It is possible to get deniable FDE with linux, Truecrypt style, but it is not an easy task. Poor mans deniable encryption: encrypt the entire drive, put the bootloader on a USB, now if they ask for password say that no password decrypts the drive and it isn't actually encrypted you just wiped it with random data. They shouldn't be able to tell a fully encrypted disk apart from one that was just wiped with a PRNG stream. If they ask why you have a bootloader on a USB stick just tell them you used to boot off of it but you have recently wiped the drive and have not yet installed a new OS .