Desktop forwarding via X using Xephyr

Posted on by nek0 in english, administration

Hello again folks. Tonight I was in an adventurous mood and wanted to see, if I can forward a desktop session from my home computer to my laptop. I had distinct interest in OpenGL applications, since my laptop is only minimally capable of it.

Before I dive into the more technical depths I would like to conclude my findings here: Generally it is possible to forward a desktop session including a window manager, but not GL applications (yet). In general this method is a possible replacement for classical VNC setups.

Before you can start, there are some prerequisites that must be met:

First you need the software Xephyr on your client system (which is the System, where you want to receive your session and work on it). To install it grab the package xserver-xephyr with the package manager of your choice. I am assuming a Debian system here, so it might be possible, that the configuration files are located elsewhere on other GNU/Linux flavours.

Secondly there are some configurations to be made on the host system (the system you want to access remotely). You need to enable X forwarding in your SSH server in /etc/ssh/sshd_config by stating:

X11Forwarding yes

After that you are ready to give it a first shot. Fire up a terminal of your choice on your client and start up Xephyr like this:

Xephyr :1 -screen 800x600 -resizeable &

Mark the capital X at the beginning. This command means: start Xephyr as display :1, -screen sets the resolution and thus the size of the emerging window. Finally -resizeable makes the window resizeable in contrast to its normal behaviour. The last & puts the process in the background.

After completing this you should see a new window, which is completely black. This means everything is, as it is meant to be. You have just created a new blank display within your existing X session.

Now it’s time to make the connection to your host system. This is done by:

DISPLAY=:1 ssh -Y <user>@<host>

Translation: set the display environment variable to :1 and start a ssh connection with the host. The -Y opens a trusted X forwarding connection. Due to the setting of the display variable the X forwarding connects to your Xephyr session, which is what we want.

Now you can start up any window manager in the ssh console, preferably something lighweight like awesome.

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