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).

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) 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(), ptsname_r(), 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.

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.

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) 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.