Some time, Linux fails to unmount a filesystem reporting “device is busy”. I understand that this helps avoid data lost by disallowing unmouting a filesystem when it is being used.
But for some situations, I am sure there is something wrong happened or I care not data lost, such as a NFS mounting while the NFS server is dead and will never be back. Under these kinds of situations, how do I force Linux to unmount a filesystem?
You can check this tutorials on how to unmount a “device is busy” filesystem: