dhclient hook for setting the hostname, updating /etc/hosts, and re-generating ssh keys on Ubuntu.Useful for creating CloudStack templates.See https://issues.apache.org/jira/browse/CLOUDSTACK-4556

cloudstack-sethostname.sh

#!/bin/sh
echo "Running dhclient change hostname script for Ubuntu. reason=${reason}"
timestamp=$(date +%s)
if grep localhost /etc/hostname; then
    echo "Current hostname:"
    cat /etc/hostname
    echo "Attempting to configure hostname"
    if [ "x$reason" = "xBOUND" ]; then

        hostname=$new_host_name
        fqdn="${hostname}.${new_domain_name}"
        ip=$new_ip_address
        echo "cloudstack-hostname: Hostname localhost detected. Changing hostname and adding hosts."
        printf " Hostname: $hostname\n FQDN: $fqdn\n IP: $ip\n\n"


        echo "Wait for filesystem to become writable"
        TESTFILE=/etc/.is_fs_writable_$timestamp
        until touch $TESTFILE; do
            echo "sleeping 1 second"
            sleep 1
        done
        rm $TESTFILE

        # Set Hosts and Hostname
        TMPHOSTS=/etc/hosts.dhcp.new
        if ! grep "$ip $fqdn $hostname" /etc/hosts; then
            # Backup hosts file
            cp /etc/hosts /etc/hosts.dhcp.bak
            # Copy everything except 127.0.1.1 from initial hosts file
            grep -v '127\.0\.1\.1 ' < /etc/hosts > $TMPHOSTS
            # Add the new ip address and name
            echo "$ip $fqdn $hostname" >> $TMPHOSTS
            mv $TMPHOSTS /etc/hosts
        fi

        # Rename Host
        echo $hostname > /etc/hostname
        hostname -b -F /etc/hostname
        echo $hostname > /proc/sys/kernel/hostname
        # Create fresh SSH keys
        export DEBIAN_FRONTEND=noninteractive
        dpkg-reconfigure openssh-server
    fi
fi

Working on Ubuntu 14.04 and survives reboots