How To Compile A Kernel - The CentOS Way - Page 2

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Submitted by falko (Contact Author) (Forums) on Sun, 2006-11-26 16:19. ::

3 Building A Kernel The Traditional Way

This chapter describes a different approach that can be used on any Linux system. As there's nothing CentOS-specific in this, of course you will not end up with a kernel rpm package.

 

3.1 Download The Kernel Sources

We download our desired kernel to /usr/src. Go to www.kernel.org and select the kernel you want to install, e.g. linux-2.6.18.3.tar.bz2 (you can find all 2.6 kernels here: http://www.kernel.org/pub/linux/kernel/v2.6/). Then you can download it to /usr/src like this:

cd /usr/src
wget http://www.kernel.org/pub/linux/kernel/v2.6/linux-2.6.18.3.tar.bz2

Then we unpack the kernel sources and create a symlink linux to the kernel sources directory:

tar xjf linux-2.6.18.3.tar.bz2
ln -s linux-2.6.18.3 linux
cd /usr/src/linux

 

3.2 Modify /etc/modprobe.conf

Now we must comment out the mptscsi module in /etc/modprobe.conf because otherwise we will get a warning like this:

WARNING: No module mptscsi found for kernel 2.6.18.3, continuing anyway

when we build our new kernel.

vi /etc/modprobe.conf

alias eth0 pcnet32
alias scsi_hostadapter mptbase
# alias scsi_hostadapter1 mptscsi
alias scsi_hostadapter2 mptfc
alias scsi_hostadapter3 mptspi
alias scsi_hostadapter4 mptsas
alias scsi_hostadapter5 mptscsih

 

3.3 Apply Patches To The Kernel Sources (Optional)

Sometimes you need drivers for hardware that isn't supported by the new kernel by default, or you need support for virtualization techniques or some other bleeding-edge technology that hasn't made it to the kernel yet. In all these cases you have to patch the kernel sources (provided there is a patch available...).

Now let's assume you have downloaded the needed patch (I call it patch.bz2 in this example) to /usr/src. This is how you apply it to your kernel sources (you must still be in the /usr/src/linux directory):

bzip2 -dc /usr/src/patch.bz2 | patch -p1 --dry-run
bzip2 -dc /usr/src/patch.bz2 | patch -p1

The first command is just a test, it does nothing to your sources. If it doesn't show errors, you can run the second command which actually applies the patch. Don't do it if the first command shows errors!

If your patches are compressed with gzip (.gz) instead of bzip2 (.bz2), then you patch your kernel as follows:

gunzip -c /usr/src/patch.gz | patch -p1 --dry-run
gunzip -c /usr/src/patch.gz | patch -p1

You can also apply kernel prepatches to your kernel sources. For example, if you need a feature that is available only in kernel 2.6.19-rc6, but the full sources haven't been released yet for this kernel. Instead, a patch-2.6.19-rc6.bz2 is available. You can apply that patch to the 2.6.18 kernel sources, but not to kernel 2.6.18.1 or 2.6.18.2 or 2.6.18.3, etc. This is explained on http://kernel.org/patchtypes/pre.html:

Prepatches are the equivalent to alpha releases for Linux; they live in the testing directories in the archives. They should be applied using the patch(1) utility to the source code of the previous full release with a 3-part version number (for example, the 2.6.12-rc4 prepatch should be applied to the 2.6.11 kernel sources, not, for example, 2.6.11.10.)

So if you want to compile a 2.6.19-rc6 kernel, you must download the 2.6.18 kernel sources (http://www.kernel.org/pub/linux/kernel/v2.6/linux-2.6.18.tar.bz2) in step 3.1 instead of kernel 2.6.18.3!

This is how you apply the 2.6.19-rc6 patch to kernel 2.6.18:

cd /usr/src
wget http://www.kernel.org/pub/linux/kernel/v2.6/testing/patch-2.6.19-rc6.bz2
cd /usr/src/linux
bzip2 -dc /usr/src/patch-2.6.19-rc6.bz2 | patch -p1 --dry-run
bzip2 -dc /usr/src/patch-2.6.19-rc6.bz2 | patch -p1

 

3.4 Configure The Kernel

It's a good idea to use the configuration of your current working kernel as a basis for your new kernel. Therefore we copy the existing configuration to /usr/src/linux:

make clean && make mrproper
cp /boot/config-`uname -r` ./.config

Then we run

make menuconfig

which brings up the kernel configuration menu. Go to Load an Alternate Configuration File and choose .config (which contains the configuration of your current working kernel) as the configuration file:

Then browse through the kernel configuration menu and make your choices. When you are finished and select Exit, answer the following question (Do you wish to save your new kernel configuration?) with Yes:

 

3.5 Build And Install The Kernel

To build and install the kernel, execute these three commands:

make all
make modules_install
make install

Now be patient, the kernel compilation can take some hours, depending on your kernel configuration and your processor speed. The last command will also automatically create a ramdisk for you as well as configure /boot/grub/menu.lst.

