openpty(3) — Linux manual page


openpty(3)              Library Functions Manual              openpty(3)

NAME         top

       openpty, login_tty, forkpty - terminal utility functions

LIBRARY         top

       System utilities library (libutil, -lutil)

SYNOPSIS         top

       #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         top

       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

       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

RETURN VALUE         top

       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         top

       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.

ATTRIBUTES         top

       For an explanation of the terms used in this section, see
       │ Interface            Attribute     Value                  │
       │ forkpty(), openpty() │ Thread safety │ MT-Safe locale         │
       │ login_tty()          │ Thread safety │ MT-Unsafe race:ttyname │

STANDARDS         top


HISTORY         top

       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.

BUGS         top

       Nobody knows how much space should be reserved for name.  So,
       calling openpty() or forkpty() with non-NULL name may not be

SEE ALSO         top

       fork(2), ttyname(3), pty(7)

COLOPHON         top

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Linux man-pages 6.9.1          2024-05-02                     openpty(3)

Pages that refer to this page: pty(7)