Ubiquity produced the following logs:
Mar 11 18:02:45 ubuntu ubiquity[3358]: dbfilter_handle_status: response 2
Mar 11 18:02:45 ubuntu ubiquity[3358]: switched to page partman
Mar 11 18:02:45 ubuntu activate-dmraid: No Serial ATA RAID disks detected
Mar 11 18:02:49 ubuntu ubiquity[3358]: Device /dev/sda1 not found in os-prober output
Mar 11 18:02:49 ubuntu ubiquity[3358]: Device /dev/sda8 not found in os-prober output
Mar 11 18:02:49 ubuntu ubiquity[3358]: Device /dev/sda7 not found in os-prober output
Mar 11 18:02:49 ubuntu ubiquity[3358]: Device /dev/sda6 not found in os-prober output
Mar 11 18:02:49 ubuntu ubiquity[3358]: Device /dev/sda1 not found in os-prober output
Mar 11 18:02:49 ubuntu ubiquity[3358]: Device /dev/sda8 not found in os-prober output
Mar 11 18:02:49 ubuntu ubiquity[3358]: Device /dev/sda7 not found in os-prober output
Mar 11 18:02:49 ubuntu ubiquity[3358]: Device /dev/sda6 not found in os-prober output
Mar 11 18:02:49 ubuntu ubiquity[3358]: Device /dev/sda1 not found in os-prober output
Mar 11 18:02:49 ubuntu ubiquity[3358]: Device /dev/sda8 not found in os-prober output
Mar 11 18:02:49 ubuntu ubiquity[3358]: Device /dev/sda7 not found in os-prober output
Mar 11 18:02:49 ubuntu ubiquity[3358]: Device /dev/sda6 not found in os-prober output
Mar 11 18:02:49 ubuntu ubiquity[3358]: switched to page partman
Mar 11 18:02:52 ubuntu ubiquity[3358]: switched to page partman
Mar 11 18:02:54 ubuntu ubiquity[3358]: debconffilter_done: ubi-partman (current: ubi-partman)
Mar 11 18:02:54 ubuntu ubiquity[3358]: dbfilter_handle_status: ('ubi-partman', 141)




ubuntu@ubuntu:~$ sudo os-prober 
/dev/sda5:Ubuntu 9.10 (9.10):Ubuntu:linux

This produce the following logs:
Mar 11 18:03:15 ubuntu os-prober: debug: running /usr/lib/os-probes/50mounted-tests on /dev/sda1
Mar 11 18:03:15 ubuntu 50mounted-tests: debug: mounted as vfat filesystem
Mar 11 18:03:15 ubuntu 50mounted-tests: debug: running subtest /usr/lib/os-probes/mounted/10freedos
Mar 11 18:03:15 ubuntu 10freedos: debug: /dev/sda1 is a FAT32 partition
Mar 11 18:03:15 ubuntu 50mounted-tests: debug: running subtest /usr/lib/os-probes/mounted/10qnx
Mar 11 18:03:15 ubuntu 10qnx: debug: /dev/sda1 is not a QNX4 partition: exiting
Mar 11 18:03:15 ubuntu 50mounted-tests: debug: running subtest /usr/lib/os-probes/mounted/20macosx
Mar 11 18:03:15 ubuntu macosx-prober: debug: /dev/sda1 is not an HFS+ partition: exiting
Mar 11 18:03:15 ubuntu 50mounted-tests: debug: running subtest /usr/lib/os-probes/mounted/20microsoft
Mar 11 18:03:15 ubuntu 20microsoft: debug: /dev/sda1 is a FAT32 partition
Mar 11 18:03:15 ubuntu 50mounted-tests: debug: running subtest /usr/lib/os-probes/mounted/30utility
Mar 11 18:03:15 ubuntu 30utility: debug: /dev/sda1 is a FAT32 partition
Mar 11 18:03:15 ubuntu 50mounted-tests: debug: running subtest /usr/lib/os-probes/mounted/40lsb
Mar 11 18:03:15 ubuntu 50mounted-tests: debug: running subtest /usr/lib/os-probes/mounted/70hurd
