---
name: "posix_openpt"
section: "2freebsd"
platform: "linux"
package: "freebsd-manpages"
version: "12.2-2"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/posix_openpt/2freebsd"
---

# posix\_openpt(2freebsd)

open a pseudo-terminal device

## NAME

**posix\_openpt** – open a pseudo-terminal device

## LIBRARY

Standard C Library (libc, -lc)

## SYNOPSIS

**#include \<fcntl.h\>**

**#include \<stdlib.h\>**

*int*\

**posix\_openpt**(*int oflag*);

## DESCRIPTION

The **posix\_openpt**() function allocates a new pseudo-terminal and establishes a connection with its master device. A slave device shall be created in */dev/pts*. After the pseudo-terminal has been allocated, the slave device should have the proper permissions before it can be used (see [grantpt(3)](/grantpt/3.md)). The name of the slave device can be determined by calling [ptsname(3)](/ptsname/3.md).

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.

- O\_CLOEXEC

  Set the close-on-exec flag for the new file descriptor.

The **posix\_openpt**() function shall fail when *oflag* contains other values.

## RETURN VALUES

Upon successful completion, the **posix\_openpt**() function shall allocate a new pseudo-terminal device and return a non-negative integer representing a file descriptor, which is connected to its master device. Otherwise, -1 shall be returned and errno set to indicate the error.

## ERRORS

The **posix\_openpt**() function shall fail if:

- \[ENFILE\]

  The system file table is full.

- \[EINVAL\]

  The value of *oflag* is not valid.

- \[EAGAIN\]

  Out of pseudo-terminal resources.

## SEE ALSO

[ptsname(3)](/ptsname/3.md), [pts(4)](/pts/4.md), [tty(4)](/tty/4.md)

## STANDARDS

The **posix\_openpt**() function conforms to IEEE Std 1003.1-2001 (“POSIX.1”). The ability to use O\_CLOEXEC is an extension to the standard.

## HISTORY

The **posix\_openpt**() function appeared in FreeBSD 5.0. In FreeBSD 8.0, this function was changed to a system call.

## NOTES

The flag O\_NOCTTY is included for compatibility; in FreeBSD, opening a terminal does not cause it to become a process's controlling terminal.

## AUTHORS

Ed Schouten ⟨*ed@FreeBSD.org*⟩