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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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POSIX_OPENPT(3P) POSIX Programmer's Manual POSIX_OPENPT(3P)
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.
posix_openpt — open a pseudo-terminal device
#include <stdlib.h>
#include <fcntl.h>
int posix_openpt(int oflag);
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.
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.
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.
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, respectively.
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;
None.
Section 2.14, File Descriptor Allocation, grantpt(3p), open(3p),
ptsname(3p), unlockpt(3p)
The Base Definitions volume of POSIX.1‐2017, fcntl.h(0p),
stdlib.h(0p)
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(3P)
Pages that refer to this page: stdlib.h(0p), grantpt(3p), ptsname(3p), unlockpt(3p)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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