forkpty(3) — Linux manual page


OPENPTY(3)                Linux Programmer's Manual               OPENPTY(3)

NAME         top

       openpty, login_tty, forkpty - terminal utility functions

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);

       Link with -lutil.

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 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         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 │

CONFORMING TO         top

       These are BSD functions, present in glibc.  They are not standardized
       in POSIX.

NOTES         top

       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         top

       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         top

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

COLOPHON         top

       This page is part of release 5.09 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

GNU                              2017-09-15                       OPENPTY(3)

Pages that refer to this page: pty(7)