"Can't open display" message when running sudo ./displaylink-debian.sh

[z-nexx]

When I run sudo ./displaylink-debian.sh on Debian Bookworm/Sid I get the following message:

$ sudo ./displaylink-debian.sh 
No protocol specified
Can't open display :0

[z-nexx]

After a quick bit of digging I found that the error message is from xrandr which can't find the X display on line 40. This is due to sudo not passing the user's environment.

The solution is to instead run the following to preserve the environment variables needed.

sudo -E ./displaylink-debian.sh

[janvlug]

On my fully up to date Librem 5 phone running PureOS, I get "Can't open display" both when running with sudo -E and running as root.

[janvlug]

On Wayland only systems, I always get Can't open display when running xrandr --listproviders.

But the command xrandr --listmonitors gives:

Monitors: 2
 0: +*XWAYLAND0 2560/600x1440/340+2560+0  XWAYLAND0
 1: +XWAYLAND1 2560/600x1440/340+0+0  XWAYLAND1

Note: when logged in via ssh running xrandr --listmonitors gives also Can't open display.

I think that out-commenting the line:

providers="$(xrandr --listproviders)"

(currently line 53)

from the displaylink-debian.sh script does not hurt and makes the script to continue on Wayland only systems.