How to recompile Kernel?

Kernel Recompilation

Compiling custom kernel has its own advantages and disadvantages.  It helps to optimize the kernel to your environment (hardware and usage patterns).  I shall try to guide you through Kernel recompilation process.

Step 1:

Download the kernel source

cd /usr/local/src

wget  http://www.kernel.org/pub/linux/kernel/v2.6/linux-x.y.z.tar.bz2

Note: Replace x.y.z with actual version number.

Step 2:

Extract the  source file

tar -xjvf linux-x.y.z.tar.bz2

Step 3:

Patching the Kernel

If you are requested to apply any patches , follow these steps

a) Move the downloaded kernel patch to the /usr/local/src directory.

b)  Extract the patch file

c)  Patch the kernel  source using the extracted  patch file

cd /usr/local/src/linux-x.y.z

patch -p1 < patchfile-2.2.x

Now the  Kernel Source is patched against known  vulnerabilities.

Step 4:

Configuration

If you are trying to upgrade the Kernel of already running server , it is always better use the existing configuration. To do this follow these steps

#uname -a
Linux  Server1  2.6.18-164.el5 #1 SMP Thu Sep 3 03:28:30 EDT 2009 x86_64 x86_64 x86_64 GNU/Linux

# cd /boot

There you can see different configuration files as given below

#ls

config-2.6.18-128.el5    initrd-2.6.18-128.el5.img  message
config-2.6.18-164.el5     initrd-2.6.18-164.el5.img  quota.user*

identify the configuration file corresponding to the version of OS installed , In our case it is config-2.6.18-164.el5 . We are  copying this file to the downloaded kernel source  to use it during configuration.

#cp -p config-2.6.18-164.el5 /usr/local/src/linux-x.y.z/.config

# make clean

# make mrproper

# make menuconfig

You have to select different options as per your need.   If you  intended to use the existing configuration ,specify the path to the file  ( .config in this case) by selecting the option

“Load an Alternative configuration file”

Step 5: Compilation

Compile the Kernel using the following commands

Compile to create a compressed kernel image

# make

Compile kernel modules:

# make modules

Install kernel modules

# make modules_install

Step 6: Install Kernel

If the above steps completed without any errors , now its the time to Install the new Kernel

# make install

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

System.map-x.y.z

config-x.y.z

vmlinuz-x.y.z

Step 7:  Create the Initrd image

Type the following command :

# cd /boot

# mkinitrd -o initrd.img-x.y.x  x.y.z

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

Step 8: Boot Loader Modification

Mofdify the boot loader to boot the new OS as default . Check the documentaions corresponding to your boot loader

Step 9: The last step

execute the following command

#reboot

Wait a few minutes and once it is up , you can see that the new Kernel is loaded