dynamic kernel linker facility
The LKM (Loadable Kernel Modules) facility has been deprecated in
and above in favor of the
interface. This interface, like its
predecessor, allows the system administrator to dynamically add and remove
functionality from a running system. This ability also helps software
developers to develop new parts of the kernel without constantly rebooting to
test their changes.
Various types of modules can be loaded into the system. There are several
defined module types, listed below, which can be added to the system in a
predefined way. In addition, there is a generic type, for which the module
itself handles loading and unloading.
system makes extensive use of loadable
kernel modules, and provides loadable versions of most file systems, the NFS
client and server, all the screen-savers, and the iBCS2 and Linux emulators.
modules are placed by default in the
directory along with their
interface is used through the
program can load either
or ELF formatted loadable modules. The
program unloads any given loaded module, if no other module is dependent upon
the given module. The
program is used to check the status of the modules currently loaded into the
Kernel modules may only be loaded or unloaded if the system security level
is less than one.
- Device Driver modules
- New block and character device drivers may be loaded into the system with
kld. Device nodes for the loaded
drivers are automatically created when a module is loaded and destroyed
when it is unloaded by
You can specify userland programs that will run when new devices become
available as a result of loading modules, or existing devices go away when
modules are unloaded, by configuring
- directory containing module binaries built for the kernel also residing in
- file containing definitions required to compile a
- example source code implementing a sample kld module
facility appeared in
and was designed as a replacement for the
facility, which was similar in
functionality to the loadable kernel modules facility provided by SunOS 4.1.3.
facility was originally implemented
by Doug Rabson
If a module B, is dependent on another module A, but is not compiled with module
A as a dependency, then
fails to load module B, even if module A is already present in the system.
If multiple modules are dependent on module A, and are compiled with module A as
a dependency, then
loads an instance of module A when any of the modules are loaded.
If a custom entry point is used for a module, and the module is compiled as an
‘ELF’ binary, then
fails to execute the entry point.
points the user to read
for any error encountered while loading a module.
When system internal interfaces change, old modules often cannot detect this,
and such modules when loaded will often cause crashes or mysterious