/usr/lib/x86_64-linux-gnu/libjackserver.so is in libjack-jackd2-dev 1.9.10+20150825git1ed50c92~dfsg-1ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libjackserver.so.0.1.0