GRANTPT(3)

NAME
grantpt, ptsname, unlockpt, posix_openpt - pseudo-terminal access functions

LIBRARY
libc

SYNOPSIS
#include <stdlib.h>
int
grantpt(int fildes);
char *
ptsname(int fildes);
int
unlockpt(int fildes);
#include <fcntl.h>
int
posix_openpt(int mode);

DESCRIPTION
The grantpt(), ptsname(), unlockpt(), and posix_openpt() functions allow access to pseudo-terminal devices. The first three functions accept a file descriptor that references the master half of a pseudo-terminal pair. This file descriptor is created with posix_openpt().

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” if it exists on the system; otherwise, it is left untouched.

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() and grantpt() have been called.

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

The posix_openpt() function opens the first available master pseudo-terminal device and returns a descriptor to it. The mode argument specifies the flags used for opening the device:

O_RDWR
    Open for reading and writing.

O_NOCTTY
    If set, do not allow the terminal to become the controlling terminal for the calling process.

RETURN VALUES

The ptsname() function returns a pointer to the name of the slave device on success; otherwise a NULL pointer is returned and the global variable errno is set to indicate the error.

The posix_openpt() function returns a file descriptor to the first available master pseudo-terminal device on success; otherwise -1 is returned and the global variable errno is set to indicate the error.

ERRORS
The grantpt(), ptsname(), and unlockpt() functions may fail and set errno to:

[EINVAL]
    fildes is not a master pseudo-terminal device.

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

[EACCES]
    The slave pseudo-terminal device could not be accessed.

The posix_openpt() function may fail and set errno to:

[EINVAL]
    mode consists of an invalid mode bit.

[EAGAIN]
    The system has no available pseudo-terminal devices.

The grantpt(), ptsname(), and unlockpt() functions may also fail and set errno for any of the errors specified for the fstat(2) system call.

The posix_openpt() function may also fail and set errno for any of the errors specified for the open(2) system call.

SEE ALSO
open(2), pty(4), tty(4)

STANDARDS
The grantpt(), ptsname(), unlockpt(), and posix_openpt() functions conform to p1003.1-2001.

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

NOTES
The purpose of the unlockpt() function has no meaning in FreeBSD.

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