/usr/lib/x86_64-linux-gnu/libgsl.so.19 is in libgsl2 2.1+dfsg-2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libgsl.so.19.0.0
/usr/lib/x86_64-linux-gnu/libgsl.so.19.0.0