static void
 update_slew(void)
 {
+  double old_slew_freq, total_freq, corr_freq, duration, excess_duration;
  struct timespec now, end_of_slew;
-  double old_slew_freq, total_freq, corr_freq, duration;

  /* Remove currently running timeout */
  SCH_RemoveTimeout(slew_timeout_id);
@@ -183,13 +193,25 @@ update_slew(void)

  stop_fastslew(&now);

-  /* Estimate how long should the next slew take */
+  /* Update the maximum excess duration, decaying even when the slew did
+     not time out (i.e. frequency was set or offset accrued), but add a small
+     value to avoid denormals */
+  slew_excess_duration = (slew_excess_duration + 1.0e-9) * SLEW_EXCESS_DURATION_DECAY;
+  excess_duration = duration - slew_duration;
+  if (slew_excess_duration < excess_duration &&
+      excess_duration <= MAX_SLEW_EXCESS_DURATION)
+    slew_excess_duration = excess_duration;
+
+  /* Calculate the duration of the new slew, considering the current correction
+     rate and previous delays in stopping of the slew */
  if (fabs(offset_register) < MIN_OFFSET_CORRECTION) {
-    duration = MAX_SLEW_TIMEOUT;
+    duration = MAX_SLEW_DURATION;
  } else {
    duration = correction_rate / fabs(offset_register);
-    if (duration < MIN_SLEW_TIMEOUT)
-      duration = MIN_SLEW_TIMEOUT;
+    if (duration < MIN_SLEW_DURATION)
+      duration = MIN_SLEW_DURATION;
+    if (duration < MIN_SLEW_DURATION_EXCESS_RATIO * slew_excess_duration)
+      duration = MIN_SLEW_DURATION_EXCESS_RATIO * slew_excess_duration;
  }

  /* Get frequency offset needed to slew the offset in the duration
@@ -232,23 +254,25 @@ update_slew(void)
     maximum timeout and try again on the next update. */
  if (fabs(offset_register) < MIN_OFFSET_CORRECTION ||
      offset_register * slew_freq <= 0.0) {
-    duration = MAX_SLEW_TIMEOUT;
+    duration = MAX_SLEW_DURATION;
  } else {
    duration = offset_register / slew_freq;
-    if (duration < MIN_SLEW_TIMEOUT)
-      duration = MIN_SLEW_TIMEOUT;
-    else if (duration > MAX_SLEW_TIMEOUT)
-      duration = MAX_SLEW_TIMEOUT;
+    if (duration < MIN_SLEW_DURATION)
+      duration = MIN_SLEW_DURATION;
+    else if (duration > MAX_SLEW_DURATION)
+      duration = MAX_SLEW_DURATION;
  }

  /* Restart timer for the next update */
  UTI_AddDoubleToTimespec(&now, duration, &end_of_slew);
  slew_timeout_id = SCH_AddTimeout(&end_of_slew, handle_end_of_slew, NULL);
  slew_start = now;
+  slew_duration = duration;

-  DEBUG_LOG("slew offset=%e corr_rate=%e base_freq=%f total_freq=%f slew_freq=%e duration=%f slew_error=%e",
-      offset_register, correction_rate, base_freq, total_freq, slew_freq,
-      duration, slew_error);
+  DEBUG_LOG("slew offset=%e corr_rate=%e base_freq=%f total_freq=%f slew_freq=%e"
+            " duration=%f excess=%f slew_error=%e",
+            offset_register, correction_rate, base_freq, total_freq, slew_freq,
+            slew_duration, slew_excess_duration, slew_error);
 }

 /* ================================================== */
@@ -385,6 +409,7 @@ SYS_Generic_CompleteFreqDriver(double max_set_freq_ppm, double max_set_freq_dela
  base_freq = (*drv_read_freq)();
  slew_freq = 0.0;
  offset_register = 0.0;
+  slew_excess_duration = 0.0;

  max_corr_freq = CNF_GetMaxSlewRate() / 1.0e6;

--- a/sys_linux.c
+++ b/sys_linux.c
@@ -35,6 +35,7 @@

 #if defined(FEAT_PHC) || defined(HAVE_LINUX_TIMESTAMPING)
 #include <linux/ptp_clock.h>
+#include <poll.h>
 #endif

 #ifdef FEAT_SCFILTER
@@ -497,6 +498,12 @@ SYS_Linux_EnableSystemCallFilter(int level, SYS_ProcessContext context)
    SCMP_SYS(getrlimit),
    SCMP_SYS(getuid),
    SCMP_SYS(getuid32),
+#ifdef __NR_membarrier
+    SCMP_SYS(membarrier),
+#endif
+#ifdef __NR_rseq
+    SCMP_SYS(rseq),
+#endif
    SCMP_SYS(rt_sigaction),
    SCMP_SYS(rt_sigreturn),
    SCMP_SYS(rt_sigprocmask),
@@ -596,6 +603,7 @@ SYS_Linux_EnableSystemCallFilter(int level, SYS_ProcessContext context)
    SCMP_SYS(select),
    SCMP_SYS(set_robust_list),
    SCMP_SYS(write),
+    SCMP_SYS(writev),

