script for pivot_root

pivot_root.sh

#!/bin/sh
# credential: http://www.bluegecko.net/amazon-web-services/ec2-persistent-boots-with-pivot-root/

PATH=/bin:/usr/bin:/sbin:/usr/sbin
NEWDEV="/dev/xvdf1"
NEWTYP="ext4"
NEWMNT="/mnt/ebs"
OLDMNT="/mnt/old"
OPTIONS="noatime,rw"
SLEEP=1

echo "Remounting writable."
mount -o remount,rw /
[ ! -d $NEWMNT ] && echo "Creating directory $NEWMNT." && mkdir -p $NEWMNT

while true ; do
echo "waiting for mounting.."
sleep $SLEEP
echo "Trying to mount $NEWDEV writable."
mount -t $NEWTYP -o rw $NEWDEV $NEWMNT || continue
echo "Mounted."
break;
done

[ ! -d $NEWMNT/$OLDMNT ] && echo "Creating directory $NEWMNT/$OLDMNT." && mkdir -p $NEWMNT/$OLDMNT

echo "Remounting $NEWMNT $OPTIONS."
mount -o remount,$OPTIONS $NEWMNT

echo "Trying to pivot."
cd $NEWMNT
pivot_root . ./$OLDMNT

for dir in /dev /proc /sys; do
echo "Moving mounted file system ${OLDMNT}${dir} to $dir."
mount --move ./${OLDMNT}${dir} ${dir}
done

echo "Chaning directory to new root"
cd ~

echo "Tying to chroot and umount $OLDMNT."
echo "init argument $*"
exec chroot . /bin/sh -c 'umount $OLDMNT; exec /sbin/init $*' < /dev/console > /dev/console 2>&1