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 November 8, 1998 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. This ability also helps software 43developers to develop new parts of the kernel without constantly rebooting 44to test their changes. 45.Pp 46Various types of modules can be loaded into the system. 47There are several defined module types, listed below, which can 48be added to the system in a predefined way. In addition, there 49is a generic type, for which the module itself handles loading and 50unloading. 51.Pp 52The 53.Fx 54system makes extensive use of loadable kernel modules, and provides loadable 55versions of most file systems, the 56.Tn NFS 57client and server, all the screen-savers, and the 58.Tn iBCS2 59and 60.Tn Linux 61emulators. 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.Sh "MODULE TYPES" 90.Bl -ohang 91.It Em "Device Driver modules" 92New block and character device 93drivers may be loaded into the system with 94.Nm . 95Device nodes for the loaded drivers are automatically created when a 96module is loaded and destroyed when it is unloaded by 97.Xr devfs 5 . 98You can specify userland programs that will run when new devices 99become available as a result of loading modules, or existing devices 100go away when modules are unloaded, by configuring 101.Xr devd 8 . 102.El 103.Sh FILES 104.Bl -tag -width /usr/include/sys/module.h -compact 105.It Pa /boot/kernel 106directory containing module binaries built for the kernel also 107residing in the directory. 108.It Pa /usr/include/sys/module.h 109file containing definitions required to compile a 110.Nm 111module 112.It Pa /usr/share/examples/kld 113example source code implementing a sample kld module 114.El 115.Sh SEE ALSO 116.Xr kldfind 2 , 117.Xr kldfirstmod 2 , 118.Xr kldload 2 , 119.Xr kldnext 2 , 120.Xr kldstat 2 , 121.Xr kldunload 2 , 122.Xr devfs 5 , 123.Xr devd 8 , 124.Xr kldload 8 , 125.Xr kldstat 8 , 126.Xr kldunload 8 127.Sh BUGS 128If a module B, is dependent on another module A, but is not compiled with 129module A as a dependency, then 130.Xr kldload 8 131fails to load module B, even if module A is already present in the system. 132.Pp 133If multiple modules are dependent on module A, and are compiled with module 134A as a dependency, then 135.Xr kldload 8 136loads an instance of module A when any of the modules are loaded. 137.Pp 138If a custom entry point is used for a module, and the module is compiled as 139an 140.Sq ELF 141binary, then 142.Xr kldload 8 143fails to execute the entry point. 144.Pp 145.Xr kldload 8 146returns the cryptic message 147.Sq Li "ENOEXEC (Exec format error)" 148for any error encountered while loading a module. 149.Pp 150When system internal interfaces change, old modules often cannot 151detect this, and such modules when loaded will often cause crashes or 152mysterious failures. 153.Sh AUTHORS 154The 155.Nm 156facility was originally implemented by 157.An Doug Rabson Aq dfr@FreeBSD.org . 158.Sh HISTORY 159The 160.Nm 161facility appeared in 162.Fx 3.0 163and was designed as a replacement for the 164.Xr lkm 4 165facility, which was similar in functionality to the loadable kernel modules 166facility provided by 167.Tn SunOS 1684.1.3. 169