[systemd-devel] How to chain services driven by a timer?

[Brian Reichert]

On Wed, Apr 10, 2024 at 01:47:47PM -0600, Dan Nicholson wrote:
> Restarting the timer doesn't make the service run immediately. Are you
> sure logrotate.service has run again since you made this change? Just
> simulate the timer and start logrotate.service again. All the timer
> does is activate the service. For testing you don't need to wait for
> that to happen.

Ok, that is a helpful detail.

Restarting logrotate.service does now cause my post-logrotate.service
to subsequently start.

On a lark, I augmented the stock logrotate.service with some
instrumentation to show me when 'logrotate' completes, in addition to
maintaining a log file:

  #ExecStart=/usr/sbin/logrotate /etc/logrotate.conf
  ExecStart=/usr/sbin/logrotate -l /var/log/logrotate.log /etc/logrotate.conf
  ExecStartPost=/usr/bin/logger 'XXX log rotation completed'

My service is being run (yay!), but I'm wary of the out-of-order
messaging here:

  10-153-68-34:~ # journalctl -o short-precise --no-pager -u logrotate.service -u post-logrotate.service | tail -6
  Apr 10 16:57:54.061053 10-153-68-34 systemd[1]: Started Activities after logrotation.
  Apr 10 16:57:54.061140 10-153-68-34 systemd[1]: Stopped Rotate log files.
  Apr 10 16:57:54.062219 10-153-68-34 systemd[1]: Starting Rotate log files...
  Apr 10 16:57:54.104300 10-153-68-34 root[5899]: XXX post log rotation
  Apr 10 16:57:55.367522 10-153-68-34 root[5903]: XXX log rotation completed
  Apr 10 16:57:55.368789 10-153-68-34 systemd[1]: Started Rotate log files.

And systemctl shows the new post-logrotate.service started slightly
before logrotate.service ended:

  10-153-68-34:~ # systemctl show logrotate.service --property ExecMainExitTimestamp
  ExecMainExitTimestamp=Wed 2024-04-10 16:57:55 EDT
  10-153-68-34:~ # systemctl show post-logrotate.service --property ExecMainStartTimestamp
  ExecMainStartTimestamp=Wed 2024-04-10 16:57:54 EDT

(I really wish I had higher-resolution timestamps here.)

That log file's mtime:

  10-153-68-34:~ # ls -ldtr --full-time /var/log/logrotate.log
  -rw-r--r-- 1 root root 1607975 2024-04-10 16:57:55.094420531 -0400 /var/log/logrotate.log

Hopefully someone here can assure me this is just due to an artifact
of bookkeeping. I'm specifically trying to avoid doing any work
while logrotate is running.

That I got even this far is really great, so I appreciate all of the
guidance!

> --
> Dan

-- 
Brian Reichert				<reichert at numachi.com>
BSD admin/developer at large