kernel environment

This is a pretty simple kernel environment using busybox, run with Qemu.

Usage

If you want to try diffenrent kernel, just replace bzImage, to get bzImage, try compile yours.

If you want to upload any programs into file system, just copy it in initramfs, and run mkcpio.

Then run ./run to run.

How to make your own?

In case you want to make your very own environment like this, you need the following:

• busybox
• cpio
• gzip(maybe)

basic file system

First, make a file system directory, and its structure:

mkdir initramfs
# standard file system entries
mkdir -pv bin lib dev etc mnt/root proc root sbin sys

Then compile busybox using make, just do these like it is said on busybox page. I don't need to mention that here, in case it changes.

Now you need to install busybox to the fs:

cd initramfs # we are at root of our fs
cp busybox/_install/* . -rv # copy those of busybox/_install/ directory here

What's left here is the init file, which will do some mount, typing these lines to fs/init:

#!/bin/sh

mount -t proc none /proc
mount -t sysfs none /sys
mount -t devtmpfs devtmpfs /dev

setsid cttyhack setuidgid 0 sh

umount /proc
umount /sys
poweroff -d 0 -f

And, basic file system is done.

make cpio

File system like these cannot get into qemu, we need to make an cpio. This is done by using cpio, and it is like this:

cd initramfs
find . | cpio -o -H newc | gzip > ../rootfs.cpio

I just write this into a script file named mkcpio, you can do this manually as well. Note that you need to be in initramfs and do find ..

run

Run using Qemu is not difficult, but the argument is too much:

qemu-system-x86_64 -initrd initrd.cpio.gz -kernel bzImage -append 'console=ttyS0 root=/dev/ram oops=panic panic=1' -enable-kvm -monitor /dev/null -m 64M --nographic  -smp cores=1,threads=1 -cpu kvm64,+smep -s

This doesn't has a lot to explain, you can also add your own argument in it, or do this manually.

Enjoy.