How To Compile A Kernel - The Ubuntu Way

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Submitted by falko (Contact Author) (Forums) on Sun, 2006-11-05 16:01. :: Kernel | Ubuntu

How To Compile A Kernel - The Ubuntu Way

Version 1.0
Author: Falko Timme <ft [at] falkotimme [dot] com>
Last edited 11/05/2006

Each distribution has some specific tools to build a custom kernel from the sources. This article is about compiling a kernel on Ubuntu systems. It describes how to build a custom kernel using the latest unmodified kernel sources from www.kernel.org (vanilla kernel) so that you are independent from the kernels supplied by your distribution. It also shows how to patch the kernel sources if you need features that are not in there.

I have tested this on Ubuntu 6.10 Server ("Edgy Eft") and Ubuntu 6.06 Desktop ("Dapper Drake").

I want to say first that this is not the only way of setting up such a system. There are many ways of achieving this goal but this is the way I take. I do not issue any guarantee that this will work for you!

 

1 Preliminary Note

I prefer to do all the steps here as the root user. So if you haven't already created a root login, you should do so now:

sudo passwd root

Afterwards, log in as root:

su

If you would like to work as a normal user instead of root, remember to put sudo in front of all the commands shown in this tutorial. So when I run

apt-get update

you should run

sudo apt-get update

instead, etc.

 

1.1 /bin/sh on Ubuntu 6.10 ("Edgy Eft")

On Ubuntu 6.10, /bin/sh is a symlink to /bin/dash by default. /bin/dash seems to make problems when you compile software from the sources, at least I had that impression. That's why I make /bin/sh a symlink to /bin/bash instead.

If you are on Ubuntu 6.10, you should do this now:

rm -f /bin/sh
ln -s /bin/bash /bin/sh

 

2 Install Required Packages For Kernel Compilation

First we update our package database:

apt-get update

Then we install all needed packages like this:

apt-get install kernel-package libncurses5-dev fakeroot wget bzip2

 

3 Download The Kernel Sources

Next we download our desired kernel to /usr/src. Go to www.kernel.org and select the kernel you want to install, e.g. linux-2.6.18.1.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-2.6.18.1.tar.bz2

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

tar xjf linux-2.6.18.1.tar.bz2
ln -s linux-2.6.18.1 linux
cd /usr/src/linux

 

4 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!

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-rc4, but the full sources haven't been released yet for this kernel. Instead, a patch-2.6.19-rc4.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, 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-rc4 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 instead of kernel 2.6.18.1!

This is how you apply the 2.6.19-rc4 patch to kernel 2.6.18:

cd /usr/src
wget http://www.kernel.org/pub/linux/kernel/v2.6/testing/patch-2.6.19-rc4.bz2
cd /usr/src/linux
bzip2 -dc /usr/src/patch-2.6.19-rc4.bz2 | patch -p1 --dry-run
bzip2 -dc /usr/src/patch-2.6.19-rc4.bz2 | patch -p1


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Submitted by Manuel Schmitt (not registered) on Mon, 2012-04-02 14:23.

Howto to compile kernel from scratch in German:

Linux Kernel neu bauen/nachbauen/compilieren (aus Vanilla-Sourcen)

Submitted by raju (not registered) on Wed, 2010-04-07 08:21.

I have compile linux kernel version 2.6.28 , when i see the " .ko " files after the kernel was compiled the size of the ".ko"  file is very large compared files created from the installation by cd . Is their any way to reduce the size .

I assume it has to do with the dependency  Cd installation manages this dependency than when we compile the kernel . Is there a way to reduce the the size of the kernel object files ? .

Submitted by darksun93 (registered user) on Sun, 2007-06-03 05:00.

Both Ubuntu and Gentoo obviously have their strength and weaknesses, both will have a place in the Linux world for the foreseeable future and both groups of users need to recognise that. If people were willing to experiment a bit more and use the right tool for the right job, I think there would be a lot less 'fanboyism' and many people would find themselves being a lot more productive. I use Gentoo and Ubuntu, and think it's one of the great advantages of Linux world that I'm not forced to conform with my OS, but can use variants or even make my own if I see the need. Grow up, guys. Oh, and it's better to use 'sudo -s' than set up su, since the latter isn't officially supported or tested and they have the exact same effect.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - | don't buy World of Warcraft Gold, make'em. | - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Submitted by shakey_1 (registered user) on Sun, 2007-01-14 18:15.
Thank you for this How To.  It helped a lot when I was patching the kernel with the Web100 patch to set up an NDT (Network Diagnostic Tool) server.
Submitted by ramen noodle (registered user) on Sat, 2007-10-20 04:39.

Yeah same thing here, great article. I've been wanting to set up an NDT too for a while, so i used it for help with patching.

Dream your life or live your dreams?

 | ramen noodle |

Submitted by qhawk (registered user) on Sun, 2008-02-10 03:58.

As a newb, when I did the following:

apt-get install kernel-package libncurses5-dev fakeroot wget bzip2

neither package could be located.  After much searching, I figured out because I installed Ubuntu while offline, the Ubuntu setup commented out all the entries in source.list which meant apt-get would always fail.  If any other beginners hit this you can find source.list in /etc/apt/.   If you don't successfully complete this step, you'll no it when make menuconfig fails gloriously.

Thanks, qhawk 

Submitted by pulsar (registered user) on Mon, 2006-11-06 13:25.
It is absolutely unneccessary to allow root logins by setting a root password in the first step. You can get a root shell without adding insecurity to your system by typing  "sudo bash" or "sudo -i".
Submitted by hcarty (registered user) on Wed, 2006-11-08 16:36.

As another option - if you want to work fully as root without any lingering settings from your user account, use the following:

sudo su - 

This will give you a "pure" root login with no root password or other changes required from the default Ubuntu setup. 

Submitted by Vladimir (not registered) on Sun, 2009-09-06 02:12.

Why

sudo su -

Isn't

sudo -i

enough?

Submitted by meavaiua (not registered) on Wed, 2009-08-26 14:45.
Exactly. You should NEVER EVER create a root login. There is a good reason why this is disabled by default. So just don't. Use sudo su instead.
Submitted by Anonymous (not registered) on Fri, 2010-09-17 02:22.

From the link above...

"Not that I recommend dispensing with a user account, but I have no user account even on my Ubuntu system."

This guy is an arrogant ignorant (which is the worst combination, ever).

Even distributions with root active (I used to use mandrake 12 years ago) discourage users from running everything as root because it is dangerous. Mandrake had a big warning and a red background whenever running X as root. If you run firefox as root on a regular basis you might get bad surprises, from all the kind of scripts that get executred. I am not one of these no-root paranoid. I am not scared of knives but I do not walk with a knife pointing at my chest on a crowded subway train.

 What I find unacceptable is that this guy is ignorant, has bad practices, dispenses bad suggestion, and does it with so much arrogance. No way!