** Description changed: + [original message] + Hallo! I have recently - I am pretty sure it is since the 20.04 upgrade (coming from 18.04) - experienced the problem that (detached) tmux sessions don't show up anymore in the output of commands such as `who -u` or `users`. Since I have a cron job for shutting down hosts where no users are logged in, I am constantly kicking out people now who have running jobs in detached tmux sessions. We would be very happy if this could be fixed. Thanks! + + [Impact] + + This is a regression that gets tmux not to record logins through utmp for its + sessions (https://github.com/tmux/tmux/issues/2022). The bug was fixed upstream + in https://github.com/tmux/tmux/commit/54efe337993b5571728a09b247c7f39d493659a8 + by reintroducing the code that calls utempter to register the tmux session in + utmp. + + This SRU is especially important because it affects unattended-upgrades users. + unattended-upgrades uses /usr/bin/users to determine logged-in users, which + queries utmp for that purpose. If running tmux sessions are not registered, and + unattended-upgrades is configured not to reboot when there are users logged in, + then it will misbehave and forcefully kill the running (not recorded) tmux + session. + + The MP provided solves the issue by introducing the specific upstream fix into + Focal's tmux. + + [Test Plan] + + * Reproducing: + * Install tmux-3.0a-2ubuntu0.2 in Focal. + * Start a tmux session (by running tmux) and detach from the session ("ctrl+b", then press "d"). + * Run "who". You should verify that no entries for the running tmux session were recorded. + * Run "tmux attach" and exit the session. + * Verifying fix: + * Install tmux-3.0a-2ubuntu0.3 (from MP) in Focal. + * Start a tmux session (by running tmux) and detach from the session ("ctrl+b", then press "d"). + * Run "who". You should verify that there is an entry for the running tmux session recorded. + * Run "tmux attach" and exit the session. + + [Where problems could occur] + + This is a cherry-pick commit from upstream. 113 other code changes (that are + not present in this MP) were applied upstream before the patch being proposed + was introduced, meaning the code path may deviate from upstream's codepath + during execution leading to unexpected behaviour, which could result in tmux + terminating abruptly (e.g., segmetation fault) for possible not tested + scenarios when starting a tmux session. + + In special, there were a small change in an upstream struct (window_pane) is + being used in the code introduced by this patch (additional data was added). + However, the change does not seem to affect the cherry-picked change AFAICT.
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