use loginctl kill-session for logging out

[macedigital]

Commit changes logout command to gracefully terminate session using a signal only. This should prevent issues with greeters associated with a given user session becoming broken after logout.

New method successfully tested with SwayWM. More feedback for other window managers is welcome.

See #22.

[LRitzdorf]

Nice! This is much more elegant than a wrapper script with environment-specific commands.

Quick note: loginctl kill-session supports a --signal= flag to control precisely which signal is sent (i.e. instead of SIGKILL). Do we know if, say, SIGINT might be a better choice? This'll obviously be a factor of how various common DEs/WMs/compositors handle signals, but my feeling is that a "gentler" signal might be preferable.

[jluttine]

If [--signal is] omitted, [it] defaults to SIGTERM.

Source: https://www.freedesktop.org/software/systemd/man/latest/loginctl.html

I tried to read a bit but I couldn't quite understand what's the difference between using kill-session and terminate-session. For me, terminate-session has worked (I'm using SDDM + i3). Also, I couldn't find any information which one is the more "correct" way of logging out.

But if this solves an issue and doesn't cause any new issues, I suppose it's probably ok. In any case, thanks for the PR!

[macedigital]

Afaik, both commands send SIGTERM by default #36 (comment).

Best explanation of the difference I found is on ServerFault:

Similarly, loginctl terminate-session [...] will explicitly mark the .scope as "abandoned" before trying to stop it, [...].
https://serverfault.com/questions/1103060/what-is-the-functional-difference-between-loginctl-terminate-session-loginctl

My working hypothesis is that terminate-session command somehow pulls the rug under certain combinations of window manager, greeter, session management, etc. whereas kill-session (sending SIGTERM) gives the session the opportunity to handle termination and/or perform cleanup before exiting on its own terms.

Could also indicate a subtle bug in any of the underlying software components 🤷

But if this solves an issue and doesn't cause any new issues, I suppose it's probably ok.
#36 (comment)

Exactly, I would definitely wait for more feedback or "up votes" before merging.