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.\" $DragonFly: src/share/man/man4/kld.4,v 1.8 2008/09/02 11:50:46 matthias Exp $ 28.\" 29.Dd September 2, 2008 30.Dt KLD 4 31.Os 32.Sh NAME 33.Nm kld 34.Nd dynamic kernel linker facility 35.Sh DESCRIPTION 36The LKM (Loadable Kernel Modules) facility has been deprecated in 37.Fx 3.0 38and above in favor of the 39.Nm 40interface. 41This interface, like its 42predecessor, allows the system administrator to dynamically add and remove 43functionality from a running system. This 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. In addition, there 50is a generic type, for which the module itself handles loading and 51unloading. 52.Pp 53The 54.Dx 55system makes extensive use of loadable kernel modules, and provides loadable 56versions of most filesystems, the 57.Tn NFS 58client and server, all the screen-savers, and the 59.Tn Linux 60emulator. 61.Nm 62modules are placed by default in the 63.Pa /boot/modules 64directory. 65.Pp 66The 67.Nm 68interface is used through the 69.Xr kldload 8 , 70.Xr kldunload 8 71and 72.Xr kldstat 8 73programs. 74.Pp 75The 76.Xr kldload 8 77program can load either 78.Xr a.out 5 79or ELF formatted loadable modules. 80The 81.Xr kldunload 8 82program unloads any given loaded module, if no other module is dependent 83upon the given module. 84The 85.Xr kldstat 8 86program is used to check the status of the modules currently loaded into the 87system. 88.Sh "MODULE TYPES" 89.Bl -ohang 90.It Em "Device Driver modules" 91New block and character device 92drivers may be loaded into the system with 93.Nm . 94The major problem with loading 95a device driver is that the driver's 96device nodes must exist for the 97devices to be accessed. They are usually 98created by using 99.Xr MAKEDEV 8 100or 101.Xr mknod 8 102(if the device is not supported by the 103.Xr MAKEDEV 8 104script) or, by writing a 105shell script to run 106.Xr kldload 8 107which should run the appropriate program to create the devices when the 108driver has been successfully loaded. 109.El 110.Sh FILES 111.Bl -tag -width ".In sys/module.h" -compact 112.It Pa /boot/modules 113directory containing module binaries shipped with the system 114.It In sys/module.h 115file containing definitions required to compile a 116.Nm 117module 118.It Pa /usr/share/examples/kld 119example source code implementing a sample kld module 120.El 121.Sh SEE ALSO 122.Xr kldfind 2 , 123.Xr kldfirstmod 2 , 124.Xr kldload 2 , 125.Xr kldnext 2 , 126.Xr kldstat 2 , 127.Xr kldunload 2 , 128.Xr kldload 8 , 129.Xr kldstat 8 , 130.Xr kldunload 8 131.Sh HISTORY 132The 133.Nm 134facility appeared in 135.Fx 3.0 136and was designed as a replacement for the 137.Xr lkm 4 138facility, which was similar in functionality to the loadable kernel modules 139facility provided by 140.Tn SunOS 1414.1.3. 142.Sh AUTHORS 143The 144.Nm 145facility was originally implemented by 146.An Doug Rabson Aq dfr@FreeBSD.org . 147.Sh BUGS 148If a module B, is dependent on another module A, but is not compiled with 149module A as a dependency, then 150.Xr kldload 8 151fails to load module B, even if module A is already present in the system. 152.Pp 153If multiple modules are dependent on module A, and are compiled with module 154A as a dependency, then 155.Xr kldload 8 156loads an instance of module A when any of the modules are loaded. 157.Pp 158If a custom entry point is used for a module, and the module is compiled as 159an 160.Sq ELF 161binary, then 162.Xr kldload 8 163fails to execute the entry point. 164.Pp 165.Xr kldload 8 166returns the cryptic message 167.Sq Li "Exec format error" 168for any error encountered while loading a module. 169.Pp 170When system internal interfaces change, old modules often cannot 171detect this, and such modules when loaded will often cause crashes or 172mysterious failures. 173