What does sudo ldconfig do in Ubuntu?

In the directories supplied on the command line, in the file /etc/ld.so.conf, and in the trusted directories (/lib and /usr/lib), ldconfig generates the required links and cache to the most recent shared libraries. The run-time linker, http://ld.so or http://ld-linux.so, uses the cache. When selecting which versions of libraries should have their links changed, ldconfig looks at the header and filenames of the libraries it comes across.