Manpages - openpty.3

openpty, login_tty, forkpty - terminal utility functions

  #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.

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.

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.

*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.

For an explanation of the terms used in this section, see *attributes*(7).

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

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.

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

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

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