Custom Linux Kernels Trim Fat and Tune Performance - page 2
You can get
freshly-baked kernels and the latest patches from Kernel.org. These are called
kernels because this is where the original, unmodified kernels
live. Then you need to assemble your build environment. Both Fedora
and Debian make this easy. On Fedora, install the
Tools package group:
# yum groupinstall 'Development Tools'
You'll also want Qt:
# yum install qt-devel
On Debian use this command:
# aptitude install build-essential libqt3-mt-dev qt3-dev-tools
Documentation/Changes file in your unpacked source
tarball gives you a basic list of applications that you need for a
build environment. In fact you should invest a lot of time exploring
the documentation that comes in the kernel tarball--there is a wealth
of knowledge squirreled away in there.
When you download and unpack your new kernel sources don't put
/usr/src, and pay no attention to all the people who
tell you to do that. Create a directory in your home directory to keep
your source trees in. The kernel README itself says:
"...put the kernel tarball in a directory where you have permissions (eg. your home directory)...Do NOT use the /usr/src/linux area! This area has a (usually incomplete) set of kernel headers that are used by the library header files. They should match the library, and not get messed up by whatever the kernel-du-jour happens to be."
Unpack your kernel tarball with
linux-2.6.22.tar.bz2, using your correct version of course. Then
change to the top-level kernel source directory and open the Makefile
in your favorite text editor. Change the
EXTRAVERSION = line to
something unique, like
EXTRAVERSION = .1-carla.
Next, let's see what options the
make command has:
$ make help
This is going to spit out a lot of information. Take some time to look it over. Read the Makefile itself, which is a plain-text file. Then do a bit of housecleaning:
$ make mrproper
Read the output of
make help to see what this does. It
shouldn't be necessary at this stage, but it's cheap insurance and
sometimes you inherit funky stuff.
Now we get to the fun part- configuring our new kernel-to-be:
$ make xconfig
You'll see something like Figure 1.
This is the part that takes a lot of time. If you don't have a
config file in your kernel source tree or supply one on
xconfig will use your
This isn't a problem, but a good starting point. You can change
anything you want anyway. Click the Help button to see how to use
xconfig. Every configuration option has a description, and next
week we'll review some of them.
Once you are happy with your configuration, run the
command with no options. This will take some time, maybe up to an hour
or more. Then change to root and run these commands:
# make modules_install # mkinitrd -o /boot/initrd-2.6.22.img # cp ~/kernel/linux-2.6.22/arch/i386/boot/bzImage /boot/vmlinuz-2.6.22 # cp ~/kernel/linux-2.6.22/System.map /boot/System.map-2.6.22
arch/i386/boot/bzImage is your new kernel, and it must
be copied to the
/boot directory. Copy over the matching
System.map, and your new
initrd image should already be
Add all of this to your GRUB menu, reboot, and give it a whirl.
This is an example
title homebrew 2.6.22 kernel root (hd0,0) kernel /boot/vmlinuz-2.6.22 root=UUID=b099f554-db0b-45d4-843e-0d6a1c43ba44 ro initrd /boot/initrd-2.6.22.img
The kernel names and
initrd image names are arbitrary;
you could call them anything you want, as long your
entries match. GRUB counts from zero, so
/dev/hda1, which is
the first partition on the first hard drive, equals
The root partition's UUID comes from running the
$ blkid /dev/sda1: UUID="b099f554-db0b-45d4-843e-0d6a1c43ba44" SEC_TYPE="ext2" TYPE="ext3" /dev/hda1: UUID="1a5408ad-7d1d-4e24-b9db-d132d76e9e8e" SEC_TYPE="ext2" TYPE="ext3"
In this shiny new era of
udev, you should use UUIDs to
identify your block devices because
/dev names are no longer
static, but at the mercy of
udev. You need to create an
initrd image because the
/dev directory is not populated
until after boot, so there is no way (that I know of) to build the
boot device into the kernel anymore.
Next time we'll learn the Debian and the Fedora way of customizing kernels, and review some of the meelyuns of kernel compilation options.
- Debian Kernel Handbook
- Compiling a Custom Linux Kernel
- Advanced kernel customizers might try the dphys- kernel-packages package for creating configuation files for automating the creation of custom kernels
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