Undefined reference to clock_gettime, gcc 4.6 & cmake

Question

I'm having a link error under cmake that I don't have when compiling on a system with an older version of gcc.

The specific error is "undefined reference to clock_gettime" but -lrt is appearing on the command line.

My gcc version:

gcc (Ubuntu/Linaro 4.6.1-9ubuntu3) 4.6.1
Copyright (C) 2011 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

cmake version 2.8.5

I am including the required "-lrt" through target_link_libraries in my CMakeLists.txt file. I can see it appear in the compiler line with make VERBOSE=1

I've read that gcc 4.6 is picky about the position of link libraries on the command line.

How can I fix this for CMake?

EDIT: Link line

Linking CXX executable ../bin/obbsd
cd /home/matt/Desktop/Matt/OBBS/Build/server && /usr/bin/cmake -E cmake_link_script \
     CMakeFiles/obbsd.dir/link.txt --verbose=1   
/usr/bin/c++   -g    CMakeFiles/obbsd.dir/Block.cpp.o \
     CMakeFiles/obbsd.dir/BlockFileCache.cpp.o \
      CMakeFiles/obbsd.dir/BlockFileStore.cpp.o \
      CMakeFiles/obbsd.dir/BlockMemoryCache.cpp.o \
      CMakeFiles/obbsd.dir/BlockStore.cpp.o CMakeFiles/obbsd.dir/Config.cpp.o \
      CMakeFiles/obbsd.dir/DeleteBlockSession.cpp.o \
      CMakeFiles/obbsd.dir/mConfigFile.cpp.o \
      CMakeFiles/obbsd.dir/mNetworkPacketReader.cpp.o \
      CMakeFiles/obbsd.dir/mNetworkPacketWriter.cpp.o \
      CMakeFiles/obbsd.dir/obbsd.cpp.o \
      CMakeFiles/obbsd.dir/ReadBlockSession.cpp.o CMakeFiles/obbsd.dir/Server.cpp.o \
      CMakeFiles/obbsd.dir/Session.cpp.o CMakeFiles/obbsd.dir/Utility.cpp.o \
      CMakeFiles/obbsd.dir/WriteBlockSession.cpp.o  -o ../bin/obbsd -rdynamic \
      -lpthread -lrt ../lib/libLibUtil.a 
../lib/libLibUtil.a(mTimer.cpp.o): In function `mTimer::GetTick()':
/home/matt/Desktop/Matt/OBBS/LibUtil/src/mTimer.cpp:108: undefined reference to
     `clock_gettime'

Why is ../lib/libLibUtil.a appearing after -lrt when LibUtil (what would be libLibUtil.a) is before rt?

CMakeLists.txt includes...

...
add_executable(obbsd ${SERVER_SOURCE_FILES})
find_package(Threads REQUIRED)
target_link_libraries(obbsd ${CMAKE_THREAD_LIBS_INIT} LibUtil rt)

Answer 1

You should ensure that -lpthread -lrt appear after your libraries like ../lib/libLibUtil.a