Root Window

In the X Window System, every window is contained within another window, called its parent. This makes the windows form a hierarchy. The root window is the root of this hierarchy. It is as large as the screen, and all other windows are either children or descendants of it.

Since every window covers the part of its parent it is staying on, all other windows appear to be above the root window. As a result, the root window is visible as the part of the screen that is behind all other windows. In other words, the root window forms the background of the screen. An image can be used as the wallpaper of the screen by setting it as the background image of the root window. This can be done for example using the xsetroot or the xv programs.

The direct children of the root window are called top-level windows. These windows are usually drawn with a decorative frame and a title bar (which are actually added by the window manager). The top-level windows are, informally, the regular windows in the terminology of most GUIs. The windows that are not top-level are used for buttons, textboxes, etc.

The properties of the root window are sometimes used as a rudimentary form of inter-client communication means. For example, the cut buffers are properties of the root window that are used for copying selected text from a window to another, and the dwm window manager displays the root window's name in a status area. The X resources are also stored, during execution, in a property of the root window.