Bug#1034015: exim4: exim paniclog on lenovo has non-zero size

[Peter Bex]

Dear maintainer,

I have the same issue on my server.  It seems to happen any time the
exim4 daemon gets restarted.  Logs indicate that the process is not shut
down correctly, leaving a stale daemon listening on the old port, which
causes the error on startup for the new daemon.  After an update just
now:

Oct 02 16:46:37 scully.more-magic.net systemd[1]: Stopping exim4.service - LSB: exim Mail Transport Agent...
Oct 02 16:46:37 scully.more-magic.net exim4[574161]: Stopping MTA:.
Oct 02 16:46:37 scully.more-magic.net systemd[1]: exim4.service: Deactivated successfully.
Oct 02 16:46:37 scully.more-magic.net systemd[1]: exim4.service: Unit process 701 (exim4) remains running after unit stopped.
Oct 02 16:46:37 scully.more-magic.net systemd[1]: Stopped exim4.service - LSB: exim Mail Transport Agent.
Oct 02 16:46:37 scully.more-magic.net systemd[1]: exim4.service: Consumed 2min 17.056s CPU time.
Oct 02 16:46:40 scully.more-magic.net systemd[1]: exim4.service: Found left-over process 701 (exim4) in control group while starting unit. Ignoring.
Oct 02 16:46:40 scully.more-magic.net systemd[1]: This usually indicates unclean termination of a previous run, or service implementation deficiencies.
Oct 02 16:46:40 scully.more-magic.net systemd[1]: Starting exim4.service - LSB: exim Mail Transport Agent...
Oct 02 16:46:40 scully.more-magic.net exim4[574712]: Starting MTA: exim4.
Oct 02 16:46:40 scully.more-magic.net systemd[1]: Started exim4.service - LSB: exim Mail Transport Agent.

In /var/log/exim4/paniclog:

2023-10-02 16:51:10 socket bind() to port 25 for address (any IPv6) failed: Address already in use: daemon abandoned

If I use systemctl to stop the daemon, it leaves an exim4 process
running.  Manually calling "pkill exim4" and then using systemctl to
start exim4 resolves the issue (until the next restart).

I thought it was ipv6-related, but if I see message #5 in this bug it
seems that this is not necessarily the case.  Perhaps it is caused by
having exim listen on multiple interfaces (ipv4 and ipv6), or maybe it's
a red herring?

Anyway, I hope this helps debug the problem further!

Regards,
Peter Bex
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