Module loading

Learn to load modules with insmod and rmmod.

Loading kernel modules

The Linux kernel can be extended at runtime with modules. A module is a piece of code loaded into kernel address space; no reboot required.

insmod modul.ko loads a module, rmmod modul removes it. lsmod lists loaded modules; modprobe also resolves dependencies. Modules have the .ko suffix and must be built for the running kernel. On load, the module's module_init function runs, so modules must be written carefully.

Module lifecycle

A module's lifecycle has four stages: build, load, run and remove. At each stage the kernel tracks module state.

On load, module_init is called; it prepares resources. On remove, module_exit is called; it cleans up. If the module is in use, rmmod is refused. The reference count is managed with try_module_get and module_put. Modules must match the running kernel; mismatch fails the load.

Exercise Print module commands

Define void print_module_cmd(const char *cmd, const char *desc) with body printf("%s: %s\n", cmd, desc);. In main call it for four commands: ("insmod", "load"), ("rmmod", "unload"), ("lsmod", "list"), ("modprobe", "resolve").

Show example solution

#include <stdio.h>

void print_module_cmd(const char *cmd, const char *desc) {
    printf("%s: %s\n", cmd, desc);
}

int main(void) {
    print_module_cmd("insmod", "load");
    print_module_cmd("rmmod", "unload");
    print_module_cmd("lsmod", "list");
    print_module_cmd("modprobe", "resolve");
    return 0;
}

Test yourself

Which command loads a module?
- modprobe -r
- rmmod
- insmod
- lsmod
Show answer

insmod — insmod loads a .ko file into the kernel.

Print module name with printk

printk(KERN_INFO "Module %s loaded
", ____);

Show answer

printk(KERN_INFO "Module %s loaded
", name);

Match module commands

insmod

Loads a module
rmmod

Removes a module
lsmod

Lists loaded modules
modprobe

Resolves dependencies

Next lesson: Module structure

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