chmod

    ("Change mode") The Unix command and system
   call to change the access permissions of a named file.
   Each file (directory, device, etc.) has nine kinds of access
   which can be allowed or denied.  Different permissions apply
   to the owner of the file, the members of the group the file
   belongs to, and all users.  Each of these classes of user
   (owner, group and other) can have permission to read, write or
   execute the file.  Chmod can also set various other mode bits
   for a file or directory such as the sticky bit and the set
   user id bit.

   Unix man page: chmod

   (1995-01-31)