Supporting Multiple Kernel Versions

The kernels can be installed using the InstallKernel.pl script. InstallKernel.pl takes the full name of the kernel distribution file as input, with the “.tar.bz2” extensions. First, it checks that the distribution will not overwrite any existing file—if so, it aborts execution unless you specifically tell it to go ahead. It installs the kernel and its modules, and adds an entry to /etc/lilo.conf for this kernel. It is quite careful about how it does this. It creates a backup copy of /etc/lilo.conf, then scans it line by line until it finds a root= entry. It uses this to set the root for the new kernel. If it finds a later root= entry that specifies a different root partition, it will warn you, but will continue, using the first one it found. It will not add an entry if it finds an existing entry for this kernel image. The last thing it does is show you the differences between the saved lilo.conf and the one it has just created. InstallKernel.pl will not run LILO for you—you must do that yourself.

Another script, InstallHeaders.pl, will take care of installing the header files for you. The headers are installed as subdirectories of /usr/src/linux-headers. If you set the link /usr/src/linux to point to one of these installed sets of header files, you can compile your driver or program for a version of the kernel different from the one you are actually running. I make use of this to compile the ARLA AFS clone for all the kernels I support, without rebooting my machine.

Whichever distribution of Linux you are using, you will probably have to modify the way it decides which set of kernel modules to use. The details vary from distribution to distribution, so it is not possible to describe all the necessary changes here.

Since these kernels rely heavily on the use of modules, you may also need to create an initial RAM disk for your specific machine. This is certainly true if you have a SCSI-based system. See the man page for the mkinitrd command for details.

In order to clone the repository to build your own kernels, copy the contents of the /bin and /source directories, and modify them as you wish. KernelBuild.sh will need modifying in order to set the MY_* variables correctly. KernelConfig.exp may also need modifying to enable or disable any specific options—this may not be a trivial task. KernelBuild.cmds will need to be modified if you wish to actually change the way the kernels are built. The other scripts should never need to be altered.

At present, about 30 kernel source distributions are included in the repository, representing kernels from 2.0.34 to 2.0.36 and 2.2.0 to 2.2.7 with various patches. As the person who manages the machines running these different kernels, I find that this standardization has simplified my tasks considerably.