1.\" 2.\" Copyright (c) 1992 The Regents of the University of California 3.\" Copyright (c) 1990, 1992 Jan-Simon Pendry 4.\" All rights reserved. 5.\" 6.\" This code is derived from software donated to Berkeley by 7.\" Jan-Simon Pendry and the null layer from John Heidemann of 8.\" the UCLA Ficus proejct. 9.\" 10.\" 11.\" %sccs.include.redist.roff% 12.\" 13.\" @(#)mount_null.8 5.1 (Berkeley) 07/09/92 14.\" 15.\" 16.Dd 17.Dt MOUNT_NULL 8 18.Os BSD 4.4 19.Sh NAME 20.Nm mount_null 21.Nd mount a null layer, making a virtual copy of an existing filesystem sub-tree 22.Sh SYNOPSIS 23.Nm mount_null 24.Op Fl F Ar fsoptions 25.Ar target mount-point 26.Sh DESCRIPTION 27The 28.Nm mount_null 29command makes a sub-tree of an existing filesystem visible 30in another part of the global filesystem namespace. 31This allows existing files and directories to be accessed 32using a different pathname. 33.Pp 34Virtual file system sub-trees created by the null layer should 35be identical to those created by the loopback 36The virtual copy of a file system sub-tree created by the null 37layer should be nearly identical to one created by 38.Xr mount_lofs 8 . 39The purpose of the null layer is to serve as a basis for future 40layer development. 41.Pp 42An example of a layer constructed from the null layer is 43the umap layer (see 44.Xr mount_umap 8 ). 45.Sh HISTORY 46The 47loopback filesystem 48is 49.Ud 50