How do I automatically set the $DISPLAY variable for my current session?

Question

I see that $DISPLAY is set to localhost:0.0 if I am running over a vnc server this may not be correct, is there a way to automatically set it in my login script?

Prophase

questions like this are more about operating systems than programming and serverfault.com is where they go. – Haywoodhayyim

It seems when vncserver started, the DISPLAY variable is automatically set in the new vnc session, at least this works for me. – Lacasse

You should describe what machine your are logging into, and where the vnc server(s) are running. Any shells created in a vncserver environment would already have the correct DISPLAY variable. It sounds like you are remote logging into a remote host and trying to start apps on an already running X server. Your login script doesn't know which vnc server it should connect to any more than we do. – Coneflower

Answer 1

Here's something I've just knocked up. It inspects the environment of the last-launched "gnome-session" process (DISPLAY is set correctly when VNC launches a session/window manager). Replace "gnome-session" with the name of whatever process your VNC server launches on startup.

PID=`pgrep -n -u $USER gnome-session`
if [ -n "$PID" ]; then
    export DISPLAY=`awk 'BEGIN{FS="="; RS="\0"}  $1=="DISPLAY" {print $2; exit}' /proc/$PID/environ`
    echo "DISPLAY set to $DISPLAY"
else
    echo "Could not set DISPLAY"
fi
unset PID

You should just be able to drop that in your .bashrc file.

Spiral

login, switch user & login into another account, switch back to first account and "last launched gnome-session" is not the active one any more. – Cellulosic

@Cellulosic Good point. I've modified my answer to at least restrict processes to the current user. – Spiral

I had to change your awk line to: export DISPLAY=$(cat /proc/$PID/environ | strings | awk 'BEGIN{FS="=";} $1=="DISPLAY" {print $2; exit}') Then it worked. – Funds

Also, I changed pgrep to 'gnome-session|xfdesktop', to include xfce desktops. Full command is now: PID=$(pgrep -n -u $USER 'gnome-session|xfdesktop') – Funds

The export line can be simplified to: export $(grep -z ^DISPLAY= /proc/$PID/environ). – Gospel

Answer 2

do you use Bash? Go to the file .bashrc in your home directory and set the variable, then export it.

DISPLAY=localhost:0.0 ; export DISPLAY

you can use /etc/bashrc if you want to do it for all the users.

You may also want to look in ~/.bash_profile and /etc/profile

EDIT:

function get_xserver ()
{
    case $TERM in
       xterm )
            XSERVER=$(who am i | awk '{print $NF}' | tr -d ')''(' )    
            XSERVER=${XSERVER%%:*}
            ;;
        aterm | rxvt)           
            ;;
    esac  
}

if [ -z ${DISPLAY:=""} ]; then
    get_xserver
    if [[ -z ${XSERVER}  || ${XSERVER} == $(hostname) || \
      ${XSERVER} == "unix" ]]; then 
        DISPLAY=":0.0"          # Display on local host.
    else
        DISPLAY=${XSERVER}:0.0  # Display on remote host.
    fi
fi

export DISPLAY

Fetiparous

if i put this in my bashrc it wont work with vncserver because it creates other displays like localhost:1.0 etc so i need a little more generic solution. – Prophase

Answer 3

I'm guessing here, based on issues I've had in the past which I did solve:

• you're connecting to a vnc server on machine B, displaying it using a VNC client on machine A
• you're launching a console (xterm or equivalent) on machine B and using that to connect to machine C
• you want to launch an X-based application on machine C, having it display to the VNC server on machine B, so you can see it on machine A.

I ended up with two solutions. My original solution was based on using rsh. Since then, most of our servers have had ssh installed, which has made this easier.

Using rsh, I put together a table of machines vs OS vs custom options which would guide this process in perl. Bourne shell wasn't sufficient, and we don't have bash on Sun or HP machines (and didn't have bash on AIX at the time - AIX 5L wasn't out yet). Korn shell wasn't much of an option, either, since most of our Linux boxes don't have pdksh installed. But, if you don't face these limitations, you can implement the idea in ksh or bash, I think.

Anyway, I would basically run 'rsh $machine -l $user "$cmd"' where $machine, of course, was the machine I was logging in to, $user, similarly obvious (though when I was going in as "root" this had some variance as we have multiple roots on some machines for reasons I don't fully understand), and $cmd was basically "DISPLAY=$DISPLAY xterm", though if I were launching konsole, for example, $cmd would be "konsole --display=$DISPLAY". Since $DISPLAY was being evaluated locally (where it's set properly), and not being passed literally across rsh, the display would always be set correctly.

I also had to make sure that no one did anything silly like reset DISPLAY if it was already set.

Now, I just use ssh, make sure that X11Forwarding is set to yes on the server (sshd_config), and then I can just ssh to the machine, let X commands go across the wire encrypted, and it'll always go back to the right place.

Granny

Answer 4

Your vncserver have a configuration file somewher that set the display number. To do it automaticaly, one solution is to parse this file, extract the number and set it correctly. A simpler (better) is to have this display number set in a config script and use it in both your VNC server config and in your init scripts.

Polymorphous

Answer 5

You'll need to tell your vnc client to export the correct $DISPLAY once you have logged in. How you do that will probably depend on your vnc client.

Thin