From Birnam Designs Wiki

The linker looks in paths defined in /etc/ld.so.conf, which reference a set of conf files located in /etc/ld.so.conf.d/*.conf

When a path is added to ld.so.conf or a path is added to a new or existing file in /etc/ld.so.conf.d/, you need to refresh the cache with:

sudo ldconfig -v