socket: add support for systemd sockets

Before opening new IPv4/IPv6 server sockets, chronyd will check for
matching reusable sockets passed from the service manager (for example,
passed via systemd socket activation:
https://www.freedesktop.org/software/systemd/man/latest/sd_listen_fds.html)
and use those instead.

Aside from IPV6_V6ONLY (which cannot be set on already-bound sockets),
the daemon sets the same socket options on reusable sockets as it would
on sockets it opens itself.

Unit tests test the correct parsing of the LISTEN_FDS environment
variable.

Add 011-systemd system test to test socket activation for DGRAM and
STREAM sockets (both IPv4 and IPv6).  The tests use the
systemd-socket-activate test tool, which has some limitations requiring
workarounds discussed in inline comments.
This commit is contained in:
Luke Valenta
2023-10-26 12:48:56 -04:00
committed by Miroslav Lichvar
parent c063b9e78a
commit e6a0476eb7
7 changed files with 372 additions and 10 deletions

View File

@@ -206,6 +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_