OPENPTY

Section: Linux Programmer's Manual (3)
Updated: 2003-07-18
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NAME

openpty, login_tty, forkpty - tty utility functions  

SYNOPSIS

#include <pty.h>  /* for openpty and forkpty */
#include <utmp.h> /* for login_tty */

int openpty(int *amaster, int *aslave, char *name, struct termios *termp, struct winsize * winp);

int login_tty(int fd);

pid_t forkpty(int *amaster, char *name, struct termios *termp, struct winsize *winp);

Link with -lutil.  

DESCRIPTION

The openpty() function finds an available pseudo-terminal 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 tty fd (which may be a real tty device, or the slave of a pseudo-terminal as returned by openpty()) by creating a new session, making fd the controlling terminal for the current 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(), and login_tty() to create a new process operating in a pseudo-terminal. The file descriptor of the master side of the pseudo-terminal is returned in amaster, and the filename of the slave in name if it is not NULL. The termp and winp parameters, if not NULL, will determine the terminal attributes and window size of the slave side of the pseudo-terminal.  

RETURN VALUES

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() will fail if:
ENOENT
There are no available ttys.

login_pty() will fail if ioctl() fails to set fd to the controlling terminal of the current process.

forkpty() will fail if either openpty() or fork() fails.  

NOTES

These functions are included in libutil, hence you'll need to add -lutil to your compiler command line.

In versions of glibc before 2.0.92, openpty() returns file descriptors for a BSD pseudo-terminal pair; since glibc 2.0.92, it first attempts to open a Unix 98 pseudo-terminal pair, and falls back to opening a BSD pseudo-terminal pair if that fails.  

CONFORMING TO

These are BSD functions, present in libc5 and glibc2.  

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), pty(7)


 

Index

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUES
ERRORS
NOTES
CONFORMING TO
BUGS
SEE ALSO

linux.jgfs.net manual pages