posix_openpt man page

posix_openpt — open a pseudoterminal device


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

int posix_openpt(int flags);

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

posix_openpt(): _XOPEN_SOURCE >= 600


The posix_openpt() function opens an unused pseudoterminal master device, returning a file descriptor that can be used to refer to that device.

The flags argument is a bit mask that ORs together zero or more of the following flags:

Open the device for both reading and writing. It is usual to specify this flag.
Do not make this device the controlling terminal for the process.

Return Value

On success, posix_openpt() returns a nonnegative file descriptor which is the lowest numbered unused file descriptor. On failure, -1 is returned, and errno is set to indicate the error.


See open(2).


Glibc support for posix_openpt() has been provided since version 2.2.1.


For an explanation of the terms used in this section, see attributes(7).

posix_openpt()Thread safetyMT-Safe

Conforming to

POSIX.1-2001, POSIX.1-2008.

posix_openpt() is part of the UNIX 98 pseudoterminal support (see pts(4)).


Some older UNIX implementations that support System V (aka UNIX 98) pseudoterminals don't have this function, but it is easy to implement:

posix_openpt(int flags)
    return open("/dev/ptmx", flags);

Calling posix_openpt() creates a pathname for the corresponding pseudoterminal slave device. The pathname of the slave device can be obtained using ptsname(3). The slave device pathname exists only as long as the master device is open.

See Also

open(2), getpt(3), grantpt(3), ptsname(3), unlockpt(3), pts(4), pty(7)

Referenced By

getpt(3), grantpt(3), ptsname(3), pty(7), unlockpt(3).

Explore man page connections for posix_openpt(3).