How do I trace library loading?

If on a GNU system, try running your application with:

LD_DEBUG=libs your-application

See LD_DEBUG=help for more options or man ld.so.

If the program is loading libboost_system manually using dlopen(), you might be able to find where it is doing that using ltrace to see if it is calling dlopen(), and maybe gdb to set a breakpoint on calls to dlopen() and then generating a stack backtrace. (See also latrace.)