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 December 12, 2014 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, and all the screen-savers. 60.Nm 61modules are placed by default in the 62.Pa /boot/kernel 63directory. 64.Pp 65The 66.Nm 67interface is used through the 68.Xr kldload 8 , 69.Xr kldunload 8 70and 71.Xr kldstat 8 72programs. 73.Pp 74The 75.Xr kldload 8 76program can load either 77.Xr a.out 5 78or ELF formatted loadable modules. 79The 80.Xr kldunload 8 81program unloads any given loaded module, if no other module is dependent 82upon the given module. 83The 84.Xr kldstat 8 85program is used to check the status of the modules currently loaded into the 86system. 87.Sh FILES 88.Bl -tag -width ".In sys/module.h" -compact 89.It Pa /boot/kernel 90directory containing module binaries shipped with the system 91.It In sys/module.h 92file containing definitions required to compile a 93.Nm 94module 95.It Pa /usr/share/examples/kld 96example source code implementing a sample kld module 97.El 98.Sh SEE ALSO 99.Xr kldfind 2 , 100.Xr kldfirstmod 2 , 101.Xr kldload 2 , 102.Xr kldnext 2 , 103.Xr kldstat 2 , 104.Xr kldunload 2 , 105.Xr kldload 8 , 106.Xr kldstat 8 , 107.Xr kldunload 8 108.Sh HISTORY 109The 110.Nm 111facility appeared in 112.Fx 3.0 113and was designed as a replacement for the 114.Xr lkm 4 115facility, which was similar in functionality to the loadable kernel modules 116facility provided by 117.Tn SunOS 1184.1.3. 119.Sh AUTHORS 120The 121.Nm 122facility was originally implemented by 123.An Doug Rabson Aq Mt dfr@FreeBSD.org . 124.Sh BUGS 125If a module B, is dependent on another module A, but is not compiled with 126module A as a dependency, then 127.Xr kldload 8 128fails to load module B, even if module A is already present in the system. 129.Pp 130If multiple modules are dependent on module A, and are compiled with module 131A as a dependency, then 132.Xr kldload 8 133loads an instance of module A when any of the modules are loaded. 134.Pp 135If a custom entry point is used for a module, and the module is compiled as 136an 137.Sq ELF 138binary, then 139.Xr kldload 8 140fails to execute the entry point. 141.Pp 142.Xr kldload 8 143returns the cryptic message 144.Sq Li "Exec format error" 145for any error encountered while loading a module. 146.Pp 147When system internal interfaces change, old modules often cannot 148detect this, and such modules when loaded will often cause crashes or 149mysterious failures. 150