Here's how to restore a backup if the backup is named nightly_data.tar.gz and it is location in folder /tmp.
# screen
Force of habit for any operation that I want to run without monitoring the CLI
# amp_disable
Another force of habit, but it makes sure that nothings still writing to the database as you're trying to restore
# amp_restore -d /tmp/nightly_data.tar.gz
As restore is going on, I tend to detach myself from the session (in screen, ctrl+a then d). And then when I want to get back into that screen, if it's the only screen -> 'screen -r', if there are several screens, then you may need to do 'screen -ls' and then 'screen -r ####' where the hash is the pid number. Once restore completes, it will still be in amp_disable state, so 'amp_enable' and then wait 5-10 minutes for the GUI to become available.