Monday, 12 May 2014

How to compile Linux kernel(Stepwise)

Step # 1 Get Latest Linux kernel code
Visit and download the latest source code. File name would be linuxx.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
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 

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.
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 

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

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

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

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