AlphaServer DS10 and AlphaStation 200 4/233 running CentOS Linux.
This is a sizeable project, so let's start with an overview of the steps:
Now that you see where we're going with this, let's get started!
The kernel source itself is available from kernel.org via both http and perhaps more efficiently through FTP.
You do know how to use anonymous FTP, right? If not, see my how-to guide.
You will need the kernel tar archive file,
a rather large file named something like:
linux-release.tar.bz2
and the corresponding very small digital signature file:
linux-release.tar.bz2.sign
where release is either three or four
numbers separated by dots, something like 2.6.35
or 2.6.35.3.
You need to understand the Linux release numbering scheme. Some kernel releases are three numbers: 2.6.X to be general, or for example: 2.6.0, 2.6.1, 2.6.2, and so on. The difference between these is that 2.6.(X+1) contains new features not found in 2.6.X. New device drivers, for recent hardware (maybe a network interface based on a new chipset) or for recently added software features (maybe a new networking protocol, or a new type of file system). Plus, of course, all the bugs found and fixed in the 2.6.X. The three-number 2.6.X kernel release include new features and bug fixes as that last number X increases.
But some kernel releases are three numbers: 2.6.X.Y. These are bug fixes only — 2.6.X.1 makes a small bug fix to the 2.6.X kernel, 2.6.X.2 fixes a small bug in 2.6.X.1, and so on. The kernel organization has strict rules: these must be bug fixes only (no sneaking new features into the kernel!) and they must be small (100 lines or less of C code). The four-number 2.6.X.Y kernel releases are cumulative bug fixes to 2.6.X.
Which version do you need? That depends on your hardware — the latest 2.6.X.Y should be fine, but you may not really need the very latest if the recent bug fixes were in drivers for hardware you don't own.
Reason to use a later release — Your hardware includes a super-fast network interface chipset that was only supported starting with the 2.6.X release. You need to use at least 2.6.X!
Reason to use an even later release — You know that you need 2.6.X, and let's say it's the last stable major release. But look at the archive, is there a more recent 2.6.X.Y bug-fix release? If you are about to build a kernel, it only makes sense to include the latest tested bug fixes.
Reason not to upgrade to a later release — Your hardware is supported by the 2.6.X kernel you are already using, and there are no 2.6.X.Y bug fixes that involve drivers that you use.
You do not want to run some hacker's operating system instead of the real kernel! You must verify both the integrity of the data you just downloaded and the identity of its source. In other words, is it really the kernel source, and did it really come from the Linux kernel organization?
So, you need to check the digital signature with GNU Privacy Guard (GnuPG) or similar.
See the digital signature section of my "Just Enough Cryptography" page for an explanation of what digital signatures are.
See the page on verifying digital signatures to learn how to apply this technology. Verification is vital, but an explanation right here would make this page at least as much about digital signatures as about building Linux kernels! Really, go look at that other page, this page will be right here waiting for you when you get back....
From here forward, I will use oldrelease and release to stand for, well, whatever your old and new releases will be! You will have to think just a little.
AlphaServer DS10 and AlphaStation 200 4/233 running CentOS Linux.
You need to do some steps as root here, so become root with the su command.
Your distribution or earlier work by yourself or other administrators may have already installed kernel source under a directory named /usr/src/linux-oldrelease with a symbolic link pointing to it. Find out, and if necessary, remove that link:
# cd /usr/src # ls -l # rm linux
Extract the kernel source with the following. You must be in the right directory, /usr/src, and I leave it up to you to figure out where you put that downloaded archive file. I mean, really, if you can't handle that then you have no business trying to build a kernel. But my experience tells me that I need to put two commands here to keep some people from making horrible messes of things:
# cd /usr/src # tar xvfj /path/to/linux-release.tar.bz2
Recreate the symbolic link, so that other software can be compiled on your system. If you're really curious, software making calls to system libraries need to find the include files under /usr/src/linux/include and this will support that. Or just take my word for it, this is important:
# ln -s linux-release linux # ls -l
The tar archive may have created files owned by some random UID other than 0, meaning root. This is not good! Fix it and make sure that everything has worked so far:
# chown -R root:root linux-release # ls -laF
You should see something like the following:
total 16 drwxr-xr-x 4 root root 4096 May 28 19:02 ./ drwxr-xr-x 15 root root 4096 May 28 21:28 ../ lrwxrwxrwx 1 root root 17 May 28 19:02 linux -> linux-release@ drwxr-xr-x 19 root root 4096 May 28 19:02 linux-release/ drwxr-xr-x 19 root root 4096 Apr 06 08:29 linux-oldrelease/
Now, just to be safe, let's remove any stale object files inappropriately cluttering your source tree, so we can build a fresh clean kernel:
# cd /usr/src/linux # make clean
From here on, we will just rely on /usr/src/linux to be set up and pointing to the new source tree, making the pathnames a little simpler if we need to mention them. However, almost everything should be done in the directory /usr/src/linux and so there is little need to mention full path names!
