initrd hacking [was: booting with grub to /dev/sda]

[Jim Cromie]

Ow Mun Heng wrote:

>On Tue, 2005-01-04 at 23:45, Jim Cromie wrote:
>  
>
>>Ow Mun Heng wrote:
>>    
>>
>>
>One MSG shows you to put sda into device.map. Did you try that already?
>Can your laptop boot directly from USB?
>
>  
>
yes - didnt work.  grub doesnt see it.  says (from memory)
err 21, non-existent drive

<snipping>

>Hmm..
>
yes - I do want both
1 - full understanding of grub
2 - a 250gb 'brick' which I can use on OPC (other peoples computers)

Aside - I want a bumper sticker that says -
    my other computer is your windows box.  :-)

>>mount: errort 2 mounting none
>>    
>>
>
>Is this a Typo?? 
>
>  
>
yes.  no cut-paste practical from boot..

>>Switching to new root
>>switchroot: mount failed: 22
>>umount /initrd/dev failed : 2
>>Kernel panic -not syncing: attempted to kill init
>>
>>hangs..  CtlAltDel  doesnt clear it.  power cycling does.
>>    
>>
>
>
>Can you try to mount the initrd image via loopback and look at the
>linuxrc file?? I know it can be done simply with mkinitrd, but I've gone
>the manual part and hacked the linuxrc file.
>
>
>  
>
I have unpacked and inspected.
<aside>
    AIUI, you cant loop mount it - its a compressed cpio not an ext2 or 
cramfs
ie:
[root at harpo nomad]# mount -o loop initrd-2.6.9-1.724_FC3.img /mnt/t1
mount: you must specify the filesystem type
[root at harpo nomad]# mount -o cloop initrd-2.6.9-1.724_FC3.img /mnt/t1
mount: initrd-2.6.9-1.724_FC3.img is not a block device (maybe try `-o 
loop'?)
[root at harpo nomad]# mount -t cpio -o cloop initrd-2.6.9-1.724_FC3.img 
/mnt/t1
mount: fs type cpio not supported by kernel
[root at harpo nomad]# mount -t ext2 -o cloop initrd-2.6.9-1.724_FC3.img 
/mnt/t1
mount: initrd-2.6.9-1.724_FC3.img is not a block device (maybe try `-o 
loop'?)
[root at harpo nomad]# mount -t ext2 -o loop initrd-2.6.9-1.724_FC3.img /mnt/t1
mount: wrong fs type, bad option, bad superblock on /dev/loop3,
       or too many mounted file systems
       (could this be the IDE device where you in fact use
       ide-scsi so that sr0 or sda or so is needed?)

    Can you stack drivers ? one to decompress, other to handle FS ?
</aside>

I did unpack it.  (btw it is 'init' in fedora, not linuxrc like debian)

Ive already hacked it - indirectly - by hacking mkinitrd (a shell script)
- I turned off the setquiet in hope that it would tell me where the bug 
was :-(

here it is:#!/bin/nash

mount -t proc /proc /proc
echo Mounted /proc filesystem
echo Mounting sysfs
mount -t sysfs none /sys
echo Creating /dev
mount -o mode=0755 -t tmpfs none /dev
mknod /dev/console c 5 1
mknod /dev/null c 1 3
mknod /dev/zero c 1 5
mkdir /dev/pts
mkdir /dev/shm
echo Starting udev
/sbin/udevstart
echo -n "/sbin/hotplug" > /proc/sys/kernel/hotplug
echo "Loading jbd.ko module"
insmod /lib/jbd.ko
echo "Loading ext3.ko module"
insmod /lib/ext3.ko
echo "Loading scsi_mod.ko module"
insmod /lib/scsi_mod.ko
echo "Loading usb-storage.ko module"
insmod /lib/usb-storage.ko
sleep 5
/sbin/udevstart
echo Creating root device
mkrootdev /dev/root
umount /sys
echo Mounting root filesystem
mount -o defaults --ro -t ext3 /dev/root /sysroot
mount -t tmpfs --bind /dev /sysroot/dev
echo Switching to new root
switchroot /sysroot
umount /initrd/dev

I stalled out after looking for nash docs explaining what
"mkrootdev /dev/root" actually does.
it would make sense if its whatever is on kernel-command line,
ie root=/dev/sda1 in my case.

Id welcome other suggestions.

thx
jimc