OPENPTY(3)                OpenBSD Programmer's Manual               OPENPTY(3)

NAME
     openpty, login_tty, forkpty - tty utility functions

SYNOPSIS
     #include <termios.h>
     #include <util.h>

     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);

DESCRIPTION
     The openpty(), login_tty(), and forkpty() functions perform manipulations
     on ttys and pseudo-ttys.

     The openpty() function finds an available pseudo-tty and returns file de-
     scriptors for the master and slave in amaster and aslave.  If name is
     non-null, the filename of the slave is returned in name (a string of at
     least 16 characters).  If termp is non-null, the terminal parameters of
     the slave will be set to the values in termp.  If winp is non-null, the
     window size of the slave will be set to the values in winp.

     The openpty() function works in the following way: first it attempts to
     allocate the pseudo-tty through the /dev/ptm device (see pty(4) for de-
     tails) and if that fails it searches for a free pseudo-tty by iterating
     through all existing pseudo-tty devices in /dev.  When a free pseudo-tty
     is found, its ownership is changed to the UID of the caller, permissions
     are set to correct values, and all earlier uses of that device are re-
     voked (see revoke(2) for details).  The first method can work for any us-
     er, the second method requires super-user privileges in most cases.

     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-tty 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-tty.  The file descriptor of
     the master side of the pseudo-tty is returned in amaster, and the file-
     name of the slave in name if it is non-null.  The termp and winp parame-
     ters, if non-null, will determine the terminal attributes and window size
     of the slave side of the pseudo-tty.

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 pro-
     cess.

FILES
     /dev/pty[p-zP-T][0-9a-zA-Z]   master pseudo terminals
     /dev/tty[p-zP-T][0-9a-zA-Z]   slave pseudo terminals
     /dev/ptm                      pseudo terminal management device

ERRORS
     openpty() will fail if:

     [ENOENT]      There are no available ttys.

     login_tty() will fail if ioctl() fails to set fd to the controlling ter-
     minal of the current process.  forkpty() will fail if either openpty() or
     fork() fails.

SEE ALSO
     fork(2), revoke(2), pty(4)

OpenBSD 4.5                      May 31, 2007                                2