Although extremely unlikely, there is a race present in solely checking the
$LISTEN_PID environment variable, due to PID recycling. Fix that by introducing
$LISTEN_PIDFDID, which contains the 64-bit ID of a pidfd for the child process
that is not subject to recycling.
By default agetty will not display /run/issue.d/ if /etc/issue exists.
This is quite unfortunate and has actually been fixed upstream in:
https://github.com/util-linux/util-linux/commit/508fb0e7ac103b68531a59db2a4473897853ab52
However, no release has been tagged with this yet, and it doesn't look
like this will happen any time soon. Hence, for now, let's add a
work-around and manually override the issue files to include.
This should be reverted once a new util-linux/agetty release has been
tagged, and found its way into the relevant distributions. Given this is
mostly about cosmetics we do not have to precisely sync the package
updates on this, but only roughly.
When switching to another user it's oftentimes desirable to also spawn
the target user's shell. sudo supports this via -i flag, run0 currently
doesn't. We don't want to proactively query NSS ourselves, since
that would fall short when operating remotely. Let's instead teach
the service manager to spawn the command using the user's default shell.
I opted for "|" instead of "." in the end because the latter seems
a bit obscure. But happy to change it to something else if a better option
comes up.
Lennart Poettering
Dimitri John Ledkov
Yu Watanabe
Daniel Foster
Mike Yuan
Daan De Meyer
Michal Koutný
Luca Boccassi