Once an X server is running, X client applications can connect to it and create a GUI for the user. A range of GUIs are possible with Red Hat Enterprise Linux, from the rudimentary Tab Window Manager to the highly developed and interactive GNOME desktop environment that most Red Hat Enterprise Linux users are familiar with.
To create the latter, more advanced GUI, two main classes of X client applications must connect to the X server: a desktop environment and a window manager.
A desktop environment brings together assorted X clients which, when used together, create a common graphical user environment and development platform.
Desktop environments have advanced features allowing X clients and other running processes to communicate with one another, while also allowing all applications written to work in that environment to perform advanced tasks, such as drag and drop operations.
Red Hat Enterprise Linux provides two desktop environments:
GNOME — The default desktop environment for Red Hat Enterprise Linux based on the GTK+ 2 graphical toolkit.
KDE — An alternative desktop environment based on the Qt 3 graphical toolkit.
Both GNOME and KDE have advanced productivity applications, such as word processors, spreadsheets, and Web browsers, and provide tools to customize the look and feel of the GUI. Additionally, if both the GTK+ 2 and the Qt libraries are present, KDE applications can run in GNOME and visa versa.
Window managers are X client programs which are either part of a desktop environment or, in some cases, standalone. Their primary purpose is to control the way graphical windows are positioned, resized, or moved. Window managers also control title bars, window focus behavior, and user-specified key and mouse button bindings.
Four window managers are included with Red Hat Enterprise Linux:
kwin — The KWin window manager is the default window manager for KDE. It is an efficient window manager which supports custom themes.
metacity — The Metacity window manager is the default window manager for GNOME. It is a simple and efficient window manager which supports custom themes.
mwm — The Motif window manager is a basic, standalone window manager. Since it is designed to be a standalone window manager, it should not be used in conjunction with GNOME or KDE.
twm — The minimalist Tab Window Manager, which provides the most basic tool set of any of the window managers and can be used either as a standalone or with a desktop environment. It is installed as part of the X11R6.8 release.
These window managers can be run without desktop environments to gain a better sense of their differences. To do this, type the xinit -e <path-to-window-manager> command, where <path-to-window-manager> is the location of the window manager binary file. The binary file can be found by typing which <window-manager-name>, where <window-manager-name> is the name of the window manager you are querying.