kldload

kldload is a user-space utility in FreeBSD and related BSD systems that loads a kernel module into a running kernel. A module is typically a loadable kernel object (.ko) that adds drivers, file system support, or other functionality without requiring a reboot. Modules are usually stored under /boot/kernel or /boot/modules and are built for the system’s kernel ABI.

When invoked, kldload resolves the module’s dependencies and loads any prerequisite modules before loading the requested one. After the module is loaded, the kernel calls its initialization routine, which may register devices, hooks, or interfaces with the rest of the system. If loading fails, kldload reports an error and returns a non-zero status, and diagnostic messages may indicate the cause.

Usage generally requires root privileges. A module can be loaded by specifying its file path, for example, kldload /boot/kernel/if_tap.ko, or by name if the module resides in the system module search paths. The loader handles dependencies declared by the module itself, ensuring proper initialization order.

Unloading a module is performed with kldunload, which must consider active references to the module’s resources to avoid destabilizing the system. The current set of loaded modules can be inspected with kldstat. Kernel modules may declare dependencies using the MODULE_DEPEND mechanism in their source, guiding the loader to bring up necessary components in the correct order.

See also: kldstat, kldunload, and the kld(8) subsystem that manages dynamic kernel loading and unloading.