near disaster averted - "can not find /dev/by-id/xxxx"

[Goh Lip]

O. Sinclair wrote:
> Goh Lip wrote:
>> On Wed, 19 May 2010 14:40:13 +0200
>> "O. Sinclair" <o.sinclair at gmail.com> wrote:
>>
>>> Have no idea what happened but if this helps someone landing in the
>>> same trouble then it is worth the effort of documenting it.
>>>
>>> I am still on Karmic with all updates. Last night I was online and
>>> left the computer on over the night. No problems, all worked this
>>> morning. Shut it down to take it to where I am currently working (it
>>> is a laptop and I am currently travelling).
>>>
>>> On next boot I get to the splash and then I get "BSOD" - Black Screen
>>> of Death. A black monitor, no activity or message or anything.
>>>
>>> Reboot and go to "recovery option" that after a while ends up with
>>> the line: ...can not find /dev/by-id/xxxx long string of UUID here
>>>
>>> I am dropped into Busybox shell and can do nothing worthwhile. I
>>> reboot with a usb flash I have and can see that all works and the
>>> disks are there (one disk, 3 partitions including swap). I check
>>> grub.cfg, I check /etc/fstab and all LOOKS perfect. But no boot.
>>>
>>> I tried the 3-4 kernels and none worked. Scouted around internet for a
>>> solution and there were a few suggestion ranging from rebuilding the
>>> kernel to what eventually worked and was simple:
>>>
>>> on bootup get into the Grub menu by hitting ESC, Shift or both
>>> choose a "recovery kernel",  I chose an earlier than the latest just
>>> to be on safe side
>>> press "e" to get to edit mode
>>> replace all UUID-strings with /dev/sda(your root number), in my case
>>> /dev/sda2
>>> press ctrl+x to boot with those settings
>>> drop to a root shell
>>> run update-grub
>>> reboot
>>> all worked as before.... except now grub.cfg points to /dev/sda2
>>> instead of /dev/uuid-string
>>>
>>> Phew,
>>> Sinclair
>> You've 'sudo update-grub' and grub.cfg shows /dev/sda2?
>> Strange.  You may want to double check that.
>> But glad you've got this sorted out.
>>
>> Regards - Goh Lip
>>
> after manually editing the grub as described I dropped to a root-shell. 
> So no need for "sudo" but update-grub. And yes, following that /dev/sda2 
> has replaced /dev/uuid-endless-string
> 
> 
Sinclair, sorry for being so persistent, but I find that unusual, so I 
replicated your steps, using older kernel, dev/sdax, recovery mode, 
root-shell, update-grub (no sudo), reboot and checked the grub.cfg. I've 
got the following....


menuentry "Ubuntu, Linux 2.6.31-20-generic" {
         recordfail=1
         if [ -n ${have_grubenv} ]; then save_env recordfail; fi
	set quiet=1
	insmod ext2
	set root=(hd0,2)
	search --no-floppy --fs-uuid --set f3412cbb-51f9-428e-9ef9-1cfd34c59a60
	linux	/boot/vmlinuz-2.6.31-20-generic 
root=UUID=f3412cbb-51f9-428e-9ef9-1cfd34c59a60 ro   quiet splash
	initrd	/boot/initrd.img-2.6.31-20-generic
}
menuentry "Ubuntu, Linux 2.6.31-20-generic (recovery mode)" {
         recordfail=1
         if [ -n ${have_grubenv} ]; then save_env recordfail; fi
	insmod ext2
	set root=(hd0,2)
	search --no-floppy --fs-uuid --set f3412cbb-51f9-428e-9ef9-1cfd34c59a60
	linux	/boot/vmlinuz-2.6.31-20-generic 
root=UUID=f3412cbb-51f9-428e-9ef9-1cfd34c59a60 ro single
	initrd	/boot/initrd.img-2.6.31-20-generic
}


I do not find any trace of "/dev/sdax" anywhere in above, but of course, 
I had a good working bootable system to try on in the first place.


Well okay, Sinclair, whatever works; just thought you might want to know.

Regards, take care - Goh Lip