umount: /johnext: device is busy.
(In some cases useful info about processes that use
the device is found by lsof(8) or fuser(1))
c: current directory.
e: executable being run.
f: open file. f is omitted in default display mode.
F: open file for writing. F is omitted in default display mode.
r: root directory.
m: mmap'ed file or shared library.
$ fuser /johnext/ # 檢視在 mount 點有哪些 process 在跑.
/johnext: 26674c
$ ps -aux | grep 26674
#kill -9 26674
#umount /johnext/