Trying to start a GUI process on a second machine

Question

Background:

I am helping out create a media wall from spare computers/screens for a local university to use processing.org/java to distribute renders across several machines. However, it's still buggy and I need to restart the clients occasionally.

Problem:

I'm currently having trouble figuring out how to re-launch the client java app remotely from the server. Note: the clients are connected directly to dual screens - rather than rendering headless

Investigation:

I have recreated a similar environment on AWS/EC2 where I can get the client-server model to work, but just can't start the gui client remotely. I keep getting:

Can't open Display.

Specific issue:

Currently I use the following from the server:

ssh ubuntu@guiclient1 "export DISPLAY=:0; cd ~/wallclient/; xclock &"

Extra:

I monitor the same guiclient1 desktop using x2go. I haven't done any specific xauth / xhost configuration - as haven't seen any issues related to this yet.

What should I be configuring differently? I haven't found much help online - I don't want to do port forwarding back to server, which is what most questions answer.

Thanks

Answer 1

For direct connection in X over the network

X has a permission model for allowing remote clients{*} to use a particular display. Read the manpage for xhost, but the short version is

server$ xhost remote_client

to interactively allow remote_client to use your screen.

Then on the client you just run

client$ xeyes

Direct ssh

Connecting through a ssh is another matter. You should use the -X or -Y or set the corresponding values in .ssh/config (ForwardX11 for -X). Your ssh client should then set the proper value for DISPLAY and you shouldn't mess with it.

server$ ssh -X client
client(by ssh)$ printenv DISPLAY
localhost:10.0
client(by ssh)$ xeyes

Tunneling ssh

Open the tunnel through the firewall with something like

server$ ssh -X -L 1111:client:22 user@firewall

then in another shell

server$ ssh -X -p 1111 user@localhost
client(by ssh)$ printenv DISPLAY
localhost:10.0
client(by ssh tunnel)$ xeyes

(note the -X again) to open a shell running on destination. As with the direct ssh connection your DISPLAY variable should be set for you.

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{*} Here I follow the X tradition of saying that the computer on which display occurs is the server because it makes its display available to multiple programs running on client mahcines.

This will probably seem backwards, as you are probably used to the machine your are working at being the "client" and the one tucked in the closet being the "server".