x                  Pointer to a passwd structure, if successful.
    NULL               Indicates an end-of-file or error occurred.
                       The function sets errno to one of the
                       following values:

                       o  EIO - Indicates that an I/O error occurred
                          or the user does not have appropriate
                          privileges enabled to access the user
                          authorization file (SYSUAF).

                       o  EMFILE - OPEN_MAX file descriptors are
                          currently open in the calling process.

                       o  ENFILE - The maximum allowable number of
                          files is currently open in the system.