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.

Rebuilding kernel from SRPM

Download

Source RPM for OpenVZ kernel can be download from the official downloads at http://openvz.org/download/kernel/. Beta versions of kernels for different OS distributions can be also found at http://openvz.org/download/beta/.

Installation

Install the downloaded SRC RPM with the following command:

# rpm -ihv ovzkernel-2.6.16-026test012.1.src.rpm

After successfull installation you can find kernel sources in /usr/src/<distro>/SOURCES/ and kernel spec file (kernel-ovz.spec) in /usr/src/<distro>/SPECS, where <distro> is your distribution-specific directory. For example, for RedHat based distros it is 'redhat', for SUSE it is 'packages'.

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 SOURCES directory. Put your patch into SOURCES directory with the following command:

# cp <patch> /usr/src/<distro>/SOURCES/

Then open spec file /usr/src/<distro>/SPECS/kernel-ovz.spec in the editor and add the following lines:

Patch10000: <patch-name>

and

%patch10000 -p1

in appropriate places where similar text lines are.

Building RPMs

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 official OpenVZ kernels). To do so, edit /usr/src/<distro>/SPECS/kernel-ovz.spec file and replace the following line:

%define ksubrelease 1

with

%define ksubrelease 1-my.kernel.v1

To rebuild the kernel type the following commands then:

# cd /usr/src/<distro>/SPECS
# rpmbuild -ba --target=i686 kernel-ovz.spec

After successfull kernel compilation binary RPMs can be found at /usr/src/<distro>/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. 2.6.16 kernel can be downloaded from linux-2.6.16.tar.bz2.

Appropriate OpenVZ patches for this kernel version can be found at http://openvz.org/download/, e.g. at the moment there is a patch patch-026test012-combined.gz available.

Kernel configs are also available at OpenVZ download site. Most usually SMP config is used, so let's download kernel-2.6.16-026test012-i686-smp.config.ovz for this example.

Building

First, extract the kernel sources from archive:

# tar vjxf linux-2.6.16.tar.bz2
# cd linux-2.6.16

Apply OpenVZ patches to the kernel:

# gzip -dc patch-026test012-combined.gz | patch -p1

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

# cp kernel-2.6.16-026test012-i686-smp.config.ovz .config
# make oldconfig
# make
# make modules

Installation

After successfull build of 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.