How do I trace library loading?
If on a GNU system, try running your application with:
LD_DEBUG=help for more options or
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.)