Bug#989317: systemd kill background processes after user logs out (#825394 regression)

[Matt Corallo]

On 6/8/21 12:31, Michael Biebl wrote:
> Am 08.06.2021 um 18:08 schrieb Matt Corallo:
>> Hmmm, with set-linger and --scope I can't seem to reproduce now either, its possible I had forgotten the --scope at 
>> some point while testing set-linger before, sorry for the noise here.
>>
>> Still, based on my read of #825394, it seems like it should be the case that you do not need set-linger and the 
>> default behavior should be that things aren't automatically killed in the background? Is that something that was an 
>> intentional change?
> 
> Change to what exactly?
> 
> I guess we need to differentiate between login and user sessions.
> It's my understanding that KillUserProcesses= only affects a login session.

I admit I am definitely not a systemd expert (which I suppose should be obvious by now :) ), so have no idea what this 
means, and systemd-run's man page doesn't really elucidate it. Not Debian's or your problem, of course, though.

> If you start a process as part of a user session (which is what systemd-run --user does), ending that user session will 
> stop that process.

Is there an alternate way to run things that lxc should instead be recommending? In my interactions with the lxc folks 
it seems this workaround is only relevant for Debian bullseye, so maybe other distros are patching systemd or changing 
cgroup settings such that interacting with systemd isn't required.

Similar to the discussion in 825394, having daemons  spontaneously killed is incredibly surprising, maybe it makes sense 
to enable-linger by default?

 > Did you use systemd-run in buster to start your lxc containers?
 > You need to be very explicit, otherwise I can only guess what exactly you were/are doing.

No, but also didn't need to, its only with bullseye that (systemd's ?) cgroup settings prevent direct calls to 
lxc-start, which is what makes the whole thing such a mess - one cannot simply call lxc functions anymore because 
systemd gets in the way. Using systemd for this, sadly, is an excercize in puzzling through man pages and lack of 
documentation for how to do any of this (half of the lxc docs for how to do this are because I had to ask lxc 
maintainers how to do basic lxc things with bullseye).

Thanks,
Matt