    /* Miscellaneous */
    SCMP_SYS(getrandom),
@@ -630,6 +638,9 @@ SYS_Linux_EnableSystemCallFilter(int level, SYS_ProcessContext context)
    { SOL_IP, IP_PKTINFO }, { SOL_IP, IP_FREEBIND }, { SOL_IP, IP_TOS },
 #ifdef FEAT_IPV6
    { SOL_IPV6, IPV6_V6ONLY }, { SOL_IPV6, IPV6_RECVPKTINFO },
+#ifdef IPV6_TCLASS
+    { SOL_IPV6, IPV6_TCLASS },
+#endif
 #endif
 #ifdef SO_BINDTODEVICE
    { SOL_SOCKET, SO_BINDTODEVICE },
@@ -647,7 +658,7 @@ SYS_Linux_EnableSystemCallFilter(int level, SYS_ProcessContext context)
  const static int fcntls[] = { F_GETFD, F_SETFD, F_GETFL, F_SETFL };

  const static unsigned long ioctls[] = {
-    FIONREAD, TCGETS,
+    FIONREAD, TCGETS, TIOCGWINSZ,
 #if defined(FEAT_PHC) || defined(HAVE_LINUX_TIMESTAMPING)
    PTP_EXTTS_REQUEST, PTP_SYS_OFFSET,
 #ifdef PTP_PIN_SETFUNC
@@ -791,73 +802,25 @@ SYS_Linux_CheckKernelVersion(int req_major, int req_minor)

 #if defined(FEAT_PHC) || defined(HAVE_LINUX_TIMESTAMPING)

-#define PHC_READINGS 10
-
 static int
-process_phc_readings(struct timespec ts[][3], int n, double precision,
-                     struct timespec *phc_ts, struct timespec *sys_ts, double *err)
+get_phc_readings(int phc_fd, int max_samples, struct timespec ts[][3])
 {
-  double min_delay = 0.0, delays[PTP_MAX_SAMPLES], phc_sum, sys_sum, sys_prec;
-  int i, combined;
-
-  if (n > PTP_MAX_SAMPLES)
-    return 0;
-
-  for (i = 0; i < n; i++) {
-    delays[i] = UTI_DiffTimespecsToDouble(&ts[i][2], &ts[i][0]);
-
-    if (delays[i] < 0.0) {
-      /* Step in the middle of a PHC reading? */
-      DEBUG_LOG("Bad PTP_SYS_OFFSET sample delay=%e", delays[i]);
-      return 0;
-    }
-
-    if (!i || delays[i] < min_delay)
-      min_delay = delays[i];
-  }
-
-  sys_prec = LCL_GetSysPrecisionAsQuantum();
-
-  /* Combine best readings */
-  for (i = combined = 0, phc_sum = sys_sum = 0.0; i < n; i++) {
-    if (delays[i] > min_delay + MAX(sys_prec, precision))
-      continue;
-
-    phc_sum += UTI_DiffTimespecsToDouble(&ts[i][1], &ts[0][1]);
-    sys_sum += UTI_DiffTimespecsToDouble(&ts[i][0], &ts[0][0]) + delays[i] / 2.0;
-    combined++;
-  }
-
-  assert(combined);
-
-  UTI_AddDoubleToTimespec(&ts[0][1], phc_sum / combined, phc_ts);
-  UTI_AddDoubleToTimespec(&ts[0][0], sys_sum / combined, sys_ts);
-  *err = MAX(min_delay / 2.0, precision);
-
-  return 1;
-}
-
-/* ================================================== */
-
-static int
-get_phc_sample(int phc_fd, double precision, struct timespec *phc_ts,
-               struct timespec *sys_ts, double *err)
-{
-  struct timespec ts[PHC_READINGS][3];
  struct ptp_sys_offset sys_off;
  int i;

+  max_samples = CLAMP(0, max_samples, PTP_MAX_SAMPLES);
+
  /* Silence valgrind */
  memset(&sys_off, 0, sizeof (sys_off));

-  sys_off.n_samples = PHC_READINGS;
+  sys_off.n_samples = max_samples;

  if (ioctl(phc_fd, PTP_SYS_OFFSET, &sys_off)) {
    DEBUG_LOG("ioctl(%s) failed : %s", "PTP_SYS_OFFSET", strerror(errno));
    return 0;
  }

-  for (i = 0; i < PHC_READINGS; i++) {
+  for (i = 0; i < max_samples; i++) {
    ts[i][0].tv_sec = sys_off.ts[i * 2].sec;
    ts[i][0].tv_nsec = sys_off.ts[i * 2].nsec;
    ts[i][1].tv_sec = sys_off.ts[i * 2 + 1].sec;
@@ -866,31 +829,31 @@ get_phc_sample(int phc_fd, double precision, struct timespec *phc_ts,
    ts[i][2].tv_nsec = sys_off.ts[i * 2 + 2].nsec;
  }

