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. The directory specified by
mount_point is converted to an absolute path before use.
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),
fd(4),
tty(4),
fstab(5),
mount(8)
HISTORY
The
mount_fdesc utility first appeared in
4.4BSD.
BUGS
This filesystem may not be NFS-exported.