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/share/man/man5/fdescfs.5

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  1.\" Copyright (c) 1996
  2.\"	Mike Pritchard <mpp@FreeBSD.org>.  All rights reserved.
  3.\"
  4.\" Copyright (c) 1992, 1993, 1994
  5.\"	The Regents of the University of California.  All rights reserved.
  6.\" All rights reserved.
  7.\"
  8.\" This code is derived from software donated to Berkeley by
  9.\" Jan-Simon Pendry.
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 39.\" $FreeBSD$
 40.\"
 41.Dd September 18, 2010
 42.Dt FDESCFS 5
 43.Os
 44.Sh NAME
 45.Nm fdescfs
 46.Nd file-descriptor file system
 47.Sh SYNOPSIS
 48.Bd -literal
 49fdescfs	/dev/fd	fdescfs rw 0 0
 50.Ed
 51.Sh DESCRIPTION
 52The file-descriptor file system, or
 53.Nm ,
 54provides access to the per-process file descriptor
 55namespace in the global file system namespace.
 56The conventional mount point is
 57.Pa /dev/fd .
 58.Pp
 59The file system's contents
 60appear as a list of numbered files
 61which correspond to the open files of the process reading the
 62directory.
 63The files
 64.Pa /dev/fd/0
 65through
 66.Pa /dev/fd/#
 67refer to file descriptors which can be accessed through the file
 68system.
 69If the file descriptor is open and the mode the file is being opened
 70with is a subset of the mode of the existing descriptor, the call:
 71.Bd -literal -offset indent
 72fd = open("/dev/fd/0", mode);
 73.Ed
 74.Pp
 75and the call:
 76.Bd -literal -offset indent
 77fd = fcntl(0, F_DUPFD, 0);
 78.Ed
 79.Pp
 80are equivalent.
 81.Pp
 82Flags to the
 83.Xr open 2
 84call other than
 85.Dv O_RDONLY ,
 86.Dv O_WRONLY
 87and
 88.Dv O_RDWR
 89are ignored.
 90.Pp
 91.Em "Note:"
 92.Pa /dev/fd/0 ,
 93.Pa /dev/fd/1
 94and
 95.Pa /dev/fd/2
 96files are created by default when devfs alone is mounted.
 97.Nm
 98creates entries for all file descriptors opened by the process.
 99.Sh FILES
100.Bl -tag -width /dev/stderr -compact
101.It Pa /dev/fd/#
102.El
103.Sh EXAMPLES
104To mount a
105.Nm
106volume located on
107.Pa /dev/fd :
108.Pp
109.Dl "mount -t fdescfs null /dev/fd"
110.Sh SEE ALSO
111.Xr devfs 5 ,
112.Xr mount 8
113.Sh HISTORY
114The
115.Nm
116file system first appeared in
117.Bx 4.4 .
118The
119.Nm
120manual page first appeared in
121.Fx 2.2 .
122.Sh AUTHORS
123.An -nosplit
124The
125.Nm
126manual page was written by
127.An Mike Pritchard Aq mpp@FreeBSD.org ,
128and was based on the
129manual page written by
130.An Jan-Simon Pendry .