Starting a UNIX/Linux Desktop Using SSH

Using XDMCP, users are unable to start a UNIX/Linux desktop, such as CDE (Common Desktop Environment), over SSH. This technical note explains why and provides an alternative way to start the desktop over SSH.

To bypass this problem and start a UNIX/Linux desktop XDM session without using XDMCP, follow the steps below.

Warning: When using this workaround, not all of the UNIX/Linux desktop parameters are set, and users may not be able to exit the desktop session normally. If this happens, users should reset or close Reflection X to terminate the session. This causes no problems for Reflection X, but the host processes for the session might not be terminated properly. If you have concerns about this issue, please talk to your host administrator before proceeding.

1. Use Reflection X 14.x or Reflection X Advantage to make a Secure Shell terminal connection (such as xterm, hpterm, or ddterm) to the host.

2. Enter the following command in the terminal window, and then press enter.

Your UNIX/Linux desktop should now be displayed on your workstation through the SSH tunnel.

If a message such as "Xsession: not found" is displayed, Xsession is probably not in the path set for your host account. You will need to enter the full path to Xsession. The paths are typically:

If you are still unable to start Xsession, it might be located in a different path or XDM may not be running on your host. Use the findcommand to locate Xsession (find / -name Xsession), or see Technical Note 1229 (section H) for information on determining the status of XDM.

Note: The sample commands in Reflection X Advantage include some commands that launch desktop sessions. To see these commands, select your Host type in the client definition. Then, use the Command drop-down list to see sample commands for this host type.

If you experience any typing or keyboard problems, they may be resolved by not allowing X clients to remap the keyboard. (In Reflection X Advantage, this ability is disabled by default.)

In Reflection X Advantage 5.0:

1. Select the Session definition you will be working with.
2. In the Session Definition in the right pane, click the Keyboard tab.
3. Confirm that “Permit X clients to remap the keyboard" is unchecked.

In Reflection X Advantage 4.2:

1. Select the X Server definition you will be working with.
2. In the Server Definition in the right pane, expand the General section.
3. Confirm that “Permit X clients to remap the keyboard" is unchecked.

In Reflection X 14.x:

1. Click Settings > Keyboard.
2. Disable "Allow clients to remap keyboard."
3. Click OK.

Secure Shell (SSH) provides secure, encrypted communications between a host and a workstation. However, Secure Shell does not support UDP packets, which means that if the host is configured to permit only Secure Shell connections, users cannot connect to the host using XDMCP.
Attempts to use XDMCP to connect to a host that requires SSH will fail and an error message will be displayed.

When remotely starting a UNIX/Linux desktop, XDMCP (X Display Manager Control Protocol) is typically used to establish the connection between the host's XDM daemon and the remote X server (Reflection X). Once the connection has been established, and the user has successfully authenticated, the XDM daemon launches the X client session, which is displayed on the user's workstation.

XDMCP uses UDP (User Datagram Protocol) packets as a transport type.

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