[root@sftp /]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/vda1 50G 2.2G 45G 5% /
/dev/vdb1 95G 3.9G 87G 5% /data
/dev/vdb3 796G 17G 739G 3% /opt

正常卸載：

umount /opt

報錯：

[root@sftp sftp]# umount /opt/
umount: /opt: device is busy.
(In some cases useful info about processes that use
the device is found by lsof(8) or fuser(1))

強制卸載

[root@sftp ~]# fuser -cu /opt
/opt: 12954cm(root)

[root@sftp ~]# fuser -ck /opt
/opt: 12954cm
[root@sftp ~]# fuser -c /opt
[root@sftp ~]# umount /opt/
[root@sftp ~]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/vda1 50G 2.2G 45G 5% /
/dev/vdb1 95G 3.8G 87G 5% /data

umount卸載