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.Dd January 13, 2014 27.Dt KLD 4 28.Os 29.Sh NAME 30.Nm kld 31.Nd dynamic kernel linker facility 32.Sh DESCRIPTION 33The LKM (Loadable Kernel Modules) facility has been deprecated in 34.Fx 3.0 35and above in favor of the 36.Nm 37interface. 38This interface, like its 39predecessor, allows the system administrator to dynamically add and remove 40functionality from a running system. 41This ability also helps software 42developers to develop new parts of the kernel without constantly rebooting 43to test their changes. 44.Pp 45Various types of modules can be loaded into the system. 46There are several defined module types, listed below, which can 47be added to the system in a predefined way. 48In 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 Linux 59emulator. 60.Nm 61modules are placed by default in the 62.Pa /boot/kernel 63directory along with their matching kernel. 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.Pp 88Kernel modules may only be loaded or unloaded if the system security level 89.Va kern.securelevel 90is less than one. 91.Sh "MODULE TYPES" 92.Bl -ohang 93.It Em "Device Driver modules" 94New block and character device 95drivers may be loaded into the system with 96.Nm . 97Device nodes for the loaded drivers are automatically created when a 98module is loaded and destroyed when it is unloaded by 99.Xr devfs 4 . 100You can specify userland programs that will run when new devices 101become available as a result of loading modules, or existing devices 102go away when modules are unloaded, by configuring 103.Xr devd 8 . 104.El 105.Sh FILES 106.Bl -tag -width /usr/include/sys/module.h -compact 107.It Pa /boot/kernel 108directory containing module binaries built for the kernel also 109residing in the directory. 110.It Pa /usr/include/sys/module.h 111file containing definitions required to compile a 112.Nm 113module 114.It Pa /usr/share/examples/kld 115example source code implementing a sample kld module 116.El 117.Sh SEE ALSO 118.Xr kldfind 2 , 119.Xr kldfirstmod 2 , 120.Xr kldload 2 , 121.Xr kldnext 2 , 122.Xr kldstat 2 , 123.Xr kldunload 2 , 124.Xr devfs 4 , 125.Xr devd 8 , 126.Xr kldload 8 , 127.Xr kldstat 8 , 128.Xr kldunload 8 , 129.Xr sysctl 8 130.Sh HISTORY 131The 132.Nm 133facility appeared in 134.Fx 3.0 135and was designed as a replacement for the 136.Nm lkm 137facility, which was similar in functionality to the loadable kernel modules 138facility provided by 139.Tn SunOS 1404.1.3. 141.Sh AUTHORS 142The 143.Nm 144facility was originally implemented by 145.An Doug Rabson Aq Mt dfr@FreeBSD.org . 146.Sh BUGS 147If a module B, is dependent on another module A, but is not compiled with 148module A as a dependency, then 149.Xr kldload 8 150fails to load module B, even if module A is already present in the system. 151.Pp 152If multiple modules are dependent on module A, and are compiled with module 153A as a dependency, then 154.Xr kldload 8 155loads an instance of module A when any of the modules are loaded. 156.Pp 157If a custom entry point is used for a module, and the module is compiled as 158an 159.Sq ELF 160binary, then 161.Xr kldload 8 162fails to execute the entry point. 163.Pp 164.Xr kldload 8 165points the user to read 166.Xr dmesg 8 167for any error encountered while loading a module. 168.Pp 169When system internal interfaces change, old modules often cannot 170detect this, and such modules when loaded will often cause crashes or 171mysterious failures. 172