[Bug 13463] Please consider using the IP_FREEBIND socket option

https://bugzilla.samba.org/show_bug.cgi?id=13463

--- Comment #3 from Andreas Hasenack <[email protected]> ---
Thanks for all the opinions. I have one remaining issue, and that is with
"systemctl start rsync.service" not detecting the failure right away.

The systemd unit file calls rsync like this:

[Service]
ExecStart=/usr/bin/rsync --daemon --no-detach

This is correct, specially the --no-detach option. systemd should be able to
tell immediately if the service started or not, but according to the
systemd.service manpage, it will signal success in any case for type=simple
services. It's not much better for type=exec.

If I run rsync with an invalid config, it exits non-zero right away:

root@j1-rsyncd:~# rsync --daemon --no-detach ; echo $?
10


But via systemctl, it exits 0:
root@j1-rsyncd:~# systemctl start rsync; echo $?
0

root@j1-rsyncd:~# systemctl status rsync
× rsync.service - fast remote file copy program daemon
     Loaded: loaded (/lib/systemd/system/rsync.service; disabled; vendor
preset: enabled)
     Active: failed (Result: exit-code) since Wed 2022-03-30 19:10:03 UTC; 3s
ago
       Docs: man:rsync(1)
             man:rsyncd.conf(5)
    Process: 4305 ExecStart=/usr/bin/rsync --daemon --no-detach (code=exited,
status=10)
   Main PID: 4305 (code=exited, status=10)
        CPU: 3ms

Mar 30 19:10:03 j1-rsyncd rsyncd[4305]: bind() failed: Cannot assign requested
address (address-family 2)
Mar 30 19:10:03 j1-rsyncd systemd[1]: Started fast remote file copy program
daemon.
Mar 30 19:10:03 j1-rsyncd rsyncd[4305]: unable to bind any inbound sockets on
port 873
Mar 30 19:10:03 j1-rsyncd systemd[1]: rsync.service: Main process exited,
code=exited, status=10/n/a
Mar 30 19:10:03 j1-rsyncd rsyncd[4305]: rsync error: error in socket IO (code
10) at socket.c(545) [Receiver=3.2.3]
Mar 30 19:10:03 j1-rsyncd systemd[1]: rsync.service: Failed with result
'exit-code'.


This seems to be the norm for this type of systemd service (type=simple,
type=exec), and looks like the most reliable way to have systemctl start detect
immediately if the service failed or not would be to implement systemd's
notify[1] mechanism in rsync.

Type=forking might be an alternative, but this timeout would have to be tuned:

root@j1-rsyncd:~# time systemctl start rsync
Job for rsync.service failed because a timeout was exceeded.
See "systemctl status rsync.service" and "journalctl -xeu rsync.service" for
details.

real    1m30.246s


With TimeoutStartSec=5 in the unit file:

root@j1-rsyncd:~# time systemctl start rsync
Job for rsync.service failed because a timeout was exceeded.
See "systemctl status rsync.service" and "journalctl -xeu rsync.service" for
details.

real    0m5.287s




1. https://www.freedesktop.org/software/systemd/man/sd_notify.html

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