And if you fail gym, you'll never get into college.

Saturday, 14 November 2009

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



Comments On This Entry

[gravitar] Aigars Mahinovs

Submitted at 20:38:52 on 14 november 2009

That's "legacy USB support" in BIOS where I've seen that.

[author] Steve Kemp

Submitted at 03:15:49 on 15 november 2009

Thanks for the tip; yes that's what it is called on mine too - setting it appropriately allows the USB boot to succeed even from a coldboot.

[gravitar] Daniel Bo

Submitted at 02:01:15 on 16 november 2009

I have a couple of computers which don't like to boot from USB and which don't have working CD-ROMs. While I'd normally just download the kernel and initrd for a netboot install, one of them is on wireless and not easily cabled.

I found out that GRUB can boot from a USB system, but it appears as a floppy disk and you need to place all the appends manually after the kernel. (You can generally find the appends in the bootloader config files.


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