jammy (3) openpty.3.gz

NAME

       openpty, login_tty, forkpty - terminal utility functions

SYNOPSIS

       #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

       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

       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

       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

       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 │
       └─────────────────────┴───────────────┴────────────────────────┘

CONFORMING TO

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

NOTES

       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

       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

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

COLOPHON

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       information  about  reporting  bugs,  and  the  latest  version  of  this   page,   can   be   found   at
       https://www.kernel.org/doc/man-pages/.