/usr/share/zoneinfo/posix/Etc/GMT-6 is in tzdata 2016d-0ubuntu0.16.04.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/zoneinfo/posix/Etc/../../Etc/GMT-6
/usr/share/zoneinfo/posix/Etc/../../Etc/GMT-6