v239.1: PID file not removed when elogind is terminated

[Yamakuzure]

I got an e-mail from Stefan about elogind not removing its PID file if it is shutdown using signal 15 (SIGTERM).

As /run is on tmpfs nowadays, this is of no real concern if elogind crashes on reboot or if the whole machine comes down. However, not all systems are like that and some have not put /run into RAM.

On these systems elogind fails to start on next reboot if a stale PID file exists.

There are two reasons for this:

1. The installation of the signal handlers is not correct. This is a follow-up on issue Failed to register SIGINT handler [elogind 239.1] #90, which is not properly fixed by now.
2. elogind does not check whether the PID in a found PID file actually points to an elogind instance, or is stale.

Stefan has already provided fixes for the 1st point, which I am currently testing.
The second point will be tackled thereafter.

[Yamakuzure]

The second task, making elogind to actually check the PID file if one is found, is on my TODO list.

[daym]

Checking the PID in the PID file doesn't sound safe - what if it's coincidentially the same as it was in the previous boot (f.e. a deterministic boot process could easily make that happen every time).

Better would be not to use a pid file but something else. Doesn't elogind provide a dbus service? How come it's not enough to try to register the dbus service and if that doesn't work (because it's already there), fail?

[Yamakuzure]

Well, elogind checks the presence of a PID file, before it would create its own.

• If the contained PID is its own, then everything is in order.
• If the contained PID is different and belongs to an elogind[-daemon] process, then elogind is already running.
• If the contained PID is different and belongs to something else. then it's a stale PID file that can be overwritten.

Unfortunately service managers like OpenRC need such a PID file to know where to send SIGTERM when shuting down the device.

[udeved]

@Yamakuzure

Would openrc do if elogind service was supervised?
Runit doesn't need it afaik, it uses the supervisor pid.

[Yamakuzure]

@udeved : Not that I know of. The start-stop-daemon() command needs a PID file.

Well, I just noticed, that from the three points above the first two were already implemented, and the third was easy. See: 59e70b3

[markhindley]

Sven,

I think the fix in 59e70b3 has an error. See `https://bugs.debian.org/916212.

The attached patch fixes it for me

Fix_stale_pidfile.patch.txt

Mark

[Yamakuzure]

@markhindley : Yes, you are right.