-  return process_phc_readings(ts, PHC_READINGS, precision, phc_ts, sys_ts, err);
+  return max_samples;
 }

 /* ================================================== */

 static int
-get_extended_phc_sample(int phc_fd, double precision, struct timespec *phc_ts,
-                        struct timespec *sys_ts, double *err)
+get_extended_phc_readings(int phc_fd, int max_samples, struct timespec ts[][3])
 {
 #ifdef PTP_SYS_OFFSET_EXTENDED
-  struct timespec ts[PHC_READINGS][3];
  struct ptp_sys_offset_extended sys_off;
  int i;

+  max_samples = CLAMP(0, max_samples, PTP_MAX_SAMPLES);
+
  /* Silence valgrind */
  memset(&sys_off, 0, sizeof (sys_off));

-  sys_off.n_samples = PHC_READINGS;
+  sys_off.n_samples = max_samples;

  if (ioctl(phc_fd, PTP_SYS_OFFSET_EXTENDED, &sys_off)) {
    DEBUG_LOG("ioctl(%s) failed : %s", "PTP_SYS_OFFSET_EXTENDED", strerror(errno));
    return 0;
  }

-  for (i = 0; i < PHC_READINGS; i++) {
+  for (i = 0; i < max_samples; i++) {
    ts[i][0].tv_sec = sys_off.ts[i][0].sec;
    ts[i][0].tv_nsec = sys_off.ts[i][0].nsec;
    ts[i][1].tv_sec = sys_off.ts[i][1].sec;
@@ -899,7 +862,7 @@ get_extended_phc_sample(int phc_fd, double precision, struct timespec *phc_ts,
    ts[i][2].tv_nsec = sys_off.ts[i][2].nsec;
  }

-  return process_phc_readings(ts, PHC_READINGS, precision, phc_ts, sys_ts, err);
+  return max_samples;
 #else
  return 0;
 #endif
@@ -908,12 +871,14 @@ get_extended_phc_sample(int phc_fd, double precision, struct timespec *phc_ts,
 /* ================================================== */

 static int
-get_precise_phc_sample(int phc_fd, double precision, struct timespec *phc_ts,
-		       struct timespec *sys_ts, double *err)
+get_precise_phc_readings(int phc_fd, int max_samples, struct timespec ts[][3])
 {
 #ifdef PTP_SYS_OFFSET_PRECISE
  struct ptp_sys_offset_precise sys_off;

+  if (max_samples < 1)
+    return 0;
+
  /* Silence valgrind */
  memset(&sys_off, 0, sizeof (sys_off));

@@ -923,11 +888,11 @@ get_precise_phc_sample(int phc_fd, double precision, struct timespec *phc_ts,
    return 0;
  }

-  phc_ts->tv_sec = sys_off.device.sec;
-  phc_ts->tv_nsec = sys_off.device.nsec;
-  sys_ts->tv_sec = sys_off.sys_realtime.sec;
-  sys_ts->tv_nsec = sys_off.sys_realtime.nsec;
-  *err = MAX(LCL_GetSysPrecisionAsQuantum(), precision);
+  ts[0][0].tv_sec = sys_off.sys_realtime.sec;
+  ts[0][0].tv_nsec = sys_off.sys_realtime.nsec;
+  ts[0][1].tv_sec = sys_off.device.sec;
+  ts[0][1].tv_nsec = sys_off.device.nsec;
+  ts[0][2] = ts[0][0];

  return 1;
 #else
@@ -971,23 +936,23 @@ SYS_Linux_OpenPHC(const char *path, int phc_index)
 /* ================================================== */

 int
-SYS_Linux_GetPHCSample(int fd, int nocrossts, double precision, int *reading_mode,
-                       struct timespec *phc_ts, struct timespec *sys_ts, double *err)
+SYS_Linux_GetPHCReadings(int fd, int nocrossts, int *reading_mode, int max_readings,
+                         struct timespec tss[][3])
 {
-  if ((*reading_mode == 2 || !*reading_mode) && !nocrossts &&
-      get_precise_phc_sample(fd, precision, phc_ts, sys_ts, err)) {
+  int r = 0;
+
+  if ((*reading_mode == 2 || *reading_mode == 0) && !nocrossts &&
+      (r = get_precise_phc_readings(fd, max_readings, tss)) > 0) {
    *reading_mode = 2;
-    return 1;
-  } else if ((*reading_mode == 3 || !*reading_mode) &&
-      get_extended_phc_sample(fd, precision, phc_ts, sys_ts, err)) {
+  } else if ((*reading_mode == 3 || *reading_mode == 0) &&
+             (r = get_extended_phc_readings(fd, max_readings, tss)) > 0) {
    *reading_mode = 3;
-    return 1;
-  } else if ((*reading_mode == 1 || !*reading_mode) &&
-      get_phc_sample(fd, precision, phc_ts, sys_ts, err)) {
+  } else if ((*reading_mode == 1 || *reading_mode == 0) &&
+             (r = get_phc_readings(fd, max_readings, tss)) > 0) {
    *reading_mode = 1;
-    return 1;
  }
-  return 0;
+
+  return r;
 }

