os-prober 1.40 doesn't detect another ubuntu installation anymore

Can you try mounting the filesystem in question, unmounting it straight away, and then running os-prober? If this works around the problem (I'm not suggesting it as a permanent solution), then this is the same as bug 683355.

Status changed to 'Confirmed' because the bug affects multiple users.

Hi Colin,

yes, this bug happens for me, too, with the os-prober versions from natty (1.44ubuntu1) and oneiric (1.49ubuntu1), but not from maverick (1.39). Except that the other OS is a Debian Sid and not another Ubuntu. But I don't think this makes a difference here.

Mounting the root as well as the /boot filesystem neither shows a warning about an uncleanly unmounted filesystem.

It seems that os-prober works fine, but linux-boot-prober does not. The other Linux on this box has /boot on /dev/sda1 and / on /dev/sda5. linux-boot-prober /dev/sda5 just returns nothing while linux-boot-prober /dev/sda1 finds all kernels, but claims the root filesystem is /dev/sda1 while it is /dev/sda5 as os-prober correctly found out.

U 53/0/2 root@loadrunner:pts/0 03:14:44 [~] # os-prober /dev/sda1
/dev/sda5:Debian GNU/Linux (wheezy/sid):Debian:linux
U 54/0/2 root@loadrunner:pts/0 03:14:52 [~] # os-prober /dev/sda5
/dev/sda5:Debian GNU/Linux (wheezy/sid):Debian:linux
U 55/0/2 root@loadrunner:pts/0 03:14:58 [~] # linux-boot-prober /dev/sda1
/dev/sda1:/dev/sda1::/vmlinuz-2.6.31-1-686:/initrd.img-2.6.31-1-686:root=/dev/sda1
/dev/sda1:/dev/sda1::/vmlinuz-2.6.32-4-686:/initrd.img-2.6.32-4-686:root=/dev/sda1
/dev/sda1:/dev/sda1::/vmlinuz-2.6.32-5-686:/initrd.img-2.6.32-5-686:root=/dev/sda1
/dev/sda1:/dev/sda1::/vmlinuz-2.6.33-2-686:/initrd.img-2.6.33-2-686:root=/dev/sda1
/dev/sda1:/dev/sda1::/vmlinuz-2.6.34-1-686:/initrd.img-2.6.34-1-686:root=/dev/sda1
/dev/sda1:/dev/sda1::/vmlinuz-2.6.35-trunk-686:/initrd.img-2.6.35-trunk-686:root=/dev/sda1
/dev/sda1:/dev/sda1::/vmlinuz-2.6.36-trunk-686:/initrd.img-2.6.36-trunk-686:root=/dev/sda1
/dev/sda1:/dev/sda1::/vmlinuz-2.6.37-2-686:/initrd.img-2.6.37-2-686:root=/dev/sda1
/dev/sda1:/dev/sda1::/vmlinuz-2.6.37-trunk-686:/initrd.img-2.6.37-trunk-686:root=/dev/sda1
/dev/sda1:/dev/sda1::/vmlinuz-2.6.38-2-686:/initrd.img-2.6.38-2-686:root=/dev/sda1
/dev/sda1:/dev/sda1::/vmlinuz-2.6.39-1-686-pae:/initrd.img-2.6.39-1-686-pae:root=/dev/sda1
/dev/sda1:/dev/sda1::/vmlinuz-2.6.39-2-686-pae:/initrd.img-2.6.39-2-686-pae:root=/dev/sda1
/dev/sda1:/dev/sda1::/vmlinuz-3.0.0-1-686-pae:/initrd.img-3.0.0-1-686-pae:root=/dev/sda1
/dev/sda1:/dev/sda1::/vmlinuz-3.0.0-rc6-686-pae:/initrd.img-3.0.0-rc6-686-pae:root=/dev/sda1
/dev/sda1:/dev/sda1::/vmlinuz-3.1.0-rc4-686-pae:/initrd.img-3.1.0-rc4-686-pae:root=/dev/sda1
/dev/sda1:/dev/sda1::/vmlinuz-3.1.0-rc6-686-pae:/initrd.img-3.1.0-rc6-686-pae:root=/dev/sda1
/dev/sda1:/dev/sda1::/vmlinuz-3.1.0-rc7-686-pae:/initrd.img-3.1.0-rc7-686-pae:root=/dev/sda1
U 56/0/2 root@loadrunner:pts/0 03:15:05 [~] # linux-boot-prober /dev/sda5
U 57/0/2 root@loadrunner:pts/0 03:15:14 [~] #

With the os-prober version from maverick (1.39) installed on oneiric, it looks like this:

