Ttyjfyk

I seem to be unable to start gparted from the command line. I am using Trisquel 8 (based on Ubuntu 16.04) with LXDE. If I try to open it, I get the following error and nothing happens:

$ sudo gparted

(gpartedbin:7820): Gtk-WARNING **: cannot open display: 

However, it seems to open fine from the graphical application menu.

I searched a bit online and one recommendation was to try:

xhost +localhost

However, that didn't help. Apparently, it seems there can be an issue with opening gtk applications from the command line as root in Wayland; however, I am using X11. This is just on a local laptop - no ssh-ing or remote systems involved.

It seems strange, because I have always been able to open gparted from the command line in the past. I have also tried re-installing gparted and that didn't seem to help.

Update:

Following meuh's suggestions in the comments, I added DISPLAY=:0 to the /etc/environment file, so it should be passed when using sudo. However, I am still experiencing an error, but it has now changed:

$ sudo gparted
No protocol specified

(gpartedbin:5549): Gtk-WARNING **: cannot open display: :0

It seems that the DISPLAY variable is now being passed, but I'm not sure what that 'no protocol' message means.

To access X you need environment variables DISPLAY and XAUTHORITY. Depending on setup, sudo may delete them. You can check that with sudo env to see the environment variables.

To preserve your users environment, you can use sudo -E. That has the pitfall setting HOME to your users home, and config files may get wrong file permissions. However, to avoid that, sudo -H sets HOME to /root.

Combine this for gparted:

sudo -EH gparted

Only desired variables can be set with:

sudo env DISPLAY=$DISPLAY XAUTHORITY=$XAUTHORITY gparted

Error messages:

cannot open display: means DISPLAY is empty or does not exist.

no protocol specified means DISPLAYis set and vaild, but XAUTHORITY pointing to authentication cookie is not set or the cookie is invalid. Alternativly, xhost +SI:localuser:root allows root temporary access to X until logout.

Similar goes for Wayland access with WAYLAND_DISPLAY and XDG_RUNTIME_DIR. Wayland root access issues can be solved with sudo -EH, too. For detail and a pitfall with XDG_RUNTIME_DIR see Will Wayland ever support graphical sudo?

There is kdesudo, gsudo, and some other sudos that solve this.

Here is one, I hacked together (not security audited/tested).

#/bin/bash

inner() 
 sed -e s/^/:/ ) " 

if [ "$1" = "---innermode" ]
then
 shift
 user="$1"
 display="$2"
 shift 2
 inner "$@"
else
 self="$0"
 sudo "$self" ---innermode "$USER" "$DISPLAY" "$@"
fi