 /* ================================================== */
@@ -1005,7 +970,7 @@ SYS_Linux_SetPHCExtTimestamping(int fd, int pin, int channel,
  pin_desc.func = enable ? PTP_PF_EXTTS : PTP_PF_NONE;
  pin_desc.chan = channel;

-  if (ioctl(fd, PTP_PIN_SETFUNC, &pin_desc)) {
+  if (pin >= 0 && ioctl(fd, PTP_PIN_SETFUNC, &pin_desc)) {
    DEBUG_LOG("ioctl(%s) failed : %s", "PTP_PIN_SETFUNC", strerror(errno));
    return 0;
  }
@@ -1034,6 +999,16 @@ int
 SYS_Linux_ReadPHCExtTimestamp(int fd, struct timespec *phc_ts, int *channel)
 {
  struct ptp_extts_event extts_event;
+  struct pollfd pfd;
+
+  /* Make sure the read will not block in case we have multiple
+     descriptors of the same PHC (O_NONBLOCK does not work) */
+  pfd.fd = fd;
+  pfd.events = POLLIN;
+  if (poll(&pfd, 1, 0) != 1 || pfd.revents != POLLIN) {
+    DEBUG_LOG("Missing PHC extts event");
+    return 0;
+  }

  if (read(fd, &extts_event, sizeof (extts_event)) != sizeof (extts_event)) {
    DEBUG_LOG("Could not read PHC extts event");
--- a/sys_linux.h
+++ b/sys_linux.h
@@ -41,8 +41,8 @@ extern int SYS_Linux_CheckKernelVersion(int req_major, int req_minor);

 extern int SYS_Linux_OpenPHC(const char *path, int phc_index);

-extern int SYS_Linux_GetPHCSample(int fd, int nocrossts, double precision, int *reading_mode,
-                                  struct timespec *phc_ts, struct timespec *sys_ts, double *err);
+extern int SYS_Linux_GetPHCReadings(int fd, int nocrossts, int *reading_mode, int max_readings,
+                                    struct timespec tss[][3]);

 extern int SYS_Linux_SetPHCExtTimestamping(int fd, int pin, int channel,
                                           int rising, int falling, int enable);
--- a/test/compilation/002-scanbuild
+++ b/test/compilation/002-scanbuild
@@ -7,9 +7,9 @@ for opts in \
 	"--host-system=NetBSD" \
 	"--host-system=FreeBSD" \
 	"--without-nettle" \
-	"--without-nettle --without-nss" \
-	"--without-nettle --without-nss --without-tomcrypt" \
-	"--without-nettle --without-nss --without-tomcrypt --without-gnutls"
+	"--without-nettle --without-gnutls" \
+	"--without-nettle --without-gnutls --without-nss" \
+	"--without-nettle --without-gnutls --without-nss --without-tomcrypt"
 do
 	./configure $opts
 	scan-build make "$@" || exit 1
--- a/test/compilation/003-sanitizers
+++ b/test/compilation/003-sanitizers
@@ -2,6 +2,8 @@
 # Run the unit and simulation tests with different compiler sanitizers
 # and under valgrind

+valgrind_opts="--leak-check=full --errors-for-leak-kinds=definite"
+
 cd ../..

 if [ "$(uname -sm)" != "Linux x86_64" ]; then
@@ -23,12 +25,13 @@ touch Makefile
 for extra_config_opts in \
  "--all-privops" \
  "--disable-ipv6" \
+  "--disable-nts" \
  "--disable-scfilter" \
-  "--without-gnutls" \
+  "--without-aes-gcm-siv" \
  "--without-nettle" \
-  "--without-nettle --without-nss" \
-  "--without-nettle --without-nss --without-tomcrypt" \
-  "--without-nettle --without-nss --without-tomcrypt --without-gnutls"; \
+  "--without-nettle --without-gnutls" \
+  "--without-nettle --without-gnutls --without-nss" \
+  "--without-nettle --without-gnutls --without-nss --without-tomcrypt"; \
 do
  for arch_opts in "-m32" ""; do
    pushd test/simulation/clknetsim || exit 1
@@ -42,7 +45,7 @@ do
      export CC

      for san_options in "" "-fsanitize=address" "-fsanitize=memory"; do
-        export CFLAGS="-O2 -g -fsanitize=undefined -fsanitize=float-divide-by-zero -fno-sanitize-recover=undefined,float-divide-by-zero $san_options $arch_opts"
+        export CFLAGS="-O2 -g -fsanitize=undefined -fsanitize=float-divide-by-zero -fsanitize=float-cast-overflow -fno-sanitize-recover=all $san_options $arch_opts"

