1.\" $NetBSD: mount_fdesc.8,v 1.12 2001/11/16 11:26:55 wiz Exp $ 2.\" 3.\" Copyright (c) 1992, 1993, 1994 4.\" The Regents of the University of California. All rights reserved. 5.\" 6.\" This code is derived from software donated to Berkeley by 7.\" Jan-Simon Pendry. 8.\" 9.\" Redistribution and use in source and binary forms, with or without 10.\" modification, are permitted provided that the following conditions 11.\" are met: 12.\" 1. Redistributions of source code must retain the above copyright 13.\" notice, this list of conditions and the following disclaimer. 14.\" 2. Redistributions in binary form must reproduce the above copyright 15.\" notice, this list of conditions and the following disclaimer in the 16.\" documentation and/or other materials provided with the distribution. 17.\" 3. All advertising materials mentioning features or use of this software 18.\" must display the following acknowledgement: 19.\" This product includes software developed by the University of 20.\" California, Berkeley and its contributors. 21.\" 4. Neither the name of the University nor the names of its contributors 22.\" may be used to endorse or promote products derived from this software 23.\" without specific prior written permission. 24.\" 25.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 26.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 27.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 28.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 29.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 30.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 31.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 32.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 33.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 34.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 35.\" SUCH DAMAGE. 36.\" 37.\" @(#)mount_fdesc.8 8.2 (Berkeley) 3/27/94 38.\" 39.Dd March 27, 1994 40.Dt MOUNT_FDESC 8 41.Os 42.Sh NAME 43.Nm mount_fdesc 44.Nd mount the file-descriptor file system 45.Sh SYNOPSIS 46.Nm "" 47.Op Fl o Ar options 48.Ar fdesc 49.Ar mount_point 50.Sh DESCRIPTION 51The 52.Nm 53command attaches an instance of the per-process file descriptor 54namespace to the global filesystem namespace. 55The conventional mount point is 56.Pa /dev 57and the filesystem should be union mounted in order to augment, 58rather than replace, the existing entries in 59.Pa /dev . 60This command is normally executed by 61.Xr mount 8 62at boot time. 63.Pp 64The options are as follows: 65.Bl -tag -width indent 66.It Fl o 67Options are specified with a 68.Fl o 69flag followed by a comma separated string of options. 70See the 71.Xr mount 8 72man page for possible options and their meanings. 73.El 74.Pp 75The contents of the mount point are 76.Pa fd , 77.Pa stderr , 78.Pa stdin , 79.Pa stdout 80and 81.Pa tty . 82.Pp 83.Pa fd 84is a directory whose contents 85appear as a list of numbered files 86which correspond to the open files of the process reading the 87directory. 88The files 89.Pa /dev/fd/0 90through 91.Pa /dev/fd/# 92refer to file descriptors which can be accessed through the file 93system. 94If the file descriptor is open and the mode the file is being opened 95with is a subset of the mode of the existing descriptor, the call: 96.Bd -literal -offset indent 97fd = open("/dev/fd/0", mode); 98.Ed 99.Pp 100and the call: 101.Bd -literal -offset indent 102fd = fcntl(0, F_DUPFD, 0); 103.Ed 104.Pp 105are equivalent. 106.Pp 107The files 108.Pa /dev/stdin , 109.Pa /dev/stdout 110and 111.Pa /dev/stderr 112appear as symlinks to the relevant entry in the 113.Pa /dev/fd 114sub-directory. 115Opening them is equivalent to the following calls: 116.Bd -literal -offset indent 117fd = fcntl(STDIN_FILENO, F_DUPFD, 0); 118fd = fcntl(STDOUT_FILENO, F_DUPFD, 0); 119fd = fcntl(STDERR_FILENO, F_DUPFD, 0); 120.Ed 121.Pp 122Flags to the 123.Xr open 2 124call other than 125.Dv O_RDONLY , 126.Dv O_WRONLY 127and 128.Dv O_RDWR 129are ignored. 130.Pp 131The 132.Pa /dev/tty 133entry is an indirect reference to the current process's controlling terminal. 134It appears as a named pipe (FIFO) but behaves in exactly the same way as 135the real controlling terminal device. 136.Sh FILES 137.Bl -tag -width /dev/stderr -compact 138.It Pa /dev/fd/# 139.It Pa /dev/stdin 140.It Pa /dev/stdout 141.It Pa /dev/stderr 142.It Pa /dev/tty 143.El 144.Sh SEE ALSO 145.Xr mount 2 , 146.Xr unmount 2 , 147.Xr tty 4 , 148.Xr fstab 5 , 149.Xr mount 8 150.Sh HISTORY 151The 152.Nm 153utility first appeared in 154.Bx 4.4 . 155.Sh BUGS 156This filesystem may not be NFS-exported. 157