You purchased a new hardware but the current kernel does not support it, or need to add functionality to the kernel that does not come from the factory.

It is at those times that is necessary to compile a new kernel for the device to be recognized or a new functionality can be used by the software, for example.

I will show you how to compile a new kernel on CentOS / Red Hat Linux.

Pre-requisite

• CentOS / RedHat 5.3 minimal installation (Portuguese only)

Download latest kernel do Linux

The latest version can be get straight from http://www.kernel.org/pub/linux/kernel/v2.6/

Downloading the kernel source (at this moment is 2.6.30.5)

wget http://www.kernel.org/pub/linux/kernel/v2.6/linux-2.6.30.5.tar.bz2

After you have done it, extract to /usr/src

tar jxvf linux-2.6.30.5.tar.bz2 -C /usr/src

...
linux-2.6.30.5/virt/
linux-2.6.30.5/virt/kvm/
linux-2.6.30.5/virt/kvm/coalesced_mmio.c
linux-2.6.30.5/virt/kvm/coalesced_mmio.h
linux-2.6.30.5/virt/kvm/ioapic.c
linux-2.6.30.5/virt/kvm/ioapic.h
linux-2.6.30.5/virt/kvm/iodev.h
linux-2.6.30.5/virt/kvm/iommu.c
linux-2.6.30.5/virt/kvm/irq_comm.c
linux-2.6.30.5/virt/kvm/kvm_main.c
linux-2.6.30.5/virt/kvm/kvm_trace.c

To made things simple, go to /usr/src and create a symlink to source code called linux, do this:

cd /usr/src
ln -sf linux-2.6.30.5 linux

Result:

ls -al

drwxr-xr-x  3 root root 4.0K Sep  2 06:18 .
drwxr-xr-x 13 root root 4.0K Aug 31 14:25 ..
lrwxrwxrwx  1 root root   14 Sep  2 06:18 linux -> linux-2.6.30.5
drwxrwxr-x 22 root root 4.0K Aug 16 18:19 linux-2.6.30.5

Preparing the environment to compile Kernel

To compile the Kernel on Linux, the OS need to be prepared, with gcc, ncurses etc.

If your CentOS or Red Hat installation is the minimal, the devel packages weren’t installed, it is needed to do it now, it’s simple with Yum that will resolve all dependencies.

yum install gcc make bison ncurses-devel rpm-build

...
Installed: bison.i386 0:2.3-2.1 gcc.i386 0:4.1.2-44.el5 ncurses-devel.i386 0:5.5-24.20060715
Dependency Installed: cpp.i386 0:4.1.2-44.el5 glibc-devel.i386 0:2.5-34.el5_3.1 glibc-headers.i386 0:2.5-34.el5_3.1 kernel-headers.i386 0:2.6.18-128.7.1.el5 libgomp.i386 0:4.3.2-7.el5
Updated: glibc.i686 0:2.5-34.el5_3.1 glibc-common.i386 0:2.5-34.el5_3.1 nscd.i386 0:2.5-34.el5_3.1

Compiling the kernel to CentOS or Red Hat

Before starting the compilation, it is interesting to clean the garbage that should left behind.

make clean

A good idea is to take the parameters of configuration that comes with the factory one, this file can be found at /boot dir, let’s copy it to the root of our kernel source and execute make menuconfig.

cd /usr/src/linux
cp /boot/config-`uname -r` .config

Be sure to stay on /usr/src/linux.
Accessing the configuration menu is the easy way to configure it.

make menuconfig

As this is a custom compilation, I suggest you to add a custom tag that will identify the new kernel, to accomplish this, do that:

• On initial screen, go to General setup  —>

• Select Local version – append to kernel release

With this done, the resulting kernel.rpm will have the tag identifying it.

It is time to customize the kernel configuration to fit with your hardware.

After this task, it’s time to quit from menuconfig and start the compilation.

While you get out the configuration, you will be asked to save the changes. Answer Yes.

The most awaited time… compiling!

Run make rpm

make rpm

...
  HOSTLD  scripts/kconfig/conf
scripts/kconfig/conf -s arch/x86/Kconfig
make clean
set -e; cd ..; ln -sf /usr/src/linux-2.6.30.5 kernel-2.6.30.5fogonacaixadagua
/bin/sh /usr/src/linux-2.6.30.5/scripts/setlocalversion > /usr/src/linux-2.6.30.5/.scmversion
set -e; cd ..; tar -cz --exclude SCCS --exclude BitKeeper --exclude .svn --exclude CVS --exclude .pc --exclude .hg --exclude .git -f kernel-2.6.30.5fogonacaixadagua.tar.gz kernel-2.6.30.5fogonacaixadagua/.
...

