Compile Linux Kernel 2.6

I have never done a blog on "kernel" compile in the past and with the growing ease of using Linux nowadays one would ask.  Who needs compiling it? Apparently, it has its uses and for those experimenting with Linux and or maybe doing a sort of review, prior to taking an exam.  I came across this wonderfully crafted easy to use kernel compile tutorial.  When I sifted through it, I realised how simple it was to compile Linux kernel.

I am taking this opportunity to re-post this article for purposes of good archiving as with all my other post.  I look for a candidate where I can equally enjoy and have the luxury of messing up the system if something goes wrong it won't be a big deal.  The target machine was a debian lenny 5.0 which I just downloaded (11-28-2010).  Installed the base and configured networking to set the stage. Read on.

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-2.6.36.1.tar.bz2 represents 2.6.36.1 kernel version. Use wget command to download kernel source code:
$ cd /tmp
$ wget http://www.kernel.org/pub/linux/kernel/v2.6/linux-2.6.36.1.tar.bz2
Note: Replace x.y.z with actual version number (in my case its the actual current kernel on the site).

Step # 2 Extract tar (.tar.bz2) file

Type the following command:
# tar -xjvf linux-2.6.36.1.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.

Step # 4 Compile kernel

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.

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-2.6.36.1
• config-2.6.36.1
• vmlinuz-2.6.36.1

Step # 6: Create an initrd image

Type the following command at a shell prompt:
# cd /boot
# mkinitrd -o initrd.img-2.6.36.1 2.6.36.1
* In my case I used mkinitramfs -o initrd.img-2.6.25 (which ever version number of kernel you downloaded)

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 2.6.36.1 Default
root            (hd0,0)
kernel          /boot/vmlinuz-2.6.36.1 root=/dev/hdb1 ro
initrd          /boot/initrd.img-2.6.36.1 

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 
... Searching for GRUB installation directory ... found: /boot/grub
Searching for default file ... found: /boot/grub/default
Testing for an existing GRUB menu.lst file ... found: /boot/grub/menu.lst
Searching for splash image ... none found, skipping ...
Found kernel: /vmlinuz-2.6.36.1
Found kernel: /vmlinuz-2.6.26-2-686
Updating /boot/grub/menu.lst ... done


Neat. Huh?

Step # 8 : Reboot computer and boot into your new kernel

Just issue reboot command:
# reboot

So depending on how you setup your menuconfig in the first part would dictate on how long the compile and the installation of the modules for the new kernel will take.  In my case its almost one day.  Good luck.


Notes:

1. If for example you experienced an error during the initial "make" chances are you have several packages that is missing one such package is the libncurses5-dev (if you are using debian based system) package.
2. Make sure you have enough disc space on the directory you will be building the sources, in my recent experience, I needed at least 6Gb of free space under /usr/src to get it done.