U 58/0/2 root@loadrunner:pts/0 03:18:30 [~] # os-prober /dev/sda5
/dev/sda5:Debian GNU/Linux (wheezy/sid):Debian:linux
U 59/0/2 root@loadrunner:pts/0 03:18:38 [~] # linux-boot-prober /dev/sda5
/dev/sda5:/dev/sda1:Debian GNU/Linux, kernel 3.1.0-rc7-686-pae:/boot/vmlinuz-3.1.0-rc7-686-pae:/boot/initrd.img-3.1.0-rc7-686-pae:root=UUID=42e2321b-f075-42d8-8223-d13a9d45f3ab ro
/dev/sda5:/dev/sda1:Debian GNU/Linux, kernel 3.1.0-rc7-686-pae (single-user mode):/boot/vmlinuz-3.1.0-rc7-686-pae:/boot/initrd.img-3.1.0-rc7-686-pae:root=UUID=42e2321b-f075-42d8-8223-d13a9d45f3ab ro single
/dev/sda5:/dev/sda1:Debian GNU/Linux, kernel 3.1.0-rc6-686-pae:/boot/vmlinuz-3.1.0-rc6-686-pae:/boot/initrd.img-3.1.0-rc6-686-pae:root=UUID=42e2321b-f075-42d8-8223-d13a9d45f3ab ro
/dev/sda5:/dev/sda1:Debian GNU/Linux, kernel 3.1.0-rc6-686-pae (single-user mode):/boot/vmlinuz-3.1.0-rc6-686-pae:/boot/initrd.img-3.1.0-rc6-686-pae:root=UUID=42e2321b-f075-42d8-8223-d13a9d45f3ab ro single
/dev/sda5:/dev/sda1:Debian GNU/Linux, kernel 3.1.0-rc4-686-pae:/boot/vmlinuz-3.1.0-rc4-686-pae:/boot/initrd.img-3.1.0-rc4-686-pae:root=UUID=42e2321b-f075-42d8-8223-d13a9d45f3ab ro
/dev/sda5:/dev/sda1:Debian GNU/Linux, kernel 3.1.0-rc4-686-pae (single-user mode):/boot/vmlinuz-3.1.0-rc4-686-pae:/boot/initrd.img-3.1.0-rc4-686-pae:root=UUID=42e2321b-f075-42d8-8223-d13a9d45f3ab ro single
/dev/sda5:/dev/sda1:Debian GNU/Linux, kernel 3.0.0-1-686-pae:/boot/vmlinuz-3.0.0-1-686-pae:/boot/initrd.img-3.0.0-1-686-pae:root=UUID=42e2321b-f075-42d8-8223-d13a9d45f3ab ro
/dev/sda5:/dev/sda1:Debian GNU/Linux, kernel 3.0.0-1-686-pae (single-user mode):/boot/vmlinuz-3.0.0-1-686-pae:/boot/initrd.img-3.0.0-1-686-pae:root=UUID=42e2321b-f075-42d8-8223-d13a9d45f3ab ro single
/dev/sda5:/dev/sda1:Debian GNU/Linux, kernel 3.0.0-rc6-686-pae:/boot/vmlinuz-3.0.0-rc6-686-pae:/boot/initrd.img-3.0.0-rc6-686-pae:root=UUID=42e2321b-f075-42d8-8223-d13a9d45f3ab ro
/dev/sda5:/dev/sda1:Debian GNU/Linux, kernel 3.0.0-rc6-686-pae (single-user mode):/boot/vmlinuz-3.0.0-rc6-686-pae:/boot/initrd.img-3.0.0-rc6-686-pae:root=UUID=42e2321b-f075-42d8-8223-d13a9d45f3ab ro single
/dev/sda5:/dev/sda1:Debian GNU/Linux, kernel 2.6.39-2-686-pae:/boot/vmlinuz-2.6.39-2-686-pae:/boot/initrd.img-2.6.39-2-686-pae:root=UUID=42e2321b-f075-42d8-8223-d13a9d45f3ab ro
/dev/sda5:/dev/sda1:Debian GNU/Linux, kernel 2.6.39-2-686-pae (single-user mode):/boot/vmlinuz-2.6.39-2-686-pae:/boot/initrd.img-2.6.39-2-686-pae:root=UUID=42e2321b-f075-42d8-8223-d13a9d45f3ab ro single
/dev/sda5:/dev/sda1:Debian GNU/Linux, kernel 2.6.39-1-686-pae:/boot/vmlinuz-2.6.39-1-686-pae:/boot/initrd.img-2.6.39-1-686-pae:root=UUID=42e2321b-f075-42d8-8223-d13a9d45f3ab ro
/dev/sda5:/dev/sda1:Debian GNU/Linux, kernel 2.6.39-1-686-pae (single-user mode):/boot/vmlinuz-2.6.39-1-686-pae:/boot/initrd.img-2.6.39-1-686-pae:root=UUID=42e2321b-f075-42d8-8223-d13a9d45f3ab ro single
/dev/sda5:/dev/sda1:Debian GNU/Linux, kernel 2.6.38-2-686:/boot/vmlinuz-2.6.38-2-686:/boot/initrd.img-2.6.38-2-686:root=UUID=42e2321b-f075-42d8-8223-d13a9d45f3ab ro
/dev/sda5:/dev/sda1:Debian GNU/Linux, kernel 2.6.38-2-686 (single-user mo...

I, too, have "lost" my other Ubuntu partition. I installed 12.04 on sda1 using Btrfs; it booted fine. Then I installed another 12.04 on sda2 (/boot) and sda3 (swap) and sda4 (/), and it boots fine, but now I can't boot from sda1. Mounting and then unmounting sda1 as suggested in comment #2 does not help.

$ sudo fdisk -l /dev/sda

Disk /dev/sda: 128.0 GB, 128035676160 bytes
255 heads, 63 sectors/track, 15566 cylinders, total 250069680 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00076ab2

   Device Boot Start End Blocks Id System
/dev/sda1 * 2048 13672447 6835200 83 Linux
/dev/sda2 * 13672448 14258175 292864 83 Linux
/dev/sda3 14258176 24023039 4882432 82 Linux swap / Solaris
/dev/sda4 24023040 250068991 113022976 83 Linux
$ sudo os-prober
$

Comment #2 of http://ubuntuforums.org/showthread.php?t=1969614 says that renaming the grub.cfg on the _hidden partition_ allows update-grub to work, but this did not help in my situation.