[ Thanks to Falko
Timme for this link. ]
“This tutorial shows how you can mirror your web site from your
main web server to a backup server that can take over if the main
server fails. We use the tool rsync for this, and we make it run
through a cron job that checks every x minutes if there is
something to update on the mirror. Thus your backup server should
usually be up to date if it has to take over.“rsync updates only files that have changed, so you do not need
to transfer 5 GB of data whenever you run rsync. It only mirrors
new/changed files, and it can also delete files from the mirror
that have been deleted on the main server. In addition to that it
can preserve permissions and ownerships of mirrored files and
directories; to preserve the ownerships, we need to run rsync as
root which is what we do here. If permissions and/or ownerships
change on the main server, rsync will also change them on the
backup server…”