        # clang msan doesn't work on i686 and otherwise requires patches
        echo $CFLAGS | grep -q 'sanitize=memory' && continue
@@ -75,7 +78,7 @@ do
        pushd test/unit || exit 1
        make "$@" || exit 1
        if [ "$san_options" = "" ]; then
-          make check TEST_WRAPPER="valgrind --error-exitcode=1" || exit 1
+          make check TEST_WRAPPER="valgrind $valgrind_opts --error-exitcode=1" || exit 1
        else
          make check || exit 1
        fi
@@ -87,7 +90,7 @@ do
        pushd test/simulation || exit 1
        export CLKNETSIM_RANDOM_SEED=101
        if [ "$arch_opts" = "" -a "$san_options" = "" ]; then
-          CLKNETSIM_CLIENT_WRAPPER=valgrind ./run -i 1 || exit 1
+          CLKNETSIM_CLIENT_WRAPPER="valgrind $valgrind_opts" ./run -i 1 || exit 1
        elif [ "$CC" = "gcc" ] && ! echo $CFLAGS | grep -q "-static-libasan"; then
          libasan=$(ldd ../../chronyd | grep -o '/.*lib.*/libasan.so.[0-9]')
          CLKNETSIM_PRELOAD=$libasan ./run -i 1 || exit 1
--- a/test/simulation/008-ntpera
+++ b/test/simulation/008-ntpera
@@ -29,7 +29,7 @@ echo "$ntp_start" | grep -q '-' && test_skip

 for time_offset in -1e-1 1e-1; do
 	for start_offset in 0 "2^32 - $limit"; do
-		export CLKNETSIM_START_DATE=$(awk "BEGIN {print $ntp_start + $start_offset}")
+		export CLKNETSIM_START_DATE=$(awk "BEGIN {printf \"%.0f\", $ntp_start + $start_offset}")
 		run_test || test_fail
 		check_chronyd_exit || test_fail
 		check_source_selection || test_fail
@@ -38,7 +38,7 @@ for time_offset in -1e-1 1e-1; do
 	done

 	for start_offset in -$limit "2^32"; do
-		export CLKNETSIM_START_DATE=$(awk "BEGIN {print $ntp_start + $start_offset}")
+		export CLKNETSIM_START_DATE=$(awk "BEGIN {printf \"%.0f\", $ntp_start + $start_offset}")
 		run_test || test_fail
 		check_chronyd_exit || test_fail
 		check_source_selection || test_fail
--- a/test/simulation/101-poll
+++ b/test/simulation/101-poll
@@ -27,4 +27,30 @@ for poll in $(seq 1 14); do
 	check_sync || test_fail
 done

+min_sync_time=$default_min_sync_time
+max_sync_time=$default_max_sync_time
+client_max_min_out_interval=$default_client_max_min_out_interval
+client_min_mean_out_interval=$default_client_min_mean_out_interval
+
+limit=10
+
+for poll in $(seq -7 2 -1); do
+	client_server_options="minpoll $poll maxpoll $poll"
+
+	base_delay=1e-4
+
+	run_test || test_fail
+	check_chronyd_exit || test_fail
+	check_source_selection || test_fail
+	check_file_messages "	2	1	" \
+		$[2**-poll * limit * 9 / 10] $[2**-poll * limit] log.packets || test_fail
+
+	base_delay=2e-2
+
+	run_test || test_fail
+	check_chronyd_exit || test_fail
+	check_source_selection || test_fail
+	check_file_messages "	2	1	" $[limit * 9 / 10] $limit log.packets || test_fail
+done
+
 test_pass
--- a/test/simulation/106-refclock
+++ b/test/simulation/106-refclock
@@ -1,12 +1,15 @@
 #!/usr/bin/env bash

 . ./test.common
-test_start "SHM refclock"
+test_start "reference clocks"

 check_config_h 'FEAT_REFCLOCK 1' || test_skip
 check_config_h 'FEAT_PHC 1' || test_skip
 check_config_h 'FEAT_CMDMON 1' || test_skip

+export CLKNETSIM_PHC_DELAY=1e-6
+export CLKNETSIM_PHC_JITTER=1e-7
+
 servers=0
 limit=1000
 refclock_jitter=$jitter
@@ -15,7 +18,7 @@ max_sync_time=70
 chronyc_start=70
 chronyc_conf="tracking"

-for refclock in "SHM 0" "PHC /dev/ptp0"; do
+for refclock in "SHM 0" "PHC /dev/ptp0" "PHC /dev/ptp0:nocrossts"; do
 	client_conf="refclock $refclock stratum 3 delay 1e-3 refid GPS
 logdir tmp
 log refclocks"
@@ -32,7 +35,11 @@ Root delay      : 0.001000000 seconds
 Update interval : 16\.. seconds
 .*$" || test_fail

-	check_file_messages "20.* GPS.*[0-9] N " 997 1001 refclocks.log || test_fail
+	if echo "$refclock" | grep -q 'PHC.*nocrossts'; then
+		check_file_messages "20.* GPS.*[0-9] N " 650 750 refclocks.log || test_fail
+	else
+		check_file_messages "20.* GPS.*[0-9] N " 997 1001 refclocks.log || test_fail
+	fi
 	check_file_messages "20.* GPS.*- N " 61 63 refclocks.log || test_fail
 	rm -f tmp/refclocks.log
 done
@@ -106,4 +113,31 @@ Root delay      : 0\.000000001 seconds
 	rm -f tmp/refclocks.log
 fi

