Xvfb

Xvfb, or X virtual framebuffer, is a display server that implements the X11 protocol and renders graphics to an in-memory framebuffer rather than to a physical monitor. It enables X11 applications to run on systems without a connected display, such as headless servers, containers, or automation environments.

Xvfb is widely used for automated testing, continuous integration, remote rendering, and screenshot generation of GUI applications. By providing a DISPLAY variable that points to a virtual display, programs can operate as if they were running on a real X server without requiring hardware graphics output. It can be combined with tools and wrappers to simplify usage in scripts.

In operation, Xvfb runs as a background process with a chosen display number, for example :1. It creates one or more screens defined by the -screen option, such as -screen 0 1024x768x24, where the resolution and color depth are specified. Applications connect to the server via the specified display and render to the virtual framebuffer. Output can later be captured or exported to image files, videos, or through auxiliary services.

Usage commonly involves starting Xvfb directly or using a wrapper like xvfb-run, which launches a command within the virtual display environment. For example: Xvfb :1 -screen 0 1024x768x24 & export DISPLAY=:1; my_gui_application. This approach avoids configuring a real X server and is particularly common in CI pipelines and headless testing.

Limitations include the absence of real hardware output, which can affect applications relying on physical displays or certain GPU features. GLX and hardware acceleration may be limited or require software rendering. Xvfb is often complemented by other virtual display tools when full desktop interactions are needed.