grantpt(3) Library Functions Manual grantpt(3)

grantpt - grant access to the slave pseudoterminal

Standard C library (libc, -lc)

#include <stdlib.h>
int grantpt(int fd);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):


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

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.

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

The corresponding slave pseudoterminal could not be accessed.
The fd argument is not a valid open file descriptor.
The fd argument is valid but not associated with a master pseudoterminal.

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

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


glibc 2.1. POSIX.1-2001.

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

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).

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

2024-05-02 Linux man-pages 6.8