Syslinux - Dec 2006 - modifying initrd.img to run custom application

Im n/w booting machine with kernel - vmlinuz and
initrd initrd.img.
I copied vmlinuz & initrd.img from RHEL4 iso.

I want to modify initrd.img so that when 2nd stage
boot loader loads initrd, my custom application gets
executed.

linuxrc in initrd.img is sym-link to /sbin/init.
 My steps:
1.  Renamed linuxrc to linuxrc1
2.  created new linuxrc script & invoked "/linuxrc1"
from script
(Once initialization is done - i can invoke my custom
application)

But I get "Kernel Panic" error while booting.
EXT2-fs: unable to read superblock
isofs_fill_super: bread failed, dev=md1,
iso_blknum=16, block=32
kernel panic - not syncing: VFS: Unable to mount root
fs on unknown-block(9,1)

I also tried creating initrd.img from scratch from
mkird script mentioned at
http://www-128.ibm.com/developerworks/linux/library/l-initrd.html.
But I get same error.

Please suggest the correct steps to modify initrd.img
so that I can invoke my custom application.



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> Message: 1
> Date: Thu, 28 Dec 2006 05:06:58 -0800 (PST)
> From: pankaj takawale <pankaj_takawale at yahoo.com>
> Subject: [syslinux] modifying initrd.img to run custom application
> To: syslinux at zytor.com
> Im n/w booting machine with kernel - vmlinuz and
> initrd initrd.img.
> I copied vmlinuz & initrd.img from RHEL4 iso.
> 
> I want to modify initrd.img so that when 2nd stage
> boot loader loads initrd, my custom application gets
> executed.
  What applications are you running?  Do they need to be started before the rest
of the system?

  I have done it by executing the start up at 'init 4' level.  Put what
you want to do in /etc/rcd.4. Change
  inittab to make your system start init 4.  Make the last program
('S99Start' for example) change to
  init 3, 5 or whatever you want.  
> 
> But I get "Kernel Panic" error while booting.
> EXT2-fs: unable to read superblock
> isofs_fill_super: bread failed, dev=md1,
> iso_blknum=16, block=32
> kernel panic - not syncing: VFS: Unable to mount root
> fs on unknown-block(9,1)
  You get this because the the file system was not installed correctly at boot
time.  Your boot loader
  will load the Kernel and then your initrdr.img mounted as '/',  The
root file system must be mounted
  and a 'pivot' is done to make it '/'.
> Please suggest the correct steps to modify initrd.img
> so that I can invoke my custom application.
  If you really want to change inittrd.img(?), you can decompress it, mount it
on a loopback, modify
  what you want to change, umount it and recompress it.  

  I have done it both ways.

  Do 'file' on your initrd.img to see what kind of compress data file it
is.  Some systems use gzip
  other use other compreesion program.

  From example:
    file /boot/initrd-2.6.17-1.2157_FC5.img
    /boot/initrd-2.6.17-1.2157_FC5.img: gzip compressed data, from Unix, 
     last modified: Thu Aug  3 11:08:51 2006, max compression

  Let me know if you need more help.

-- 
  Thanks for your time.

William Estrada

Email      : MrUmunhum at popdial dot com
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