+refclock_offset="(+ 0.399 (sum 1e-3))"
+refclock_jitter=1e-6
+servers=1
+freq_offset="(* 1e-4 (sine 1000))"
+base_delay="(* -1.0 (equal 0.1 (min time 5000) 5000))"
+client_server_options="minpoll 4 maxpoll 4 filter 5 minsamples 64"
+client_conf="
+refclock PHC /dev/ptp0 local poll 2
+logdir tmp
+log refclocks tracking"
+chronyc_conf=""
+limit=10000
+max_sync_time=5000
+time_max_limit=1e-3
+time_rms_limit=5e-4
+freq_max_limit=2e-5
+freq_rms_limit=5e-6
+
+run_test || test_fail
+check_chronyd_exit || test_fail
+check_sync || test_fail
+
+check_file_messages "20.* PHC0 .* [0-9] ? " 9999 10001 refclocks.log || test_fail
+check_file_messages "20.* PHC0 .* - ? " 2499 2501 refclocks.log || test_fail
+check_file_messages "20.* PHC0 " 0 0 tracking.log || test_fail
+rm -f tmp/refclocks.log tmp/tracking.log
+
 test_pass
--- a/test/simulation/110-chronyc
+++ b/test/simulation/110-chronyc
@@ -91,6 +91,18 @@ check_chronyd_exit || test_fail
 check_chronyc_output "^C0A87B01,192\.168\.123\.1,2,12623049..\..........,-?0\.0000.....,-?0\.000......,0\.000......,(99|100)\....,-?[0-9]\....,[0-9]\....,0\.000......,0\.000......,[0-9]+\..,Normal$" \
 	|| test_fail

+chronyc_options="-c -e"
+chronyc_conf="sources"
+
+run_test || test_fail
+check_chronyd_exit || test_fail
+
+check_chronyc_output "^#,.,SHM0.*
+\^,.,192\.168\.123\.1.*
+\^,.,192\.168\.123\.2.*
+\.$" \
+	|| test_fail
+
 chronyc_options=""
 server_strata=0
 chronyc_start=0.5
@@ -102,7 +114,7 @@ limit=1
 for chronyc_conf in \
 	"accheck 1.2.3.4" \
 	"add peer 10.0.0.0 minpoll 2 maxpoll 6" \
-	"add server 10.0.0.0 minpoll 6 maxpoll 10 iburst burst key 1 certset 2 maxdelay 1e-3 maxdelayratio 10.0 maxdelaydevratio 10.0 mindelay 1e-4 asymmetry 0.5 offset 1e-5 minsamples 6 maxsamples 6 filter 3 offline auto_offline prefer noselect trust require xleave polltarget 20 port 123 presend 7 minstratum 3 version 4 nts ntsport 4460 copy extfield F323" \
+	"add server 10.0.0.0 minpoll 6 maxpoll 10 iburst burst key 1 certset 2 maxdelay 1e-3 maxdelayratio 10.0 maxdelaydevratio 10.0 maxdelayquant 0.5 mindelay 1e-4 asymmetry 0.5 offset 1e-5 minsamples 6 maxsamples 6 filter 3 offline auto_offline prefer noselect trust require xleave polltarget 20 port 123 presend 7 minstratum 3 version 4 nts ntsport 4460 copy extfield F323 extfield F324" \
 	"add server node1.net1.clk" \
 	"allow 1.2.3.4" \
 	"allow 1.2" \
@@ -164,6 +176,9 @@ for chronyc_conf in \
 	"reselectdist 1e-3" \
 	"reset sources" \
 	"selectdata" \
+	"selectopts 1.2.3.4 -noselect +trust +require +prefer" \
+	"selectopts ID#0000000001 +prefer" \
+	"selectopts PPS0 +prefer" \
 	"settime 16:30" \
 	"settime 16:30:05" \
 	"settime Nov 21, 2015 16:30:05" \
@@ -231,6 +246,7 @@ RX timestamping : Kernel
 Total TX        : 1
 Total RX        : 1
 Total valid RX  : 1
+Total good RX   : 0
 S Name/IP Address        Auth COpts EOpts Last Score     Interval  Leap
 =======================================================================
 M node1\.net1\.clk            N ----- -----    0   1\.0    \+0ns    \+0ns  N
@@ -244,7 +260,13 @@ NTS-KE connections dropped : 0
 Authenticated NTP packets  : 0
 Interleaved NTP packets    : 0
 NTP timestamps held        : 0
-NTP timestamp span         : 0$" || test_fail
+NTP timestamp span         : 0
+NTP daemon RX timestamps   : 0
+NTP daemon TX timestamps   : 1
+NTP kernel RX timestamps   : 1
+NTP kernel TX timestamps   : 0
+NTP hardware RX timestamps : 0
+NTP hardware TX timestamps : 0$" || test_fail