There are thousands of choices to be made when configuring a kernel build, and if you just dive in and start answering them you probably will not get enough of them right to produce a kernel that boots.
However, you are running some kernel that boots and runs on your hardware. I would presume that it is probably of an earlier release if you are like most people who would read this page, but its configuration would be a good starting point.
The very best solution would be to ask the running kernel how it is configured. That way you would get the truth. So, try that:
# zcat /proc/config.gz > .config
If that didn't work, maybe your kernel supports this but only as a loadable module. So, let's try loading that module and asking again:
# modprobe ikconfig # zcat /proc/config.gz > .config
If that worked, great, move on to the next step. If it did not work, you will need to find a configuration file that your distribution has probably stashed away somewhere on the system. Try this while paying attention to the available file name or names. Pick the latest if you have a choice:
# ls /boot # cp /boot/config-release-distro .config
Red Hat has been known to hide the configuration files in other places:
# ls /usr/src/linux-oldrelease/configs # ls /usr/src/linux-oldrelease/.config
If all else fails:
# find / -name 'config-2*'
Or, worse yet, try the following, where CONFIG_EXPERIMENTAL is a configuration variable set in the file regardless of architecture. You will probably find that string in other files so you will need to think a little about what you find.
# find / -type f -exec grep 'CONFIG_EXPERIMENTAL=[yn]' {} /dev/null \;
You need to somehow install something reasonably relevant as /usr/src/linux/.config.
Let's say that you would like your new kernel to describe
itself as version
2.6.X-whatever
instead of plain old
2.6.X
when someone runs the command
$ uname -r
or
$ uname -a
The trick is to edit the file Makefile and change its opening to the following:
VERSION = 2 PATCHLEVEL = 6 SUBLEVEL = X EXTRAVERSION = -whatever
Be careful — you must be very conservative in what you put here! The string needs to be fairly short and contain nothing but letters, numbers, "." and "-". Any other punctuation marks or white space will cause horrible problems later.
If you are doing this with a 2.6.X.Y kernel, the EXTRAVERSION string will have been some .Y (where Y was really a number, of course). So, for this example you would use the following, leaving X and Y as whatever they already were:
VERSION = 2 PATCHLEVEL = 6 SUBLEVEL = X EXTRAVERSION = .Y-whatever
Now you are ready for the fun part! You are finally ready to run the kernel build configuration tool. I say "kernel build configuration" instead of "kernel configuration" because that's what you are doing. You are specifying how to build a kernel as opposed to configuring some pre-existing kernel.
The more friendy interface is started like this:
# make gconfig &
However, that may require some Gnome or GTK packages that you haven't installed, and either you haven't set up YUM or urpmi to make installation easy or you just don't want to add those packages. In that case try the following. If that doesn't work either, then it's time to install those packages....
# make xconfig &
The terminal emulator where you ran that command will have lots of output, including some error messages about setting kernel variables that were not defined and perhaps about specified settings for kernel variables that do not exist. Don't panic! Remember what you did — you started with the configuration of an older kernel to build a newer one. The kernel feature set changes from version to version, and so we expect to see these rather mild warning messages.
I believe that it only makes sense to build the kernel
configuration into the kernel itself.
Do this:
Under General Setup select:
Kernel .config support
and then select:
Enable access to .config through /proc/config.gz
If you build it into the monolithic kernel (shown as a check
mark in the configuration tool) it will always be there.
