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
     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.

     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 Linux emulator.  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
     system.

     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
                                compile 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)

HISTORY
     The kld facility appeared in FreeBSD 3.0 and was designed as a
     replacement for the lkm 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>.

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
     module 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) points the user to read dmesg(8) 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.

FreeBSD 13.1-RELEASE-p6        January 13, 2014        FreeBSD 13.1-RELEASE-p6