 chronyc_conf="
 deny all
@@ -326,6 +348,10 @@ maxupdateskew 192.168.123.1 10.0
 minpoll 192.168.123.1 3
 minstratum 192.168.123.1 1
 polltarget 192.168.123.1 10
+selectopts 192.168.123.1 +trust +prefer -require
+selectdata
+selectopts 192.168.123.1 +noselect -prefer -trust +require
+selectdata
 delete 192.168.123.1"

 run_test || test_fail
@@ -344,6 +370,14 @@ check_chronyc_output "^200 OK
 200 OK
 200 OK
 200 OK
+200 OK
+S Name/IP Address        Auth COpts EOpts Last Score     Interval  Leap
+=======================================================================
+M node1\.net1\.clk            N \-PT\-\- \-PT\-\-    0   1\.0    \+0ns    \+0ns  \?
+200 OK
+S Name/IP Address        Auth COpts EOpts Last Score     Interval  Leap
+=======================================================================
+M node1\.net1\.clk            N N\-\-R\- N\-\-R\-    0   1\.0    \+0ns    \+0ns  \?
 200 OK$" || test_fail

 chronyc_conf="
--- a/test/simulation/114-presend
+++ b/test/simulation/114-presend
@@ -3,6 +3,7 @@
 . ./test.common
 test_start "presend option"

+limit=9900
 min_sync_time=136
 max_sync_time=260
 client_server_options="presend 6 maxdelay 16"
@@ -22,4 +23,29 @@ check_source_selection || test_fail
 check_packet_interval || test_fail
 check_sync || test_fail

+limit=10
+base_delay=$default_base_delay
+client_conf="logdir tmp
+log measurements"
+
+client_server_options="presend 5"
+
+run_test || test_fail
+check_chronyd_exit || test_fail
+check_packet_interval || test_fail
+
+check_file_messages "20.*123\.1.* 111 111 0111" 1 1 measurements.log || test_fail
+check_file_messages "20.*123\.1.* 111 111 1111" 1 1 measurements.log || test_fail
+rm -f tmp/measurements.log
+
+client_server_options="presend 5 xleave"
+
+run_test || test_fail
+check_chronyd_exit || test_fail
+check_packet_interval || test_fail
+
+check_file_messages "20.*123\.1.* 111 111 0111" 2 2 measurements.log || test_fail
+check_file_messages "20.*123\.1.* 111 111 1111" 1 1 measurements.log || test_fail
+rm -f tmp/measurements.log
+
 test_pass
--- a/test/simulation/118-maxdelay
+++ b/test/simulation/118-maxdelay
@@ -25,4 +25,18 @@ for client_server_options in "maxpoll 6 maxdelay 2e-5"; do
 	check_sync && test_fail
 done

+min_sync_time=10
+client_conf="
+logdir tmp
+log rawmeasurements"
+client_server_options="minpoll 2 maxpoll 2 maxdelayquant 0.1"
+
+run_test || test_fail
+check_chronyd_exit || test_fail
+check_packet_interval || test_fail
+check_sync || test_fail
+
+check_file_messages "20.*123\.1.* 111 111 1111" 200 500 measurements.log || test_fail
+check_file_messages "20.*123\.1.* 111 111 1101" 2000 2300 measurements.log || test_fail
+
 test_pass
--- a/test/simulation/122-xleave
+++ b/test/simulation/122-xleave
@@ -15,10 +15,11 @@ check_chronyd_exit || test_fail
 check_source_selection || test_fail
 check_sync || test_fail

-check_file_messages "111 111 1111.* 4I [DKH] [DKH]\$" 0 0 measurements.log || test_fail
+check_file_messages "111 111 .111.* 4I [DKH] [DKH]\$" 0 0 measurements.log || test_fail
 rm -f tmp/measurements.log

 server_conf=""
+max_sync_time=270

 run_test || test_fail
 check_chronyd_exit || test_fail
@@ -28,6 +29,7 @@ check_sync || test_fail

 check_file_messages "111 111 1111.* 4B [DKH] [DKH]\$" 2 2 measurements.log || test_fail
 check_file_messages "111 111 1111.* 4I [DKH] [DKH]\$" 30 200 measurements.log || test_fail
+check_file_messages "111 111 0111.* 4I [DKH] [DKH]\$" 1 1 measurements.log || test_fail
 rm -f tmp/measurements.log

 clients=2
--- a/test/simulation/127-filter
+++ b/test/simulation/127-filter
@@ -4,7 +4,7 @@

 test_start "filter option"

-client_server_options="minpoll 4 maxpoll 4 filter 15"
+client_server_options="minpoll 4 maxpoll 4 filter 15 maxdelay 3.5e-4"
 min_sync_time=710
 max_sync_time=720
 client_max_min_out_interval=16.1
@@ -16,4 +16,28 @@ check_source_selection || test_fail
 check_packet_interval || test_fail
 check_sync || test_fail

