Hi! I have made an backup script for ISPConfig 3, it backup all sites and databases and it compress all of these things in a tar.gz I have tested it successfully on debian 8, instructions on the readme on github. Github: https://github.com/SergiX44/ISPConfigBackup
Will this cover things like /etc/group /etc/shadow /etc/passwd? I've been having some issues restoring a server and am looking for a good backup solution in the future.