Say you're logged into your laptop as lisa and want to give another
user on the same machine access to your X session, i.e. open graphical
applications. For years, I disabled X's authentication mechanism
alltogeter with:
$ whoami
lisa
$ xhost +
The john user could now start graphical appliations:
$ whoami
john
$ export DISPLAY=:0
$ xeyes &
However, there's a better way. To grant only john access to your
graphical dispaly, instead do:
$ whoami
lisa
$ xhost +SI:localuser:john
Now, as john, export the display to the local one and start the
graphical application:
$ whoami
john
$ export DISPLAY=:0
$ xeyes &
You can turn off access to your X server by:
$ xhost -
