The joy of X - master the Linux GUI

David M Williams
Sunday, 12 October 2008 11:11

Opinion and Analysis

Call up a command prompt to begin our exploration of X. Enter the command

ps -e | grep X

and you will see two running processes listed, with output similar to mine

2537 tty7 00:00:46 Xorg
3022 ?    00:00:00 Xsession

Let’s get more detail; add the –f modifier to the ps command:

ps -ef | grep X

Your output should now be like this:

root  2537 2536 1 12:28 tty7 00:00:46 /usr/bin/Xorg :0 –br –verbose –auth ...
david 3022 2883 0 12:33 ?    00:00:00 /bin/bash /etc/gdm/Xsession gnome-session

I truncated the command on the first line because it will be lengthy, but you can see some very important and interesting things here.

Firstly, running under the root user’s authority is a process called Xorg. This is X itself. It is launched when your computer fires up its graphical interface.

The first parameter to Xorg is :0 which means it is managing the first monitor on my computer. In a multi-monitor environment the number can vary. Also, a computer name can appear before the colon (“:”) which would mean X is managing the display for another computer, or terminal.

Many instances of X can be running on the one computer, each administering a different display over a range of network devices. For most of us, we will just have the one X session for the single display on our own machine.

Next, running under my name is a X session. This launched when I logged in. The parameter to Xsession is a command titled gnome-session. As you might expect, this fires the GNOME desktop environment on my Linux system.

It will make sense to you that the Xsession process could start something other than GNOME. And you will also appreciate that no matter whether I am running GNOME or KDE, or another desktop environment altogether, they are still residing within the overall X scheme of things.

You might also have guessed that if the gnome-session launches when I log in it's conceivable any individual user on the one computer could have a totally different session.

No matter which environment I will use, it is still X managing the display and it is still an X session that is used when I log in. (There are more processes involved than just the two I mentioned; specifically, there are some other elements to gdm but the above is sufficient for our purposes.)

With this under your belt, here are some ways to configure your X programs however you like.

CONTINUED