openpty, login_tty, forkpty - terminal utility functions
System utilities library (
libutil,
-lutil)
#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);
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.
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.
openpty() fails if:
- ENOENT
- There are no available terminals.
login_tty() fails if
ioctl(2) fails to set
fd to the
controlling terminal of the calling process.
forkpty() fails if either
openpty() or
fork(2) fails.
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 |
These are BSD functions, present in glibc. They are not standardized in POSIX.
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
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.
Nobody knows how much space should be reserved for
name. So, calling
openpty() or
forkpty() with non-NULL
name may not be
secure.
fork(2),
ttyname(3),
pty(7)