MOUNT_FDESC
Section: Maintenance Commands (8)
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BSD mandoc
BSD 4.4
NAME
mount_fdesc
- mount the file-descriptor file system
SYNOPSIS
mount_fdesc
[-o options
]
fdesc
mount_point
DESCRIPTION
The
mount_fdesc
command attaches an instance of the per-process file descriptor
namespace to the global filesystem namespace.
The conventional mount point is
/dev
and the filesystem should be union mounted in order to augment,
rather than replace, the existing entries in
/dev
This command is normally executed by
mount(8)
at boot time.
The options are as follows:
- -o
-
Options are specified with a
-o
flag followed by a comma separated string of options.
See the
mount(8)
man page for possible options and their meanings.
The contents of the mount point are
fd
stderr
stdin
stdout
and
tty
fd
is a directory whose contents
appear as a list of numbered files
which correspond to the open files of the process reading the
directory.
The files
/dev/fd/0
through
/dev/fd/#
refer to file descriptors which can be accessed through the file
system.
If the file descriptor is open and the mode the file is being opened
with is a subset of the mode of the existing descriptor, the call:
fd = open("/dev/fd/0", mode);
and the call:
fd = fcntl(0, F_DUPFD, 0);
are equivalent.
The files
/dev/stdin
/dev/stdout
and
/dev/stderr
appear as symlinks to the relevant entry in the
/dev/fd
sub-directory.
Opening them is equivalent to the following calls:
fd = fcntl(STDIN_FILENO, F_DUPFD, 0);
fd = fcntl(STDOUT_FILENO, F_DUPFD, 0);
fd = fcntl(STDERR_FILENO, F_DUPFD, 0);
Flags to the
open(2)
call other than
O_RDONLY ,
O_WRONLY
and
O_RDWR
are ignored.
The
/dev/tty
entry is an indirect reference to the current process's controlling terminal.
It appears as a named pipe (FIFO) but behaves in exactly the same way as
the real controlling terminal device.
FILES
- /dev/fd/#
-
- /dev/stdin
-
- /dev/stdout
-
- /dev/stderr
-
- /dev/tty
-
SEE ALSO
mount(2),
unmount(2),
tty(4),
fstab(5),
mount(8)
CAVEATS
No
.
and
..
entries appear when listing the contents of the
/dev/fd
directory.
This makes sense in the context of this filesystem, but is inconsistent
with usual filesystem conventions.
However, it is still possible to refer to both
.
and
..
in a pathname.
This filesystem may not be NFS-exported.
HISTORY
The
mount_fdesc
utility first appeared in 4.4BSD.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- FILES
-
- SEE ALSO
-
- CAVEATS
-
- HISTORY
-
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Time: 04:30:06 GMT, April 24, 2025