This is literally what dd does and what I would have recommended, if this person hadn’t beaten me to it.
However, if you’re cloning to another disk or partition that will be plugged in at the same time as your existing installation, you’ll wind up with two partitions with the same identifier — a recipe for eventual disaster. In that case, I would run through setup (with your current disk unplugged) and then rsync over the new root partition.
This is literally what dd does and what I would have recommended, if this person hadn’t beaten me to it.
However, if you’re cloning to another disk or partition that will be plugged in at the same time as your existing installation, you’ll wind up with two partitions with the same identifier — a recipe for eventual disaster. In that case, I would run through setup (with your current disk unplugged) and then rsync over the new root partition.