devfb0

devfb0, commonly referred to as /dev/fb0, is the first framebuffer device node exposed by the Linux kernel’s framebuffer subsystem. It provides a simple, memory-mapped interface to the display hardware, allowing programs to render graphics directly to the screen in a pixel-based format.

The device is created by framebuffer drivers that correspond to the system’s video hardware. When a compatible driver is loaded, it registers the framebuffer device and exposes it to user space as /dev/fb0 (with additional devices like /dev/fb1 when more framebuffers are present). Access to the device is typically restricted to privileged users or those granted access to the video group, depending on system policy.

Interaction with /dev/fb0 is primarily through ioctl calls and direct memory access. Two main data structures describe the display: fb_fix_screeninfo (static properties such as the line length and framebuffer memory start) and fb_var_screeninfo (variable properties such as resolution, bits-per-pixel, and color depth). Userspace programs can obtain and modify these parameters, and map the framebuffer into their address space with mmap to write pixel data directly. Pixel formats vary by driver and mode but commonly include 8, 16, 24, or 32 bits per pixel.

On modern systems, the kernel’s DRM/KMS subsystem and graphical servers may handle rendering, with framebuffer devices retained for compatibility or early boot. As a result, /dev/fb0 may not always represent active graphics output in use, especially on systems using full KMS-based pipelines.

Related concepts include additional framebuffer devices like /dev/fb1, various framebuffer drivers (vesa, intelfb, omapfb), and tools such as fbset or simple graphics utilities that operate through the framebuffer. Proper permissions and driver support determine accessibility and functionality.