From njw@cs.city.ac.uk (Nick Williams):

/sbin/umount does not return the correct exit status due to incorrect
logic in its internals.

Further, because of the nature of the code, you *cannot* use it to
umount a directory from a union mountpoint. Well, you can sometimes,
it depends on if the directory is at the top of the union stack or not :)

Submitted by:	njw@cs.city.ac.uk (Nick Williams)

1 files changed, 22 insertions, 0 deletions

diff --git a/sbin/umount/umount.8 b/sbin/umount/umount.8
index 234eb8f..d1d02d0 100644
--- a/sbin/umount/umount.8
+++ b/sbin/umount/umount.8
@@ -116,6 +116,28 @@ file system table
 .Xr unmount 2 ,
 .Xr fstab 5 ,
 .Xr mount 8
+.Sh BUGS
+When using union filesystems,
+.Xr umount 8
+cannot always determine the node which is the mountpoint.
+In this case,
+it is necessary to specify the relevant directory to be unmounted
+in the same form as that displayed by
+.Xr mount 8 .
+For example, given a mount entry like this:
+.Bd -literal -offset indent
+<above>/tmpdir on /cdrom (local, user mount)
+.Ed
+.Pp
+then the command:
+.Bd -literal -offset indent
+umount '<above>/tmpdir'
+.Ed
+.Pp
+would unmount 
+.Ar /tmpdir 
+from the mountpoint
+.Ar /cdrom .
 .Sh HISTORY
 A
 .Nm umount