2023-11-21 1/17 A journey to resolve the xdg-autostart-generator issue TAKEYAMA, Fuminobu 武山 文信

2023-11-21 2/17 The xdg-autostart-generator issue? ● In Jul., 2022, I received a report that IBus does not work under Tumbleweed – ibus-daemon did not start after login at all – No changes in IBus side – Only under KDE environment ● KDE Plasma just started to use xdg-autostart-generator for XDG Autostart ● Also affects other applications – fcitx, pkcs11-register, spice-vdagent, dropbox, ... https://bugzilla.opensuse.org/show_bug.cgi?id=1201421

2023-11-21 3/17 XDG Autostart ● A mechanism to start applications automatically after desktop login ● Applications specified in *.desktop files in – /etc/xdg/autostart – ~/.config/autostart ● Each desktop environment launches those application

2023-11-21 4/17 systemd-xdg-autostart-generator ● A new mechanism/implementation for XDG autostart ● Start applications by using Systemd as user services ● How? Convert *.desktop files dynamically to *.service files – /var/run/${uid}/systemd/generator.late/app-${name}@autostart.service

2023-11-21 5/17 An example of an auto-generated service file # Automatically generated by systemd-xdg-autostart-generator [Unit] Documentation=man:systemd-xdg-autostart-generator(8) SourcePath=/etc/xdg/autostart/ibus-autostart.desktop PartOf=graphical-session.target Description=IBus After=graphical-session.target [Service] Type=exec ExecStart=:/usr/bin/ibus-autostart Restart=no TimeoutSec=5s Slice=app.slice [Desktop Entry] Name=IBus GenericName=IBus Daemon Comment=Start IBus daemon Exec=ibus-autostart Icon=ibus-setup Terminal=false Type=Application StartupNotify=false NoDisplay=true X-KDE-autostart-after=panel X-KDE-StartupNotify=false ibus-autostart.desktop app-ibus\\[email protected] Convert dynamically

2023-11-21 6/17 Let’s back to the problem ● The generated service file looks fine but it does not work ● Two sub-problems 1. systemd-xdg-autostart-generator ignores/skips desktop files containing X-GNOME-Autostart-Phase key • A service file for IBus was not generated at all 2. Daemonized applications are soon killed by Systemd • Encountered after fixing the 1st problem

2023-11-21 7/17 (1) X-GNOME-Autostart-Phase ● Systemd ignored desktop files with X-G-A-P because such desktop files should be handled by GNOME – And expected to be unnecessary under the other DEs – Even though they are necessary for DEs other than GNOME ● Solutions – openSUSE side: ● removed unnecessary X-GNOME-Autostart-Phase from packages ● migrated from a XDG autostart desktop to a native Systemd service – Upstream side: ● check the current DE before starting a service by ExecCondition=/usr/lib/systemd/systemd-xdg-autostart-condition ● Do not skip desktop files anymore

2023-11-21 8/17 (2) Daemonized applications are soon killed by Systemd ● Daemonized (or forking) – Applications running background – A main process exits soon but their sub processes keep running $ ibus-daemon --daemonize # the main process exits soon after forking $ # but its children keep running in background

2023-11-21 9/17 Type=exec to cgroup ● When the main process of a service exits, Systemd stop the service if Type=exec – Systemd kills all the remaining processes of the stopped service ● So Type=exec cannot be used for daemonized applications because the main process exits soon ● Solution: ExitType=cgroup – The upstream introduced a new ExitType – A service exit when all the process (in the cgroup) of the service exits [Service] Type=exec ExecStart=:/usr/bin/ibus-autostart [Service] Type=exec ExitType=cgroup ExecStart=:/usr/bin/ibus-autostart Note: Type=forking cannot be applied for every applications in XDG autostart Type=simple might be enough, but I’m not sure why not

2023-11-21 10/17 State machine (ExitType=main) RUNNING SIGCHLD The main process exited. START DEAD FDs for output of the main process is opened. systemctl start Start the main process of service

2023-11-21 11/17 State machine (ExitType=cgroup) cgroup empty (all the process of a service exited) RUNNING SIGCHLD The main process exited. START DEAD FDs for output of the main process is opened. systemctl start Start the main process of service

2023-11-21 12/17 It still does not work ● IBus is soon killed due to timeout – It’s state does not change from START to RUNNING – It seems that Systemd cannot detect IBus has started successfully ● Race condition – systemd-xdg-autostart-generator terminating process a bit too eagerly? #27919 https://github.com/systemd/systemd/issues/27919

2023-11-21 13/17 What was happening? cgroup empty (all the process of a service exited) RUNNING SIGCHLD The main process exited. START DEAD FDs for output of the main process is opened. systemctl start undefined SIGCHLD The main process exited.

2023-11-21 14/17 Writing a patch ● Why SIGCHLD happens during the RUNNING state? – It’s signal – While an event that the main process has started in a queue, Systemd might catch the signal – If the application exits very quickly ● I wrote a patch and submitted to the upstream

2023-11-21 15/17 The last version (ExitType=cgroup) cgroup empty (all the process of a service exited) RUNNING SIGCHLD The main process exited. START DEAD FDs for output of the main process is opened. systemctl start OR SIGCHLD The main process exited.

2023-11-21 16/17 The current status in openSUSE ● Does this problem still reproduce even on Leap 15.5? – Yes – A workaround to disable systemd-xdg-autostart-generator $ kwriteconfig5 --file startkderc --group General --key systemdBoot false – Uses old Systemd and cannot import a new feature to resolve this issue – KDE maintainer would not roll back to the former mechanism ● Already fixed in Tumbleweed (with Systemd v254) – Still need test systemd-xdg-autostart-generator carefully https://bugzilla.opensuse.org/show_bug.cgi?id=1213156

2023-11-21 17/17 Conclusion ● KDE Plasma now uses systemd-xdg-autostart-generator for XDG autostart ● It did not work if a service has – X-GNOME-Autostart-Phase – A main process that forks child processes and exit soon ● This problem have been resolved in Tumbleweed but not in Leap 15.5 – The patch has been already merged by the upstream