Ubuntu – How to run update-grub on a chroot filesystem

grub2

I've been building a live ubuntu server (10.04 LTS) to run off a thumb drive and it's nearly there.
However, I've gotten stuck at one step.

I need to run update-grub but it's complaining about:

/usr/sbin/grub-probe: error: cannot find a device for / (is /dev mounted?).

My fstab file contains:

# filesystem   mount point     type    options                 dump    pass
UUID=76d2077e-9726-4f95-abab-323cb426b099       /               ext2    defaults                0       0
proc            /proc           proc    nodev,noexec,nosuid 0       0
sys             /sys            sysfs   defaults                0       0

Best Answer

oops... my bad. It's as simple as mounting dev.

Strangely enough I tried this at about 1am last night and that didn't work. This morning it did, so I'm not sure what was different.

To get a full environment just

sudo chroot /media/flash-drive
mount proc
mount sys
mount dev

And in case you have a separate boot partition

mount boot

After doing that I was able to see my devices in /dev

And update-grub actually works. Now to figure out why it's not booting... that's another problem.

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Ubuntu – Windows 7 doesn’t boot after Ubuntu install

From your BootInfo Script, I can see that GRUB2 resides erroneously on /sda1, your Windows boot partition. I'm not much into Windows anymore, but from what I know there are tools on the Windows CD that allow restoration of bootsectors. You need to boot from the Windows CD and start the repair mode. On the command line, you can try

bootrec.exe /fixboot

to restore your Windows partition boot sector.

Then, however, you won't be able to boot Ubuntu, because there will be no more GRUB2. GRUB2 should have been installed in the MBR of /sda which is not so in your case. This means you will either have to reinstall GRUB (using a Ubuntu live CD) there, or you may find it less time consuming to reinstall Ubuntu as a whole. The latter should not be a great thing if you only installed it recently for testing. In any case, take note that you should not install Grub2 on your Windows boot sector again.

Ubuntu – How to get a USB thumb drive to boot with grub2

Fixed it.

In case anyone is wondering. This is what I did to get it operating.

Thumb drive appears as /dev/sdb

Run these commands

sudo mount /dev/sdb1 /mnt
for i in /dev /dev/pts /proc /sys; do sudo mount -B $i /mnt/$i;  done
sudo chroot /mnt
grub-install /dev/sdb
update-grub

Then edit /boot/grub/grub.cfg Changed all lines that say (hd1,1) to (hd0,1)

Then run...

exit
for i in /dev/pts /dev /proc /sys; do sudo umount /mnt/$i ; done

Next.

List item
Totally power down the server.
Pull the power cords out. Wait 10s.
Plug power back in.
Insert Thumb drive and power on.
Linux now boots fully from the thumb drive.

It seems that there were two problems. They were to do with having the wrong device referenced in grub.cfg (i.e. hd1 should be hd0).

Secondly, a bug in the server bios. It kept referring to a uuid for a filesystem on a different thumb drive that I'd be earlier playing with. Warm reboot seemed to keep that uuid in there. A cold boot fixed it.

Best Answer

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