Panic in user service on logout from desktop environment

[Majiir]

I use the systemd user service to run yubikey-touch-detector. I'm using NixOS 23.05 with GNOME 44.2.

When I log out of GNOME, the service logs the following and crashes:

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x20 pc=0x544e51]
goroutine 67 [running]:
github.com/esiqveland/notify.notifier.handleSignal({0xc00022a000, 0xc00028e540, 0xc0002ea000, 0xc000292160, 0x5d4710, 0xc0002e6c50, {0x602180, 0xc00011c000}}, 0x0)
        github.com/esiqveland/notify@v0.11.0/notification.go:274 +0x51
github.com/esiqveland/notify.notifier.eventLoop({0xc00022a000, 0xc00028e540, 0xc0002ea000, 0xc000292160, 0x5d4710, 0xc0002e6c50, {0x602180, 0xc00011c000}})
        github.com/esiqveland/notify@v0.11.0/notification.go:264 +0x109
created by github.com/esiqveland/notify.New
        github.com/esiqveland/notify@v0.11.0/notification.go:253 +0x391

This only happens when I log out from a GNOME session. If I log in or out of another TTY, the service continues to run.

The service stays in this failed state when logging back in.

[maximbaz]

Interesting bug! I think this happens because you are using libnotify, which in turn obviously requires a graphical session to be running. There are two ways to fix it, either updating the systemd service to stop yubikey-touch-detector when you exit GNOME, or to update the libnotify detector to gracefully handle presence or absence of graphical session.

For the former, I suppose you'd want something like this:

[Unit]
Description=Detects when your YubiKey is waiting for a touch
Requires=yubikey-touch-detector.socket
PartOf=graphical-session.target
After=graphical-session.target

[Service]
ExecStart=/usr/bin/yubikey-touch-detector
Restart=always
EnvironmentFile=-%E/yubikey-touch-detector/service.conf

[Install]
Also=yubikey-touch-detector.socket
WantedBy=graphical-session.target

See if it helps you, we can't have that merged though, because libnotify is not a required dependency, so it would be wrong to enforce dependency on graphical-session onto everyone (also it would make it impossible to use the app purely in TTY).

Otherwise, I can merge a PR for a graceful handling of presence or absence of a graphical session, but since I don't use the libnotify functionality, I won't be the one implementing it.

[Majiir]

Thanks for the tip!

• Adding WantedBy=graphical-session.target ensures the service comes back on the next graphical login, although the panic is still logged.

• Adding PartOf=graphical-session.target causes the service to stop properly on logout instead of panicking.

[thomaseizinger]

I'm using NixOS 23.05

I ran into the same thing. Here is how I applied the above:

# File: configuration.nix

  systemd.packages = [ pkgs.yubikey-touch-detector ];
  systemd.user.services.yubikey-touch-detector = {
    path = [ pkgs.gnupg ];
    wantedBy = [ "graphical-session.target" ];
    partOf = [ "graphical-session.target" ]; # Otherwise the program segfaults in libnotify: https://github.com/maximbaz/yubikey-touch-detector/issues/47
  };

I think a proper fix would be to bundle the systemd config with https://github.com/NixOS/nixpkgs/blob/nixos-23.11/pkgs/tools/security/yubikey-touch-detector/default.nix but I don't (yet) know how to do that :)