---
name: "unlockpt"
section: "3"
platform: "freebsd"
package: "base"
version: "16.0-CURRENT-20261027-61c70dc16a79"
release: "FreeBSD 16.0-CURRENT (2026-10-27)"
platforms: ["linux", "freebsd"]
url: "https://new.carta.tech/grantpt"
---

# unlockpt(3)

pseudo-terminal access functions

Part of [grantpt(3)](/grantpt/3.md).

## NAME

**grantpt**, **ptsname**, **ptsname\_r**, **unlockpt** – pseudo-terminal access functions

## LIBRARY

Standard C Library (libc, -lc)

## SYNOPSIS

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

*int*\

**grantpt**(*int fildes*);

*char \**\

**ptsname**(*int fildes*);

*int*\

**ptsname\_r**(*int fildes*, *char \*buffer*, *size\_t buflen*);

*int*\

**unlockpt**(*int fildes*);

## DESCRIPTION

The **grantpt**(), **ptsname**(), and **unlockpt**() functions allow access to pseudo-terminal devices. These three functions accept a file descriptor that references the master half of a pseudo-terminal pair. This file descriptor is created with [posix\_openpt(2)](/posix_openpt/2.md).

The **grantpt**() function is used to establish ownership and permissions of the slave device counterpart to the master device specified with *fildes*. The slave device's ownership is set to the real user ID of the calling process, and the permissions are set to user readable-writable and group writable. The group owner of the slave device is also set to the group “tty”.

The **ptsname**() function returns the full pathname of the slave device counterpart to the master device specified with *fildes*. This value can be used to subsequently open the appropriate slave after [posix\_openpt(2)](/posix_openpt/2.md) and **grantpt**() have been called.

The **ptsname\_r**() function is the thread-safe version of **ptsname**(). The caller must provide storage for the results of the full pathname of the slave device in the *buffer* and *bufsize* arguments.

The **unlockpt**() function clears the lock held on the pseudo-terminal pair for the master device specified with *fildes*.

## RETURN VALUES

The **grantpt()** and **unlockpt()** functions return the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indicate the error.

The **ptsname**() function returns a pointer to the name of the slave device on success; otherwise a NULL pointer is returned.

The **ptsname\_r**() function returns the value 0 if successful; otherwise a nonzero value is returned and the global variable *errno* is set to indicate the error. Note: **ptsname\_r**() was previously documented as returning -1 on error. In the future it will be changed to return an error number, for POSIX compatibility. Therefore, callers should not check for -1.

## ERRORS

The **grantpt**(), **ptsname**(), **ptsname\_r**() and **unlockpt**() functions may fail and set *errno* to:

- \[EBADF\]

  *fildes* is not a valid open file descriptor.

- \[EINVAL\]

  *fildes* is not a master pseudo-terminal device.

In addition, the **ptsname\_r**() function may set *errno* to:

- \[ERANGE\]

  The buffer was too small.

In addition, the **grantpt**() function may set *errno* to:

- \[EACCES\]

  The slave pseudo-terminal device could not be accessed.

## SEE ALSO

[posix\_openpt(2)](/posix_openpt/2.md), [pts(4)](/pts/4.md), [tty(4)](/tty/4.md)

## STANDARDS

The **ptsname**() function conforms to IEEE Std 1003.1-2008 (“POSIX.1”).

This implementation of **grantpt**() and **unlockpt**() does not conform to IEEE Std 1003.1-2008 (“POSIX.1”), because it depends on [posix\_openpt(2)](/posix_openpt/2.md) to create the pseudo-terminal device with proper permissions in place. It only validates whether *fildes* is a valid pseudo-terminal master device. Future revisions of the specification will likely allow this behaviour, as stated by the Austin Group.

## HISTORY

The **grantpt**(), **ptsname**() and **unlockpt**() functions appeared in FreeBSD 5.0.