Hello, I am implementing a serial port protocol in a Linux based library. We build boost ourselves (1.86.0) for inclusion in thrift so I am trying to use as much as I can just from the Boost libraries to gain some experience with them. My serial port driver is using the serial_port class from Boost ASIO. It's super cool and working well. To include Boost ASIO in my CMake target, all I have done is this: cmake_minimum_required(VERSION 3.30) set(CMAKE_CXX_STANDARD 20) set(BOOST_ROOT "${PROJECT_SOURCE_DIR}/../dataman_service/boost-install-x86_64-Debug/") find_package(Boost CONFIG) #This is an alternate use? #find_package(Boost NO_MODULE) add_library(L2PUtility             L2Packet.cpp             L1Transport.cpp             crc1021.cpp) target_include_directories(L2PUtility PUBLIC ${CMAKE_SOURCE_DIR} ${BOOST_ROOT}/include) Note there is no target_link_libraries, but ASIO works. I thought that was because it's an HPP/Header only implementation? Since I need to add some threading to the project, I thought I would use the boost_thread library. Examples online show the inclusion of boost/thread.hpp, so I assumed it is another header only implementation and no link library is needed but I am getting a linking error: [2/4] Linking CXX executable L2PSecondary FAILED: L2PSecondary : && /usr/bin/c++ -g CMakeFiles/L2PSecondary.dir/main.cpp.o -o L2PSecondary libL2PUtility.a && : /usr/bin/ld: libL2PUtility.a(L1Transport.cpp.o): warning: relocation against `_ZTVN5boost6detail16thread_data_baseE' in read-only section `.text._ZN5boost6detail16thread_data_baseC2Ev[_ZN5boost6detail16thread_data_baseC5Ev]' /usr/bin/ld: libL2PUtility.a(L1Transport.cpp.o): in function `L1Transport::start_detached()': /home/rhaley/tuleap/BoostAsioL2p/L1Transport.cpp:440:(.text+0x1b32): undefined reference to `boost::thread::detach()' /usr/bin/ld: libL2PUtility.a(L1Transport.cpp.o): in function `boost::detail::thread_data_base::thread_data_base()': /home/rhaley/tuleap/BoostAsioL2p/../stroma_dataman_service/boost-install-x86_64-Debug/include/boost/thread/pthread/thread_data.hpp:162:(.text._ZN5boost6detail16thread_data_baseC2Ev[_ZN5boost6detail16thread_data_baseC5Ev]+0x24): undefined reference to `vtable for boost::detail::thread_data_base' /usr/bin/ld: libL2PUtility.a(L1Transport.cpp.o): in function `boost::thread::start_thread()': /home/rhaley/tuleap/BoostAsioL2p/../stroma_dataman_service/boost-install-x86_64-Debug/include/boost/thread/detail/thread.hpp:182:(.text._ZN5boost6thread12start_threadEv[_ZN5boost6thread12start_threadEv]+0x28): undefined reference to `boost::thread::start_thread_noexcept()' /usr/bin/ld: libL2PUtility.a(L1Transport.cpp.o): in function `boost::thread::~thread()': /home/rhaley/tuleap/BoostAsioL2p/../stroma_dataman_service/boost-install-x86_64-Debug/include/boost/thread/detail/thread.hpp:257:(.text._ZN5boost6threadD2Ev[_ZN5boost6threadD5Ev]+0x18): undefined reference to `boost::thread::detach()' /usr/bin/ld: libL2PUtility.a(L1Transport.cpp.o): in function `boost::thread::get_id() const': /home/rhaley/tuleap/BoostAsioL2p/../stroma_dataman_service/boost-install-x86_64-Debug/include/boost/thread/detail/thread.hpp:738:(.text._ZNK5boost6thread6get_idEv[_ZNK5boost6thread6get_idEv]+0x27): undefined reference to `boost::thread::native_handle()' /usr/bin/ld: libL2PUtility.a(L1Transport.cpp.o): in function `boost::thread::join()': /home/rhaley/tuleap/BoostAsioL2p/../stroma_dataman_service/boost-install-x86_64-Debug/include/boost/thread/detail/thread.hpp:762:(.text._ZN5boost6thread4joinEv[_ZN5boost6thread4joinEv]+0x90): undefined reference to `boost::thread::join_noexcept()' /usr/bin/ld: libL2PUtility.a(L1Transport.cpp.o): in function `boost::detail::thread_data<boost::_bi::bind_t<void, boost::_mfi::mf<void (L1Transport::*)(), void, L1Transport>, boost::_bi::list<boost::_bi::value<L1Transport*> > > >::~thread_data()': /home/rhaley/tuleap/BoostAsioL2p/../stroma_dataman_service/boost-install-x86_64-Debug/include/boost/thread/detail/thread.hpp:94:(.text._ZN5boost6detail11thread_dataINS_3_bi6bind_tIvNS_4_mfi2mfIM11L1TransportFvvEvS6_JEEENS2_4listIJNS2_5valueIPS6_EEEEEEEED2Ev[_ZN5boost6detail11thread_dataINS_3_bi6bind_tIvNS_4_mfi2mfIM11L1TransportFvvEvS6_JEEENS2_4listIJNS2_5valueIPS6_EEEEEEEED5Ev]+0x26): undefined reference to `boost::detail::thread_data_base::~thread_data_base()' /usr/bin/ld: libL2PUtility.a(L1Transport.cpp.o):(.data.rel.ro._ZTIN5boost6detail11thread_dataINS_3_bi6bind_tIvNS_4_mfi2mfIM11L1TransportFvvEvS6_JEEENS2_4listIJNS2_5valueIPS6_EEEEEEEEE[_ZTIN5boost6detail11thread_dataINS_3_bi6bind_tIvNS_4_mfi2mfIM11L1TransportFvvEvS6_JEEENS2_4listIJNS2_5valueIPS6_EEEEEEEEE]+0x10): undefined reference to `typeinfo for boost::detail::thread_data_base' /usr/bin/ld: warning: creating DT_TEXTREL in a PIE collect2: error: ld returned 1 exit status I tried adding a target_link_library: target_link_libraries(L2PUtility PUBLIC boost_thread) To no avail. I now get a missing library in the EXECUTABLE, not in the library that actually includes boost_thread! Does that mean it found it for the L2Utility library? (so confused...) Here is my executable target: add_executable(L2PSecondary main.cpp) target_include_directories(L2PSecondary PRIVATE ${CMAKE_SOURCE_DIR} ${BOOST_ROOT}/include) target_link_libraries(L2PSecondary PRIVATE L2PUtility) And here is the linking error: [1/2] Linking CXX executable L2PSecondary FAILED: L2PSecondary : && /usr/bin/c++ -g CMakeFiles/L2PSecondary.dir/main.cpp.o -o L2PSecondary libL2PUtility.a -lboost_thread && : /usr/bin/ld: cannot find -lboost_thread: No such file or directory collect2: error: ld returned 1 exit status ninja: build stopped: subcommand failed. I confirmed that my boost installation has the library libboost_tread.a. rhaley@linuxdev2:~/tuleap/dataman_service/boost-install-x86_64-Debug$ find . -iname "*thread*.a" ./lib/libboost_thread.a Adding link libraries to the executable targets doesn't fix anything. Can anyone point out what I am doing wrong? Thanks in advance, Russ