Linux Kernel Module Code

Install Build tools:

sudo apt update
sudo apt install build-essential linux-headers-$(uname -r)

Create the module:

hello.c


#include <linux/init.h>   // Initialization macros
#include <linux/module.h> // Core headers for modules
#include <linux/kernel.h> // Kernel logging

MODULE_LICENSE("GPL");          // License type
MODULE_AUTHOR("Silly Snail");   // Author of the module
MODULE_DESCRIPTION("A Simple Hello World Kernel Module");
MODULE_VERSION("1.0");

// Function executed when module is loaded
static int __init hello_init(void) {
    printk(KERN_INFO "Hello, Kernel! Module Loaded.\n");
    return 0; // Return 0 on success
}

// Function executed when module is unloaded
static void __exit hello_exit(void) {
    printk(KERN_INFO "Goodbye, Kernel! Module Unloaded.\n");
}

// Register module entry and exit points
module_init(hello_init);
module_exit(hello_exit);

Create a make file:

Makefile


obj-m += hello.o  # Compile hello.c into hello.ko (kernel object)

KDIR := /lib/modules/$(shell uname -r)/build
PWD  := $(shell pwd)

all:
	$(MAKE) -C $(KDIR) M=$(PWD) modules

clean:
	$(MAKE) -C $(KDIR) M=$(PWD) clean

Build and test it:

make

sudo insmod hello.ko
lsmod | grep hello
sudo dmesg | tail -10
sudo rmmod hello
dmesg | tail -10
make clean