If you build it as a loadable module then it will only appear
when the appropriate module is loaded, you will need to
first do something like this:
# modprobe ikconfig
and then the kernel data structure will appear as
/proc/config.gz.
I would suggest simply building this into the monolithic
kernel so the configuration is always available.
Your configuration should be pretty close to what you want, and in many or even most cases it would be reasonable to just save the settings at that point and exit the tool.
However, you probably should explore the kernel configuration just to learn about how many things the Linux kernel can support.
Just try not to do anything terribly silly like disabling support for your hard drive controller. Unless you really do want a kernel that will not boot...
Save and exit when you have finished exploring.
This is much easier than many people expect. Start by seeing the list of available build targets:
# make help | less
There are two main ways of doing this. The traditional method builds a monolithic kernel and a huge collection of load modules, and a later step easily puts them all into their proper locations.
However, wouldn't it be better to include your kernel in your configuration management? That requires building it as a package, which is also very easy to do. So:
Start building the monolithic kernel and loadable modules:
# make all
Let's build both source and binary RPM packages:
# make rpm-pkg
Now go get some coffee. Or a pot of tea. Or maybe lunch. This will take a while.
This is much easier than it used to be. It hasn't been difficult for some time, but some people are still scared off by criticisms that haven't been appropriate for ages now.
# make modules_install # make install
First, let's see what got built:
# tree /usr/src/*/*RPMS
Let's be cautiously confident — our new kernel is almost certainly going to work! But just in case it doesn't, we don't want to remove our existing and functioning kernel. So, we need to simply install the new kernel, leaving the old one in place, as opposed to doing it as an upgrade and removing the old one. Something like this, modified as needed to reflect your architecture and kernel release:
# rpm -ivh /usr/src/whatever/RPMS/kernel-release.arch.rpm
We still need to build and install an "initrd", an initial RAM disk image, and then modify the boot loader. That sounds awfully complicated, and it used to be. Now it's just one long command.
# new-kernel-pkg --mkinitrd --install --make-default --depmod release
Edit /boot/grub/menu.lst or grub.conf to move the stanza for your new kernel to the top of the list and change the default to 0 (GRUB starts counting at zero). Notice that if you built it as a package, one of the options to our new-kernel-pkg command has already made this the default! It is going to work, right?
Do comment out any hiddenmenu line that your distribution might have installed initially because they thought that you shouldn't see what's going on.
default=0
timeout=10
splashimage=(hd0,0)/grub/splash.xpm.gz
## hiddenmenu
title linux-2.6.xx-whatever
root (hd0,0)
kernel /vmlinuz-2.6.X-whatever ro root=LABEL=/ quiet
initrd /initrd-2.6.X-whatever.img
title Mandriva Linux 2.6.33.6-desktop
root (hd0,0)
kernel /vmlinuz-2.6.33.6-desktop ro root=LABEL=/ quiet
initrd /initrd-2.6.33.6-desktop.img
If you're still using LILO and you don't want to upgrade, then you will need to edit /etc/lilo.conf and make the appropriate changes before running lilo -v to recreate the boot block. But seriously, LILO? Today?
If you're doing this on an Alpha, ignore all this about GRUB and LILO and modify /etc/aboot.conf and then go see my page specifically about building kernels on Alphas for some further details.
# aboot default configurations # NOTICE: You have a /boot partition. This means that # all kernel paths are relative to /boot/ 0:2/vmlinuz-2.6.X-whatever initrd=/initrd-2.6.X-whatever root=/dev/sda4 quiet 1:2/vmlinuz-current initrd=/initrd-current root=/dev/sda4 quiet 2:2/vmlinuz-previous initrd=/initrd-previous root=/dev/sda4 quiet
You didn't do anything silly like get rid of your functional old kernel, right? Or configure your boot loader in such a way that it isn't available? Did you??
You should have made the very reasonable choice of asking for the kernel's configuration, the .config file, to be built into the kernel and made available as /proc/config.gz. That means that all you have to keep track of is your kernel release and a copy of your .config file, a file of a little over 100 kbytes, about a quarter of that if compressed with gzip.
Click here to explore Linux kernel details.
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| © Bob Cromwell Sep 2010. Created with /bin/vi and ImageMagick, hosted on OpenBSD with Apache. Root password available here, privacy policy here. |
