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+Notes on Red Hat 5.2 kernel installation (See Addendum for RH6.1)
+=================================================================
+
+Warning: We (the FreeS/WAN Project http://www.xs4all.nl/~freeswan/)
+had nothing to do with designing the kernel installation process. This
+document explains some tricky points that we wish we had been told.
+We don't know if these notes apply to systems other than Red Hat 5.2.
+This is meant as a supplement to other kernel install guides (such as
+the Red Hat 5.2 Installation Guide section 11.6).
+
+Goal: install a new kernel on RH5.2 in such a way that it doesn't
+interfere with any other kernels. This should be repeatable: each new
+kernel should have this property. Each should remain bootable.
+
+Problem: there are several components to a kernel, and each must be
+segregated. How are the parts kept apart? How are they found?
+
+All the parts live in the file system, so it all comes down to
+pathnames. Well, except for the fiddly bits in /etc/lilo.conf. What
+are the parts?
+
+ /lib/modules/VER/ directory for kernel modules
+ /boot/vmlinux-VER the kernel
+ /boot/System.map-VER the kernel symbol table
+ /boot/initrd-VER.img the initial ramdisk (for modules needed
+ at boot time -- usually not necessary)
+ /boot/boot.b the second-stage loader
+ /boot/map the map file, an index into system index for
+ all files used by boot loader (all kernels,
+ all initrds, perhaps /boot/boot.b, and itself)
+
+This list does not include /boot/module-info-VER. That is supplied
+by RedHat, and it isn't clear to me how to build it or why.
+
+In each entry, I've used "VER" to signify a version number. For
+RH-supplied kernels, these look like 2.0.36-0.7 (the original 5.2) or
+2.0.36-3 (the kernel updates).
+
+There are also symbolic links:
+ /lib/modules/preferred created by /etc/rc.d/rc.sysinit
+ /boot/System.map created by /etc/rc.d/rc.sysinit
+ /boot/module-info created by /etc/rc.d/rc.sysinit
+ /vmlinuz created by ???
+I don't know when the /vmlinuz symlink is set up and I don't know
+for what it is used.
+
+If you follow the RH procedures, documented in 11.6 of their Installation
+Guide, all your VERs will be 2.0.36. This is very bad: all your builds
+will step on each other. Worse, your new module directory will be half
+picked up when you boot a stock RH kernel binary!
+
+It is important to know how the various parts of the built kernel are
+found at booting.
+
+- the kernel path is specified in the image= option in lilo.conf.
+ (Lilo.conf may specify several and one is selected at boot time
+ by default or user selection.) The kernel is loaded by the
+ boot loader.
+
+- The initial ramdisk is a per-image option (initrd=) specified in
+ lilo.conf. (It isn't described in the RH5.2 lilo.conf(5) manpage!).
+ The initial ramdisk is loaded into RAM by the boot loader.
+
+- Since the boot loader doesn't know about the file system, it needs a
+ map to figure out which absolute disk blocks to load, and where.
+ This is /boot/map. It is built by the lilo command (also known as
+ the map installer). It will have indices for the all the kernels
+ that can be booted, all their initial ram disks, perhaps
+ /boot/boot.b, and itself. This is why moving the blocks of these
+ files throws off the boot loader -- lilo must be rerun after even a
+ cp command to one of them.
+
+- the modules directory is found two different ways. Unfortunately,
+ they don't mesh properly:
+
+ + at boot time, /etc/rc.d/rc.sysinit tries to figure out the correct
+ subdirectory of /lib/modules, using the .rhkmvtag trick (see
+ later). It then builds a symlink /lib/modules/preferred to
+ record this. It also invokes depmod to build the module
+ dependency info. At the same time, it creates the symlinks
+ /boot/System.map and /boot/module-info, using the inferred
+ value for VER!
+
+ + modprobe and friends stupidly look first in /lib/modules/2.0.36
+ (more precisely, /lib/modules/`uname -r`) and then in
+ /lib/modules/preferred. So if there is a /lib/modules/2.0.36 and
+ it is the wrong one, you are in trouble.
