Linux.Desktop.Hacks [Electronic resources] نسخه متنی

Hack 9. Graphics on the Console

Some of you might be familiar with a picture of Tux the
penguin in the upper-left corner of the screen when your system is
booting. Ever since kernel 2.2, this popular feature has graced many
a Linux boot sequence. To the untrained eye, it simply looks like a
penguin, but to the trained technical eye, it is a cunning use of the
Linux frame buffer.

A frame buffer is an abstraction for graphics hardware. This
abstraction provides a common set of instructions that programs can
use to access the graphics hardware on the computer. Most people see
the frame buffer as a grinning Tux when the system boots. However,
there's more to the frame buffer than a cartoon
penguin. Typically, frame buffers are used to render the console
graphically so that a resolution can be set on it. Frame buffers are
useful in a number of situations, some of which include the
following:

Providing a higher resolution

This allows for the display area to be much larger than before.

Greater color depth

When you use frame buffers, you can use more colors.

Bypassing X Windows

In some instances, certain Linux programs such as Mplayer can use the
frame buffer immediately, thus reducing the overhead of having to run
an X Windows desktop such as KDE or GNOME. This is suitable for use
on resource-limited embedded systems.

1.10.1. Setting Up the Kernel

Support for the frame buffer comes from the kernel itself. Most stock
kernels are supplied with frame-buffer support built into them, so
this shouldn't be a problem for most people. To
check if your kernel has support already, you can query it:

foo@bar:~$ grep -i config_fb /boot/config-$(uname -r)
CONFIG_FB=y

If you have frame buffers set, the line
CONFIG_FB=y will be displayed (in which case you
can move on to the next section "Configuring the
Bootloader"). If # CONFIG_FB is not
set is displayed instead, you will need to compile support
for the frame buffer into your kernel.

1.10.2. Configuring the Kernel

Details on compiling a kernel are discussed in [Hack #88], and in this hack, I will
simply discuss which options need to be included. The first thing to
do is to make sure development features
have
been enabled within the "Code maturity
level" options. Then, to enable frame buffers, go to
the "Console drivers" page and
enable "VGA text console" and
"Video mode selection" support.

There is a subsection under Console called
"Frame-buffer support." Underneath
that, you need to enable "Support for frame buffer
devices," "VESA VGA graphics
console," and "VGA 16-color
graphics console."

In addition, the subsection "Advanced low level
driver options" appears under
"Frame-buffer support." Under this
menu, you can enable specific levels of pixel support.

Now you can go ahead and compile the kernel.

You might see a frame-buffer driver specifically written for your video card and be tempted to use it instead of the VESA VGA driver. This can lead to serious problems if you also use an accelerated graphics driver for your video card. For example, never pick "nVidia riva" frame-buffer support if you plan to use the third-party NVIDIA accelerated graphics drivers. These two drivers do not play well together, and you're sure to have video crashes.

1.10.3. Configuring the Bootloader

When the bootloader loads the kernel, it will
pass
to it the parameters which you specify and these parameters affect
how you use the frame buffer. Just like you would normally tell it
which partition is your root partition, you can do the same thing by
telling the kernel the values you want to use for the frame buffer.

When using the frame buffer, people commonly require a higher
resolution for the command-line console. To set this option, you will
need to pass to the kernel the right video mode to use to enable the
frame buffer. Refer to Table 1-1 to determine the
code to use for your desired video mode.

When you have determined the correct video mode to use, you can pass
the kernel the vga parameter to set the mode.

1.10.3.1 Configure LILO

To configure LILO
to use a value from the table (as an example, 1024x768 with 16-bit
color), edit /etc/lilo.conf and find the
following line:

vga=normal

Change this to the mode you want, which in this example is
0x317:

vga=0x317

Finally, save the file, and as root run /sbin/lilo
-v.

1.10.3.2 Configure GRUB

You configure GRUB in much the
same way you configure LILO. The configuration file varies from
distribution to distribution, and this is discussed in [Hack #1]. Edit your grub configuration
file and add the vga parameter on the kernel line:

title foo
root (hd0,0)
kernel /vmlinuz ro root=/dev/hda2 vga=0x317

Thomas Adam