Ubuntu – Grub error 15 (file not found)

gentoogrub-legacygrub2Ubuntu

I'm trying to fix a problem with a new installation. I'm running this existing distro (Ubuntu) from /dev/sdb with a new OS, Gentoo, installed on /dev/sda. I'm glad I took the trouble of setting these up on different disks because I can't boot into the new OS. All I get is grub error 15 "File not found". It also gives the UUID which I have verified is correct:

sudo blkid
/dev/sda1: LABEL="boot" UUID="b891774a-0b2d-4ab4-bcfa-23a11a97cae5" TYPE="ext2" 
/dev/sda2: UUID="fc34999a-e85d-4c7b-8775-30510eb4c396" TYPE="swap" 
/dev/sda3: LABEL="main" UUID="65a90a0d-a651-4215-8552-0c1859ab61dd" TYPE="ext4"

The menu.lst (on /dev/sdb) for the new OS is

title Gentoo Linux 3.10.7-r1
uuid b891774a-0b2d-4ab4-bcfa-23a11a97cae5
#root (hd0,0)
kernel /kernel-3.10.7-gentoo root=UUID=65a90a0d-a651-4215-8552-0c1859ab61dd

I also tried

kernel /boot/kernel-3.10.7-gentoo root=UUID=65a90a0d-a651-4215-8552-0c1859ab61dd

but since the UUID goes directly to the boot partition I think this is wrong.

The kernel should be correct; if I mount dev/sda1 and ls I see

grub  kernel-3.10.7-gentoo

Any ideas what I'm doing wrong? It might be very basic; I've only been using Linux for a few years and never Gentoo except for a few days in a chroot.

I should mention I also have grub2 installed on dev/sda1 though I don't get as far there: it just shows the grub 'command line'.

Best Answer

I agree to the points about the error by @rMistero. So now the grub boot from mbr and partition boot record but can't load the basic modules because they can't find it on the expected place (/boot/grub) of that partition. So reinstalling grub will fix that and the best solution is to boot to Gentoo the owner OS of grub legacy (Am I right ?), and reinstall grub.
As you have grub2 available run the following commands 1 by 1 from the grub2 prompt. 

set UUID=65a90a0d-a651-4215-8552-0c1859ab61dd

search -u $UUID --set=root
linux /kernel-3.10.7-gentoo root=UUID=$UUID
boot

In case it doesn't work give the output of above commands and this one search -u $UUID and search -l main. Also tell the version of Ubuntu and Gentoo, number of storage devices, OS installed on each storage device, whether Windows installed

Related Question