If you've read Cory Doctorow's Little Brother (a wonderful novel, by the way) you'll know that the main character sets up a Truecrypt-esque hidden volume on his phone. It opens to the login prompt, and he can give a username and password that could either lead to the "innocent" volume or the not-so-innocent one.
Is there a way to do this on login (or on boot) on an Ubuntu/Linux Mint system? I'm open to switching OSes but I'm rather attached to Ubuntu at the moment.
Yes
Hidden Operating System
If your system partition or system drive is encrypted using TrueCrypt, you need to enter your pre-boot authentication password in the TrueCrypt Boot Loader screen after you turn on or restart your computer. It may happen that you are forced by somebody to decrypt the operating system or to reveal the pre-boot authentication password. There are many situations where you cannot refuse to do so (for example, due to extortion). TrueCrypt allows you to create a hidden operating system whose existence should be impossible to prove (provided that certain guidelines are followed — see below). Thus, you will not have to decrypt or reveal the password for the hidden operating system.
(emphasis mine)
