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 is 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 master  pseudo-terminal  device  and
       return  a  non-negative  integer  representing  the lowest numbered unused 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

       grantpt(), open(), ptsname(), unlockpt()

       The Base Definitions volume of POSIX.1‐2008, <fcntl.h>, <stdlib.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition,
       Standard  for  Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electrical and Electronics Engineers,  Inc
       and  The  Open Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/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 .