This is an initramfs for cm9 so you can boot Arch Linux instead of Android.

This only uses the Android Kernel does not get to the Android init, it should
switch_root to Arch Linux if an SD Card is inserted


How to build
Run the following in the directory of the initramfs to generate a ramdisk.img

find . -name .git -a -type d -prune -o -print0 | cpio --null -ov --format=newc | gzip -9 > ../ramdisk.img

For the i9300 run mkbootimg from Cyanogenmod (or however else you want to make
it for your device)

~/android/system/out/host/linux-x86/bin/mkbootimg --kernel kernel --cmdline console=tty0 --base 0x40000000 --pagesize 2048 --ramdisk ramdisk.img --output boot.img

Flash the boot.img by odin/heimdall or package and then flash with cwm

Thanks to
gabx
gokhanmoral (for help with mounting issues)