desmontar sshfs do ponto de montagem

dispositivo raspberry pi montado via sshfs:

sshfs osmc@rpi.: /home/user/pi

informações de montagem:

user@azimuth:~$ mount | grep osmc

osmc@rpi.: on /home/user/pi type fuse.sshfs (rw,nosuid,nodev,relatime,user_id=1000,group_id=1000)

Por que não consigo umount?

user@azimuth:~$ sudo umount /home/user/pi
[sudo] password for user: 
umount: /home/user/pi: target is busy
        (In some cases useful info about processes that
         use the device is found by lsof(8) or fuser(1).)

Como desmontar o compartilhamento sshfs?

ATUALIZAÇÕES:

user@azimuth:~$ sudo lsof | grep /home/user/pi
lsof: WARNING: can't stat() fuse.gvfsd-fuse file system /run/user/1000/gvfs
      Output information may be incomplete.
lsof: WARNING: can't stat() fuse.sshfs file system /home/user/nas
      Output information may be incomplete.