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I've checked some similar answers which suggest holding "shift" until the screen shows up, this does not work for me. I also tried restarting the system several times in a row and even powering off during the boot sequence, since grub is supposed to detect failures and show the boot screen after such an event, no luck...

I got into this mess because of changing my graphic card configuration and now the system will not even show the Ubuntu log in screen. I know the grub boot menu is intact because immediately after the system failed to boot the first time, I restarted saw the menu and decided, to try to boot normally once more... When in hind sight I would be fine if I'd only chosen to start in safe graphics mode.

I've booted the system with a 10.10 installation disk and can get to any files but grub2 now required editing /etc/default/grub and then sudo update-grub but since I'm running from CD/DVD I this isn't going to work right...

Edit: I don't yet understand the answer provided by psusi. If I say

sudo chroot /media/661ae4bd-7dde-42c9-b944-f75cebeaa1ad 
sudo update-grub

I get

/usr/lib/grub/grub-mkconfig_lib: 38: cannot create /dev/null: Permission denied
/usr/sbin/grub-probe: error: cannot find a device for / (is /dev mounted?).
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2 Answers 2

up vote 3 down vote accepted

To show the Grub 2 menu at boot time it is only the right hand shift key that works

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I thought I tried both, but I think something funny happens if I hold down shift during the initial bios screen... not sure but holding down both shift keys after the initial boot screen passed worked... –  Quaternion Apr 8 '11 at 21:03
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When you mount the disk from the live cd, you can run update-grub with chroot. Assuming you mounted the hard disk in /mnt:

for f in sys proc dev ; do sudo mount --bind /$f /mnt/$f ; done
sudo chroot /mnt
update-grub
exit
for f in sys proc dev ; do sudo umount /mnt/$f ; done
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Ok when I boot there is 480GB filesystem under "Places" selecting this causes the following mount /media/661ae4bd-7dde-42c9-b944-f75cebeaa1ad but using that value does not work. I'll edit my question because formatting is easer and show the result. –  Quaternion Apr 8 '11 at 20:04
    
@Quanternion you forgot the for loop to bind mount /dev, /sys, and /proc into the chroot. –  psusi Apr 9 '11 at 3:05
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