#!/bin/sh
echo "Status: 503"
echo "Content-Type: text/html; charset=iso-8859-1"
echo ""
cat <
503 - Service temporary unavailable
503 - Service temporary unavailable
Sorry, this website is currently down for maintainance please
retry in a few minutes
EOF
Then add this to your virtual host config and reload Apache:
ScriptAlias / /path/to/your/503.sh/
Please note the trailing slash! It's needed!