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.
Add a new set of tests for testing basic functionality, starting chronyd
with root privileges on the actual system instead of the simulator.
Tests numbered in the 100-199 range are considered destructive and
intended to be used only on machines dedicated for development or
testing. They are started by the run script only with the -d option.
They may adjust/step the system clock and other clocks, block the RTC,
enable HW timestamping, create SHM segments, etc.
Other tests should not interfere with the system and should work even
when another NTP server/client is running.
