When the connection to a remote resource, mounted using sshfs, is broken you can not access the directory using command like ls.
And if you try to umount the remote file system you get this error:
$ sudo umount /mnt/target
umount: /mnt/target: device is busy.
(In some cases useful info about processes that use
the device is found by lsof(8) or fuser(1))
In this case you have to umount using -l option
umount -l /mnt/target
or
umount -f /mnt/target
-l Lazy unmount. Detach the filesystem from the filesystem hierar‐ chy now, and cleanup all references to the filesystem as soon as it is not busy anymore. (Requires kernel 2.4.11 or later.)
-f Force unmount (in case of an unreachable NFS system). (Requires kernel 2.1.116 or later.)
to check the problem you can use mount or mount -v
$ mount -v umount: /mnt/target is not mounted (according to mtab)
If this can not resolve the trouble, you can use fuser to show pids of the processes which using mounted device
fuser -m /mnt/target
Then you have to kill thoose processes and then try again umount
sudo kill id-process or sudo kill -9 id-process
You can use lsof, too. Lsof tell you open files.
lsof /mnt/target
As ultimate choice we have to restart the computer this removes all mounted points.
Nel blog:
maurizio siagri 