initramfs

init.sh

#!/bin/sh

# Create the folder structure
mkdir -p work/initramfs/{bin,sbin,etc,proc,sys,newroot}
cd work

touch initramfs/etc/mdev.conf
cp /bin/busybox initramfs/bin/busybox
chmod +x initramfs/bin/busybox
ln -s busybox initramfs/bin/sh

# lvm
cp /usr/sbin/lvm.static initramfs/bin/lvm

cat << "__EOF__" > initramfs/init
#!/bin/sh

#Mount things needed by this script
mount -t proc proc /proc
mount -t sysfs sysfs /sys

#Disable kernel messages from popping onto the screen
echo 0 > /proc/sys/kernel/printk

#Clear the screen
clear

#Create all the symlinks to /bin/busybox
busybox --install -s

#Create device nodes
mknod /dev/null c 1 3
mknod /dev/tty c 5 0
mdev -s

# lvm
lvm vgscan --mknodes
lvm lvchange -aly vg/root

#Function for parsing command line options with "=" in them
# get_opt("init=/sbin/init") will return "/sbin/init"
get_opt() {
	echo "$@" | cut -d "=" -f 2
}

#Defaults
init="/sbin/init"
root="/dev/vg/root"

#Process command line options
for i in $(cat /proc/cmdline); do
	case $i in
		root\=*)
			root=$(get_opt $i)
			;;
		init\=*)
			init=$(get_opt $i)
			;;
	esac
done

#Mount the root device
mount "${root}" /newroot

#Check if $init exists and is executable
if [[ -x "/newroot/${init}" ]] ; then
	#Unmount all other mounts so that the ram used by
	#the initramfs can be cleared after switch_root
	umount /sys /proc
	
	#Switch to the new root and execute init
	exec switch_root /newroot "${init}"
fi

#This will only be run if the exec above failed
echo "Failed to switch_root, dropping to a shell"
exec sh
__EOF__

chmod +x initramfs/init

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