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
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:
Options are specified with a -o flag followed by a
string of options. See the mount(8) man page for
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);
The files /dev/stdin, /dev/stdout and /dev/stderr appear as
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
The /dev/tty entry is an indirect reference to the current
terminal. It appears as a named pipe (FIFO) but
behaves in exactly
the same way as the real controlling terminal device.
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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