xfce4-notifyd fails to start on displays other than :0

[Simon Tatham]

I work remotely by running an XFCE session inside an X display created by vnc4server. On Ubuntu xenial, this causes xfce4-notifyd to fail to start up.

A transcript of my VNC startup script and the results:

simon@xenial:~$ cat ~/.vnc/xstartup
#!/bin/sh
exec setsid xfce4-session
simon@xenial:~$ vncserver :1

New 'xenial:1 (simon)' desktop is xenial:1

Starting applications specified in /home/simon/.vnc/xstartup
Log file is /home/simon/.vnc/xenial:1.log

simon@xenial:~$ ps xf | grep xfce4-notifyd
 4017 pts/0 S+ 0:00 \_ grep --color=auto xfce4-notifyd
simon@xenial:~$ systemctl --user status xfce4-notifyd.service
● xfce4-notifyd.service - XFCE notifications service
   Loaded: loaded (/usr/lib/systemd/user/xfce4-notifyd.service; static; vendor preset: enabled)
   Active: failed (Result: exit-code) since Wed 2020-10-07 11:29:41 BST; 27s ago
  Process: 3943 ExecStart=/usr/lib/x86_64-linux-gnu/xfce4/notifyd/xfce4-notifyd (code=exited, status
 Main PID: 3943 (code=exited, status=1/FAILURE)

Oct 07 11:29:41 xenial systemd[3794]: Starting XFCE notifications service...
Oct 07 11:29:41 xenial xfce4-notifyd[3943]: Unable to init server: Could not connect: Connection ref
Oct 07 11:29:41 xenial xfce4-notifyd[3943]: cannot open display:
Oct 07 11:29:41 xenial systemd[3794]: xfce4-notifyd.service: Main process exited, code=exited, statu
Oct 07 11:29:41 xenial systemd[3794]: xfce4-notifyd.service: Failed with result 'exit-code'.
Oct 07 11:29:41 xenial systemd[3794]: Failed to start XFCE notifications service.
simon@xenial:~$ exit

If I manually edit /usr/lib/systemd/user/xfce4-notifyd.service so that it adds "--display :1" to the command line, then xfce4-notifyd starts up correctly. (But obviously this is a horrible bodge that I only did temporarily for diagnostic purposes :-)

So I conjecture that the X display parameter is somehow not finding its way to xfce4-notifyd during startup, and that in the normal case nobody notices because xfce4-notifyd defaults to trying to connect to :0.

System details: this can be reproduced on a clean, freshly installed xubuntu 18.04 system (in a test VM, installed on 2020-10-07). The only configuration I performed was to edit my ~/.vnc/xstartup so that it runs xfce4-session (as shown in the transcript above).

simon@xenial:~$ lsb_release -rd
Description: Ubuntu 18.04 LTS
Release: 18.04
simon@xenial:~$ apt-cache policy xfce4-notifyd
xfce4-notifyd:
  Installed: 0.4.2-0ubuntu2
  Candidate: 0.4.2-0ubuntu2
  Version table:
 *** 0.4.2-0ubuntu2 500
        500 http://gb.archive.ubuntu.com/ubuntu bionic/universe amd64 Packages
        100 /var/lib/dpkg/status

[Simon Tatham (sgtatham)]

Now I think about it harder, I suppose I should mention a few more details.

On the test VM I spun up for the reproducer, I was doing all of this by logging in on a text virtual console. On the real machine where I had this problem originally, I'm doing remote working by SSHing in, running vncserver to start up the X session, and then connecting a VNC client to it.

So, in both cases, the user-level systemd process is already running *before* I set up the new X display. I wouldn't be surprised if that was a key part of the problem: if you logged in on a display other than :0 via a normal display manager, it might well have set DISPLAY before even starting "systemd --user", and then everything might work. (But I haven't tried it.)

Also, when I say "vncserver", that's the one from the "vnc4server" package. (I think that is probably not critical to the behaviour, but just in case.)