This FAQ assumes basic familiarity with the kernel. If the kernel is new to you, here's a great introduction.

There is also an official Framebuffer FAQ now available from http://www.tahallah.demon.co.uk/programming/Framebuffer-HOWTO-1.0.html (Even though this FAQ only lists the TGA card as working the Matrox cards will also work).

Q: What is the Linux frame buffer?
A: This is answered in the file Documentation/fb/framebuffer.txt which comes with the kernel source code. To summarize: "The frame buffer device provides an abstraction for the graphics hardware. It represents the frame buffer of some video hardware and allows application software to access the graphics hardware through a well defined interface, so the software doesn't need to know anything about the low-level (hardware register) stuff." The frame buffer is one of the new features of the 2.2 Linux kernel.

Q: Why is it helpful?
A: Two reasons: security and performance. Security is an issue because graphics hardware can copy data to and from memory using direct memory access, so allowing users unfettered access is a potential security hole. For this reason, only root (system administrator) can directly access the hardware, so graphics programs like X windows can only run as root. The kernel frame buffer interface prevents abuse of the hardware, so X windows running on the frame buffer can be run as the user, with fewer potential security problems. A simplistic argument goes like this: the frame buffer subroutines involve a few thousand lines of code, whereas X windows consists of about a million and a half, so it's easier to make the frame buffer code airtight. Performance is mainly an issue where the frame buffer can be used instead of X windows. The frame buffer adds about 50K to the size of a compressed alpha kernel, and uses vastly less RAM. However, there are currently very few programs that run in the frame buffer without X. (Some of them use GGI, the General Graphics Interface.)

Q: Does it work on Alpha?
A: Yes, the TGA frame buffer works fine and the Matrox Millennium frame buffer will work under some circumstances (other cards are unknown to the author).

Q: How do I make it work?
A: To use it, you have to build your own kernel, the first step of which is to type make config in the source directory. The Matrox frame buffer drivers are still experimental, you will need to answer `y' to the first question, "Prompt for development and/or incomplete code/drivers?" In the "Console drivers" section, answer `y' to "Support for frame buffer devices" and then answer subsequent questions according to your video hardware.

The kernel with Matrox Millennium frame buffer can not boot in graphics mode on alpha (with the penguin logo); the reason is currently unknown (it's not a logo drawing problem, and the init flag doesn't work). To boot in text mode, add video=matrox:vesa:0x108 (or any of the other text modes, e.g. 0x10B or 0x10C) to your boot line. You can switch into graphics mode after booting using the fbset program, which can change the resolution, timings, color depth, and acceleration status of the frame buffer. This switch can be made in /etc/rc.d/rc.sysinit if desired. NOTE: the documentation gives a URL for fbset 1.0, which no longer works. You can get the 2.0-pre source here (comes with documentation). Also, there is a bug in the 12/30 version (which will be fixed in the next version) such that using the -depth or -mode flags requires you add -accel true to the end of the command, e.g. fbset -depth 24 -accel true. Without this your system will crash. This may be required for other fbset commands as well.

The frame buffer can be built as a kernel module by answering `m' instead of `y' to all of the questions which allow it in the frame buffer section of make config. Start the frame buffer after booting using the modprobe command.

Q: Are there any problems with the frame buffer?
A: Yes, it can not boot with the Matrox frame buffer in graphics mode as mentioned above. (If you get it to work, please let me know!) When you change the screen width, problems can occur in programs which only check the width at startup, like bash (the Bourne Again Shell). You can restart bash after changing the screen width using exec bash -login. When ending an X session, you might get a blank screen or a solid block of color; switching the console a few times (alt-F2 or F3) eventually restores things. The Matrox Millennium II frame buffer does not currently seem to work on UX systems.

Q: Is there a mailing list?
A: Yes, there's a general frame buffer list. To join, send mail to Majordmo@vu.union.edu with message body "subscribe linux-fbdev".

Q: Which graphics cards are supported?
A: Currently the Matrox family of cards (Millennium, Mystique, G100/200) and the Digital TGA cards are supported for Alpha.

Q: How do I change fonts or start in different fonts?
A: Use the setkfont package by Petr Vandrovec which you can get here. For Matrox with non-8xY fonts though, such as SUN12x22, you need to add ,fastfont:50000 to your boot line video variable (no spaces), or add fastfont=50000 to your insmod matroxfb command, or your system will hang.

Q: How do I set up Xwindows with the frame buffer device?
A: You need to compile your own XFree86 libraries. Compile XF68_FBDev by enabling it in one of the config files (xc/config/cf/*cf).