title: Force unmount of NFS-mounted directory
body: <p>I have an NFS-mounted directory on a Linux machine that has hung. I've tried to force an unmount, but it doesn't seem to work:</p>
  
  <pre><code>$ umount -f /mnt/data
  $ umount2: Device or resource busy
  $ umount: /mnt/data: device is busy
  </code></pre>
  
  <p>If I type "<code>mount</code>", it appears that the directory is no longer mounted, but it hangs if I do "<code>ls /mnt/data</code>", and if I try to remove the mountpoint, I get:</p>
  
  <pre><code>$ rmdir /mnt/data
  rmdir: /mnt/data: Device or resource busy
  </code></pre>
  
  <p>Is there anything I can do other than reboot the machine?</p>