xdpyinfo

xdpyinfo [-display displayname] [-queryExtensions]

-display displayname
    Specifies the X server to connect to. If not specified, the value of the DISPLAY environment variable is used.

-queryExtensions
    Queries for the available extensions and prints them to the output. Defaults to `off` if it's not specified.

The xdpyinfo command displays information about an X server, such as its vendor, version, extensions supported, screen sizes, and available fonts and colors. It's a valuable tool for diagnosing X server configuration issues, identifying supported capabilities, and understanding the environment in which graphical applications will run.

It queries the X server using the X11 protocol and presents the retrieved data in a human-readable format. The information displayed can be useful for developers to understand the capabilities of the X server where their application will run. This is particularly useful in heterogeneous environments where different X servers with different capabilities may be present. The command provides insights into the resources and features available on a particular X server instance.

The information displayed by xdpyinfo is dependent on the capabilities reported by the X server itself. Some X servers might not accurately report all supported features or extensions. This command requires a connection to an X server to function properly.

The output of xdpyinfo is structured into several sections, including server vendor, version, list of extensions, number of screens, and visual information for each screen. Each screen has additional details regarding depth, resolutions and color maps. Examining this information helps understand the server's setup and available features.

The xdpyinfo command has been a part of the X Window System since its early days. It was developed as a utility for querying and displaying information about the X server, providing a standardized way to determine the server's capabilities and configuration. Its primary purpose was to aid developers and administrators in understanding and troubleshooting X server environments. Over time, the basic functionality has remained relatively consistent, with updates primarily focusing on supporting newer X server extensions and features.

xprop(1), xwininfo(1), xrandr(1)