Remote X

The X Window System is a client-server graphics system:

the server manages the display hardware, each typically including one or more video cards and monitors, one or more keyboards, and one or more mice or other pointing devices.
the client software connects to the server through one of several network transports to draw on the display, get status information, and receive input from the keyboard and mouse.

In a typical Linux system, the server and clients run on the same computer, although one or more clients may also be remotely connected.

Displayspecs

X servers are identified by a display specification or displayspec: [server]:display[.screen]

Where:

server is the hostname of the server: blank for local connections via the fastest avilable means; localhost for local connections via TCP/IP; or a hostname for remote connections via TCP/IP.
display is the display number. These are numbered starting at zero. The port number used for TCP/IP connections is (6000+display).
screen is the screen number if the display supports multiple screens (this is mostly obsolete; most multi-screen X servers now merge them into a single display, using the Xinerama protocol extension).

Therefore:

the default local display number is :0
display 0 on the host red.example.com is red.example.com:0

Displayspecs are communicated to client programs through the DISPLAY environment variable (or, less often, through command-line arguments).

Remote Access to an X Server with SSH

To run a client in a remote location from the server, you can run the raw X protocol over tcp/ip or other network transports. However, this is very insecure and is not recommended. Instead, current best practice is to use an ssh session to tunnel the X traffic.

Most standard ssh clients can set up the tunnel, X authentication, and other details necessary by simply including the -X or -Y command line parameters.

In these examples:

red is the local computer, running an X server
blue is the remote computer on which the client program will be run
user is the name of the user on blue

To connect to blue and start a shell, from which any program may be run:

ssh -XC user@blue

The -X argument sets up the X tunnel, while the -C argument turns on data compression for improved performance.

To connect to blue and start the program gnome-calculator:

ssh -XC user@blue gnome-calculator

Not for Benchmarking
This is not a good solution for benchmarking because the performance will vary with network conditions.

Using VNC

VNC is a remote display software that originated at Olivetti Research Labs in Cambridge UK. It is cross-platform and very lightweight. The underlying protocol is called rfb (for remote frame buffer). There are many different software packages that support various aspects of the vnc/rfb system.

When used with the X Window System, it is necessary to have a dual server that functions as both an X server and a VNC server. The easiest way to do this is to run the vncserver script from the tigervnc-server package, which configures and then start the Xvnc server. To connect X client, set and export the DISPLAY environment variable; to connect a VNC client, use this command: vncviewer -via blue localhost:display

Using Xvfb

Xvfb<code> is a dummy X server that does not display output on any device. This is useful where a program needs to connect to an X server, perhaps for testing purposes, but the actual image drawn does not have to be viewed anywhere. Xvnb would typically be invoked with a command such as:

Xvfb :0 -ac

Where <code>:0 is the display number and -ac disables access control to allow any local client to connect. You can then connect a client by setting and exporting the DISPLAY variable and starting the client:

export DISPLAY=:0
gnome-calculator

Resources

X Power Tools, a book by Chris Tyler published by O'Reilly Media and available through the Seneca Libraries on-line services.