diskdev_cmds/mount_fdesc.tproj/mount_fdesc.8

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  37 .\"     @(#)mount_fdesc.8       8.2 (Berkeley) 3/27/94
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  40 .Dd March 27, 1994
  41 .Dt MOUNT_FDESC 8
  42 .Os BSD 4.4
  43 .Sh NAME
  44 .Nm mount_fdesc
  45 .Nd mount the file-descriptor file system
  46 .Sh SYNOPSIS
  47 .Nm mount_fdesc
  48 .Op Fl o Ar options
  49 .Ar fdesc
  50 .Ar mount_point
  51 .Sh DESCRIPTION
  52 The
  53 .Nm mount_fdesc
  54 command attaches an instance of the per-process file descriptor
  55 namespace to the global filesystem namespace.
  56 The conventional mount point is
  57 .Pa /dev
  58 and the filesystem should be union mounted in order to augment,
  59 rather than replace, the existing entries in
  60 .Pa /dev .
  61 This command is normally executed by
  62 .Xr mount 8
  63 at boot time.
  64 .Pp
  65 The options are as follows:
  66 .Bl -tag -width indent
  67 .It Fl o
  68 Options are specified with a
  69 .Fl o
  70 flag followed by a comma separated string of options.
  71 See the
  72 .Xr mount 8
  73 man page for possible options and their meanings.
  74 .El
  75 .Pp
  76 The contents of the mount point are
  77 .Pa fd ,
  78 .Pa stderr ,
  79 .Pa stdin ,
  80 .Pa stdout
  81 and
  82 .Pa tty .
  83 .Pp
  84 .Pa fd
  85 is a directory whose contents
  86 appear as a list of numbered files
  87 which correspond to the open files of the process reading the
  88 directory.
  89 The files
  90 .Pa /dev/fd/0
  91 through
  92 .Pa /dev/fd/#
  93 refer to file descriptors which can be accessed through the file
  94 system.
  95 If the file descriptor is open and the mode the file is being opened
  96 with is a subset of the mode of the existing descriptor, the call:
  97 .Bd -literal -offset indent
  98 fd = open("/dev/fd/0", mode);
  99 .Ed
 100 .Pp
 101 and the call:
 102 .Bd -literal -offset indent
 103 fd = fcntl(0, F_DUPFD, 0);
 104 .Ed
 105 .Pp
 106 are equivalent.
 107 .Pp
 108 The files
 109 .Pa /dev/stdin ,
 110 .Pa /dev/stdout
 111 and
 112 .Pa /dev/stderr
 113 appear as symlinks to the relevant entry in the
 114 .Pa /dev/fd
 115 sub-directory.
 116 Opening them is equivalent to the following calls:
 117 .Bd -literal -offset indent
 118 fd = fcntl(STDIN_FILENO,  F_DUPFD, 0);
 119 fd = fcntl(STDOUT_FILENO, F_DUPFD, 0);
 120 fd = fcntl(STDERR_FILENO, F_DUPFD, 0);
 121 .Ed
 122 .Pp
 123 Flags to the
 124 .Xr open 2
 125 call other than
 126 .Dv O_RDONLY ,
 127 .Dv O_WRONLY
 128 and
 129 .Dv O_RDWR
 130 are ignored.
 131 .Pp
 132 The
 133 .Pa /dev/tty
 134 entry is an indirect reference to the current process's controlling terminal.
 135 It appears as a named pipe (FIFO) but behaves in exactly the same way as
 136 the real controlling terminal device.
 137 .Sh FILES
 138 .Bl -tag -width /dev/stderr -compact
 139 .It Pa /dev/fd/#
 140 .It Pa /dev/stdin
 141 .It Pa /dev/stdout
 142 .It Pa /dev/stderr
 143 .It Pa /dev/tty
 144 .El
 145 .Sh SEE ALSO
 146 .Xr mount 2 ,
 147 .Xr unmount 2 ,
 148 .Xr tty 4 ,
 149 .Xr fstab 5 ,
 150 .Xr mount 8
 151 .Sh CAVEATS
 152 No
 153 .Pa .
 154 and
 155 .Pa ..
 156 entries appear when listing the contents of the
 157 .Pa /dev/fd
 158 directory.
 159 This makes sense in the context of this filesystem, but is inconsistent
 160 with usual filesystem conventions.
 161 However, it is still possible to refer to both
 162 .Pa .
 163 and
 164 .Pa ..
 165 in a pathname.
 166 .Pp
 167 This filesystem may not be NFS-exported.
 168 .Sh HISTORY
 169 The
 170 .Nm mount_fdesc
 171 utility first appeared in 4.4BSD.