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 FreeBSD 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 filesystems, 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 /modules 65directory. 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 . 95The major problem with loading 96a device driver is that the driver's 97device nodes must exist for the 98devices to be accessed. They are usually 99created by using 100.Xr MAKEDEV 8 101or 102.Xr mknod 8 103(if the device is not supported by the 104.Xr MAKEDEV 8 105script) or, by writing a 106shell script to run 107.Xr kldload 8 108which should run the appropriate program to create the devices when the 109driver has been successfully loaded. 110.El 111.Sh FILES 112.Bl -tag -width /usr/include/sys/module.h -compact 113.It Pa /modules 114directory containing module binaries shipped with the system 115.It Pa /usr/include/sys/module.h 116file containing definitions required to compile a 117.Nm 118module 119.It Pa /usr/share/examples/kld 120example source code implementing a sample kld module 121.El 122.Sh SEE ALSO 123.Xr kldfind 2 , 124.Xr kldfirstmod 2 , 125.Xr kldload 2 , 126.Xr kldnext 2 , 127.Xr kldstat 2 , 128.Xr kldunload 2 , 129.Xr kldload 8 , 130.Xr kldstat 8 , 131.Xr kldunload 8 132.Sh BUGS 133If a module B, is dependent on another module A, but is not compiled with 134module A as a dependency, then 135.Xr kldload 8 136fails to load module B, even if module A is already present in the system. 137.Pp 138If multiple modules are dependent on module A, and are compiled with module 139A as a dependency, then 140.Xr kldload 8 141loads an instance of module A when any of the modules are loaded. 142.Pp 143If a custom entry point is used for a module, and the module is compiled as 144an 145.Sq ELF 146binary, then 147.Xr kldload 8 148fails to execute the entry point. 149.Pp 150.Xr kldload 8 151returns the cryptic message 152.Sq Li "ENOEXEC (Exec format error)" 153for any error encountered while loading a module. 154.Pp 155When system internal interfaces change, old modules often cannot 156detect this, and such modules when loaded will often cause crashes or 157mysterious failures. 158.Sh AUTHORS 159The 160.Nm 161facility was originally implemented by 162.An Doug Rabson Aq dfr@FreeBSD.org . 163.Sh HISTORY 164The 165.Nm 166facility appeared in 167.Fx 3.0 168and was designed as a replacement for the 169.Xr lkm 4 170facility, which was similar in functionality to the loadable kernel modules 171facility provided by 172.Tn SunOS 1734.1.3. 174