mount_fdesc - mount the file-descriptor file system
mount_fdesc [-o options] fdesc mount_point
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 invoked by mount(8) when using the syntax
mount [options] -t fdesc fdesc mount_point
This command is normally executed by mount(8) at boot time.
The options are as follows:
-o options
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.
/dev/fd/#
/dev/stdin
/dev/stdout
/dev/stderr
/dev/tty
mount(2), tty(4), fstab(5), mount(8), umount(8)
The mount_fdesc utility first appeared in 4.4BSD.
This filesystem may not be NFS-exported.
OpenBSD 3.6 March 27, 1994
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