How to: Compile Linux kernel 2.6

Compiling custom kernel has its own advantages and disadvantages. However, new Linux user / admin find it difficult to compile Linux kernel. Compiling kernel needs to understand few things and then just type couple of commands. This step by step howto covers
compiling Linux kernel version 2.6.xx under Debian GNU Linux. However, instructions remains the same for any other distribution except for apt-get command.

Step # 1 Get Latest Linux kernel code

Visit http://kernel.org/ and download the latest source code. File name would be linux-x.y.z.tar.bz2, where x.y.z is actual version number. For example file
inux-2.6.25.tar.bz2 represents 2.6.25 kernel version. Use wget command to download kernel source code:

$
 cd /tmp

$ wget http://www.kernel.org/pub/linux/kernel/v2.6/linux-x.y.z.tar.bz2[/code] 
Note: Replace x.y.z with actual version number.

Step # 2 Extract tar (.tar.bz3) file
Type the following command:

#
 tar -xjvf linux-2.6.25.tar.bz2 -C /usr/src

# cd /usr/src


Step # 3 Configure kernel
Before you configure kernel make sure you have development tools (gcc compilers and related tools) are installed on your system. If gcc compiler and tools are not installed then use apt-get command under Debian Linux to install development tools.

#
 apt-get install gcc


Now you can start kernel configuration by typing any one of the command:

$ make menuconfig - Text based color menus, radiolists & dialogs. This option also useful on remote server if you wanna compile kernel remotely.
$ make xconfig - X windows (Qt) based configuration tool, works best under KDE desktop
$ make gconfig - X windows (Gtk) based configuration tool, works best under Gnome Dekstop.

For example make menuconfig command launches following screen:

$
 make menuconfig


You have to select different options as per your need. Each configuration option has HELP button associated with it so select help button to get help.

Step # 4 Compile kernel
Start compiling to create a compressed kernel image, enter:

$
 make


Start compiling to kernel modules:

$
 make modules


Install kernel modules (become a root user, use su command):

$
 su -

# make modules_install


Step # 5 Install kernel
So far we have compiled kernel and installed kernel modules. It is time to install kernel itself.

#
 make install


It will install three files into /boot directory as well as modification to your kernel grub configuration file:

System.map-2.6.25
config-2.6.25
vmlinuz-2.6.25


Step # 6: Create an initrd image
Type the following command at a shell prompt:

#
 cd /boot

# mkinitrd -o initrd.img-2.6.25 2.6.25


initrd images contains device driver which needed to load rest of the operating system later on. Not all computer requires initrd, but it is safe to create one.

Step # 7 Modify Grub configuration file - /boot/grub/menu.lst
Open file using vi:

#
 vi /boot/grub/menu.lst

title           Debian GNU/Linux, kernel 2.6.25 Default
root            (hd0,0)
kernel          /boot/vmlinuz root=/dev/hdb1 ro
initrd          /boot/initrd.img-2.6.25
savedefault
boot


Remember to setup correct root=/dev/hdXX device. Save and close the file. If you think editing and writing all lines by hand is too much for you, try out update-grub command to update the lines for each kernel in /boot/grub/menu.lst file. Just type the command:

#
 update-grub


Neat. Huh?

Step # 8 : Reboot computer and boot into your new kernel
Just issue reboot command:

#
 reboot


For more information see:

Our Exploring Linux kernel article and Compiling
 Linux Kernel module only.
Official README file has more information on kernel and software requirement to compile it. This file is kernel source directory tree.
Documentation/ directory has interesting kernel documentation for you in kernel source tree.

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