Now edit /boot/grub/menu.lst. You should find a stanza for your new kernel at the top of the list, but to make sure that the new kernel gets booted instead of your old one, you must set the value of default to 0.

vi /boot/grub/menu.lst

My menu.lst looks 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 (2.6.18.3)
        root (hd0,0)
        kernel /vmlinuz-2.6.18.3 ro root=/dev/VolGroup00/LogVol00
        initrd /initrd-2.6.18.3.img
title CentOS (2.6.9-42.0.3.EL)
        root (hd0,0)
        kernel /vmlinuz-2.6.9-42.0.3.EL ro root=/dev/VolGroup00/LogVol00
        initrd /initrd-2.6.9-42.0.3.EL.img
title CentOS-4 i386 (2.6.9-42.EL)
        root (hd0,0)
        kernel /vmlinuz-2.6.9-42.EL ro root=/dev/VolGroup00/LogVol00
        initrd /initrd-2.6.9-42.EL.img

Now reboot the system:

shutdown -r now

If everything goes well, it should come up with the new kernel. You can check if it's really using your new kernel by running

uname -r

This should display something like

2.6.18.3

If the system doesn't start, restart it, and when you see this:

press any key to enter the GRUB menu:

Select your old kernel and start the system. You can now try again to compile a working kernel. Don't forget to remove the stanza of the not-working kernel from /boot/grub/menu.lst.

 

4 Links


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Submitted by Luther Woodrum (not registered) on Sun, 2009-07-12 16:27.

You left out two very important steps.  Without these there will be no modules

and you will get a msg like this:

 "No modules available for kernel "2.6.29.3-july11c"

The two missing steps have to be after the make rpm and before the mkinitrd,and they are

make modules

make modules_install

Then mkinitrd etc..

You can see what modules have been compiled with

 ls -la /lib/modules  .. e.g.

drwxr-xr-x  6 root root 4096 Jul  8 13:14 2.6.18-128.1.16.el5
drwxr-xr-x  6 root root 4096 Jul  7 22:32 2.6.18-128.el5
drwxr-xr-x  3 root root 4096 Jul 11 18:03 2.6.29.3-july11
drwxr-xr-x  3 root root 4096 Jul 11 19:36 2.6.29.3-july11a
drwxr-xr-x  3 root root 4096 Jul 12 11:05 2.6.29.3-july11c

Another thing you left out is the fact that after the make rpm (or make bzImage) the BUILD directory is not removed, and after you compile 4 or 5 times all the old BUILD diredctories will still be there, and you will run out of disk space on /usr.

Here is where they are:

ls -la  /usr/src/redhat/BUILD

drwxr-xr-x  3 root root 4096 Jul 11 22:15 .
drwxr-xr-x  7 root root 4096 Jul  7 22:29 ..
drwxr-xr-x 23 root root 4096 Jul 11 22:51 kernel-2.6.29.3july11c

You can safely erase the BUILD directories after you have finished the above steps, e.g.

rm -rf  /usr/src/redhat/BUILD/*

 

Submitted by pjwelsh (registered user) on Thu, 2008-06-19 21:03.

Nice howto. Thank you for time and effort in helping us!

At least with CentOS 5.x, you can ditch all of the mkinitrd and grub.conf manual changes by just running something like:

/sbin/new-kernel-pkg --package kernel --mkinitrd --depmod --install 2.6.25.7

as root to do all of that for you.

Also, you can now run "make rpm" for the kernel to create a well behaved kernel.rpm (minus the "new-kernel-pkg" from above).

Submitted by nqabile (registered user) on Mon, 2007-03-12 22:00.
Falko, this is a great tutorial. Thanks. I would include up front that ncurses-devel package has to be installed or "make menuconfig" doesn't work.