I installed boost-all-dev using apt-get on Ubuntu. I am trying to compile this example program of sync_client.cpp http://www.boost.org/doc/libs/1_45_0/doc/html/boost_asio/example/http/client... I get this error .. $ sudo g++ sync_client.cpp -I usr/local/include/boost -L /usr/local/lib /tmp/ccaVkCWp.o: In function `__static_initialization_and_destruction_0(int, int)': sync_client.cpp:(.text+0xd61): undefined reference to `boost::system::generic_category()' sync_client.cpp:(.text+0xd6d): undefined reference to `boost::system::generic_category()' sync_client.cpp:(.text+0xd79): undefined reference to `boost::system::system_category()' /tmp/ccaVkCWp.o: In function `boost::system::error_code::error_code()': sync_client.cpp:(.text._ZN5boost6system10error_codeC2Ev[_ZN5boost6system10error_codeC5Ev]+0x17): undefined reference to `boost::system::system_category()' /tmp/ccaVkCWp.o: In function `boost::asio::error::get_system_category()': sync_client.cpp:(.text._ZN5boost4asio5error19get_system_categoryEv[boost::asio::error::get_system_category()]+0x5): undefined reference to `boost::system::system_category()' /tmp/ccaVkCWp.o: In function `boost::asio::detail::posix_tss_ptr_create(unsigned int&)': sync_client.cpp:(.text._ZN5boost4asio6detail20posix_tss_ptr_createERj[boost::asio::detail::posix_tss_ptr_create(unsigned int&)]+0x19): undefined reference to `pthread_key_create' /tmp/ccaVkCWp.o: In function `boost::asio::detail::posix_thread::~posix_thread()': sync_client.cpp:(.text._ZN5boost4asio6detail12posix_threadD2Ev[_ZN5boost4asio6detail12posix_threadD5Ev]+0x26): undefined reference to `pthread_detach' /tmp/ccaVkCWp.o: In function `boost::asio::detail::posix_thread::join()': sync_client.cpp:(.text._ZN5boost4asio6detail12posix_thread4joinEv[boost::asio::detail::posix_thread::join()]+0x2b): undefined reference to `pthread_join' /tmp/ccaVkCWp.o: In function `boost::asio::detail::posix_tss_ptr<boost::asio::detail::call_stack<boost::asio::detail::task_io_service>::context>::~posix_tss_ptr()': sync_client.cpp:(.text._ZN5boost4asio6detail13posix_tss_ptrINS1_10call_stackINS1_15task_io_serviceEE7contextEED2Ev[_ZN5boost4asio6detail13posix_tss_ptrINS1_10call_stackINS1_15task_io_serviceEE7contextEED5Ev]+0x15): undefined reference to `pthread_key_delete' /tmp/ccaVkCWp.o: In function `boost::asio::detail::posix_tss_ptr<boost::asio::detail::call_stack<boost::asio::detail::strand_service::strand_impl>::context>::~posix_tss_ptr()': sync_client.cpp:(.text._ZN5boost4asio6detail13posix_tss_ptrINS1_10call_stackINS1_14strand_service11strand_implEE7contextEED2Ev[_ZN5boost4asio6detail13posix_tss_ptrINS1_10call_stackINS1_14strand_service11strand_implEE7contextEED5Ev]+0x15): undefined reference to `pthread_key_delete' collect2: ld returned 1 exit status How can I solve this error?