1. A distributed file system comprising: a storage device for holding files, multiple clients for carrying out file operations on said storage device, a server using tokens to control rights to file reading and writing operations by the client, and a network connecting said clients, said storage device and said server, wherein: said server contains a token revoke request means for sending a token revoke request for demanding the return of a token granting rights to write on said file, to said client holding said token, and said token revoke request means sends a token revoke request containing information on a client requesting said file, and information showing the contents of a token said client is requesting.