How to set the DISPLAY variable

The DISPLAY variable can be a little confusing to set-up. This variable allows X application to stablish the connection to X Server. This is normally use to start X application in local X server emulators like Reflection-X.

This piece of code can be added to the current user ".profile" enviroment or to all the users on /etc/profile so the proper variable is set after each ssh logging.

if [ ${DISPLAY:-setdisplay} = setdisplay ]
then
    # irix sets REMOTEHOST
    if [ ${REMOTEHOST:-islocal} != islocal ]
    then
        DISPLAY=${REMOTEHOST}:0
    else
        if [ "${SSH_CLIENT:-notssh}" != "notssh" ]
        then
            echo "Warning: using ssh w/o X11 fwd"
            DISPLAY=`echo "$SSH_CLIENT" | sed -e 's/ .*/:0.0/'`
        else
            # Try to guess DISPLAY
            case $ARCH in
                sunos-sun4|osf-alpha)
                TTY=`tty | sed 's:/dev/::'`
                DISPLAY=`who am i | grep $TTY | tail -1 | \
                    sed -e 's/.*(//' -e 's/[\.)].*//'`:0.0
                ;;

                irix-mips)
                DISPLAY=:0.0
                ;;

                *)
                DISPLAY=`who am i | sed -e 's/^.*(//' -e 's/[:)].*//'`:0.0
                ;;
            esac
        fi
    fi
    export DISPLAY
fi

If you get the script error message "Warning: using ssh w/o X11 fwd" that means that the X session will not use ssh encryption. For more secure connection, check your ssh client.

Reference

• http://webdiis.unizar.es/~spd/sec/X11.txt