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openpty(3) — Linux manual page

openpty(3)               Library Functions Manualopenpty(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(intfd);

DESCRIPTION        top

       Theopenpty() function finds an available pseudoterminal and       returns file descriptors for the master and slave inamaster andaslave.  Ifname is not NULL, the filename of the slave is       returned inname.  Iftermp is not NULL, the terminal parameters       of the slave will be set to the values intermp.  Ifwinp is not       NULL, the window size of the slave will be set to the values inwinp.       Thelogin_tty() function prepares for a login on the terminal       referred to by the file descriptorfd (which may be a real       terminal device, or the slave of a pseudoterminal as returned byopenpty()) by creating a new session, makingfd the controlling       terminal for the calling process, settingfd to be the standard       input, output, and error streams of the current process, and       closingfd.       Theforkpty() function combinesopenpty(),fork(2), andlogin_tty() to create a new process operating in a pseudoterminal.       A file descriptor referring to master side of the pseudoterminal       is returned inamaster.  Ifname is not NULL, the buffer it points       to is used to return the filename of the slave.  Thetermp andwinp 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 toopenpty(),login_tty(), orforkpty() is not       successful, -1 is returned anderrno is set to indicate the error.       Otherwise,openpty(),login_tty(), and the child process offorkpty() return 0, and the parent process offorkpty() returns       the process ID of the child process.

ERRORS        top

openpty() fails if:ENOENTThere are no available terminals.login_tty() fails ifioctl(2) fails to setfd to the controlling       terminal of the calling process.forkpty() fails if eitheropenpty() orfork(2) fails.

ATTRIBUTES        top

       For an explanation of the terms used in this section, seeattributes(7).       ┌───────────────────────┬───────────────┬────────────────────────┐       │Interface│Attribute│Value│       ├───────────────────────┼───────────────┼────────────────────────┤       │forkpty(),openpty()  │ Thread safety │ MT-Safe locale         │       ├───────────────────────┼───────────────┼────────────────────────┤       │login_tty()           │ Thread safety │ MT-Unsafe race:ttyname │       └───────────────────────┴───────────────┴────────────────────────┘

STANDARDS        top

       BSD.

HISTORY        top

       Theconstmodifiers were added to the structure pointer arguments       ofopenpty() andforkpty() 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 forname.  So,       callingopenpty() orforkpty() with non-NULLname may not be       secure.

SEE ALSO        top

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

COLOPHON        top

       This page is part of theman-pages (Linux kernel and C library       user-space interface documentation) project.  Information about       the project can be found at        ⟨https://www.kernel.org/doc/man-pages/⟩.  If you have a bug report       for this manual page, see       ⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.       This page was obtained from the tarball man-pages-6.15.tar.gz       fetched from       ⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on       2025-08-11.  If you discover any rendering problems in this HTML       version of the page, or you believe there is a better or more up-       to-date source for the page, or you have corrections or       improvements to the information in this COLOPHON (which isnot       part of the original manual page), send a mail to       man-pages@man7.orgLinux man-pages 6.15            2025-05-17openpty(3)

Pages that refer to this page:pty(7)

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