January 13, 2012

Kernel 3.1.6 - watch out for "Unable to mount root fs" panic

While testing kernel 3.1.6 for bug #396469 I got the common kernel panic "not syncing: VFS: Unable to mount root fs".

It's easy to fix, here's the grub config before:

title Gentoo Linux
root (hd0,0)
kernel /boot/vmlinuz-3.1.6-gentoo

And fixed one:

title Gentoo Linux
root (hd0,0)
kernel /boot/vmlinuz-3.1.6-gentoo root=/dev/sda1

I had to pass an explicit root= parameter. How to figure it out? mount -l or cat /proc/mounts are not so helpful:

rootfs on / type rootfs (rw)
/dev/root on / type ext3 (rw,noatime,errors=continue,barrier=1,data=writeback)

So I used "fdisk -l" just to make sure whether it's sda or something else...

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1              63    59006744    29503341   83  Linux
/dev/sda2        59006745    62910539     1951897+  82  Linux swap / Solaris