<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"> <HTML> <HEAD> <META NAME="GENERATOR" CONTENT="SGML-Tools 1.0.9"> <TITLE>RedHat Linux KickStart HOWTO: Modifying the RedHat installer</TITLE> <LINK HREF="KickStart-HOWTO-10.html" REL=next> <LINK HREF="KickStart-HOWTO-8.html" REL=previous> <LINK HREF="KickStart-HOWTO.html#toc9" REL=contents> </HEAD> <BODY> <A HREF="KickStart-HOWTO-10.html">Next</A> <A HREF="KickStart-HOWTO-8.html">Previous</A> <A HREF="KickStart-HOWTO.html#toc9">Contents</A> <HR> <H2><A NAME="s9">9. Modifying the RedHat installer</A></H2> <P> <P>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 <EM>misc/src/install</EM> under the <EM>i386</EM> distribution top level directory. <P> <P>If you examine the RedHat boot disk you'll see that, in addition to the Linux kernel <EM>vmlinuz</EM>, there's a large file <EM>initrd.img</EM>: <P> <P> <BLOCKQUOTE><CODE> <PRE> - -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 </PRE> </CODE></BLOCKQUOTE> <P> <P>You guessed it, this is another <CODE>ext2</CODE> 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. <P> <P> <BLOCKQUOTE><CODE> <PRE> # gzip -dc /mnt/boot/initrd.img >/tmp/initrd.ext2 # mkdir /mnt/initrd # mount -o loop /tmp/initrd.ext2 /mnt/initrd </PRE> </CODE></BLOCKQUOTE> <P> <P>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 <EM>vmlinuz</EM> 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. <P> <P>The modules collection is the file <EM>modules/modules.cgz</EM>. Wondering what that might be ? It's actually a compressed <CODE>cpio</CODE> archive, believe it or not! And you thought nobody used <CODE>cpio</CODE> any more... Actually RPM itself uses <CODE>cpio</CODE> internally, too. Here's how to hack around with it: <P> <P> <BLOCKQUOTE><CODE> <PRE> # gzip -dc /mnt/initrd/modules/modules.cgz >/tmp/modules.cpio # cpio -itv <modules.cpio >modules.listing # mkdir modules # cpio -idumv <../modules.cpio </PRE> </CODE></BLOCKQUOTE> <P> <P>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! <P> <P>If you change anything, remember to: <P> <P> <OL> <LI> Use <CODE>cpio</CODE> to recreate the archive. How to do this is left as an exercise for the reader...</LI> <LI> Use <CODE>gzip</CODE> to compress the resulting archive.</LI> <LI> Copy it to <EM>/mnt/initrd</EM>, or wherever you put the uncompressed <EM>initrd.img</EM> archive.</LI> <LI> Unmount <EM>/mnt/initrd</EM> (or whatever you called it).</LI> <LI> Compress the new <EM>initrd.img</EM> using <CODE>gzip</CODE> again.</LI> <LI> Copy the resulting archive onto the boot disk image - <EM>/mnt/boot/initrd.img</EM> in our example.</LI> <LI> Unmount the boot disk image, e.g. <EM>/mnt/boot</EM>. </LI> </OL> <P> <P>Finally, you can now create new boot floppies using this modified boot disk setup, e.g. <P> <P> <BLOCKQUOTE><CODE> <PRE> # cat boot.img >/dev/fd0 </PRE> </CODE></BLOCKQUOTE> <P> <P> <P> <HR> <A HREF="KickStart-HOWTO-10.html">Next</A> <A HREF="KickStart-HOWTO-8.html">Previous</A> <A HREF="KickStart-HOWTO.html#toc9">Contents</A> </BODY> </HTML>