Mar 11 18:03:15 ubuntu 50mounted-tests: debug: running subtest /usr/lib/os-probes/mounted/80minix
Mar 11 18:03:15 ubuntu 50mounted-tests: debug: running subtest /usr/lib/os-probes/mounted/90linux-distro
Mar 11 18:03:15 ubuntu 50mounted-tests: debug: running subtest /usr/lib/os-probes/mounted/90solaris
Mar 11 18:03:15 ubuntu os-prober: debug: running /usr/lib/os-probes/50mounted-tests on /dev/sda2
Mar 11 18:03:15 ubuntu 50mounted-tests: debug: /dev/sda2 is a swap partition; skipping
Mar 11 18:03:15 ubuntu os-prober: debug: os detected by /usr/lib/os-probes/50mounted-tests
Mar 11 18:03:15 ubuntu os-prober: debug: running /usr/lib/os-probes/50mounted-tests on /dev/sda4
Mar 11 18:03:15 ubuntu 50mounted-tests: debug: /dev/sda4 type not recognised; skipping
Mar 11 18:03:15 ubuntu os-prober: debug: os detected by /usr/lib/os-probes/50mounted-tests
Mar 11 18:03:15 ubuntu os-prober: debug: running /usr/lib/os-probes/50mounted-tests on /dev/sda5
Mar 11 18:03:15 ubuntu kernel: [  517.002207] EXT4-fs (sda5): mounted filesystem with ordered data mode
Mar 11 18:03:15 ubuntu 50mounted-tests: debug: mounted as ext4 filesystem
Mar 11 18:03:15 ubuntu 50mounted-tests: debug: running subtest /usr/lib/os-probes/mounted/10freedos
Mar 11 18:03:15 ubuntu 10freedos: debug: /dev/sda5 is not a FAT partition: exiting
Mar 11 18:03:15 ubuntu 50mounted-tests: debug: running subtest /usr/lib/os-probes/mounted/10qnx
Mar 11 18:03:15 ubuntu 10qnx: debug: /dev/sda5 is not a QNX4 partition: exiting
Mar 11 18:03:15 ubuntu 50mounted-tests: debug: running subtest /usr/lib/os-probes/mounted/20macosx
Mar 11 18:03:15 ubuntu macosx-prober: debug: /dev/sda5 is not an HFS+ partition: exiting
Mar 11 18:03:15 ubuntu 50mounted-tests: debug: running subtest /usr/lib/os-probes/mounted/20microsoft
Mar 11 18:03:15 ubuntu 20microsoft: debug: /dev/sda5 is not a MS partition: exiting
Mar 11 18:03:15 ubuntu 50mounted-tests: debug: running subtest /usr/lib/os-probes/mounted/30utility
Mar 11 18:03:15 ubuntu 30utility: debug: /dev/sda5 is not a FAT partition: exiting
Mar 11 18:03:15 ubuntu 50mounted-tests: debug: running subtest /usr/lib/os-probes/mounted/40lsb
Mar 11 18:03:16 ubuntu 40lsb: result: /dev/sda5:Ubuntu 9.10 (9.10):Ubuntu:linux
Mar 11 18:03:16 ubuntu 50mounted-tests: debug: os found by subtest /usr/lib/os-probes/mounted/40lsb
Mar 11 18:03:16 ubuntu os-prober: debug: os detected by /usr/lib/os-probes/50mounted-tests
Mar 11 18:03:16 ubuntu os-prober: debug: running /usr/lib/os-probes/50mounted-tests on /dev/sda6
Mar 11 18:03:16 ubuntu kernel: [  517.214324] EXT4-fs (sda6): mounted filesystem with ordered data mode
Mar 11 18:03:16 ubuntu 50mounted-tests: debug: mounted as ext4 filesystem
Mar 11 18:03:16 ubuntu 50mounted-tests: debug: running subtest /usr/lib/os-probes/mounted/10freedos
Mar 11 18:03:16 ubuntu 10freedos: debug: /dev/sda6 is not a FAT partition: exiting
Mar 11 18:03:16 ubuntu 50mounted-tests: debug: running subtest /usr/lib/os-probes/mounted/10qnx
