Shared Libraries in Linux

The main administrative task for shared libraries is to tell programs how to find libraries. It can be done by setting a library path. You can set it systemwide or temporarily.
To change or add path systemwide, you need to add path or conf file, containing path, to /etc/ld.so.conf:/path include /etc/ld.so.conf.d/*.conf
For changes take effect you need to launch ldconfig
/lib and /usr/lib are always in library path, even if they aren't listed in /etc/ld.so.conf
To add or change path temporarily you need to set the LD_LIBRARY_PATH environment variable:
$ export LD_LIBRARY_PATH=/usr/local/testlib:/opt/newlib
You can use ldd command to see what libraries the program links to.