The simplest Linux kernel module.

hello-kernel/Makefile

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+# Makefile for hello world kernel module
+obj-m := hello.o	# Module Name is hello.c
+
+KDIR  := /lib/modules/$(shell uname -r)/build
+
+all:
+	$(MAKE) -C $(KDIR) M=$(PWD) modules
+
+clean:
+	$(MAKE) -C $(KDIR) M=$(PWD) clean
+	$(RM) Module.markers modules.order

hello-kernel/README.md

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+hello.c
+---
+
+The simplest kernel module.
+
+### Getting started
+
+Hmmm...
+
+### Building
+
+Yeah... try `make`
+
+### Testing
+
+`./test.sh`
+
+Expected output: http://showterm.io/b0ef83393d4ba67b40480
+
+### Credits
+
+Thanks to [this tutorial](http://www.tldp.org/LDP/lkmpg/2.6/html/) by [Peter Jay Salzman](http://dirac.org/).
+
+And some thanks to my friend [Dimitris Zervas](http://dzervas.gr/) for helping me realize what a Makefile
+requires to build a kernel module.

hello-kernel/hello.c

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+/*
+ * hello.c - The simplest Linux kernel module.
+ */
+
+#include <linux/module.h>  /* Needed by all modules */
+#include <linux/kernel.h>  /* Needed for KERN_ALERT */
+
+int init_module(void)
+{
+        printk(KERN_ALERT "Hello from the Kernel!\n");
+
+        // A non 0 return means init_module failed; module can't be loaded.
+        return 0;
+}
+
+void cleanup_module(void)
+{
+        printk(KERN_ALERT "Goodbye, I'm out.\n");
+}
+
+MODULE_LICENSE("GPL");

hello-kernel/test.sh

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+#!/bin/bash
+# Tests the kernel module
+echo 'Begin tests'
+
+# Build
+echo 'Running "make all" to build module'
+make all
+
+# Load module
+echo 'Running "sudo insmod hello.ko" to load module'
+sudo insmod hello.ko
+
+# Test if module loaded
+echo 'Running "lsmod | grep 'hello'" to test if module loaded properly'
+lsmod | grep 'hello'
+
+# Unload module
+echo 'Running "sudo rmmod hello" to unload module'
+sudo rmmod hello
+
+# Test if module unloaded
+echo 'Running "lsmod | grep 'hello'" to test if module unloaded properly'
+lsmod | grep 'hello'
+
+# Clean up like a good kid
+echo 'Running "make clean" to clean everything up'
+make clean
+
+# Check module
+echo 'Running "tail -n 10 /var/log/syslog" to see if module did what it was supposed to'
+tail -n 10 /var/log/syslog
+journalctl -r
+
+echo 'Tests finished'