Restarting systemd-logind kills x server

[groxxda]

Issue description

When I restart systemd-logind, my X server dies. logind is restarted on system upgrades.

Steps to reproduce

• Start a x session from a display manager that supports passing file descriptors (for example gdm)
• Open console and run systemctl restart systemd-logind

systemd changelog

https://github.com/systemd/systemd/blob/master/NEWS#L103-L112

          systemd-logind may now be restarted without losing state. It stores
          the file descriptors for devices it manages in the system manager
          using the FDSTORE= mechanism. Please note that further changes in
          other components may be required to make use of this (for example
          Xorg has code to listen for stops of systemd-logind and terminate
          itself when logind is stopped or restarted, in order to avoid using
          stale file descriptors for graphical devices, which is now
          counterproductive and must be reverted in order for restarts of
          systemd-logind to be safe. See
          https://cgit.freedesktop.org/xorg/xserver/commit/?id=dc48bd653c7e101.)

Technical details

• System: (NixOS: 17.09)
• systemd: v234
• gdm: 3.24.2

Journal

/nix/store/rhngsh1xfczlwyx2zgpk487c5cdi3qnz-gdm-3.24.2/libexec/gdm-x-session[4414]: Fatal server error:
/nix/store/rhngsh1xfczlwyx2zgpk487c5cdi3qnz-gdm-3.24.2/libexec/gdm-x-session[4414]: (EE) systemd-logind disappeared (stopped/restarted?)
/nix/store/rhngsh1xfczlwyx2zgpk487c5cdi3qnz-gdm-3.24.2/libexec/gdm-x-session[4414]: (EE)
/nix/store/rhngsh1xfczlwyx2zgpk487c5cdi3qnz-gdm-3.24.2/libexec/gdm-x-session[4414]: Please consult the The X.Org Foundation support
/nix/store/rhngsh1xfczlwyx2zgpk487c5cdi3qnz-gdm-3.24.2/libexec/gdm-x-session[4414]:          at http://wiki.x.org
/nix/store/rhngsh1xfczlwyx2zgpk487c5cdi3qnz-gdm-3.24.2/libexec/gdm-x-session[4414]:  for help.
/nix/store/rhngsh1xfczlwyx2zgpk487c5cdi3qnz-gdm-3.24.2/libexec/gdm-x-session[4414]: (EE) Please also check the log file at "/dev/null" f
/nix/store/rhngsh1xfczlwyx2zgpk487c5cdi3qnz-gdm-3.24.2/libexec/gdm-x-session[4414]: (EE)

[eqyiel]

This happens for me too, I think it's related to this: #28053 (comment)

[groxxda]

@eqyiel I can reproduce the error by solely restarting systemd-logind without touching any files.

[eqyiel]

@groxxda I see, in any case I'm seeing the same thing as you every time I run nixos-rebuild switch!

[globin]

CC @jtojnar, @teh, @zimbatm

[Mic92]

Maybe the following patch solve it?

diff --git a/nixos/modules/system/boot/systemd.nix b/nixos/modules/system/boot/systemd.nix
index ed1f5d20af..dd9ba71044 100644
--- a/nixos/modules/system/boot/systemd.nix
+++ b/nixos/modules/system/boot/systemd.nix
@@ -875,7 +875,12 @@ in
     systemd.services.systemd-remount-fs.restartIfChanged = false;
     systemd.services.systemd-update-utmp.restartIfChanged = false;
     systemd.services.systemd-user-sessions.restartIfChanged = false; # Restart kills all active sessions.
-    systemd.services.systemd-logind.restartTriggers = [ config.environment.etc."systemd/logind.conf".source ];
+    # Restarting systemd-logind breaks X11
+    # - upstream commit: https://cgit.freedesktop.org/xorg/xserver/commit/?id=dc48bd653c7e101
+    # - systemd announcement: https://github.com/systemd/systemd/blob/22043e4317ecd2bc7834b48a6d364de76bb26d91/NEWS#L103-L112
+    # - this might be addressed in the future by xorg
+    #systemd.services.systemd-logind.restartTriggers = [ config.environment.etc."systemd/logind.conf".source ];
+    systemd.services.systemd-logind.restartIfChanged = false;
     systemd.services.systemd-logind.stopIfChanged = false;
     systemd.services.systemd-journald.restartTriggers = [ config.environment.etc."systemd/journald.conf".source ];
     systemd.services.systemd-journald.stopIfChanged = false;

[teh]

@Mic92's patch is what @zimbatm and I discussed last Sunday as well. I think it's probably the correct solution. I had wanted to investigate what issues a never-restarted logind would cause. The linked commit message says it's OK so +1 from me.

[Mic92]

commit was applied.