what differnet between the kernel booted from floppy and hardisk

[frederick van tagero]

Dear friends,

the same bzImage can be boot from hda, and the modules of ext3 will install in the bootscript somewhere by insmod;then, I dd the bzImage file to one floppy as :
dd bs=1k if=bzImage of=/dev/fd0, the restart the machine,
it recognize the bzImage directly, but can not find the root fs(for it is the ext3 file system), I wonder what different between such two process?

Best Regards,
Frederick

[Stuart Browne · Accepted solution]

There are unfortunately a nubmer of differences, especially where modules are involved.

I'm going to assume that you are using a RedHat system here (as you've not specified).

A tool exists called 'mkbootdisk' which will create a working boot disk from your current image.

The issue you ahve currently is that you will have an 'initrd' configured on your system, but when you 'dd' the kernel (and only the kernel) to the floppy, you are missing out on (in particular) the ext3.o module.

If this is a kernel you've compiled on your own, then I suggest you read through the documentation in the source on how to create a floppy boot image.

[Goran Koruga]

Hi Frederick.

The problem may be that you're using initrd image which is not available when booting from a floppy or that your boot loader pases root= parameter to kernel which isn't the case when booting from a floppy.

You can set default root device using rdev script, see man page for details. In short, something like :

rdev /dev/fd0 /dev/hda1

Also check for any initrd parameters in your boot loader's config file.

G.

[Goran Koruga]

Hmm, rdev is of course a binary, not a script - it's obviously too early for me.

G.

[Balaji N]

hi frederick,
as others have already pointed out, just dd'ing a bzimage file will not work for creating a boot floppy.

bzimage is just the kernel. you need boot loader, inittab and other configuration etc.

so the best way is to use mkbootdisk with the kernel version as the argument to creat e a boot disk.

hth
-balaji

[U.SivaKumar_2]

Hi,

dd method will not work for ext3 root filesystem as ext3.o module has to be loaded for the kernel to get EXT3 supporting capability.

regards,
U.SivaKumar

[Balaji N]

hi frederick,

while browsing through lost (http://lost.sourceforge.net) found this info. might be of some use to you.


:
####[ Linux One Stanza Tip (LOST) ]###########################

Sub : How to make a Loadlin bootdisk LOST #119

This is the simplest way making your own boot disk. Totally a
DOS prompt job. In DOS [1] "format a: /s/v" [2] Copy two files
your kernel (usually vmlinuz) and "loadlin.exe" to it, [3] and
make a one-line config.sys to point to your / device and boot:
e.g. "shell=a:\loadlin.exe a:\vmlinuz root=/dev/hda2 ro"

########################################
:

hth
-balaji