/usr/lib/x86_64-linux-gnu/ is in libgazebo9-dev 9.0.0+dfsg5-3ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/x86_64-linux-gnu/libgazebo_msgs.so
/usr/lib/x86_64-linux-gnu/libgazebo_ode.so
/usr/lib/x86_64-linux-gnu/libgazebo_opcode.so
/usr/lib/x86_64-linux-gnu/cmake/
/usr/lib/x86_64-linux-gnu/cmake/gazebo/
/usr/lib/x86_64-linux-gnu/cmake/gazebo/gazebo-config-version.cmake
/usr/lib/x86_64-linux-gnu/cmake/gazebo/gazebo-config.cmake
/usr/lib/x86_64-linux-gnu/pkgconfig/
/usr/lib/x86_64-linux-gnu/pkgconfig/gazebo.pc
/usr/lib/x86_64-linux-gnu/pkgconfig/gazebo_ode.pc
/usr/lib/x86_64-linux-gnu/pkgconfig/gazebo_transport.pc
/usr/lib/x86_64-linux-gnu/libgazebo.so
/usr/lib/x86_64-linux-gnu/libgazebo_client.so
/usr/lib/x86_64-linux-gnu/libgazebo_common.so
/usr/lib/x86_64-linux-gnu/libgazebo_gimpact.so
/usr/lib/x86_64-linux-gnu/libgazebo_gui.so
/usr/lib/x86_64-linux-gnu/libgazebo_opende_ou.so
/usr/lib/x86_64-linux-gnu/libgazebo_physics.so
/usr/lib/x86_64-linux-gnu/libgazebo_rendering.so
/usr/lib/x86_64-linux-gnu/libgazebo_sensors.so
/usr/lib/x86_64-linux-gnu/libgazebo_transport.so
/usr/lib/x86_64-linux-gnu/libgazebo_util.so