---
name: "grantpt"
section: "3"
platform: "linux"
package: "man-pages"
version: "6.19-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux", "freebsd", "macos"]
url: "https://new.carta.tech/grantpt"
---

# grantpt(3)

grant access to the slave pseudoterminal

## NAME

grantpt - grant access to the slave pseudoterminal

## LIBRARY

Standard C library (*libc*, *-lc*)

## SYNOPSIS

```
#define _XOPEN_SOURCE
#include <stdlib.h>
```

**int grantpt(int** *fd***);**

Feature Test Macro Requirements for glibc (see [**feature\_test\_macros**(7)](/feature_test_macros/7.md)):

**grantpt**():

```
    Since glibc 2.24:
        _XOPEN_SOURCE >= 500
    glibc 2.23 and earlier:
        _XOPEN_SOURCE
```

## DESCRIPTION

The **grantpt**() function changes the mode and owner of the slave pseudoterminal device corresponding to the master pseudoterminal referred to by the file descriptor *fd*. The user ID of the slave is set to the real UID of the calling process. The group ID is set to an unspecified value (e.g., *tty*). The mode of the slave is set to 0620 (crw--w----).

The behavior of **grantpt**() is unspecified if a signal handler is installed to catch **SIGCHLD** signals.

## RETURN VALUE

When successful, **grantpt**() returns 0. Otherwise, it returns -1 and sets *errno* to indicate the error.

## ERRORS

- **EACCES**

  The corresponding slave pseudoterminal could not be accessed.

- **EBADF**

  The *fd* argument is not a valid open file descriptor.

- **EINVAL**

  The *fd* argument is valid but not associated with a master pseudoterminal.

## ATTRIBUTES

For an explanation of the terms used in this section, see [**attributes**(7)](/attributes/7.md).

| | | |
| --- | --- | --- |
| **Interface** | **Attribute** | **Value** |
| **grantpt**() | Thread safety | MT-Safe locale |

## STANDARDS

POSIX.1-2008.

## HISTORY

glibc 2.1. POSIX.1-2001.

This is part of the UNIX 98 pseudoterminal support, see [**pts**(4)](/pts/4.md).

Historical systems implemented this function via a set-user-ID helper binary called "pt\_chown". glibc on Linux before glibc 2.33 could do so as well, in order to support configurations with only BSD pseudoterminals; this support has been removed. On modern systems this is either a no-op —with permissions configured on pty allocation, as is the case on Linux— or an [**ioctl**(2)](/ioctl/2.md).

## SEE ALSO

[**open**(2)](/open/2.md), [**posix\_openpt**(3)](/posix_openpt/3.md), [**ptsname**(3)](/ptsname/3.md), [**unlockpt**(3)](/unlockpt/3.md), [**pts**(4)](/pts/4.md), [**pty**(7)](/pty/7.md)