卸载NFS，结果出现无法卸载的情况
umount /mnt/
umount: /mnt: device is busy
使用umount -f，问题依旧
umount -f /mnt/
umount2: Device or resource busy
umount: /mnt: device is busy
umount2: Device or resource busy
umount: /mnt: device is busy
使用fuser命令，先确认有那些进程需要杀掉
fuser -cu /mnt
/mnt: 15060c(root)
其次向进程发出SIGKILL信号
fuser -ck /mnt
/mnt: 15060c
fuser -c /mnt
[1]+ Killed dd if=1g of=/dev/null bs=1M (wd: /mnt)
(wd now: /)