bug#74912: Shepherd: Growing number of user shepherds when relogging

[Tomas Volf <~@wolfsden.cz>]

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Ludovic Courtès <ludo@gnu.org> writes:

> Hello,
>
> Jake <jforst.mailman@gmail.com> skribis:
>
>> I think I'm experiencing a bug in Shepherd since version 1.0.
>> Whenever I log out and log back in again, my user shepherd from the
>> previous login session is still present, and a new user shepherd spawns for
>> the current login session.
>> So relogging N times results in N+1 user shepherds.
>
> I have a user shepherd via Guix Home and I experience the same problem
> (though because I rarely log out it’s not really annoying :-)).
>
> I suspect the problem has to do with how Guix Home determines whether or
> not it should launch shepherd, but I haven’t checked yet.

When you have another login session active when you log out and in
again, new shepherd is *not* spawned.  I am guessing here but probably
last log out causes XDG_RUNTIME_DIR to be removed (by elogind in my
case), so on log in there is no /run/user/$UID/on-first-login-executed,
so it runs again and starts the shepherd.

But even if that would be solved, since the runtime directory was nuked,
there is no shepherd socket around anymore, so the (still running)
shepherd from previous login session cannot be contacted by herd.

Of the top of my head I can think of two possible solutions:

1. Stop the shepherd on log out.  So as we have on-first-login, we would
have on-last-logout.  I have no idea how to implement that.  Maybe we
could use ~/.bash_logout?  Or some PAM thing?

2. Shepherd could shutdown gracefully when the control socket is deleted
from the file system.  It is arguable how useful running shepherd is
without the socket anyway.

Any other ideas?

Tomas

-- 
There are only two hard things in Computer Science:
cache invalidation, naming things and off-by-one errors.

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