Linux Kernel

Posted on July 2, 2014

Tags: operatingsys

boot directory

cd /boot
uname -r
#>5.16.0-kali7-amd64

#>vmlinuz-5.16.0-kali7-amd64 is the kernel we are booted in

“vmlinuz-5.16.0-kali7-amd64” kernel will be loaded into memory by GRUB bootloader and then GRUB will transfer control to it

1 Listing hardware

lspci | more #lists all devices connected to pci
lsusb #lists usb devices

2 Kernel

#include <linux/init.h>
#include <linux/module.h>
MODULE_LICENSE("Dual BSD/GPL");
static int hello_init(void)
{
 printk(KERN_ALERT "Hello, world\n");
 return 0;
}
static void hello_exit(void)
{
 printk(KERN_ALERT "Goodbye, cruel world\n");
}
module_init(hello_init);
module_exit(hello_exit);

obj-m=kmain.o
EXTRA_CFLAGS += $(CFLAGS_EXTRA) -fno-pie

all:
		make -C /lib/modules/`uname -r`/build/ M=$(PWD) modules

clean:
		make -C /lib/modules/`uname -r`/build M=$(PWD) clean

sudo insmod kmain.ko #load kernel file
modinfo kmain.ko 
sudo cat /var/log/kern.log | grep "Hello, world"
sudo dmesg | grep "Hello, world"
sudo rmmod kmain.ko #unload kernel file

Note the only way you can “see” the output is by grepping the kernel logs.