1.\" Copyright (c) 1993 Christopher G. Demetriou 2.\" All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. The name of the author may not be used to endorse or promote products 13.\" derived from this software without specific prior written permission 14.\" 15.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 16.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 17.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 18.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 19.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 20.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 21.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 22.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 23.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 24.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 25.\" 26.\" $FreeBSD: src/share/man/man4/kld.4,v 1.5.2.6 2001/08/17 13:08:38 ru Exp $ 27.\" 28.Dd August 6, 2009 29.Dt KLD 4 30.Os 31.Sh NAME 32.Nm kld 33.Nd dynamic kernel linker facility 34.Sh DESCRIPTION 35The LKM (Loadable Kernel Modules) facility has been deprecated in 36.Fx 3.0 37and above in favor of the 38.Nm 39interface. 40This interface, like its 41predecessor, allows the system administrator to dynamically add and remove 42functionality from a running system. 43This ability also helps software 44developers to develop new parts of the kernel without constantly rebooting 45to test their changes. 46.Pp 47Various types of modules can be loaded into the system. 48There are several defined module types, listed below, which can 49be added to the system in a predefined way. 50In addition, there 51is a generic type, for which the module itself handles loading and 52unloading. 53.Pp 54The 55.Dx 56system makes extensive use of loadable kernel modules, and provides loadable 57versions of most filesystems, the 58.Tn NFS 59client and server, all the screen-savers, and the 60.Tn Linux 61emulator. 62.Nm 63modules are placed by default in the 64.Pa /boot/modules 65directory. 66.Pp 67The 68.Nm 69interface is used through the 70.Xr kldload 8 , 71.Xr kldunload 8 72and 73.Xr kldstat 8 74programs. 75.Pp 76The 77.Xr kldload 8 78program can load either 79.Xr a.out 5 80or ELF formatted loadable modules. 81The 82.Xr kldunload 8 83program unloads any given loaded module, if no other module is dependent 84upon the given module. 85The 86.Xr kldstat 8 87program is used to check the status of the modules currently loaded into the 88system. 89.Sh FILES 90.Bl -tag -width ".In sys/module.h" -compact 91.It Pa /boot/modules 92directory containing module binaries shipped with the system 93.It In sys/module.h 94file containing definitions required to compile a 95.Nm 96module 97.It Pa /usr/share/examples/kld 98example source code implementing a sample kld module 99.El 100.Sh SEE ALSO 101.Xr kldfind 2 , 102.Xr kldfirstmod 2 , 103.Xr kldload 2 , 104.Xr kldnext 2 , 105.Xr kldstat 2 , 106.Xr kldunload 2 , 107.Xr kldload 8 , 108.Xr kldstat 8 , 109.Xr kldunload 8 110.Sh HISTORY 111The 112.Nm 113facility appeared in 114.Fx 3.0 115and was designed as a replacement for the 116.Xr lkm 4 117facility, which was similar in functionality to the loadable kernel modules 118facility provided by 119.Tn SunOS 1204.1.3. 121.Sh AUTHORS 122The 123.Nm 124facility was originally implemented by 125.An Doug Rabson Aq Mt dfr@FreeBSD.org . 126.Sh BUGS 127If a module B, is dependent on another module A, but is not compiled with 128module A as a dependency, then 129.Xr kldload 8 130fails to load module B, even if module A is already present in the system. 131.Pp 132If multiple modules are dependent on module A, and are compiled with module 133A as a dependency, then 134.Xr kldload 8 135loads an instance of module A when any of the modules are loaded. 136.Pp 137If a custom entry point is used for a module, and the module is compiled as 138an 139.Sq ELF 140binary, then 141.Xr kldload 8 142fails to execute the entry point. 143.Pp 144.Xr kldload 8 145returns the cryptic message 146.Sq Li "Exec format error" 147for any error encountered while loading a module. 148.Pp 149When system internal interfaces change, old modules often cannot 150detect this, and such modules when loaded will often cause crashes or 151mysterious failures. 152