Why can't I run GUI apps from 'root': "No protocol specified"?

  • I installed debian onto my machine last night. Now, I don't understand why I can't run GUI apps from a terminal when running as root.

    For example:

    sudo -i

    Generates the following output:

    No protocol specified
    Error: couldn't open display :0

    But when I first open the terminal I can run glxgears from the user account. Its only after I do sudo -i that the problem crops up. This happens for any GUI app that I try to run. I think its probably related to X11, but I'm not sure.

    http://stackoverflow.com/a/20612084 this worked perfectly for me.

  • michas

    michas Correct answer

    7 years ago

    Accessing the X server requires two things:

    • The $DISPLAY variable pointing to the correct display (usually :0)
    • Proper authentication information

    The authentication information can be explicitly specified via $XAUTHORITY, and defaults to ~/.Xauthority otherwise.

    If $DISPLAY and $XAUTHORITY is set for your user, sudo will set them for the new shell, too, and everything should work fine.

    If they are not set, they will probably default to the wrong values and you cannot start and X applications.

    In Debian $XAUTHORITY is usually not set explicitly. Just add

    export XAUTHORITY=~/.Xauthority

    to your .bashrc or explicitly say XAUTHORITY=~/.Xauthority sudo ... and everything should work.

    You can also use xauth list to check whether proper authentication information are available.

    `xauth info` shows path to authority file

    `xhost +` fixed my problem

    Be aware that `xhost +` completely deactivates authentication and allows everyone to access all application on your screen...

    for debian, do I type the XAUTHORITY export as root? because it's not working on deb10? I login with sudo su

    @marinara use `sudo -i` instead of `sudo su -`.

    Now that Debian 10 (Buster) is out, how do you do this with `wayland`?

    `xhost +si:localuser:root` seems to work similar.

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Content dated before 6/26/2020 9:53 AM