This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface

       This  function  is  a  method  for portably obtaining a file descriptor of a master terminal device for a
       pseudo-terminal. The grantpt() and ptsname() functions can be  used  to  manipulate  mode  and  ownership
       permissions, and to obtain the name of the slave device, respectively.

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard
       for  Information  Technology  --  Portable  Operating  System  Interface  (POSIX),  The  Open  Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical  and  Electronics
       Engineers, Inc and The Open Group.  In the event of any discrepancy between this version and the original
       IEEE  and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document.
       The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

       Any typographical or formatting errors that appear in this page are most likely to have  been  introduced
       during   the   conversion  of  the  source  files  to  man  page  format.  To  report  such  errors,  see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                                   2017                                  POSIX_OPENPT(3POSIX)

       The  posix_openpt()  function  shall establish a connection between a master device for a pseudo-terminal
       and a file descriptor. The file descriptor  shall  be  allocated  as  described  in  Section2.14,  FileDescriptorAllocation and can be used by other I/O functions that refer to that pseudo-terminal.

       The  file  status  flags and file access modes of the open file description shall be set according to the
       value of oflag.

       Values for oflag are constructed by a bitwise-inclusive OR of flags from the following list,  defined  in
       <fcntl.h>:

       O_RDWR      Open for reading and writing.

       O_NOCTTY    If  set posix_openpt() shall not cause the terminal device to become the controlling terminal
                   for the process.

       The behavior of other values for the oflag argument is unspecified.

       The posix_openpt() function shall fail if:

       EMFILE All file descriptors available to the process are currently open.

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

       The posix_openpt() function may fail if:

       EINVAL The value of oflag is not valid.

       EAGAIN Out of pseudo-terminal resources.

       ENOSR  Out of STREAMS resources.

       Thefollowingsectionsareinformative.

OpeningaPseudo-TerminalandReturningtheNameoftheSlaveDeviceandaFileDescriptor
           #include <fcntl.h>
           #include <stdio.h>

           int masterfd, slavefd;
           char *slavedevice;

           masterfd = posix_openpt(O_RDWR|O_NOCTTY);

           if (masterfd == -1
               || grantpt (masterfd) == -1
               || unlockpt (masterfd) == -1
               || (slavedevice = ptsname (masterfd)) == NULL)
               return -1;

           printf("slave device is: %s\n", slavedevice);

           slavefd = open(slavedevice, O_RDWR|O_NOCTTY);
           if (slavefd < 0)
               return -1;

       None.

       posix_openpt — open a pseudo-terminal device

       This  manual  page  is part of the POSIX Programmer's Manual.  The Linux implementation of this interface
       may differ (consult the corresponding Linux manual page for details of Linux behavior), or the  interface
       may not be implemented on Linux.

       The  standard  developers  considered  the  matter  of adding a special device for cloning master pseudo-
       terminals: the /dev/ptmx device. However, consensus could not be reached, and it was felt that  adding  a
       new  function  would  permit other implementations. The posix_openpt() function is designed to complement
       the grantpt(), ptsname(), and unlockpt() functions.

       On implementations supporting the /dev/ptmx clone device, opening the master device of a  pseudo-terminal
       is simply:

           mfdp = open("/dev/ptmx", oflag );
           if (mfdp < 0)
               return -1;

       Upon successful completion, the posix_openpt() function shall open a file descriptor for a master pseudo-
       terminal device and return a non-negative integer representing the file descriptor. Otherwise,  -1  shall
       be returned and errno set to indicate the error.

Section2.14, FileDescriptorAllocation, grantpt(), open(), ptsname(), unlockpt()

       The Base Definitions volume of POSIX.1‐2017, <fcntl.h>, <stdlib.h>

       #include <stdlib.h>
       #include <fcntl.h>

       int posix_openpt(int oflag);