PROLOG

       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.

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 a Pseudo-Terminal and Returning the Name of the Slave Device and a 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 .