xdpyinfo

xdpyinfo [-display <displayname>] [-queryExtensions] [-queryBigRequests] [-querySecurity] [-queryShm] [-queryXFree86-Misc] [-queryXFree86-VidMode] [-queryDPMI] [-version] [-help]

-display <displayname>
    Specifies the X server display to connect to (e.g., :0, hostname:0.0). This overrides the DISPLAY environment variable.

-queryExtensions
    Reports whether various X extensions are supported by the server. This is usually the default behavior unless specific queries are requested.

-queryBigRequests
    Reports whether the BIG-REQUESTS extension, enabling large X protocol requests, is supported by the server.

-querySecurity
    Reports whether the SECURITY extension for server-side access control and authentication is supported.

-queryShm
    Reports whether the MIT-SHM (shared memory) extension, for efficient image transfer between client and server, is supported.

-queryXFree86-Misc
    Reports whether the XFree86-Misc extension, offering various miscellaneous features specific to XFree86, is supported.

-queryXFree86-VidMode
    Reports whether the XFree86-VidMode extension, for changing video modes and adjusting display settings, is supported.

-queryDPMI
    Reports whether the DPMI (Display Power Management Signaling) extension is supported. Note: This extension is largely obsolete and may not be present in modern X servers.

-version
    Prints the program version information for xdpyinfo and exits immediately.

-help
    Prints a usage message detailing command options and exits.

xdpyinfo is a fundamental command-line utility for the X Window System, designed to provide comprehensive details about the capabilities and configuration of a connected X server. Upon execution, it establishes a connection to the specified X display and outputs a rich array of technical data.

This includes essential information such as screen dimensions, available visual types (like color depths, pixel formats, and colormap classes), a list of supported X extensions (e.g., RANDR for screen resizing, GLX for OpenGL rendering, Xinerama for multi-head setups, or MIT-SHM for shared memory), configured font paths, and server-specific details like vendor information and release version. Furthermore, it can report on keyboard and pointer capabilities.

xdpyinfo serves as an invaluable diagnostic tool for troubleshooting display-related issues, verifying graphics driver installations, debugging X applications, and understanding the precise rendering environment. It empowers users and developers to quickly ascertain which X features and configurations are available, which is crucial for ensuring application compatibility and optimal performance within a specific X server setup.

Some extensions (e.g., DPMI, XFree86-*) are historical and may not be supported by modern X servers, often leading to 'no such extension' messages in the output.

The default output of xdpyinfo is very verbose, containing a large amount of technical detail. Users frequently pipe its output to tools like less for pagination or grep for filtering specific information (e.g., xdpyinfo | grep "GLX").

xdpyinfo requires a running X server and an active display connection to function correctly. Without these, it will fail to connect.

xdpyinfo is often the first tool to use when diagnosing X-related issues, such as unexpected resolutions, graphics driver problems, or application compatibility. By examining the server's reported capabilities, users can verify whether required features (e.g., specific visual depths or extensions) are available.

Due to its structured output, xdpyinfo is highly scriptable. System administrators and developers often combine it with other command-line utilities like grep, awk, or sed to extract specific configuration details for automated checks, logging, or dynamic environment setup.

xdpyinfo is a foundational utility that has been an integral part of the X Window System since its inception in the mid-1980s. Its development has closely mirrored the evolution of the X protocol, adapting to new extensions and features introduced over the decades. As X passed through different development phases (e.g., from XFree86 to X.Org), xdpyinfo consistently provided a standardized command-line interface for querying server capabilities, remaining a stable and essential tool for understanding the underlying X server environment.

xwininfo(1), xprop(1), xlsfonts(1), xrandr(1), xvinfo(1)