Comment 52 for bug 1951491

I am experiencing this problem too. using VNC (tigervnc-standalone-server).
I read the entire thread. I tried damn near all of the workarounds. None worked.

The symptom is that I can't start Firefox in my xfce4 session .
madbrain@u22041:~/Desktop$ firefox
/system.slice/vncserver.service is not a snap cgroup

Here is my xstartup :

madbrain@u22041:~/.vnc$ cat xstartup
#!/bin/sh
# Start up the standard system desktop
unset SESSION_MANAGER
unset DBUS_SESSION_BUS_ADDRESS

/usr/bin/startxfce4
#/usr/bin/gnome-session

[ -x /etc/vnc/xstartup ] && exec /etc/vnc/xstartup
[ -r $HOME/.Xresources ] && xrdb $HOME/.Xresources
x-window-manager &

And my systemd unit :

[Unit]
Description=Tiger VNC server
After=syslog.target network.target

[Service]
Type=forking
User=madbrain
PIDFile=/home/madbrain/.vnc/%H:5902.pid
ExecStartPre=-/usr/bin/vncserver -kill :2 > /dev/null 2>&1
ExecStart=/usr/bin/vncserver -geometry 3840x2160 -localhost no :2
ExecStop=/usr/bin/vncserver -kill :2

[Install]
WantedBy=multi-user.target

I think the issue is related to my systemd. If I start
vncserver :2
from a terminal, then Tim's workaround from comment 31 works.*

But if I start it through systemd, it fails.