Method for unmounting of filesystem

A method for unmounting a file system is provided to generate no expense burden caused from rebooting of a server system and forcibly unmount the file system of a busy state without turning off power of the server system, and affecting a process or a file separately operated from the file system. It is checked whether the file system to be unmounted by responding to a forcible unmount request is a root file system or not(S110). In case that the unmounted file system is not the root file system, access to the unmounted file system and files included in the unmounted file system is blocked to other processes(S115). The first process executing a program binary file present in the unmounted file system is terminated. The second process waiting for obtaining lock for all files opened in the unmounted file system is awakened and the lock is removed(S125). All opened files are closed without affecting the third process opening the file of the unmounted file system. It is informed to the fourth process executed in a directory present in the unmounted file system that the directory is valid any longer.