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 iBCS2 61and 62.Tn Linux 63emulators. 64.Nm 65modules are placed by default in the 66.Pa /boot/kernel 67directory along with their matching kernel. 68.Pp 69The 70.Nm 71interface is used through the 72.Xr kldload 8 , 73.Xr kldunload 8 74and 75.Xr kldstat 8 76programs. 77.Pp 78The 79.Xr kldload 8 80program can load either 81.Xr a.out 5 82or ELF formatted loadable modules. 83The 84.Xr kldunload 8 85program unloads any given loaded module, if no other module is dependent 86upon the given module. 87The 88.Xr kldstat 8 89program is used to check the status of the modules currently loaded into the 90system. 91.Pp 92Kernel modules may only be loaded or unloaded if the system security level 93.Va kern.securelevel 94is less than one. 95.Sh "MODULE TYPES" 96.Bl -ohang 97.It Em "Device Driver modules" 98New block and character device 99drivers may be loaded into the system with 100.Nm . 101Device nodes for the loaded drivers are automatically created when a 102module is loaded and destroyed when it is unloaded by 103.Xr devfs 5 . 104You can specify userland programs that will run when new devices 105become available as a result of loading modules, or existing devices 106go away when modules are unloaded, by configuring 107.Xr devd 8 . 108.El 109.Sh FILES 110.Bl -tag -width /usr/include/sys/module.h -compact 111.It Pa /boot/kernel 112directory containing module binaries built for the kernel also 113residing in the directory. 114.It Pa /usr/include/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 devfs 5 , 129.Xr devd 8 , 130.Xr kldload 8 , 131.Xr kldstat 8 , 132.Xr kldunload 8 , 133.Xr sysctl 8 134.Sh HISTORY 135The 136.Nm 137facility appeared in 138.Fx 3.0 139and was designed as a replacement for the 140.Nm lkm 141facility, which was similar in functionality to the loadable kernel modules 142facility provided by 143.Tn SunOS 1444.1.3. 145.Sh AUTHORS 146The 147.Nm 148facility was originally implemented by 149.An Doug Rabson Aq Mt dfr@FreeBSD.org . 150.Sh BUGS 151If a module B, is dependent on another module A, but is not compiled with 152module A as a dependency, then 153.Xr kldload 8 154fails to load module B, even if module A is already present in the system. 155.Pp 156If multiple modules are dependent on module A, and are compiled with module 157A as a dependency, then 158.Xr kldload 8 159loads an instance of module A when any of the modules are loaded. 160.Pp 161If a custom entry point is used for a module, and the module is compiled as 162an 163.Sq ELF 164binary, then 165.Xr kldload 8 166fails to execute the entry point. 167.Pp 168.Xr kldload 8 169points the user to read 170.Xr dmesg 8 171for any error encountered while loading a module. 172.Pp 173When system internal interfaces change, old modules often cannot 174detect this, and such modules when loaded will often cause crashes or 175mysterious failures. 176