Microsoft windows XP has runas command which allows a user to run specific tools and programs with different permissions than the user's current logon provides. Linux and other UNIX like operating system provides the su or sudo command for same purpose. However, su/sudo command is not so useful when it comes to X program. For example when you logged in as a normal user, you need to run an X window application as root. If I run application as follows:
$ su -
It will bump you back with an error:
(program:15082): Gtk-WARNING **: cannot open display:
** WARNING ** cannot open display
However both KDE and Gnome come with tools to deal with this problem.
Method # 1:
If you are using KDE then use following command at shell prompt:
$ kdesu xeyes
Method # 2:
If you are using Gnome then use following command at shell prompt:
$ alias runas='su -c $@'
Add above alias to your bash startup script
$ echo "alias runas='su -c $@'" >> .bash_profile
You can now use alias as follows to start any x program
$ runas program-name $ runas xeyes
Method # 4: The old way
The problem is with two environment variable DISPLAY and XAUTHORITY. You need to setup them correctly to run X windows program as a root user while logged in as a normal user. So how do you fix this problem? Simply set these two variables to point to current logged in users environment variable. Let us assume you are currently login as vivek user.
Step # 1 Become super-use
vivek@debian:~$ su -
Step # 2 Setup variables
# export DISPLAY=0:0 # export XAUTHORITY=/home/vivek/.Xauthority
Step # 3 Execute X program as a root user