Updated: 2021/Apr/14

MOUNT_FDESC(8)              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
     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

     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.


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

     The mount_fdesc utility first appeared in 4.4BSD.

     This filesystem may not be NFS-exported.

NetBSD 9.99                    December 29, 2013                   NetBSD 9.99