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.\" $FreeBSD$ 27.\" 28.Dd January 13, 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.Fx 56system makes extensive use of loadable kernel modules, and provides loadable 57versions of most file systems, 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/kernel 65directory along with their matching kernel. 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.Pp 90Kernel modules may only be loaded or unloaded if the system security level 91.Va kern.securelevel 92is less than one. 93.Sh "MODULE TYPES" 94.Bl -ohang 95.It Em "Device Driver modules" 96New block and character device 97drivers may be loaded into the system with 98.Nm . 99Device nodes for the loaded drivers are automatically created when a 100module is loaded and destroyed when it is unloaded by 101.Xr devfs 5 . 102You can specify userland programs that will run when new devices 103become available as a result of loading modules, or existing devices 104go away when modules are unloaded, by configuring 105.Xr devd 8 . 106.El 107.Sh FILES 108.Bl -tag -width /usr/include/sys/module.h -compact 109.It Pa /boot/kernel 110directory containing module binaries built for the kernel also 111residing in the directory. 112.It Pa /usr/include/sys/module.h 113file containing definitions required to compile a 114.Nm 115module 116.It Pa /usr/share/examples/kld 117example source code implementing a sample kld module 118.El 119.Sh SEE ALSO 120.Xr kldfind 2 , 121.Xr kldfirstmod 2 , 122.Xr kldload 2 , 123.Xr kldnext 2 , 124.Xr kldstat 2 , 125.Xr kldunload 2 , 126.Xr devfs 5 , 127.Xr devd 8 , 128.Xr kldload 8 , 129.Xr kldstat 8 , 130.Xr kldunload 8 , 131.Xr sysctl 8 132.Sh HISTORY 133The 134.Nm 135facility appeared in 136.Fx 3.0 137and was designed as a replacement for the 138.Nm lkm 139facility, which was similar in functionality to the loadable kernel modules 140facility provided by 141.Tn SunOS 1424.1.3. 143.Sh AUTHORS 144The 145.Nm 146facility was originally implemented by 147.An Doug Rabson Aq Mt dfr@FreeBSD.org . 148.Sh BUGS 149If a module B, is dependent on another module A, but is not compiled with 150module A as a dependency, then 151.Xr kldload 8 152fails to load module B, even if module A is already present in the system. 153.Pp 154If multiple modules are dependent on module A, and are compiled with module 155A as a dependency, then 156.Xr kldload 8 157loads an instance of module A when any of the modules are loaded. 158.Pp 159If a custom entry point is used for a module, and the module is compiled as 160an 161.Sq ELF 162binary, then 163.Xr kldload 8 164fails to execute the entry point. 165.Pp 166.Xr kldload 8 167points the user to read 168.Xr dmesg 8 169for any error encountered while loading a module. 170.Pp 171When system internal interfaces change, old modules often cannot 172detect this, and such modules when loaded will often cause crashes or 173mysterious failures. 174