Licensing
The TrueCrypt License has not been officially approved by the Open Source Initiative and is not considered "free" by several major Linux distributions (Arch Linux, Debian, Ubuntu, Fedora, openSUSE, Gentoo), mainly because of distribution and copyright-liability reasons.
TrueCrypt 6.3a (released Nov 2009) comes under TrueCrypt License Version 2.8 which was changed in some places from the 2.5 license, but TrueCrypt is still not included in any of the major Linux distributions.
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