MOUNT_FDESC man page on 4.4BSD

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MOUNT_FDESC(8)		  BSD System Manager's Manual		MOUNT_FDESC(8)

     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 conven‐
     tional 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 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 sepa‐
	     rated 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 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 equiva‐
     lent 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

     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
     exactly the same way as the real controlling terminal device.


     mount(2), unmount(2), tty(4), fstab(5), mount(8)

     No ~.  and .. entries appear when listing the contents of the /dev/fd
     directory.	 This makes sense in the context of this filesystem, but is
     inconsistent with usual filesystem conventions.  However, it is still
     possible to refer to both ~.  and .. in a pathname.

     This filesystem may not be NFS-exported.

     The mount_fdesc utility first appeared in 4.4BSD.

4.4BSD				March 27, 1994				4.4BSD

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