Abstract: Protection for a file system is provided. The protection includes generating first digital signature keys and a system security manager's certificate for a system security manager. A system security manager's certificate is stored onto a security kernel when installing an operating system on a server computer. Second digital signature keys and a user's certificate are generated for a general user. An access authority of the file system is set. A user is identified through a digital signature authentication method when the user tries to access the file system. The user is given access authority for the file in accordance with an identification result.