Cannot Unmount a File System: Device is Busy

Symptom: Unmounting (umount) fails with a message: device is busy. For example:
sudo umount -f 10.x.x.x:/fs-export-path /mnt/yourmountpoint
device is busy

Cause 1: You're attempting to run the umount command from within the mountpoint directory.

Solution 1: Move to a directory outside the file system mount point, and retry the umount command.

Cause 2: An abrupt disconnect from the file system's mount target occurred.

More Information: An NFS message similar to the example below is displayed:
parrm: B cannot remove 'mnt/directory/.nfs <unique_id>':
 Device or resource busy
Solution 2:
  1. Use the fuser or lsof operation to find the process that has locked the file and note its ID.

    See lsof(8)- Linux Man Page for information about how to use lsof.

    See fuser(1)- Linux Man Page for information about how to use fuser.

  2. After you've identified the process that has locked the file, stop the process using the kill command. For example:
    kill <process_id>

    See kill(1)- Linux Man Page for more information.

  3. Retry the umount command.