Starting X Clients from Personal Linux Boxes

To simplify the remote access of Thor, and other systems, from Linux boxes the Computing Service provides a superior version of the standard X xon program called xcmd. If your system administrator has not already installed this program on your local box, you should download it and install it somewhere where you can run it.

NB: The xcmd program only works on Linux boxes or other systems that support the -f option on hostname.

xon and xcmd work by using rsh to execute a command on the remote system. The xcmd script automatically arranges that the target command is run with the correct DISPLAY set. The default command is an xterm.

However, for Thor to accept the rsh request at all, you will need to have a .rhosts file set up on Thor trusting your account on your Linux box. If your account name on Thor is different from your local account name then you will need to use the -user option on xcmd to pass through your Thor account name.

Examples:

local$ xcmd hammer.thor xbiff: This starts xbiff on the machine hammer.thor.cam.ac.uk. The account name on Thor must match the local account name.
local$ xcmd gloves.thor -user rjd4 emacs: This starts emacs on the machine gloves.thor.cam.ac.uk. The account name on Thor is rjd4 regardless of the local account name.
local$ xcmd belt.thor: This starts a login xterm on the machine belt.thor.cam.ac.uk. The account name on Thor must match the local account name.

Once the command has been started on Thor, the X client (xbiff, emacs or xterm in the examples above) still has to make an X connection back to the server. This has a different set of permissions, dealt with by the xcmd's -permit option. (This is the principle extension that xcmd has over xon.)

The first time you use xcmd during a given X session you should run it with the -permit option to transfer the relevant authority to Thor. You can either run it with a true X client, the default xterm or with a "null" command such as true to do no X work at all, but just transfer the authority:

local$ xcmd hammer.thor.cam.ac.uk -permit xbiff
permitted hammer.thor.cam.ac.uk access to gryphon.csi.cam.ac.uk:0.0

local$ xcmd hammer.thor.cam.ac.uk -permit
permitted hammer.thor.cam.ac.uk access to gryphon.csi.cam.ac.uk:0.0

local$ xcmd hammer.thor.cam.ac.uk -permit true
permitted hammer.thor.cam.ac.uk access to gryphon.csi.cam.ac.uk:0.0

The xcmd command has a -help option which lists all its options.

Unix Support

Starting X Clients from Personal Linux Boxes

See also