.\" $OpenBSD: openpty.3,v 1.13 2004/02/21 13:47:41 espie Exp $ .\" Copyright (c) 1995 .\" The Regents of the University of California. All rights reserved. .\" .\" This code is derived from software developed by the Computer Systems .\" Engineering group at Lawrence Berkeley Laboratory under DARPA contract .\" BG 91-66 and contributed to Berkeley. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 3. Neither the name of the University nor the names of its contributors .\" may be used to endorse or promote products derived from this software .\" without specific prior written permission. .\" .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" .Dd November 4, 1996 .Dt OPENPTY 3 .Os .Sh NAME .Nm openpty , .Nm login_tty , .Nm forkpty .Nd tty utility functions .Sh SYNOPSIS .Fd #include .Fd #include .Ft int .Fn openpty "int *amaster" "int *aslave" "char *name" "struct termios *termp" "struct winsize *winp" .Ft int .Fn login_tty "int fd" .Ft pid_t .Fn forkpty "int *amaster" "char *name" "struct termios *termp" "struct winsize *winp" .Sh DESCRIPTION The .Fn openpty , .Fn login_tty , and .Fn forkpty functions perform manipulations on ttys and pseudo-ttys. .Pp The .Fn openpty function finds an available pseudo-tty and returns file descriptors for the master and slave in .Fa amaster and .Fa aslave . If .Fa name is non-null, the filename of the slave is returned in .Fa name (a string of at least 16 characters). If .Fa termp is non-null, the terminal parameters of the slave will be set to the values in .Fa termp . If .Fa winp is non-null, the window size of the slave will be set to the values in .Fa winp . .Pp The .Fn openpty function works in the following way: first it attempts to allocate the pseudo-tty through the .Pa /dev/ptm device (see .Xr pty 4 for details) and if that fails it searches for a free pseudo-tty by iterating through all existing pseudo-tty devices in .Pa /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 revoked (see .Xr revoke 2 for details). The first method can work for any user, the second method requires super-user privileges in most cases. .Pp The .Fn login_tty function prepares for a login on the tty .Fa fd (which may be a real tty device, or the slave of a pseudo-tty as returned by .Fn openpty ) by creating a new session, making .Fa fd the controlling terminal for the current process, setting .Fa fd to be the standard input, output, and error streams of the current process, and closing .Fa fd . .Pp The .Fn forkpty function combines .Fn openpty , .Fn fork , and .Fn 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 .Fa amaster , and the filename of the slave in .Fa name if it is non-null. The .Fa termp and .Fa winp parameters, if non-null, will determine the terminal attributes and window size of the slave side of the pseudo-tty. .Sh RETURN VALUES If a call to .Fn openpty , .Fn login_tty , or .Fn forkpty is not successful, \-1 is returned and .Va errno is set to indicate the error. Otherwise, .Fn openpty , .Fn login_tty , and the child process of .Fn forkpty return 0, and the parent process of .Fn forkpty returns the process ID of the child process. .Sh FILES .Bl -tag -width /dev/[pt]ty[pqrstuvwxyzPQRST][0123456789abcdef] -compact .It Pa /dev/[pt]ty[pqrstuvwxyzPQRST][0123456789abcdef] .It Pa /dev/ptm .El .Sh ERRORS .Fn openpty will fail if: .Bl -tag -width Er .It Bq Er ENOENT There are no available ttys. .El .Pp .Fn login_tty will fail if .Fn ioctl fails to set .Fa fd to the controlling terminal of the current process. .Fn forkpty will fail if either .Fn openpty or .Fn fork fails. .Sh SEE ALSO .Xr fork 2 , .Xr revoke 2 , .Xr pty 4