POSIX_OPENPT(3P) POSIX Programmer's Manual POSIX_OPENPT(3P)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.
NAMEposix_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 mas‐
ter 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 descrip‐
tion 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 repre‐
senting 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 per‐
missions, 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. How‐
ever, consensus could not be reached, and it was felt that adding a new
function would permit other implementations. The posix_openpt() func‐
tion 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 ALSOgrantpt(), 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 Electri‐
cal 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.ker‐
nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 POSIX_OPENPT(3P)
