The grantpt() function changes the mode and owner of the slave
pseudo-terminal device (pty) corresponding to the master pty referred to by
fd. The user ID of the slave is set to the real UID of the calling
process. The group ID is set to an unspecified value (e.g. tty). The mode of
the slave is set to 0620 (crw--w----).
The behavior of grantpt() is unspecified if a signal handler is installed
to catch SIGCHLD signals.