[Discuss] Server won't boot kernel. initramfs problem?

[david at thekramers.net (David Kramer)]

My MythTV box (kubuntu 12.04) wouldn't let me ssh in or log in directly,
so I rebooted.  After I selected the kernel from grub, I eventually saw
"Kernel Panic - not syncing: VFS: Unable to mount root fs on
unknown-block(0,0)" and "Pid: 1, comm: swapper/0 Not tainted
3.2.0-35-generic".  It displayed some other stuff after that then froze
there, with the keyboard lights blinking for the full "You're screwed"
effect.

I found this page
http://askubuntu.com/questions/41930/kernel-panic-not-syncing-vfs-unable-to-mount-root-fs-on-unknown-block0-0
I followed:

|sudo fdisk -l
sudo mount /dev/sdax /mnt
sudo mount --bind /dev /mnt/dev
sudo mount --bind /dev/pts /mnt/dev/pts
sudo mount --bind /proc /mnt/proc
sudo mount --bind /sys /mnt/sys
sudo chroot /mnt|
update-initramfs -u -k 2.6.38-8-generic (or your version)
|update-grub2

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|That didn't work. I got the same error message when I rebooted. 
I saw some other pages saying that can happen if /boot fills up, but
/boot is on root and there's like 100GB free on that.  I'm able to mount
and look at the filesystem (/dev/sdb1) just fine when I mount it from
livecd.

One other suggestion I saw was to boot an older version of the kernel. 
I have 4 different versions of initrd.img and the other files. Oddly,
there's only the recent kernel in the grub boot menu (regular and
recovery mode) and memtest.  I know that grub2 lost the ability to only
list a certain number of kernels (MORE features lost for no reason), so
I don't know why that would be.  I'm pretty sure update-initramfs found
all 4 kernels, so I don't know why the others are not in the boot menu.

I've seen mentions that this can happen after a failed kernel update. 
But if you can't boot from the hard drive, how do you fix that?

One last hail-Mary I thought of: This is my MythTV box which has 4 SATA
hard drives for recordings, a separate SATA boot drive, and a SATA CDRW
drive.  If you remember, in the past I had problems with combinations of
drives preventing the machine from booting, and sometimes removing the
CDRW fixed the problem.  Maybe something like this is happening again,
and I should try removing the video hard drives.  I doubt very much this
is the problem though, because if the problem was at the har drive
level, then how is it seeing /boot to even read the grub stuff?

Any other ideas?  Thanks.



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