I booted and typoed a mount command, mounting /dev/hdb1 on the mount point
/.1 instead of /dev/hdc2 on /.1. I didn't catch this for a while, though,
and the system happily mounted it.
# df
Filesystem 1024-blocks Used Available Capacity Mounted on
/dev/hdb1 2970455 992404 1824434 35% /
/dev/hdb1 2970455 992404 1824434 35% /.1
And, of course, I can't umount it because it's busy.
I'm using mount 2.7. 2.6g and 2.6h are pointed to by Documentation/Changes
and http://www.linuxhq.com respectively. It looks like the check in the
kernel is just missing.
Does mount-2.7 even exist? The mount utils in the latest Slackware
distribution are classed as "[u]mount-2.7". For all I know it might be
flawed, and the "bug" is that I'm using some incredibly old version of mount.