OPENPTY(3) Linux Programmer's Manual OPENPTY(3)
NAME
openpty, login_tty, forkpty - terminal utility functions
SYNOPSIS
#include <pty.h>
int openpty(int *amaster, int *aslave, char *name,
const struct termios *termp,
const struct winsize *winp);
pid_t forkpty(int *amaster, char *name,
const struct termios *termp,
const struct winsize *winp);
#include <utmp.h>
int login_tty(int fd);
Link with -lutil.
DESCRIPTION
The openpty() function finds an available pseudoterminal and returns
file descriptors for the master and slave in amaster and aslave. If
name is not NULL, the filename of the slave is returned in name. If
termp is not NULL, the terminal parameters of the slave will be set to
the values in termp. If winp is not NULL, the window size of the slave
will be set to the values in winp.
The login_tty() function prepares for a login on the terminal fd (which
may be a real terminal device, or the slave of a pseudoterminal as re-
turned by openpty()) by creating a new session, making fd the control-
ling terminal for the calling process, setting fd to be the standard
input, output, and error streams of the current process, and closing
fd.
The forkpty() function combines openpty(), fork(2), and login_tty() to
create a new process operating in a pseudoterminal. The file descrip-
tor of the master side of the pseudoterminal is returned in amaster.
If name is not NULL, the buffer it points to is used to return the
filename of the slave. The termp and winp arguments, if not NULL, will
determine the terminal attributes and window size of the slave side of
the pseudoterminal.
RETURN VALUE
If a call to openpty(), login_tty(), or forkpty() is not successful, -1
is returned and errno is set to indicate the error. Otherwise,
openpty(), login_tty(), and the child process of forkpty() return 0,
and the parent process of forkpty() returns the process ID of the child
process.
ERRORS
openpty() fails if:
ENOENT There are no available terminals.
login_tty() fails if ioctl(2) fails to set fd to the controlling termi-
nal of the calling process.
forkpty() fails if either openpty() or fork(2) fails.
ATTRIBUTES
For an explanation of the terms used in this section, see at-
tributes(7).
+---------------------+---------------+------------------------+
|Interface | Attribute | Value |
+---------------------+---------------+------------------------+
|forkpty(), openpty() | Thread safety | MT-Safe locale |
+---------------------+---------------+------------------------+
|login_tty() | Thread safety | MT-Unsafe race:ttyname |
+---------------------+---------------+------------------------+
CONFORMING TO
These are BSD functions, present in glibc. They are not standardized
in POSIX.
NOTES
The const modifiers were added to the structure pointer arguments of
openpty() and forkpty() in glibc 2.8.
In versions of glibc before 2.0.92, openpty() returns file descriptors
for a BSD pseudoterminal pair; since glibc 2.0.92, it first attempts to
open a UNIX 98 pseudoterminal pair, and falls back to opening a BSD
pseudoterminal pair if that fails.
BUGS
Nobody knows how much space should be reserved for name. So, calling
openpty() or forkpty() with non-NULL name may not be secure.
SEE ALSO
fork(2), ttyname(3), pty(7)
COLOPHON
This page is part of release 5.07 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
GNU 2017-09-15 OPENPTY(3)