The reason one would want to do a kernel compilation, other than to learn
how to do so, is to enhance the performance of your machine, making it
more suitable to your needs. The generic Ubuntu kernel is meant to suit
the needs of many types of CPUs in many different circumstances
and so its features often represent the "least common denominator"
of all possibilities.
In particular,
the Ubuntu generic kernel
is not ideally suited for many fine-grained Desktop multimedia
applications for sound recording, etc. There are other limitations as
well, but we will describe these as we are going though the compilation
preparation.
Everthing is done as root, so you might as well invoke a root shell.
Here are the packages you'll need to install:
Preparation
Everything takes place in /usr/src.
The linux-source package appears to be nothing more
than the tarball.
First Kernel Compilation
The first time is the least complicated.
# cd /usr/src
# tar xjf linux-source-2.6.28.tar.bz2
# cd linux-source-2.6.28
We need to obtain the config file from the current kernel; it
needs to be copied to ".config" in the current directory.
Do
# ls /boot
# uname -r
You want the config file whose suffix is the output of the last command.
You can put it together in one step:
# cp /boot/config-$(uname -r) .config
First Kernel configuration
Run:
# make xconfig
Alternatively, if you do not have a graphical display, use:
# make menuconfig
The only changes we're going to make are in the Processor type and features
section. The features chosen depend alot on how the machine
will be used. Let's say the machine's target is being
a "high-performance desktop" as opposed to a server.
Select this line and look on the right side to make these changes:
Processor family. Set the processor type specific to yours. In our case,
we want Core 2/newer Xeon. The way you can discover this is by
$ cat /proc/cpuinfo
Preemption Model. For desktop multimedia applications you want
to choose Preemptible Kernel (Low-Latency Desktop).
Timer Frequency.
Again, high-performance multimedia applications generally want a
higher clock frequency to allow more frequent interrupts. Choose
1000 HZ.
After these changes, save the settings
(File Save) and close the configurator.
One other noteworthy setting is
High Memory Support. The lab machines have 2GB of RAM, and
so the default
setting is OK, but keep this setting in mind for newer machines,
especially newer servers, which can easily have 8GB of RAM these days.
Compilation
Compilation takes a long time. It's best to start it and not wait.
We'll show you something which will allow you to start the compilation
and go on and do other things while allowing you to monitor the
progress.
I would recommend creating a compilation script,
/usr/src/COMPILE (one level above the compilation directory),
like this:
From inside the compilation directory, one accesses this script
by "../COMPILE". Make it executable
# chmod +x ./COMPILE
The version variable, ver we've
indicated, which comes after
"--append-to-version="
is used to keep track of your kernel
version that you compile.
It must begin with a minus (-)
and must not contain whitespace.
For example, we've suggested starting with "01".
The compilation begins with the execution:
# ../COMPILE
What we've done is to background the process and redirect both
standard output and standard error to the file OUTPUT. Doing so
effectively diconnects the process from the shell.
You can log out of this shell at any time!
You can log out of the system! The process keeps running. You can
see that the compilation is running by doing:
$ w
.............. load average: 1.xx
A load average of "1.something"
usually means there is 1 CPU intensive process running.
To see what's currently going on at any time, do this
# cd /usr/src/linux-source-2.6.28
# tail -f OUTPUT
If you decide you want to terminate the compilation, it's OK.
You should be able to simply restart the compilation later and it
will take up where it left off.
To terminate, do this:
# ps ax | grep fakeroot
Look for the process id (PID) as the first number in the output line:
NNNN ? ...
Then stop the compilation by killing the process:
# kill NNNN
Install the new kernel
After compilation is done, the installation packages are in
the /usr/src directory (one level above the compilation).
# cd /usr/src
# ls linux-*.deb
linux-image-....Custom_i386.deb
linux-headers-...Custom_i386.deb
Install both of these packages.
# dpkg -i linux-*.deb
Reboot to new kernel
The new kernel is installed in these files/directories:
Edit the boot loader config file, /boot/grub/menu.lst.
This is set to run your newly installed kernel along by default,
but the other generic choices are still present.
Change
the timeout settings to give you more time to choose an alternative
kernel. Look for the line:
timeout 3
and change it to
timeout 10
That's the only change. But scroll down until you see the installed
kernel as the first "title" line:
Then reboot. When the "grub boot message" becomes visible,
hit the Escape (Esc) button
to get a list of kernel choices. Try out the new one, the default, at
the top. If something goes wrong, reboot and choose the generic one.
Subsequent kernel upgrades
It appears that subsequent kernel installations, generic or custom,
will not automatically make themselves the default boot kernel in
/boot/grub/menu.lst.
Once you have the linux-source package installed,
new kernels will reinstall a new version
of linux-source-2.6.28.tar.bz2, and so what you'll want
to do is this:
remove the old kernel compilation source:
# cd /usr/src
# rm -rf linux-source-2.6.28
and then proceed as before.
# tar xjf linux-source-2.6.28.tar.bz2
# cd linux-source-2.6.28
change the version number -nn
to the next one up
Copy the previous configuration as you current config file as
before, but, instead of "make xconfig", you probably only need
to do:
# make oldconfig
to pick up any necessary changes from the previous kernel. Often
this does nothing, but occasionally you will be queried to pick
make configuration settings. In these cases,
usually hitting Enter will choose the
best default setting.
Compile and install as before, but now you have to
edit /boot/grub/menu.lst and either move the new kernel's
boot stub to the top of the list, or change the setting
Save) and close the configurator.