We use LLVM APT repository hosted by llvm.org in Travis build, see .travis.yml. http://llvm.org/apt/ currently says, "APT mirror was temporary switched off due to excess load. We are working on bringing it back. Stay tuned!". I found email titled [IMPORTANT: APT repo temporary switched off](http://lists.llvm.org/pipermail/llvm-dev/2016-May/100303.html) sent to llvm-dev on 2016-05-31, which includes more details.