1.\" $OpenBSD: fd.4,v 1.7 2007/05/31 19:19:50 jmc Exp $ 2.\" $NetBSD: fd.4,v 1.3 1994/11/30 16:22:13 jtc Exp $ 3.\" 4.\" Copyright (c) 1990, 1991, 1993 5.\" The Regents of the University of California. All rights reserved. 6.\" 7.\" Redistribution and use in source and binary forms, with or without 8.\" modification, are permitted provided that the following conditions 9.\" are met: 10.\" 1. Redistributions of source code must retain the above copyright 11.\" notice, this list of conditions and the following disclaimer. 12.\" 2. Redistributions in binary form must reproduce the above copyright 13.\" notice, this list of conditions and the following disclaimer in the 14.\" documentation and/or other materials provided with the distribution. 15.\" 3. Neither the name of the University nor the names of its contributors 16.\" may be used to endorse or promote products derived from this software 17.\" without specific prior written permission. 18.\" 19.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 20.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 21.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 22.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 23.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 24.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 25.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 26.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 27.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 28.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 29.\" SUCH DAMAGE. 30.\" 31.\" @(#)fd.4 8.1 (Berkeley) 6/9/93 32.\" 33.Dd $Mdocdate: May 31 2007 $ 34.Dt FD 4 35.Os 36.Sh NAME 37.Nm fd , 38.Nm stdin , 39.Nm stdout , 40.Nm stderr 41.Nd file descriptor files 42.Sh DESCRIPTION 43The files 44.Pa /dev/fd/0 45through 46.Pa /dev/fd/# 47refer to file descriptors which can be accessed through the file system. 48If the file descriptor is open and the mode the file is being opened 49with is a subset of the mode of the existing descriptor, the call: 50.Bd -literal -offset indent 51fd = open("/dev/fd/0", mode); 52.Ed 53.Pp 54and the call: 55.Bd -literal -offset indent 56fd = fcntl(0, F_DUPFD, 0); 57.Ed 58.Pp 59are equivalent. 60.Pp 61Opening the files 62.Pa /dev/stdin , 63.Pa /dev/stdout , 64and 65.Pa /dev/stderr 66is equivalent to the following calls: 67.Bd -literal -offset indent 68fd = fcntl(STDIN_FILENO, F_DUPFD, 0); 69fd = fcntl(STDOUT_FILENO, F_DUPFD, 0); 70fd = fcntl(STDERR_FILENO, F_DUPFD, 0); 71.Ed 72.Pp 73Flags to the 74.Xr open 2 75call other than 76.Dv O_RDONLY , 77.Dv O_WRONLY , 78and 79.Dv O_RDWR 80are ignored. 81.Pp 82These devices may not be opened by processes which are tainted 83as a result of setuid or setgid behaviours, as documented in 84.Xr issetugid 2 . 85In those cases, an error return will occur with 86.Va errno 87set to 88.Dv EPERM . 89.Sh FILES 90.Bl -tag -width /dev/stderr -compact 91.It Pa /dev/fd/# 92.It Pa /dev/stdin 93.It Pa /dev/stdout 94.It Pa /dev/stderr 95.El 96.Sh SEE ALSO 97.Xr tty 4 98