RandR

RandR, short for Resize and Rotate, is an extension to the X Window System that enables dynamic management of display configurations. It allows X clients to query the available display outputs, set screen resolutions and refresh rates, and configure the position, orientation, and activation state of each output. RandR also handles hot-plugging of monitors so that the X server can update the layout automatically when displays are connected or removed.

The extension defines a model consisting of outputs (one per monitor port), each with a set of supported modes, a current mode, and properties such as rotation and reflection. It supports multiple screens and thus enables multi-monitor setups. The server and graphics drivers cooperate through RandR to reconfigure how content is scanned and drawn, allowing changes to be applied without restarting the X server.

Most desktop environments rely on RandR through the xrandr command-line tool to query status and apply changes, while the API is used by window managers and compositors to implement dynamic display management. Common operations include listing outputs and modes, enabling or disabling outputs, changing resolution, and rotating the display. RandR supports dynamic updates in response to hardware changes or user requests.

History and scope: RandR originated as part of the X.Org project to provide on-the-fly display configuration. It has evolved through several revisions to add features such as independent per-output configuration and improved handling of rotated and reflected displays. RandR is widely supported by modern GPUs and Unix-like operating systems and remains a standard mechanism for display management within X-based environments. In Wayland-based environments, similar functionality is provided by different subsystems, but RandR remains central to X implementations.