Password-protecting the GRUB 2 bootloader

People sometimes forget passwords, even if they're administrators. And sometimes, people buy used computers but forget to ask the seller what the password is. (Yes, I've done that.) That's okay, though, because all of the major operating systems have ways to let you either reset or recover a lost administrator password. That's handy, except that it does kind of make the whole idea of having login passwords a rather moot point when someone has physical access to the machine. Let's say that your laptop has just been stolen. If you haven't encrypted the hard drive, it would only take a few minutes for the thief to reset the password and to steal your data. If you have encrypted the drive, the level of protection would depend on which operating system you're running. With standard Windows folder encryption, the thief would be able to access the encrypted folders just by resetting the password. With LUKS whole-disk encryption on a Linux machine, the thief...