/usr/lib vs /etc/ld.so.conf.d

**TL;DR** Why is it better to place a symlink to a shared library at /etc/lib(64)/ or why is it better to create a *.conf file in /etc/ld.so.conf.d/ --- ## .conf file Assuming i have my custom binary at /opt/foo/, shipping with it's own shared libraries. The common way (known to me) is to place a file at /etc/ld.so.conf.d/foo.conf like follows:

# Link foo libraries. This file is included in /etc/ld.so.conf
/opt/foo/lib
/opt/foo/otherlibs

and run ldconfig afterwards. ## symlinks But I found out that I can also link my libraries into /usr/lib (or lib64) like this:

for f in /etc/foo/{lib,otherlibs}/*; do
  ln -s $f /usr/lib64/$(basename $f)
done

and I won't have to run ldconfig afterwards. **What are the pros/cons of these two ways?** I can imagine that the "symlink"-way isn't very nice to handle when uprading the application or the library versions. In general, the ".conf"-way seems more modular and more Linux-ish to me. I occasionally came across this because we have to encrypt (and only decrypt at runtime) a specific library. ldconfig doesn't recognize the library when encrypted (still in ELF format) so the only suitable way to me was to place a link to the specific *.so file in /usr/lib64