Multiple filesystems are mounted on same mountpoint

[lavinog]

Steps to reproduce:
1. Install some Ubuntu (ex. 10.04) on partition and add several users on them. Each of them should have own firefox configuration.
2. Run Ubuntu 12.04 Precise installation and run installation on new partition. It will hangs, because it was unable to unmount the partition with two users

Binary package hint: ubiquity

While installing Natty beta2 from USB flash drive, I was unable to complete the install due to the installer not being able to unmount /dev/sda10:
Apr 25 11:43:51 ubuntu ubiquity: umount: cannot umount /dev/sda10 -- /dev/sda6 is mounted over it on the same point.
Apr 25 11:44:06 ubuntu ubiquity: umount: cannot umount /dev/sda10 -- /dev/sda6 is mounted over it on the same point.
Apr 25 11:44:18 ubuntu ubiquity[4551]: Reverting lockdown the desktop environment.
Apr 25 11:44:19 ubuntu activate-dmraid: No Serial ATA RAID disks detected
Apr 25 11:44:19 ubuntu ubiquity: umount: /target: device is busy.
Apr 25 11:44:19 ubuntu ubiquity: (In some cases useful info about processes that use
Apr 25 11:44:19 ubuntu ubiquity: the device is found by lsof(8) or fuser(1))
Apr 25 11:44:19 ubuntu ubiquity:

It appears that multiple filesystems have been mounted on /target:
Filesystem Size Used Avail Use% Mounted on
aufs 869M 163M 662M 20% /
none 1.7G 724K 1.7G 1% /dev
/dev/sdb1 2.0G 1.6G 387M 81% /cdrom
/dev/loop0 656M 656M 0 100% /rofs
none 1.7G 1.4M 1.7G 1% /dev/shm
tmpfs 1.7G 68K 1.7G 1% /tmp
none 1.7G 96K 1.7G 1% /var/run
none 1.7G 4.0K 1.7G 1% /var/lock
/dev/sda12 11G 2.5G 8.0G 24% /target
/dev/sda13 11G 2.5G 8.0G 24% /target/home
/dev/sda10 11G 2.5G 8.0G 24% /target
/dev/sda11 11G 2.5G 8.0G 24% /target/home
/dev/sda6 11G 2.5G 8.0G 24% /target

The partition that is actually mounted on /target is the newly installed partition:
ubuntu@ubuntu:/$ cat /target/etc/lsb-release
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=11.04
DISTRIB_CODENAME=natty
DISTRIB_DESCRIPTION="Ubuntu Natty (development branch)"

/proc/mounts does not show the extra partitions being mounted:

ubuntu@ubuntu:/$ cat /proc/mounts
rootfs / rootfs rw 0 0
none /sys sysfs rw,nosuid,nodev,noexec,relatime 0 0
none /proc proc rw,nosuid,nodev,noexec,relatime 0 0
none /dev devtmpfs rw,relatime,size=1727568k,nr_inodes=431892,mode=755 0 0
none /dev/pts devpts rw,nosuid,noexec,relatime,gid=5,mode=620,ptmxmode=000 0 0
fusectl /sys/fs/fuse/connections fusectl rw,relatime 0 0
/dev/sdb1 /cdrom vfat rw,relatime,fmask=0022,dmask=0022,codepage=cp437,iocharset=iso8859-1,shortname=mixed,errors=remount-ro 0 0
/dev/loop0 /rofs squashfs ro,noatime 0 0
/dev/loop1 /cow ext3 rw,noatime,errors=continue,barrier=0,data=ordered 0 0
aufs / aufs rw,noatime,si=8dfd2b3e7eb58761 0 0
none /sys/kernel/debug debugfs rw,relatime 0 0
none /sys/kernel/security securityfs rw,relatime 0 0
none /dev/shm tmpfs rw,nosuid,nodev,relatime 0 0
tmpfs /tmp tmpfs rw,nosuid,nodev,relatime 0 0
none /var/run tmpfs rw,nosuid,relatime,mode=755 0 0
none /var/lock tmpfs rw,nosuid,nodev,noexec,relatime 0 0
binfmt_misc /proc/sys/fs/binfmt_misc binfmt_misc rw,nosuid,nodev,noexec,relatime 0 0
/dev/sda12 /target ext4 rw,relatime,errors=remount-ro,barrier=1,data=ordered 0 0
proc /target/proc proc rw,relatime 0 0
sysfs /target/sys sysfs rw,relatime 0 0
none /target/dev devtmpfs rw,relatime,size=1727568k,nr_inodes=431892,mode=755 0 0
gvfs-fuse-daemon /home/ubuntu/.gvfs fuse.gvfs-fuse-daemon rw,nosuid,nodev,relatime,user_id=999,group_id=999 0 0

ubuntu@ubuntu:/$ cat /etc/mtab
aufs / aufs rw 0 0
none /proc proc rw,noexec,nosuid,nodev 0 0
none /sys sysfs rw,noexec,nosuid,nodev 0 0
fusectl /sys/fs/fuse/connections fusectl rw 0 0
none /dev devtmpfs rw,mode=0755 0 0
none /dev/pts devpts rw,noexec,nosuid,gid=5,mode=0620 0 0
/dev/sdb1 /cdrom vfat rw,relatime,fmask=0022,dmask=0022,codepage=cp437,iocharset=iso8859-1,shortname=mixed,errors=remount-ro 0 0
/dev/loop0 /rofs squashfs ro,noatime 0 0
none /sys/kernel/debug debugfs rw 0 0
none /sys/kernel/security securityfs rw 0 0
none /dev/shm tmpfs rw,nosuid,nodev 0 0
tmpfs /tmp tmpfs rw,nosuid,nodev 0 0
none /var/run tmpfs rw,nosuid,mode=0755 0 0
none /var/lock tmpfs rw,noexec,nosuid,nodev 0 0
binfmt_misc /proc/sys/fs/binfmt_misc binfmt_misc rw,noexec,nosuid,nodev 0 0
/dev/sda12 /target ext4 rw,errors=remount-ro 0 0
/dev/sda13 /target/home ext4 rw 0 0
/dev/sda10 /target ext4 rw 0 0
/dev/sda11 /target/home ext4 rw 0 0
/dev/sda6 /target ext3 rw 0 0
/dev /target/dev none rw,bind 0 0
gvfs-fuse-daemon /home/ubuntu/.gvfs fuse.gvfs-fuse-daemon rw,nosuid,nodev,user=ubuntu 0 0

ProblemType: Bug
DistroRelease: Ubuntu 11.04
Package: ubiquity 2.6.5
ProcVersionSignature: Ubuntu 2.6.38-8.42-generic 2.6.38.2
Uname: Linux 2.6.38-8-generic x86_64
Architecture: amd64
Date: Mon Apr 25 12:38:53 2011
LiveMediaBuild: Ubuntu 11.04 "Natty Narwhal" - Beta amd64 (20110413)
ProcEnviron:
 LANGUAGE=en_US:en
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: ubiquity
UpgradeStatus: No upgrade log present (probably fresh install)

[Launchpad Janitor (janitor)]

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

[Bartosz Kosiorek (gang65)]

This bug is also present in Ubuntu 12.04 Precise Alpha.

I cannot install Precise because it trying to import the settings from another Ubuntu installation, and I have two users on partition

[Brian Murray (brian-murray)]

I'm marking this as a duplicate of newer bug 980676. Thanks for the detailed steps to recreate it though.