1 .\" Copyright (c) 1993 Christopher G. Demetriou
2 .\" All rights reserved.
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33 .Nd dynamic kernel linker facility
35 The LKM (Loadable Kernel Modules) facility has been deprecated in
37 and above in favor of the
40 This interface, like its
41 predecessor, allows the system administrator to dynamically add and remove
42 functionality from a running system.
43 This ability also helps software
44 developers to develop new parts of the kernel without constantly rebooting
45 to test their changes.
47 Various types of modules can be loaded into the system.
48 There are several defined module types, listed below, which can
49 be added to the system in a predefined way.
51 is a generic type, for which the module itself handles loading and
56 system makes extensive use of loadable kernel modules, and provides loadable
57 versions of most file systems, the
59 client and server, all the screen-savers, and the
63 modules are placed by default in the
65 directory along with their matching kernel.
69 interface is used through the
78 program can load either
80 or ELF formatted loadable modules.
83 program unloads any given loaded module, if no other module is dependent
84 upon the given module.
87 program is used to check the status of the modules currently loaded into the
90 Kernel modules may only be loaded or unloaded if the system security level
95 .It Em "Device Driver modules"
96 New block and character device
97 drivers may be loaded into the system with
99 Device nodes for the loaded drivers are automatically created when a
100 module is loaded and destroyed when it is unloaded by
102 You can specify userland programs that will run when new devices
103 become available as a result of loading modules, or existing devices
104 go away when modules are unloaded, by configuring
108 .Bl -tag -width /usr/include/sys/module.h -compact
110 directory containing module binaries built for the kernel also
111 residing in the directory.
112 .It Pa /usr/include/sys/module.h
113 file containing definitions required to compile a
116 .It Pa /usr/share/examples/kld
117 example source code implementing a sample kld module
137 and was designed as a replacement for the
139 facility, which was similar in functionality to the loadable kernel modules
146 facility was originally implemented by
147 .An Doug Rabson Aq Mt dfr@FreeBSD.org .
149 If a module B, is dependent on another module A, but is not compiled with
150 module A as a dependency, then
152 fails to load module B, even if module A is already present in the system.
154 If multiple modules are dependent on module A, and are compiled with module
155 A as a dependency, then
157 loads an instance of module A when any of the modules are loaded.
159 If a custom entry point is used for a module, and the module is compiled as
164 fails to execute the entry point.
167 points the user to read
169 for any error encountered while loading a module.
171 When system internal interfaces change, old modules often cannot
172 detect this, and such modules when loaded will often cause crashes or