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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 ter‐
minal device, or the slave of a pseudoterminal as returned by openpty()) by creating a new
session, making fd the controlling 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 descriptor of the master side of the
pseudoterminal is returned in amaster, and the filename of the slave in name if it is not
NULL. 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() will fail if:
ENOENT There are no available terminals.
login_tty() will fail if ioctl(2) fails to set fd to the controlling terminal of the call‐
ing process.
forkpty() will fail if either openpty() or fork(2) fails.
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 pseu‐
doterminal 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 3.74 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 http://www.kernel.org/doc/man-pages/.
GNU 2014-08-19 OPENPTY(3)
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