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KLD(4)		       FreeBSD Kernel Interfaces Manual			KLD(4)

NAME
     kld -- dynamic kernel linker facility

DESCRIPTION
     The LKM (Loadable Kernel Modules) facility	has been deprecated in
     FreeBSD 3.0 and above in favor of the kld 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	sev-
     eral 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.

     The FreeBSD 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.	kld
     modules are placed	by default in the /boot/kernel directory along with
     their matching kernel.

     The kld interface is used through the kldload(8), kldunload(8) and
     kldstat(8)	programs.

     The kldload(8) program can	load either a.out(5) or	ELF formatted loadable
     modules.  The kldunload(8)	program	unloads	any given loaded module, if no
     other module is dependent upon the	given module.  The kldstat(8) program
     is	used to	check the status of the	modules	currently loaded into the sys-
     tem.

     Kernel modules may	only be	loaded or unloaded if the system security
     level kern.securelevel is less than one.

MODULE TYPES
     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 devfs(5).	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 devd(8).

FILES
     /boot/kernel		directory containing module binaries built for
				the kernel also	residing in the	directory.
     /usr/include/sys/module.h	file containing	definitions required to	com-
				pile a kld module
     /usr/share/examples/kld	example	source code implementing a sample kld
				module

SEE ALSO
     kldfind(2), kldfirstmod(2), kldload(2), kldnext(2), kldstat(2),
     kldunload(2), devfs(5), devd(8), kldload(8), kldstat(8), kldunload(8),
     sysctl(8)

BUGS
     If	a module B, is dependent on another module A, but is not compiled with
     module A as a dependency, then kldload(8) 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 mod-
     ule A as a	dependency, then kldload(8) 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 kldload(8) fails to execute the entry point.

     kldload(8)	returns	the cryptic message `ENOEXEC (Exec format error)' 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
     failures.

HISTORY
     The kld facility appeared in FreeBSD 3.0 and was designed as a replace-
     ment for the lkm(4) facility, which was similar in	functionality to the
     loadable kernel modules facility provided by SunOS	4.1.3.

AUTHORS
     The kld facility was originally implemented by Doug Rabson
     <dfr@FreeBSD.org>.

FreeBSD	10.1		       November	8, 1998			  FreeBSD 10.1

NAME | DESCRIPTION | MODULE TYPES | FILES | SEE ALSO | BUGS | HISTORY | AUTHORS

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