posix_openpt(3p) — Linux manual page


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

PROLOG         top

       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         top

       posix_openpt — open a pseudo-terminal device

SYNOPSIS         top

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

       int posix_openpt(int oflag);

DESCRIPTION         top

       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-

       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         top

       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         top

       The posix_openpt() function shall fail if:

       EMFILE All file descriptors available to the process are currently

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

       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         top

   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;


       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,

RATIONALE         top

       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;



SEE ALSO         top

       grantpt(3p), open(3p), ptsname(3p), unlockpt(3p)

       The Base Definitions volume of POSIX.1‐2008, fcntl.h(0p),

COPYRIGHT         top

       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 .

IEEE/The Open Group                 2013                    POSIX_OPENPT(3P)

Pages that refer to this page: stdlib.h(0p)grantpt(3p)ptsname(3p)unlockpt(3p)