+base_delay="(+ 1e-4 (* -1 (equal 0.3 (uniform) 0.0)))"
+client_server_options="minpoll 4 maxpoll 4 filter 3"
+min_sync_time=130
+
+run_test || test_fail
+check_chronyd_exit || test_fail
+check_packet_interval || test_fail
+check_sync || test_fail
+
+limit=10
+client_server_options="minpoll -6 maxpoll -6 filter 1"
+
+base_delay=1e-4
+
+run_test || test_fail
+check_chronyd_exit || test_fail
+check_file_messages "	2	1	" 590 640 log.packets || test_fail
+
+base_delay=2e-2
+
+run_test || test_fail
+check_chronyd_exit || test_fail
+check_file_messages "	2	1	" 9 10 log.packets || test_fail
+
 test_pass
--- a/test/simulation/132-logchange
+++ b/test/simulation/132-logchange
@@ -16,6 +16,6 @@ check_chronyd_exit || test_fail
 check_source_selection || test_fail
 check_packet_interval || test_fail
 check_sync || test_fail
-check_log_messages "clock wrong by" 4 8 || test_fail
+check_log_messages "clock wrong by" 3 8 || test_fail

 test_pass
--- a/test/simulation/133-hwtimestamp
+++ b/test/simulation/133-hwtimestamp
@@ -7,32 +7,82 @@ test_start "hwtimestamp directive"
 check_config_h 'HAVE_LINUX_TIMESTAMPING 1' || test_skip

 export CLKNETSIM_TIMESTAMPING=2
+export CLKNETSIM_PHC_DELAY=1e-6
+export CLKNETSIM_PHC_JITTER=1e-7
+export CLKNETSIM_PHC_JITTER_ASYM=0.4

 refclock_jitter=1e-8
 refclock_offset=10.0
 min_sync_time=4
 max_sync_time=20
+time_rms_limit=1e-7
+freq_rms_limit=3e-8
+jitter=1e-8
+freq_offset=1e-5
 limit=200
-server_conf="hwtimestamp eth0"
-client_server_options="minpoll 0 maxpoll 0 minsamples 32 xleave"
+server_conf="
+clockprecision 1e-9
+hwtimestamp eth0"
+client_server_options="minpoll 0 maxpoll 0 xleave"
 client_chronyd_options="-d"

-for client_conf in "hwtimestamp eth0" "hwtimestamp eth0
-acquisitionport 123"; do
+for client_conf in \
+		"hwtimestamp eth0 nocrossts
+		clockprecision 1e-9" \
+		"hwtimestamp eth0
+		clockprecision 1e-9
+		acquisitionport 123"; do
 	run_test || test_fail
 	check_chronyd_exit || test_fail
 	check_source_selection || test_fail
 	check_sync || test_fail

 	if check_config_h 'FEAT_DEBUG 1'; then
+		check_log_messages "Accepted reading" 0 2 || test_fail
+		check_log_messages "Combined .* readings" 190 220 || test_fail
 		check_log_messages "HW clock samples" 190 200 || test_fail
 		check_log_messages "HW clock reset" 0 0 || test_fail
+		check_log_messages "Missing TX timestamp" 1 1 || test_fail
 		check_log_messages "Received message.*tss=KH" 195 200 || test_fail
 		check_log_messages "Received error.*message.*tss=KH" 195 200 || test_fail
 		check_log_messages "Updated RX timestamp.*tss=1" 1 1 || test_fail
 		check_log_messages "Updated RX timestamp.*tss=2" 195 200 || test_fail
-		check_log_messages "update_tx_timestamp.*Updated" 50 140 || test_fail
-		check_log_messages "update_tx_timestamp.*Unacceptable" 50 140 || test_fail
+		check_log_messages "Polling PHC" 195 220 || test_fail
+		if echo "$client_conf" | grep -q nocrossts; then
+			check_log_messages "update_tx_timestamp.*Updated" 180 200 || test_fail
+			check_log_messages "update_tx_timestamp.*Unacceptable" 0 13 || test_fail
+		else
+			check_log_messages "update_tx_timestamp.*Updated" 50 140 || test_fail
+			check_log_messages "update_tx_timestamp.*Unacceptable" 50 140 || test_fail
+		fi
+	fi
+done
+
+server_conf+="
+server 192.168.123.2 minpoll 1 maxpoll 1 noselect"
+
+for maxpoll in -1 0 1; do
+	client_conf="hwtimestamp eth0 minpoll -1 maxpoll $maxpoll nocrossts"
+	run_test || test_fail
+	check_chronyd_exit || test_fail
+	check_source_selection || test_fail
+	check_sync || test_fail
+
+	if check_config_h 'FEAT_DEBUG 1'; then
+		case $maxpoll in
+			-1)
+				check_log_messages "Polling PHC on eth0$" 360 380 || test_fail
+				check_log_messages "Polling PHC.*before" 3 25 || test_fail
+				;;
+			0)
+				check_log_messages "Polling PHC on eth0$" 8 45 || test_fail
+				check_log_messages "Polling PHC.*before" 150 190 || test_fail
+				;;
+			1)
+				check_log_messages "Polling PHC on eth0$" 1 1 || test_fail
+				check_log_messages "Polling PHC.*before" 194 199 || test_fail
+				;;
+		esac
 	fi
 done

--- a/Show More
+++ b/Show More