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reference: get TAI-UTC offset from leap second timezone

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Use the timezone specified by the leapsectz directive to get the
current TAI-UTC offset and set the offset of the system clock in order
to provide correct TAI time to applications using ntp_adjtime(),
ntp_gettime(), or clock_gettime(CLOCK_TAI).
This commit is contained in:
Miroslav Lichvar
2017-06-29 17:56:16 +02:00
parent cde0a20307
commit 29b0ad894c
2 changed files with 52 additions and 22 deletions
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26
doc/chrony.conf.adoc
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@@ -830,15 +830,23 @@ clients to safely synchronise with multiple identically configured leap
smearing servers.
[[leapsectz]]*leapsectz* _timezone_::
This directive is used to set the name of the timezone in the system tz
database which *chronyd* can use to find out when will the next leap second
occur. It will periodically check if the times 23:59:59 and 23:59:60 are valid
on Jun 30 and Dec 31 in the timezone. This typically works with the *right/UTC*
timezone.
This directive specifies a timezone in the system tz database which *chronyd*
can use to determine when will the next leap second occur and what is the
current offset between TAI and UTC. It will periodically check if 23:59:59 and
23:59:60 are valid times in the timezone. This typically works with the
_right/UTC_ timezone.
+
This directive is mainly useful with reference clocks which do not provide
leap second information. It is not necessary to restart *chronyd* if the tz
database is updated with a new leap second at least 12 hours before the event.
When a leap second is announced, the timezone needs to be updated at least 12
hours before the leap second. It is not necessary to restart *chronyd*.
+
This directive is useful with reference clocks and other time sources which do
not announce leap seconds, or announce them too late for an NTP server to
forward them to its own clients. Clients of leap smearing servers must not
use this directive.
+
It is also useful when the system clock is required to have correct TAI-UTC
offset. Note that the offset is set only when leap seconds are handled by the
kernel, i.e. <<leapsecmode,*leapsecmode*>> is set to *system*.
+
An example of the directive is:
+
@@ -2325,7 +2333,7 @@ The amount of memory used for logging client accesses can be increased in order
to enable clients to use the interleaved mode even when the server has a large
number of clients, and better support rate limiting if it is enabled by the
<<ratelimit,*ratelimit*>> directive. The system timezone database, if it is
kept up to date and includes the *right/UTC* timezone, can be used as a
kept up to date and includes the _right/UTC_ timezone, can be used as a
reliable source to determine when a leap second will be applied to UTC. The
*-r* option with the <<dumpdir,*dumpdir*>> directive shortens the time in which
*chronyd* will not be able to serve time to its clients when it needs to be