Connecting to a Linux Node with “X11 Forwarding”

X Window System is used to enable bitmap based Graphical User Interface on Unix based operating systems. This is commonly referred to as “X11”. One of the interesting usages of X11 is the ability to transfer “a window” to the terminal (a machine which an operator uses). The original X11 process runs on the server but the X11 User Interface appears on the client machine terminal, This is called “X11 forwarding”.

In order to use X11 forwarding an X11 graphic server must be run (this is called an X11 server even though it actually runs on the client machine) on the local machine.

The LifeKeeper GUI runs on X Window Platform and therefore a client that runs X11 software is required (unless a GUI login is used on these nodes directly).

Install Client Software to Microsoft Windows

To use Microsoft Windows as an “x11 server” it is necessary to install software on the Microsoft Windows client. The following page explains the basic steps required to install the software on a Windows client.

• Setup X Window Client Software on Microsoft Windows

Setup Linux Nodes to Accept X11 Forwarding

1. Find the current value of the DISPLAY environment variable as the regular user that was set up in the previous steps.

$ echo $DISPLAY
localhost:10.0

2. View the current list of xauth keys for the user and identify the one associated with the current display that X11 is being forwarded on (10 in this example).

$ xauth list
node-a/unix:11 MIT-MAGIC-COOKIE-1 7289ba26871a37b94ff359df829e2686
node-a/unix:10 MIT-MAGIC-COOKIE-1 bae592c842916f23e3ba066ba594c5d0

3. Become the root user.

$ sudo -i

4. View the DISPLAY environment variable for the root user.

# echo $DISPLAY
localhost:10.0

*Note: If the DISPLAY variable is not set for the root user, set it to the same value found in step 1:
# export DISPLAY=localhost:10.0

5. View the current list of xauth keys for the root user.

# xauth list
node-a/unix:1 MIT-MAGIC-COOKIE-1 5b249d176f8da2f7803343f6830002eb
node-a/unix:2 MIT-MAGIC-COOKIE-1 e62f7abaeda1d200576aac40aec2ba83

If there is no entry for the display found in step 1, add the relevant entry from the xauth list output in step 2 to the list of keys for the root user.

# xauth add node-a/unix:10 MIT-MAGIC-COOKIE-1 bae592c842916f23e3ba066ba594c5d0

6. Once the DISPLAY variable and xauth keys are set up correctly for the root user, it is now possible to run graphical applications as root from an SSH session.

# /opt/LifeKeeper/bin/lkGUIapp &
[1] 23957
openjdk version “12.0.2” 2019-07-16
OpenJDK Runtime Environment (build 12.0.2+10)
OpenJDK 64-Bit Server VM (build 12.0.2+10, mixed mode, sharing)
Setting up secure random number generator
Random number setup completed
Connecting to rmi://node-a:82/LKRemoteInterface at:
      Sat Mar 13 04:23:19 UTC 2021
Connection to node-a succeeded at:
      Sat Mar 13 04:23:20 UTC 2021