Thanks for pointing out this. I tried “ldconfig -l  /usr/local/cuda-8.0/lib64/libcudnn.so.5.1.5”,
it seems doesn’t work (/etc/ld.so.cache doesn’t change), though no error message.
“man ldconfig” doesn’t give detail or example usage for option -l, and it said
"Intended for use by experts only". So, I’m not expert (indeed).