Recursive umount after rbind mount

This worked for me correctly -- https://unix.stackexchange.com/a/264488/4319:

mount --rbind /dev /mnt/test
mount --make-rslave /mnt/test
umount -R /mnt/test

It was important to have the two first commands as two separate commands: do not combine --rbind and --make-rslave in one invocation of mount.

Without --make-rslave, the behavior was unwanted (and not successful):

• umount -l would affect the original old mountpoints, too,
• and umount -R would be affected by the busy (open) files under the original old mountpoints. (Very unexpected...)

The credit goes to Gilles for this answer; Gilles noted in the question comments that the '-n' switch ignores the mtab and unmounts anything listed in /proc/mounts.

From the manpage:

-n     Unmount without writing in /etc/mtab.

So to answer my question of how to unravel a --rbind mount, this is the full command that worked for me:

grep /mnt/chroot/sys /proc/mounts | cut -f2 -d" " | sort -r | xargs umount -n

Merci, Gilles!

Since util-linux v2.23 (25-Apr-2013) the umount command supports the -R, --recursive option.

Here is what the man page says:

Recursively unmount each specified directory. Recursion for each directory will stop if any unmount operation in the chain fails for any reason. The relationship between mountpoints is determined by /proc/self/mountinfo entries. The filesystem must be specified by mountpoint path; a recursive unmount by device name (or UUID) is unsupported.

For filesystems mounted with --rbind it might be needed to run mount --make-rslave before trying to unmount them if umount complains about device is busy.