x11vnc and xtightvncviewer r0x0r

I’ve been playing around a bit with x11vnc and tightvnc, and I’ve concluded that they both seriously rock. They are enabling me to do stuff I’ve wanted to do for years, but thought wasn’t reasonably possible.

Desktop Sharing

I occasionally want to share something on my desktop with other people, or visa-versa – generally to facilitate remote collaboration with them. People that use a certain evil other OS often want to use a nasty proprietary tool to accomplish the task, since they don’t know any better – but being a linux geek, and someone that values his freedom, and has an intense dislike of proprietary closed software, that’s not an option for me :)

Now, I’ve been a fan of VNC pretty much since its inception at AT&T labs. It is very cool technology, and it allows for sharing a desktop between platforms. But the original VNC was only capable of generating VNC protocol from its own X-ish sessions, or from a windoze desktop – i.e. I could create a virtual X session that multiple people could share, but I couldn’t share my everyday X display, where I’m most comfortable, and where I’m likely to be working when the urge to share something comes up :).

Enter x11vnc.

x11vnc is a fork of the VNC code, which allows me to attach the VNC protocol generation to my current X session. Not only that, but in combination with some of the cool stuff the tightvnc project has been developing, makes it extremely easy to share desktops between platforms.

On the windows side, tightvnc is very easy to set up, and well documented. On the *nix side, similar functionality requires two seperate packages (x11vnc and tightvnc), and the documentation for doing so is, umm, well, not very easy to find. So, without further ado, here’s a very simple desktop sharing script:

    #!/bin/sh
    pkill x11vnc
      
    VNC_JAVA_DIR="/usr/share/tightvnc-java"
    HTTP_PORT=5999
    VNC_COMMAND="x11vnc -display :0 -viewonly -httpdir $VNC_JAVA_DIR \
	     -httpport $HTTP_PORT -shared -nothreads -bg -alwaysshared \
	     -dontdisconnect -many -cursor"
      
    port="$($VNC_COMMAND | sed -e 's/PORT=//')"
    port=$(expr $port - 5900)
      
    zenity --display :0 --info \
	   --text="x11vnc is running on VNC display $port.  Click OK to kill"
      
    pkill x11vnc

This little script will share your desktop in view-only mode, until you click “OK” on the dialog box it pops up. It depends on having the xllvnc, zenity, and tightvnc-java packages installed on debian/ubuntu – other distros may have different names, but you get the idea. You can use a vnc viewer to connect to the shared desktop, or you can simply point a web browser at the shared machine on port 5999 (i.e. http://<shared-machine-name>:5999), and you’ll get a java applet that displays the shared desktop inside the browser. Pretty cool :)

Personally, on my desktop machine, I have a pretty large desktop, and don’t really want to share the whole thing. So I’ve taken the above script a little further, and shared only a portion of my desktop – then I start up a xlogo window on that part of my desktop, so I know where it is. Now, any window I drag into that area is automatically shared (and I can still read email, or type in IRC, or whatever on the rest of my desktop ;). Here’s my actual sharing script:

    #!/bin/sh
    killall x11vnc
    killall xlogo
      
    SHARE_GEOMETRY="1024x768+2176+432"
    VNC_JAVA_DIR="/usr/share/tightvnc-java"
    HTTP_PORT=5999
    VNC_COMMAND="x11vnc -display :0 -viewonly -httpdir $VNC_JAVA_DIR \
	     -httpport $HTTP_PORT -clip $SHARE_GEOMETRY -xinerama \
	     -shared -nothreads -bg -alwaysshared -dontdisconnect -many -cursor"
      
    xlogo -geometry $SHARE_GEOMETRY&
      
    port="$($VNC_COMMAND | sed -e 's/PORT=//')"
    port=$(expr $port - 5900)
      
    zenity --display :0 --info \
	   --text="x11vnc is running on VNC display $port.  Click OK to kill"
      
    killall x11vnc
    killall xlogo

Accessing My Desktop Remotely

The other problem I’ve been wanting to solve for a long time involves accessing the desktop running on a machine I don’t have physical access to. For example, I have occasionally found myself at home, but wanting access to an X application I left running on my workstation in my cube at work. I could run x11vnc all the time, on all machines I might possibly want to access, but that’s a painful thing to maintain, and it’s rather insecure as well.

Again, enter xllvnc and tightvnc…

It turns out that the tightvnc viewer has this really neet “-via” option, which lets you access a VNC session through a ssh tunnel. It also turns out that x11vnc can be invoked from a ssh session as well, and by default will only run for a single connection instance. And finally, it turns out that xtightvncviewer lets you customize the ssh command you use to create the “-via” tunnel, by simply setting an environment variable. Schweet.

So, here’s my (extremely simple) script for accessing the desktop on any machine you have ssh access to:

    #!/bin/sh
    VNC_HOST=`echo $1 | awk -F: '{print $1}'`
    DISP=`echo $1 | awk -F: '{print $2}'`
    if [ "x$DISP" = "x" ]; then DISP=0; fi
      
    VNC_VIA_CMD="ssh -f -L %L:%H:%R %G x11vnc -localhost -rfbport 5900 -display :$DISP; sleep 5" 
    export VNC_VIA_CMD
      
    exec xtightvncviewer -via $VNC_HOST localhost:0

Again, this script depends on the x11vnc and xtightvncviewer packages, and is trivial to extend to work through HP’s firewall, as long as you can get a ssh session through the firewall. It invokes x11vnc with the -localhost option, so the only way to connect to the session is by first logging into the machine via ssh or some other tunneling method. So it’s quite secure.