How to unmount a stale NFS mount that fails to unmount with 'device is busy' after network disconnectivity?

Solution Verified - Updated 2019-06-10T14:23:14+00:00 -

Issue

Temporarily losing network connection to the NFS Server some times causes the NFS client mount to go stale.
Standard attempts to umount fails with the EBUSY message: umount: /mnt/nfs: device is busy when using any of the following commands:
```
# mount -t nfs -o remount /mnt/nfs
# umount /mnt/nfs
# umount -f /mnt/nfs
# umount -l /mnt/nfs
# umount -lf /mnt/nfs
```

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