+
+ If there is no /lib/modules/2.0.36, then both searches above will
+ agree (a very Good Thing). So I recommend strongly that you not
+ have a /lib/boot/2.0.36 at boot time. Unfortunately, you will get
+ one during the kernel install process. Be sure to rename it. I
+ suggest using 2.0.36-x (for some unique x) as VER.
+
+- Red Hat supplied /lib/modules/VER directories contain a hidden file
+ .rhkmvtag. This file contains exactly one line. This line is
+ exactly the same as the contents of /proc/version while the
+ corresponding kernel is running. For the stock kernel, the line is:
+Linux version 2.0.36 (root@porky.redhat.com) (gcc version 2.7.2.3) #1 Tue Dec 29 13:11:13 EST 1998
+
+- At boot time, /etc/rc.d/rc.sysinit uses the .rhkmvtag files to
+ figure out which of the /lib/modules/* directories matches the
+ kernel. If it could figure out the directory, it uses this
+ information to set the symlinks mentioned above. It then runs
+ depmod to build the module dependency information (in
+ /lib/modules/preferred/modules.dep, if it created the
+ /lib/modules/preferred symlink). I recommend looking at the code.
+
+- The documented kernel install procedures DO NOT fill in the
+ .rhkmvtag file for the new modules directory! So you should do so
+ by hand. You have to figure out what the contents should be. Here
+ is is a command that will do the job, assuming that
+ /usr/src/linux/vmlinux is the kernel associated with
+ /lib/modules/2.0.36/:
+
+ strings /usr/src/linux/vmlinux \
+ | grep 'x version' >/lib/modules/2.0.36/.rhkmvtag
+
+I've recommended (above) that you use 2.0.36-x for VER when you install
+a kernel. What should x be? I have found that there is a hidden file
+/usr/src/linux/.version which contains a counter that gets incremented
+whenever you do a "make install" in the kernel (see target
+newversion). There are some other times that it gets incremented, but
+I think that it all works out. It also gets incorporated into the
+resulting kernel's /proc/version, prefixed with ``#''. This makes it
+a natural.
+
+Here is a script to do the recommended renaming:
+
+ # VER will eventually need to be updated
+ VER=2.0.36
+ VERX=${VER}-`cat /usr/src/linux/.version`
+
+ strings /usr/src/linux/vmlinux | grep 'x version' >/lib/modules/$VER/.rhkmvtag
+ mv /lib/modules/$VER /lib/modules/$VERX
+ mv /boot/System.map-$VER /boot/System.map-$VERX
+ mv /boot/vmlinuz-$VER /boot/vmlinuz-$VERX
+
+And, if an initrd has been built (usually it is best to arrange not to
+use one -- see the Red Hat Installation Guide):
+
+ /sbin/mkinitrd /boot/initrd-$VERX.img $VERX
+
+Remember: a new lilo.conf entry is needed for the new kernel, and then
+the lilo command will need to be rerun.
+
+Now that kernel installs don't overwrite the results of previous ones,
+you will need to manually delete the components and their lilo entry
+to get rid of them.
+
+Please send comments, additions, and corrections to:
+
+Hugh Redelmeier
+hugh@mimosa.com voice: +1 416 482-8253
+
+
+Addendum: Red Hat 6.1
+=====================
+
+The kernel supplied with RH6.1 kernel is out of date, so you might
+wish to use a newer one.
+
+Much of the description for 5.2 still applies, but the procedure is
+quite different because the .version file is no longer used. Instead,
+the top-level Makefile contains a definition EXTRAVERSION which adds a
+qualifier to the version for most purposes. No manual renaming is
+required.
+
+Before building the kernel, change EXTRAVERSION by editing
+/usr/src/linux/Makefile, and make an appropriate entry in /etc/lilo.conf.
+
+EXTRAVERSION is a feature of the standard kernel sources, not just the
+ones supplied by Red Hat.
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