Upgraded from 10.04 to 12.04 and grub drops to BusyBox prompt without error

Question

I updated a working server from 10.04 to 12.04.1 today. Everything upgraded without error. However, there is an odd issue with grub and the new kernel (3.2.0-30-generic). After grub boots, the system says "Starting up..." and switches to a text-based full-screen progress bar (with 4 dots) for 20 seconds, then it drops to a BusyBox shell. No matter how long I wait, I can simply type "exit" and the boot process switches back to the text-based full-screen boot progress bar and ultimately boots successfully. No errors at all.

My kernel in 10.04 (2.6.32.22), which I still have, will boot without triggering the BusyBox prompt. I have already tried running update-initramfs and my LVM volume UUID's match what's in /etc/fstab.

Is there a log I could check to see why the new kernel thinks it needs to enter the BusyBox shell, since the initramfs shell doesn't offer any clues and it boots fine after exiting the shell?

Answer 1

I finally found my answer not long after posting. This Ubuntu bug report suggested to remove the "quiet" and "splash" options from the boot arguments. I did and the error was made known:

Apparently the new kernel detects degraded software RAID volumes and will display a prompt with a 20 second timeout behind the splash screen. It's unfortunate it cannot be seen normally, and it looks like the problem has been reported (and fixed) in a past release. Also, the prompt did not accept my input. The default "N" response also didn't happen, since the RAID volumes actually do start (degraded).

If anyone is wondering, I was previously using software RAID with this system, but switched to a hardware RAID later and never went through the unnecessary risk of removing the software RAID from a working system.

Hopefully this info will help anyone else with a similar invisible boot problem.