Today I rebooted my desktop for the first time in a few months. This did not go well. Probably as a result of this issue with lvm/dmsetup/cryptsetup conflicting my system didn't boot, and the error message was non-helpful.

The error shown just after grub2 had started to load a system was :

Cannot find LVM volume group gold-vol

The actual cause was that I was missing the mdadm package. D'oh. My desktop has 2x500Gb drives setup as:

 sda1 + sdb1 = md1  = /boot [1Gb]
 sda2 + sdb2 = md0  = LVM storage [460Gb]

(It's only as I write this that I'm surprised that md1 + md0 are opposite to the fashion I'd have expected them to be. I guess I just created them in the "wrong" order at install time. Oops)

So without mdadm the LVM volume group on /dev/md0 couldn't be found, and that in turn meant my root filesystem couldn't be accessed at /dev/gold-vol/root.

Fixing this was a real pain. Because the system is the PXE network host on my LAN I couldn't boot it that way, and the machine has no CD-ROM drive connected.

My solution was to download and install System Rescue CD, which I placed upon a USB stick. This worked beautifully once I realised I had to boot with rescue64 to get a 64-bit kernel capable of letting me run chroot.

Oddly enough I had problems booting from USB. If I powered down my system and hit the "on" switch the system just ignored the USB stick. I noticed that my USB mouse and card reader didn't show any power lights at all - not until after grub had failed to boot the system.

So the process of booting from USB was eventually determined to be:

• Poweroff system.
• Power on system - wait for grub to fail to boot kernel.
• At this point the USB mouse and card reader would be initialised in some fashion and would show their LED lights.
• Press Ctrl-alt-delete - at which point the BIOS would allow the USB booting to occur.

Very very odd. I guess its a question of what does the "USB enabling". I'd previously assumed the BIOS would do this setup - but looking over at another system I notice that the USB mouse doesn't "come alive" until mid-way through the Linux boot process even though I know that BIOS has options for "Enabling USB mouse & keyboard". Maybe I'm missing something obvious ..?

In conclusion .. I restarted GDM for the first time in weeks and rebooted, and this was a bad idea.

ObFilm: Never Been Kissed

Tags: computers:gold, mdadm, recovery, usb, usb booting | 3 comments