Kernelmodule

A KernelModule is a component that extends the functionality of an operating system kernel by loading code at runtime rather than embedding it directly in the kernel image. Kernel modules run in kernel space and can be added or removed without rebooting, allowing features such as drivers, filesystems, or protocol handlers to be added dynamically.

In Linux, modules are typically built as loadable kernel objects with a .ko extension. They are loaded into the running kernel with tools like insmod or modprobe and can be removed with rmmod. Each module defines initialization and cleanup routines, usually declared with the module_init and module_exit macros. When loaded, the initialization routine runs; when the module is removed, the cleanup routine runs. Modules may register devices, create sysfs entries, or register callbacks with the kernel, and they can export symbols for use by other modules via EXPORT_SYMBOL or EXPORT_SYMBOL_GPL. Module parameters can be exposed to control behavior at load time through the module_param macro.

Modules may declare dependencies on other modules; modprobe can automatically load required peers. Compatibility with the running kernel version and configuration options is required, and some systems enforce signing or licensing policies for modules. Built-in drivers or features do not appear as modules, while optional functionality may be provided as modules.

Security and stability considerations are important: loading modules requires appropriate privileges, and a faulty module can destabilize the system. Kernel modules provide a flexible, dynamic mechanism to extend kernel capabilities while preserving a stable base kernel.