I'm trying to learn systemd services by trying to start xclock as a service; the service file is below




Any ideas what's wrong here? I'm getting an error saying "cannot connect to display."


An application needs two things to open a window on an X display. It needs to know the location of the X display; that's conveyed by the DISPLAY environment variable. It also needs to authenticate with the X server. This is conveyed through a cookie, which is a secret value generated by the X server when it starts and stored in a file that only the user who started the X server can access. The default cookie file is ~/.Xauthority.

If your X server is using the default cookie file location, then adding Environment=XAUTHORITY=/home/dogs/.Xauthority will work (assuming /home/dogs is the home directory of the user who is logged in under X). If you need to find the location, see Can I launch a graphical program on another user's desktop as root? and Open a window on a remote X display (why “Cannot open display”)?

Alternatively, running the program as the user who is running the X server will work, provided that the cookie file is in the default location (if not, you'll have to locate the cookie file, like in the root case). Add the User directive (e.g. User=dogs).

Of course the service won't run if there isn't an X display by that number owned by the user you specify.

It's rather bizarre to start a GUI program from Systemd. It wasn't designed for this. GUI programs live in an X session, started by a user. Systemd is for system processes. You should experiment with daemons instead.

  • It's not a problem using systemctl --user. Also the DISPLAY variable is not a matter then. Have a look here. – Suuuehgi May 17 at 21:24

You can add in .xinitrc :

xhost si:localuser:$USER

It works for me!

  • 1
    this is for systemd service files, not .xinitrc – slang Sep 28 '15 at 20:59

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