Linux – How to connect to remote X-Server (logged in via ssh)

1. If I recall correctly ssh -X maps the X server to the target machine and then routes connections through the channel created by SSH to the terminal (i.e. your machine). The "X server" is the software that draws the window for the "X clients" which are the programs that use those windows.

2. Yes, startx starts the X server. But on Mac OS X you start the X server by starting X11.app in Utilities.

3. You wouldn't really want that unless you are trying to restart the X server on the computer you SSH into. But that wouldn't have anything to do with your connection to that computer or the programs you want to run via that connection.

4. Not sure I understand the question. What window manager the remote server runs is inconsequential for your connection. Window managers run on X servers (they are special X clients) and the X server on your Mac and the X server on the remote machine are two separate beasts.

5. VNC is a different solution for the problem of displaying GUI apps remotely. You can combine the two but I recommend you try to understand them separately.

6. Let Paul be your Mac and Peter be the (Linux) machine you connect to:

Paul: startx (or rather, start X11.app and use the terminal window it creates for the following)

Paul: xhost +Peter

Paul: ssh -X Peter

Peter: xlogo& (this should now display on Paul's screen, if not, continue)

Peter: export DISPLAY=Paul:0

Peter: xlogo& (this should now display on Paul's screen)

You can specify a command that is executed whenever someone logs in using a ssh key.

Edit the file ~/.ssh/authorized_keys. Prepend every key you want to forward with a command=ssh user@target.

This has to be done for every user. Since this is done using a user configuration file, every user may change this. If you trust your users (or you are the only user) then this is ok. You can also prevent users from changing this by not giving them any other means to access the shell on this machine.

For more information read the sshd man page. Search for the AUTHORIZED_KEYS FILE FORMAT section, and then for command="command".

Alternatively: you can force a command using a ForceCommand in /etc/ssh/sshd_config. This option is more secure as it is enforced by sshd, and only users with root privileges can change that.

For more information read the sshd_config man page. Search for ForceCommand.