openpty(3) Library Functions Manual openpty(3)
NAME
openpty, login_tty, forkpty - terminal utility functions
LIBRARY
System utilities library (libutil, -lutil)
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);
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 referred
to by the file descriptor 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. A file descriptor
referring to 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 │
└─────────────────────────────┴───────────────┴────────────────────────┘
STANDARDS
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.
Before glibc 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)
Linux man-pages 6.03 2022-12-15 openpty(3)
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