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NetBSD 6.1.5 - man page for mount_fdesc (netbsd section 8)

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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.  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 control-
     ling 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)

HISTORY
     The mount_fdesc utility first appeared in 4.4BSD.

BUGS
     This filesystem may not be NFS-exported.

BSD					  March 27, 1994				      BSD
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