If you want to mess around with the installation procedure itself, the source code can be found on the RedHat CD-ROM or your local RedHat mirror site. It's in misc/src/install under the i386 distribution top level directory.
If you examine the RedHat boot disk you'll see that, in addition to the Linux kernel vmlinuz, there's a large file initrd.img:
- -rwxr-xr-x 1 root root 559 May 11 15:48 boot.msg - -rwxr-xr-x 1 root root 668 May 11 15:48 expert.msg - -rwxr-xr-x 1 root root 986 May 11 15:48 general.msg - -rwxr-xr-x 1 root root 968842 May 11 15:48 initrd.img - -rwxr-xr-x 1 root root 1120 May 11 15:48 kickit.msg - -r-xr-xr-x 1 root root 5352 May 11 15:48 ldlinux.sys - -rwxr-xr-x 1 root root 875 May 11 15:48 param.msg - -rwxr-xr-x 1 root root 1239 May 11 15:48 rescue.msg - -rwxr-xr-x 1 root root 402 May 11 15:48 syslinux.cfg - -rwxr-xr-x 1 root root 444602 May 11 15:48 vmlinuz
You guessed it, this is another
ext2 filesystem saved as a file
- - but with a twist. It's actually compressed as well. You can uncompress
it and then mount the result, e.g.
# gzip -dc /mnt/boot/initrd.img >/tmp/initrd.ext2 # mkdir /mnt/initrd # mount -o loop /tmp/initrd.ext2 /mnt/initrd
Probably the most important part of this filesystem is the collection of loadable kernel modules which are included with the boot disk. If you need to merge in a new version of a driver, you'll need to either replace vmlinuz with a new kernel which has this statically linked, or replace it in the modules collection. What's more, you may need to throw other modules away to make room.
The modules collection is the file modules/modules.cgz.
Wondering what that might be ? It's actually a compressed
cpio archive, believe it or not! And you thought nobody used
cpio any more... Actually RPM itself uses
internally, too. Here's how to hack around with it:
# gzip -dc /mnt/initrd/modules/modules.cgz >/tmp/modules.cpio # cpio -itv <modules.cpio >modules.listing # mkdir modules # cpio -idumv <../modules.cpio
I don't believe that there is currently a way under Linux (at least in mainstream distributions) to transparently access compressed filesystems. Let me know if you know better!
If you change anything, remember to:
cpioto recreate the archive. How to do this is left as an exercise for the reader...
gzipto compress the resulting archive.
Finally, you can now create new boot floppies using this modified boot disk setup, e.g.
# cat boot.img >/dev/fd0