forkpty(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
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 calling process.
forkpty() will fail if either openpty() or fork(2) fails.
ATTRIBUTES
For an explanation of the terms used in this section, see
attributes(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
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latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
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