Today from early morning I was called by my colleague who said that his centos6 box can’t boot after reboot. After grub screen centos show that error:
RAMDISK: incomplete write (6257 != 32768) write error Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0) Pid: 1, comm: swapper not tainted %kernel_ver% #1 Call trace:
Let fix that.
So first of all we downloaded centos livecd and run fsck on root fs (its was lvm which successfully located at /dev/mapper/vg_xxxx_lv_yyyy. Fsck says that all block are clean.
So we reboot and google that problem might be with kernel. As you know linux holds several (maybe two or three versions of kernel) so:
We just boot up our centos6 box with more older kernel through grub (when box switch on and show “loading screen” just press some buttons – similar as F8 button for windows.
After boot with old kernel – we just run yum update and update our box rpm’s (with kernel) to last version. Reboot – and all became good again.