Contents
Many thanks to Peter Wong for providing this article.
Introduction
 | RHEL 5.3
Working through a build break with these steps when building RHEL 5.3 - reported on the forum |
We are often asked to build a RHEL 5 kernel (e.g., RHEL 5.2) on Power systems for evaluating a new kernel patch or investigating a performance issue. It is actually fairly easy to build the distro kernel if you are careful with the details.
Here we will present the simple steps for re-building the ppc64 RHEL 5.2 kernel as delivered by the distro. In addition, we will provide instructions to build a kernel with 4KB pages and also with a kernel patch. These steps should also be applicable to re-building the ppc64 RHEL 5.1 kernel, of course you'll need the correct RHEL 5.1 kernel src.rpm file.
- This page is targeted at technical individuals who are running RHEL 5 on a Power system (ppc64 in the Linux community). These days this generally means the Power5 and Power6 chip architecture. Re-building kernel.org kernels is done a lot by programmers in the community and is a fairly straight-forward process, but the process of re-building the actual shipping distro kernel remains a mystery to many. So the intent here is we want to be fairly specific - what pieces do you need, what steps do you follow, and how to you tell it worked. We're not convinced these steps literally produce the "exact same kernel" as provided by the distro, but for our purposes, this is adequate.
But first, we have a very serious warning. Re-building and re-booting a distro kernel is, in concept and in practice, a fairly easy thing to do. But it is also very easy to mess your system up with a single simple typo, with the practical consequences that you may need to re-install your system. Being unable to re-boot your shared system where someone else has data that wasn't backed up is a "most unpleasant" feeling.
 | Be Wary
Danger, Will Robinson
First. We strongly urge you to practice these steps on a victim system, where you have no problems what-so-ever of completely re-installing the system. A "victim system" means there is nothing of importance on the system. No important data. No critical users or applications.
Second. These steps are provided simply as a step-by-step guide of how several of us re-build the kernels in the labs on freshly installed victim systems. We most-certainly are not the official source for the right steps, nor do we claim this will work for everyone, so you should not expect any level of support from us on this. See the "First" point above.
Third. This should be intuitive, but amazingly-enough often isn't clearly understood. Therefore, we'll say it here explicitly. If you re-build your own kernel and you use that kernel, you have invalidated any hope for "official support" from your service provider while using that kernel. See the "First" point above. |
Find the RHEL 5.2 (or 5.3) kernel source
For re-building RHEL 5.2, you'll want kernel-2.6.18-92.el5.src.rpm. It is on the source CD that comes with your CD set. You will not find it on your standard CDs.
For re-building RHEL 5.3, you'll want kernel-2.6.18-128.el5.src.rpm file.
As an example, we copied the source DVD for the RHEL 5.x release to our system, mounted it, and installed the rpm.
For RHEL 5.2
For RHEL 5.3
To determine whether you have installed the source RPM, look under /usr/src/redhat/SPECS. If there is nothing there, then you probably have not installed the correct RPM yet.
Install the kernel-2.6.18-92.el5.src.rpm
The instructions are as follows:
Build the kernel
You might have to install unifdef-1.171-5.fc6.ppc.rpm which is needed for the build.
The build instructions are as follows:
Note: During the compilation, gpg (GNU Privacy Guard) may want some system activity to generate security related keys, which causes the build process to pause.
- If this happens, you can open up another session and run "dd if=/dev/mapper/VolGroup00-LogVol00 of=/dev/null bs=1M count=500" or anything that generate system activities. The paused build process should resume after the request from gpg is satisfied.
Here's an example of the error:
Admit'ably, this is a little strange. What we have found that works is:
rpmbuild
rpmbuild is the clever program that applies all of the patches to generate the overall kernel source, builds the kernels, modules and packages all the resulting files in an RPM for installation.
The rpmbuild step will result in these final messages:
Install the newly built kernel
The instructions are as follows:
These steps install all the pieces in the right place. The /etc/yaboot.conf file is updated as follows:
The variable "default" is set to "2.6.18-92.el5.6" for the new kernel. We strongly recommend that you keep the boot entry for the RHEL 5.2 kernel around, in case the newly built kernel is having some boot issues.
Confirm the boot
Indeed you must confirm that it boots correctly.
You can verify the base page size by the following command:
Page size of 65536 bytes clearly indicates that we are running on 64KB pages.
Build a kernel with the 4KB support
After you have completed the above steps successfully, we have a good base for building other kernels. Let's build a 4KB kernel.
Let's follow the instructions below.
"--without kabichk" is used to disable ABI compatibility check. Without specifying it, the kernel cannot be built. And we assume that ABI compatibility is not crucial for what you are doing.
This should succeed. We will see the following at the end of the build.
Install the 4KB kernel
The /etc/yaboot.conf will be modified accordingly.
And reboot.
You can verify the base page size by the following command:
The page size clearly indicates that we are on 4KB pages.
Apply a kernel patch
Let's follow the instructions below.
Using the re-built RPM on other RHEL 5.2 systems
It is indeed desirable to install the built RPM on other RHEL 5.2 systems, but you need to be very careful.
Note that RHEL 5.2 systems are different in many ways, e.g., the setup of the volume manager.
Once the RPM is installed, follow the instructions below.
And then reboot.
In summary
This quick report takes you through the practical steps of rebuilding a RHEL 5.2 kernel for Power systems. This exercise is intended simply as a way to see how the RHEL 5.2 kernel is built, installed, and booted to.
