Before I begin I would like to say that while I am not a Linix newbie, I am not a guru or even a regular user so don't assume I have anything more than general Linux knowledge.

I am carrying out research involving virtualization and Single Sign On technologies and I need to display a Xen based virtual machine to the desktop before the user is logged in. This is for a demonstration system and I am trying to find a solution that involves the least amount of system modification possible.

I found a PAM module that allows for the invocation of arbitrary shell scripts which would allow me to start and display the virtual machine in question, but when trying to run the virt viewer (or any process with graphical output) I am informed that the display cannot be found. Explicitly setting the DISPLAY env to :0 before running the command has no effect.

This is where my Linux knowledge runs out. I know that there has to be some way to connect to the X session being used by the greeter, I just don't know what that method involves. The shell script is running with root privileges, so it can access whatever "X credentials" are stored locally.

I will be thankful for any assistance this forum might be able to provide, but please do not suggest alternatives to displaying a VM for my SSO needs, and please avoid any solution that involves having to write my own custom greeter. If there is absolutely no way to accomplish what I am trying to do without greeter modifications definitely tell me, but I am a security researcher, not a Linux developer so I am looking for the easiest solution to implement, even if that solution is a gross hack.

Thanks in advance.

You could try setting up the host to auto-login as a particular user and change that users shell to be a specific command

let us know how you go

cheers