POSIX_OPENPT(3)            POSIX Programmer's Manual           POSIX_OPENPT(3)



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

NAME
       posix_openpt -- open a pseudo-terminal device

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

       int posix_openpt(int oflag);

DESCRIPTION
       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 Section 2.14, File
       Descriptor Allocation 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.

RETURN VALUE
       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.

ERRORS
       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.

       The following sections are informative.

EXAMPLES
   Opening aa Pseudo-Terminal and Returning the Name of the Slave Device and aa
       File Descriptor
           #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;

APPLICATION USAGE
       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.

RATIONALE
       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;

FUTURE DIRECTIONS
       None.

SEE ALSO
       Section 2.14, File Descriptor Allocation, grantpt(), open(), ptsname(),
       unlockpt()

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

COPYRIGHT
       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(3)
