Loadable Modules

• You can add functionality to the kernel (and remove functionality as well) while the system is up and running. Each piece of code that can be added to the kernel at runtime is called a module .
• The Linux kernel offers support for quite a few different types (or classes) of modules, including, but not limited to, device drivers. Each module is made up of object code (not linked into a complete executable) that can be dynamically linked to the running kernel by the insmod program and can be unlinked by the rmmod program.
• Figure 1 identifies different classes of modules in charge of specific tasks (a module is said to belong to a specific class according to the functionality it offers). The placement of modules in Figure 7.5 covers the most important classes, but is far from complete because more and more functionality in Linux is being modularized.