Mar 11 18:03:16 ubuntu 10qnx: debug: /dev/sda6 is not a QNX4 partition: exiting
Mar 11 18:03:16 ubuntu 50mounted-tests: debug: running subtest /usr/lib/os-probes/mounted/20macosx
Mar 11 18:03:16 ubuntu macosx-prober: debug: /dev/sda6 is not an HFS+ partition: exiting
Mar 11 18:03:16 ubuntu 50mounted-tests: debug: running subtest /usr/lib/os-probes/mounted/20microsoft
Mar 11 18:03:16 ubuntu 20microsoft: debug: /dev/sda6 is not a MS partition: exiting
Mar 11 18:03:16 ubuntu 50mounted-tests: debug: running subtest /usr/lib/os-probes/mounted/30utility
Mar 11 18:03:16 ubuntu 30utility: debug: /dev/sda6 is not a FAT partition: exiting
Mar 11 18:03:16 ubuntu 50mounted-tests: debug: running subtest /usr/lib/os-probes/mounted/40lsb
Mar 11 18:03:16 ubuntu 50mounted-tests: debug: running subtest /usr/lib/os-probes/mounted/70hurd
Mar 11 18:03:16 ubuntu 50mounted-tests: debug: running subtest /usr/lib/os-probes/mounted/80minix
Mar 11 18:03:16 ubuntu 50mounted-tests: debug: running subtest /usr/lib/os-probes/mounted/90linux-distro
Mar 11 18:03:16 ubuntu 50mounted-tests: debug: running subtest /usr/lib/os-probes/mounted/90solaris
Mar 11 18:03:16 ubuntu os-prober: debug: running /usr/lib/os-probes/50mounted-tests on /dev/sda7
Mar 11 18:03:16 ubuntu kernel: [  517.419902] EXT4-fs (sda7): mounted filesystem with ordered data mode
Mar 11 18:03:16 ubuntu 50mounted-tests: debug: mounted as ext4 filesystem
Mar 11 18:03:16 ubuntu 50mounted-tests: debug: running subtest /usr/lib/os-probes/mounted/10freedos
Mar 11 18:03:16 ubuntu 10freedos: debug: /dev/sda7 is not a FAT partition: exiting
Mar 11 18:03:16 ubuntu 50mounted-tests: debug: running subtest /usr/lib/os-probes/mounted/10qnx
Mar 11 18:03:16 ubuntu 10qnx: debug: /dev/sda7 is not a QNX4 partition: exiting
Mar 11 18:03:16 ubuntu 50mounted-tests: debug: running subtest /usr/lib/os-probes/mounted/20macosx
Mar 11 18:03:16 ubuntu macosx-prober: debug: /dev/sda7 is not an HFS+ partition: exiting
Mar 11 18:03:16 ubuntu 50mounted-tests: debug: running subtest /usr/lib/os-probes/mounted/20microsoft
Mar 11 18:03:16 ubuntu 20microsoft: debug: /dev/sda7 is not a MS partition: exiting
Mar 11 18:03:16 ubuntu 50mounted-tests: debug: running subtest /usr/lib/os-probes/mounted/30utility
Mar 11 18:03:16 ubuntu 30utility: debug: /dev/sda7 is not a FAT partition: exiting
Mar 11 18:03:16 ubuntu 50mounted-tests: debug: running subtest /usr/lib/os-probes/mounted/40lsb
Mar 11 18:03:16 ubuntu 50mounted-tests: debug: running subtest /usr/lib/os-probes/mounted/70hurd
Mar 11 18:03:16 ubuntu 50mounted-tests: debug: running subtest /usr/lib/os-probes/mounted/80minix
Mar 11 18:03:16 ubuntu 50mounted-tests: debug: running subtest /usr/lib/os-probes/mounted/90linux-distro
Mar 11 18:03:16 ubuntu 50mounted-tests: debug: running subtest /usr/lib/os-probes/mounted/90solaris
Mar 11 18:03:16 ubuntu os-prober: debug: running /usr/lib/os-probes/50mounted-tests on /dev/sda8
Mar 11 18:03:16 ubuntu kernel: [  517.568411] EXT4-fs (sda8): mounted filesystem with ordered data mode
