Kernel build

This FAQ will help you in case you want to apply some patches to the kernel on your own or rebuild it from sources. On RPM based distros such as RedHat Enterprise Linux/CentOS, Fedora Core or SUSE one can simpy rebuild kernel from SRPM. For other distros it is required to install sources, build and install kernel manually. The below are given the details for both cases.

Contents

Rebuilding kernel from SRPM

Find out $TOPDIR

Note: paths in some of the commands below include $TOPDIR, which is distribution-dependent and can be further redefined by user. To find out the proper location of $TOPDIR on your system, issue this command:

TOPDIR=$(rpm --eval "%{_topdir}"); echo $TOPDIR

Download

Source RPMS for different OpenVZ kernel branches can be downloaded from http://openvz.org/download/kernel/. You can also access http://download.openvz.org/kernel/ directly, or use one of the mirrors.

Installation

Install the downloaded SRC RPM with the following command:

# rpm -ihv ovzkernel-2.6.18-028stab056.1.src.rpm

After successfull installation, you can usually find kernel sources in $TOPDIR/SOURCES/ and kernel spec file (kernel-ovz.spec) in $TOPDIR/SPECS.

Adding your own patches

To modify the kernel one needs just to add specific patches to the kernel spec file and put this patch into $TOPDIR/SOURCES directory.

Put your patch into SOURCES directory with the following command:

# cp <patch> $TOPDIR/SOURCES/

Then open spec file $TOPDIR/SPECS/kernel-ovz.spec in the editor and add the following lines:

Patch100000: <patch-name>

and

%patch100000 -p1

in appropriate places where similar text lines are.

Adjust kernel version

Before rebuilding the kernel make sure that you adjusted the kernel version in kernel-ovz.spec. This will help you to distinguish binaries then from already existing kernels (or from the official OpenVZ kernels). To do so, edit the $TOPDIR/SPECS/kernel-ovz.spec file and replace the following line:

%define ksubrelease 1

with something like

%define ksubrelease 1my.kernel.v1

Modifying configs

If you want to modify the kernel config, you need to do the following before you continue with the next step.

# cd $TOPDIR/SPECS
# rpmbuild -bp kernel-ovz.spec
# cd $TOPDIR/BUILD/kernel-2.6.18/linux-2.6.18

Note: Make sure all OpenVZ related options are set. See kernel configuration

There you will find the configuration files in the subdirectory config/*.config. Copy the one you want to modifiy to $TOPDIR/BUILD/kernel-2.6.18/linux-2.6.18/.config. Then you can do a make menuconfig or something similar to adjust the kernel configuration. Note that some kernel configuration issues are described at kernel configuration.

Next, copy $TOPDIR/BUILD/kernel-2.6.18/linux-2.6.18/.config to the $TOPDIR/SOURCES directory, but use the corresponding file name in the target directory.

Building RPMs

To rebuild the kernel, type the following commands:

# cd $TOPDIR/SPECS
# rpmbuild -ba --target=i686 kernel-ovz.spec

After successfull kernel compilation binary RPMs can be found at $TOPDIR/RPMS/i686.

Rebuilding kernel from sources

Download

To compile OpenVZ linux kernel one need to download the original linux kernel sources and OpenVZ patches for it.

Linux kernel can be found at kernel.org, e.g. 2.6.18 kernel can be downloaded from here.

Appropriate OpenVZ patches for this kernel version can be found at http://openvz.org/download/kernel/branches/<branch>/<version>/patches/. For example, at the moment there is a patch patch-ovz028stab056.1-combined.gz available.

Kernel configs are also available at OpenVZ download site. Most frequently SMP config is used, so let's download kernel-2.6.18-i686-smp.config.ovz for this example.

Prepare

First, extract the kernel sources from archive:

# tar vjxf linux-2.6.18.tar.bz2
# cd linux-2.6.18

Apply OpenVZ patches to the kernel:

# gzip -dc patch-ovz028stab056.1-combined.gz | patch -p1

Configure

Now we need to place the config and build the kernel:

# cp kernel-2.6.18-i686-smp.config.ovz .config
# make oldconfig

On this stage, you can modify your kernel configuration to better suit your needs.

Note: Make sure all OpenVZ related options are set. See kernel configuration.

Build

# make
# make modules

Installation

After a successful build of the kernel it can be installed on the machine with the following commands run under root user:

# make install
# make modules_install

Also you need to edit your GRUB or LILO config to make your kernel available for boot.