When dynamic load libraries are changed (e.g. with the new files you installed in /usr/lib/x86_64-linux-gnu/) it is necessary to execute
/sbin/ldconfig to update the cache used by the loader. When libraries are updated by package managers (aptget, dpkg, yum and others), this is done automatically; when you build something yourself, it usually is not, in order to allow a person to test the application before it is shared by all users. Of course, an application can be tested where it is built, before "make install" is run, and that is clearly wise, but it also is useful to test after "make install" and before general use, in case something in the installation process is not right. /etc/ldconfig -p displays the current cache contents, but does not change the cache. Therefore, use of this command before and after /etc/ldconfig will divulge what may have changed in the cache.