Mar 11 18:03:16 ubuntu 50mounted-tests: debug: mounted as ext4 filesystem
Mar 11 18:03:16 ubuntu 50mounted-tests: debug: running subtest /usr/lib/os-probes/mounted/10freedos
Mar 11 18:03:16 ubuntu 10freedos: debug: /dev/sda8 is not a FAT partition: exiting
Mar 11 18:03:16 ubuntu 50mounted-tests: debug: running subtest /usr/lib/os-probes/mounted/10qnx
Mar 11 18:03:16 ubuntu 10qnx: debug: /dev/sda8 is not a QNX4 partition: exiting
Mar 11 18:03:16 ubuntu 50mounted-tests: debug: running subtest /usr/lib/os-probes/mounted/20macosx
Mar 11 18:03:16 ubuntu macosx-prober: debug: /dev/sda8 is not an HFS+ partition: exiting
Mar 11 18:03:16 ubuntu 50mounted-tests: debug: running subtest /usr/lib/os-probes/mounted/20microsoft
Mar 11 18:03:16 ubuntu 20microsoft: debug: /dev/sda8 is not a MS partition: exiting
Mar 11 18:03:16 ubuntu 50mounted-tests: debug: running subtest /usr/lib/os-probes/mounted/30utility
Mar 11 18:03:16 ubuntu 30utility: debug: /dev/sda8 is not a FAT partition: exiting
Mar 11 18:03:16 ubuntu 50mounted-tests: debug: running subtest /usr/lib/os-probes/mounted/40lsb
Mar 11 18:03:16 ubuntu 50mounted-tests: debug: running subtest /usr/lib/os-probes/mounted/70hurd
Mar 11 18:03:16 ubuntu 50mounted-tests: debug: running subtest /usr/lib/os-probes/mounted/80minix
Mar 11 18:03:16 ubuntu 50mounted-tests: debug: running subtest /usr/lib/os-probes/mounted/90linux-distro
Mar 11 18:03:16 ubuntu 50mounted-tests: debug: running subtest /usr/lib/os-probes/mounted/90solaris
Mar 11 18:03:16 ubuntu os-prober: debug: running /usr/lib/os-probes/mounted/10freedos on mounted /dev/sdb1
Mar 11 18:03:16 ubuntu 10freedos: debug: /dev/sdb1 is a FAT32 partition
Mar 11 18:03:16 ubuntu os-prober: debug: running /usr/lib/os-probes/mounted/10qnx on mounted /dev/sdb1
Mar 11 18:03:16 ubuntu 10qnx: debug: /dev/sdb1 is not a QNX4 partition: exiting
Mar 11 18:03:16 ubuntu os-prober: debug: running /usr/lib/os-probes/mounted/20macosx on mounted /dev/sdb1
Mar 11 18:03:16 ubuntu macosx-prober: debug: /dev/sdb1 is not an HFS+ partition: exiting
Mar 11 18:03:16 ubuntu os-prober: debug: running /usr/lib/os-probes/mounted/20microsoft on mounted /dev/sdb1
Mar 11 18:03:16 ubuntu 20microsoft: debug: /dev/sdb1 is a FAT32 partition
Mar 11 18:03:16 ubuntu os-prober: debug: running /usr/lib/os-probes/mounted/30utility on mounted /dev/sdb1
Mar 11 18:03:16 ubuntu 30utility: debug: /dev/sdb1 is a FAT32 partition
Mar 11 18:03:16 ubuntu os-prober: debug: running /usr/lib/os-probes/mounted/40lsb on mounted /dev/sdb1
Mar 11 18:03:16 ubuntu os-prober: debug: running /usr/lib/os-probes/mounted/70hurd on mounted /dev/sdb1
Mar 11 18:03:16 ubuntu os-prober: debug: running /usr/lib/os-probes/mounted/80minix on mounted /dev/sdb1
Mar 11 18:03:16 ubuntu os-prober: debug: running /usr/lib/os-probes/mounted/90linux-distro on mounted /dev/sdb1
Mar 11 18:03:16 ubuntu os-prober: debug: running /usr/lib/os-probes/mounted/90solaris on mounted /dev/sdb1