LUKS documentation from Red Hat is a 404 link to the RHEL6 LUKS docs.

Updated link for RHEL7 appears to be: https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/7/html/Security_Guide/sec-Encryption.html.

Perhaps we should be linking to a more general page (eg. LUKS on Wikipedia) rather than a specific Linux distro.