openpty(3) - Linux manual page (original) (raw)

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
   _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)](../man2/fork.2.html), 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](../man3/errno.3.html)_ 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)](../man2/ioctl.2.html) fails to set _fd_ to the controlling
   terminal of the calling process.

   **forkpty**() fails if either **openpty**() or [fork(2)](../man2/fork.2.html) fails.

ATTRIBUTES top

   For an explanation of the terms used in this section, see
   [attributes(7)](../man7/attributes.7.html).
   ┌───────────────────────┬───────────────┬────────────────────────┐
   │ **Interface** │ **Attribute** │ **Value** │
   ├───────────────────────┼───────────────┼────────────────────────┤
   │ **forkpty**(), **openpty**()  │ Thread safety │ MT-Safe locale         │
   ├───────────────────────┼───────────────┼────────────────────────┤
   │ **login_tty**()           │ Thread safety │ MT-Unsafe race:ttyname │
   └───────────────────────┴───────────────┴────────────────────────┘

STANDARDS top

   BSD.

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
   secure.

SEE ALSO top

   [fork(2)](../man2/fork.2.html), [ttyname(3)](../man3/ttyname.3.html), [pty(7)](../man7/pty.7.html)

COLOPHON top

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Linux man-pages 6.10 2024-07-23 openpty(3)

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