Understanding access permissions

There are three types of permissions:

   r  read the file or directory
   w  write to the file or directory
   x  execute the file or search the directory

Each of these permissions can be set for any one of three types of user:

   u  the user who owns the file (usually you)
   g  members of the group to which the owner belongs
   o  all other users

The access permissions for all three types of user can be given as a string of nine characters:

   user    group   others
   r w x   r w x   r w x

These permissions have different meanings for files and directories.