The above error is a linker error... the linker a program that takes one or more objects generated by a compiler and combines them into a single executable program.
You must add -lboost_system to you linker flags which indicates to the linker that it must look for symbols like boost::system::system_category() in the library libboost_system.so.
If you have main.cpp, either:
g++ main.cpp -o main -lboost_system
OR
g++ -c -o main.o main.cpp
g++ main.o -lboost_system