172 lines
4.6 KiB
Groff
172 lines
4.6 KiB
Groff
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.\"
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.\" Copyright (c) 1992, 1993, 1994
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.\" The Regents of the University of California. All rights reserved.
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.\" All rights reserved.
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.\"
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.\" This code is derived from software donated to Berkeley by
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.\" Jan-Simon Pendry.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)mount_fdesc.8 8.2 (Berkeley) 3/27/94
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.\"
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.\"
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.Dd March 27, 1994
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.Dt MOUNT_FDESC 8
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.Os BSD 4.4
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.Sh NAME
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.Nm mount_fdesc
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.Nd mount the file-descriptor file system
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.Sh SYNOPSIS
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.Nm mount_fdesc
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.Op Fl o Ar options
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.Ar fdesc
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.Ar mount_point
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.Sh DESCRIPTION
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The
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.Nm mount_fdesc
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command attaches an instance of the per-process file descriptor
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namespace to the global filesystem namespace.
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The conventional mount point is
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.Pa /dev
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and the filesystem should be union mounted in order to augment,
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rather than replace, the existing entries in
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.Pa /dev .
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This command is normally executed by
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.Xr mount 8
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at boot time.
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.Pp
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The options are as follows:
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.Bl -tag -width indent
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.It Fl o
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Options are specified with a
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.Fl o
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flag followed by a comma separated string of options.
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See the
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.Xr mount 8
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man page for possible options and their meanings.
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.El
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.Pp
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The contents of the mount point are
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.Pa fd ,
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.Pa stderr ,
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.Pa stdin ,
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.Pa stdout
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and
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.Pa tty .
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.Pp
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.Pa fd
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is a directory whose contents
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appear as a list of numbered files
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which correspond to the open files of the process reading the
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directory.
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The files
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.Pa /dev/fd/0
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through
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.Pa /dev/fd/#
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refer to file descriptors which can be accessed through the file
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system.
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If the file descriptor is open and the mode the file is being opened
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with is a subset of the mode of the existing descriptor, the call:
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.Bd -literal -offset indent
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fd = open("/dev/fd/0", mode);
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.Ed
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.Pp
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and the call:
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.Bd -literal -offset indent
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fd = fcntl(0, F_DUPFD, 0);
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.Ed
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.Pp
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are equivalent.
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.Pp
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The files
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.Pa /dev/stdin ,
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.Pa /dev/stdout
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and
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.Pa /dev/stderr
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appear as symlinks to the relevant entry in the
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.Pa /dev/fd
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sub-directory.
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Opening them is equivalent to the following calls:
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.Bd -literal -offset indent
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fd = fcntl(STDIN_FILENO, F_DUPFD, 0);
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fd = fcntl(STDOUT_FILENO, F_DUPFD, 0);
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fd = fcntl(STDERR_FILENO, F_DUPFD, 0);
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.Ed
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.Pp
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Flags to the
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.Xr open 2
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call other than
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.Dv O_RDONLY ,
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.Dv O_WRONLY
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and
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.Dv O_RDWR
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are ignored.
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.Pp
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The
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.Pa /dev/tty
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entry is an indirect reference to the current process's controlling terminal.
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It appears as a named pipe (FIFO) but behaves in exactly the same way as
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the real controlling terminal device.
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.Sh FILES
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.Bl -tag -width /dev/stderr -compact
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.It Pa /dev/fd/#
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.It Pa /dev/stdin
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.It Pa /dev/stdout
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.It Pa /dev/stderr
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.It Pa /dev/tty
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.El
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.Sh SEE ALSO
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.Xr mount 2 ,
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.Xr unmount 2 ,
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.Xr tty 4 ,
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.Xr fstab 5 ,
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.Xr mount 8
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.Sh CAVEATS
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No
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.Pa .
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and
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.Pa ..
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entries appear when listing the contents of the
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.Pa /dev/fd
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directory.
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This makes sense in the context of this filesystem, but is inconsistent
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with usual filesystem conventions.
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However, it is still possible to refer to both
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.Pa .
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and
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.Pa ..
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in a pathname.
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.Pp
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This filesystem may not be NFS-exported.
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.Sh HISTORY
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The
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.Nm mount_fdesc
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utility first appeared in 4.4BSD.
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