MOUNT_FDESC(8) BSD System Manager's Manual MOUNT_FDESC(8)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 com-
mand 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 separat-
ed string of options. See the mount(8) man page for possible op-
tions 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 exist-
ing 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 con-
trolling terminal. It appears as a named pipe (FIFO) but behaves in ex-
actly the same way as the real controlling terminal device.
FILES
/dev/fd/#
/dev/stdin
/dev/stdout
/dev/stderr
/dev/tty
SEE ALSOmount(2), tty(4), fstab(5), mount(8), umount(8)HISTORY
The mount_fdesc utility first appeared in 4.4BSD.
CAVEATS
This filesystem may not be NFS-exported.
MirOS BSD #10-current March 27, 1994 1