Automatic hostnames for Raspberry Pi instead of all 'raspberrypi'

rc.local

# If you have many Raspberry Pis that you want to setup from a common image, 
# add this to `/etc/rc.local` before you create the image, but do not run it. 

# On first-run it will change the name from `raspberrypi` to `crowd-XXXXXX` where XXXXXX 
# is the serial number of the Raspberry Pi. (Change 'crowd' in the line below.)

MAC="crowd-""$(grep 'Serial' /proc/cpuinfo | sed 's/^Serial.*000\([1-9a-f][0-9a-f]*\)$/\1/')"
CURRENT_HOSTNAME=$(cat /proc/sys/kernel/hostname)

if [ $CURRENT_HOSTNAME != $MAC ]
then
echo "Changing name to" $MAC "from" $CURRENT_HOSTNAME
chattr -i /etc/hostname
echo "$MAC" > "/etc/hostname"
# If you are using SaltStack include this next line also
echo "$MAC" > "/etc/salt/minion_id"
chattr -i /etc/hosts
sed -i "s/127.0.1.1\s*$CURRENT_HOSTNAME/127.0.1.1\t$MAC/g" /etc/hosts
hostname $MAC
#chattr +i /etc/hostname
#chattr +i /etc/hosts
fi