The compilation will start, it will take a looong time.

At the end of process, without errors:

...
Wrote: /usr/src/redhat/SRPMS/kernel-2.6.30.5fogonacaixadagua-1.src.rpm
Wrote: /usr/src/redhat/RPMS/i386/kernel-2.6.30.5fogonacaixadagua-1.i386.rpm
...

The kernel was compiled and a .rpm was generated to be installed.

To confirm that the new kernel really exists in a rpm format, run:

ls -alh /usr/src/redhat/RPMS/i386/

total 164M
drwxr-xr-x 2 root root 4.0K Sep  2 11:45 .
drwxr-xr-x 9 root root 4.0K Sep  2 10:39 ..
-rw-r--r-- 1 root root 164M Sep  2 11:45 kernel-2.6.30.5fogonacaixadagua-1.i386.rpm

RPM of the new kernel (32 bits)

I’m putting the compiled kernel and packaged here, feel free to download it.

• kernel-2.6.30.5fogonacaixadagua-1.i386.rpm

Installing the new kernel

How was generated a RPM of kernel, the installation becomes quite simple

rpm -ivh /usr/src/redhat/RPMS/i386/kernel-2.6.30.5fogonacaixadagua-1.i386.rpm

Preparing...                ########################################### [100%]
   1:kernel                 ########################################### [100%]

Confirming that the new kernel was installed.

ls /boot

config-2.6.18-128.el5                 symvers-2.6.18-128.el5.gz
config-2.6.30.5-fogonacaixadagua      System.map-2.6.18-128.el5
grub                                  System.map-2.6.30.5-fogonacaixadagua
initrd-2.6.18-128.el5.img             vmlinux-2.6.30.5-fogonacaixadagua.bz2
initrd-2.6.30.5-fogonacaixadagua.img  vmlinuz-2.6.18-128.el5
lost+found                            vmlinuz-2.6.30.5-fogonacaixadagua

Creating the initrd for the new kernel

To create the dependencies for the modules:

depmod 2.6.30.5-fogonacaixadagua

You must create a new initrd so the OS can start and pre-load the modules necessary to your hardware.

mkinitrd -v /boot/initrd-2.6.30.5-fogonacaixadagua.img 2.6.30.5-fogonacaixadagua

In case the following error occour:

No module dm-mem-cache found for kernel 2.6.30.5-fogonacaixadagua, aborting.

mkinitrd --without-dmraid -v /boot/initrd-2.6.30.5-fogonacaixadagua.img 2.6.30.5-fogonacaixadagua

Editing grub

Final phase, it remains only edit the grub.conf to use the new kernel.

With your favorite text editor, add the following lines:

title CentOS (2.6.30.5-fogonacaixadagua)
        root (hd0,0)
        kernel /vmlinuz-2.6.30.5-fogonacaixadagua ro root=/dev/VolGroup00/LogVol00
        initrd /initrd-2.6.30.5-fogonacaixadagua.img

The file /boot/grub/grub.conf will be like this:

# grub.conf generated by anaconda
#
# Note that you do not have to rerun grub after making changes to this file
# NOTICE:  You have a /boot partition.  This means that
#          all kernel and initrd paths are relative to /boot/, eg.
#          root (hd0,0)
#          kernel /vmlinuz-version ro root=/dev/VolGroup00/LogVol00
#          initrd /initrd-version.img
#boot=/dev/sda
default=0
timeout=5
splashimage=(hd0,0)/grub/splash.xpm.gz
hiddenmenu
title CentOS (2.6.18-128.el5)
	root (hd0,0)
	kernel /vmlinuz-2.6.18-128.el5 ro root=/dev/VolGroup00/LogVol00
	initrd /initrd-2.6.18-128.el5.img
title CentOS (2.6.30.5-fogonacaixadagua)
        root (hd0,0)
        kernel /vmlinuz-2.6.30.5-fogonacaixadagua ro root=/dev/VolGroup00/LogVol00
        initrd /initrd-2.6.30.5-fogonacaixadagua.img

For the first boot, let the line default=0 to test, if the new kernel boot with no trouble it will be ok to change the line to default=1 to always boot with the new kernel.

Testing a boot with the new kernel

Reboot.

shutdown -r now

• Press any key on boot screen to enter the selection kernel

• Select the new kernel configured into Grub

• At the end of the boot, it will be possible to see that the new one booted properly