title: /usr/bin/ld: cannot find -lpthreads
body: <p>I'm compiling NVIDIA Caffe tool on a Fedora 22 and I having problems to find <code>lpthread</code> library:</p>
  
  <pre><code>Determining if the pthread_create exist failed with the following output:
  Change Dir: /home/user1/Sources/caffe/build/CMakeFiles/CMakeTmp
  
  Run Build Command:"/usr/bin/gmake" "cmTC_d410e/fast"
  /usr/bin/gmake -f CMakeFiles/cmTC_d410e.dir/build.make CMakeFiles/cmTC_d410e.dir/build
  gmake[1]: Entering directory '/home/user1/Sources/caffe/build/CMakeFiles/CMakeTmp'
  Building C object CMakeFiles/cmTC_d410e.dir/CheckSymbolExists.c.o
  /usr/bin/cc    -o CMakeFiles/cmTC_d410e.dir/CheckSymbolExists.c.o   -c /home/user1/Sources/caffe/build/CMakeFiles/CMakeTmp/CheckSymbolExists.c
  Linking C executable cmTC_d410e
  /usr/bin/cmake -E cmake_link_script CMakeFiles/cmTC_d410e.dir/link.txt --verbose=1
  /usr/bin/cc       CMakeFiles/cmTC_d410e.dir/CheckSymbolExists.c.o  -o cmTC_d410e -rdynamic 
  CMakeFiles/cmTC_d410e.dir/CheckSymbolExists.c.o: En la función `main':
  CheckSymbolExists.c:(.text+0x16): referencia a `pthread_create' sin definir
  collect2: error: ld devolvió el estado de salida 1
  CMakeFiles/cmTC_d410e.dir/build.make:97: recipe for target 'cmTC_d410e' failed
  gmake[1]: Leaving directory '/home/user1/Sources/caffe/build/CMakeFiles/CMakeTmp'
  Makefile:126: recipe for target 'cmTC_d410e/fast' failed
  gmake[1]: *** [cmTC_d410e] Error 1
  gmake: *** [cmTC_d410e/fast] Error 2
  
  File /home/user1/Sources/caffe/build/CMakeFiles/CMakeTmp/CheckSymbolExists.c:
  /* */
  #include &lt;pthread.h&gt;
  
  int main(int argc, char** argv)
  {
    (void)argv;
  #ifndef pthread_create
    return ((int*)(&amp;pthread_create))[argc];
  #else
    (void)argc;
    return 0;
  #endif
  }
  
  Determining if the function pthread_create exists in the pthreads failed with the following output:
  Change Dir: /home/user1/Sources/caffe/build/CMakeFiles/CMakeTmp
  
  Run Build Command:"/usr/bin/gmake" "cmTC_e693b/fast"
  /usr/bin/gmake -f CMakeFiles/cmTC_e693b.dir/build.make CMakeFiles/cmTC_e693b.dir/build
  gmake[1]: Entering directory '/home/user1/Sources/caffe/build/CMakeFiles/CMakeTmp'
  Building C object CMakeFiles/cmTC_e693b.dir/CheckFunctionExists.c.o
  /usr/bin/cc   -DCHECK_FUNCTION_EXISTS=pthread_create   -o CMakeFiles/cmTC_e693b.dir/CheckFunctionExists.c.o   -c /usr/share/cmake/Modules/CheckFunctionExists.c
  Linking C executable cmTC_e693b
  /usr/bin/cmake -E cmake_link_script CMakeFiles/cmTC_e693b.dir/link.txt --verbose=1
  /usr/bin/cc   -DCHECK_FUNCTION_EXISTS=pthread_create    CMakeFiles/cmTC_e693b.dir/CheckFunctionExists.c.o  -o cmTC_e693b -rdynamic -lpthreads 
  /usr/bin/ld: cannot find -lpthreads
  collect2: error: ld outputs 1
  CMakeFiles/cmTC_e693b.dir/build.make:97: recipe for target 'cmTC_e693b' failed
  gmake[1]: Leaving directory '/home/user1/Sources/caffe/build/CMakeFiles/CMakeTmp'
  Makefile:126: recipe for target 'cmTC_e693b/fast' failed
  gmake[1]: *** [cmTC_e693b] Error 1
  gmake: *** [cmTC_e693b/fast] Error 2
  </code></pre>
  
  <p>It seems that it doesn't find pthreads lib (<code>/usr/bin/ld: cannot find -lpthreads</code>), but running command <code>find / name "*pthread*"</code> it outputs this:</p>
  
  <pre><code>/usr/lib64/libpthread.so
  /usr/lib64/libpthread.a
  /usr/lib64/libpthread_nonshared.a
  /usr/lib64/libpthread-2.21.so
  /usr/lib64/libpthread.so.0
  </code></pre>
  
  <p>But there is something strange with this, becaue CMakeOutut.log has this:
  Determining if the function pthread_create exists in the pthread passed with the following output:</p>
  
  <pre><code>Change Dir: /home/user1/Sources/caffe/build/CMakeFiles/CMakeTmp
  
  Run Build Command:"/usr/bin/gmake" "cmTC_705ba/fast"
  /usr/bin/gmake -f CMakeFiles/cmTC_705ba.dir/build.make CMakeFiles/cmTC_705ba.dir/build
  gmake[1]: Entering directory '/home/user1/Sources/caffe/build/CMakeFiles/CMakeTmp'
  Building C object CMakeFiles/cmTC_705ba.dir/CheckFunctionExists.c.o
  /usr/bin/cc   -DCHECK_FUNCTION_EXISTS=pthread_create   -o CMakeFiles/cmTC_705ba.dir/CheckFunctionExists.c.o   -c /usr/share/cmake/Modules/CheckFunctionExists.c
  Linking C executable cmTC_705ba
  /usr/bin/cmake -E cmake_link_script CMakeFiles/cmTC_705ba.dir/link.txt --verbose=1
  /usr/bin/cc   -DCHECK_FUNCTION_EXISTS=pthread_create    CMakeFiles/cmTC_705ba.dir/CheckFunctionExists.c.o  -o cmTC_705ba -rdynamic -lpthread 
  gmake[1]: Leaving directory '/home/user1/Sources/caffe/build/CMakeFiles/CMakeTmp'
  </code></pre>
  
  <p>It has this line using <code>lpthread</code>:</p>
  
  <pre><code>/usr/bin/cc   -DCHECK_FUNCTION_EXISTS=pthread_create    CMakeFiles/cmTC_705ba.dir/CheckFunctionExists.c.o  -o cmTC_705ba -rdynamic -lpthread
  </code></pre>
  
  <p>And this is CMakeList.txt:</p>
  
  <pre><code>cmake_minimum_required(VERSION 2.8.7)
  
  # ---[ Caffe project
  project(Caffe C CXX)
  
  # ---[ Caffe version
  set(CAFFE_TARGET_VERSION "0.14.5")
  set(CAFFE_TARGET_SOVERSION "0.14")
  add_definitions(-DCAFFE_VERSION=${CAFFE_TARGET_VERSION})
  
  # ---[ Using cmake scripts and modules
  list(APPEND CMAKE_MODULE_PATH ${PROJECT_SOURCE_DIR}/cmake/Modules)
  
  include(ExternalProject)
  
  include(cmake/Utils.cmake)
  include(cmake/Targets.cmake)
  include(cmake/Misc.cmake)
  include(cmake/Summary.cmake)
  include(cmake/ConfigGen.cmake)
  
  # ---[ Options
  caffe_option(CPU_ONLY  "Build Caffe without CUDA support" OFF) # TODO: rename to USE_CUDA
  caffe_option(USE_CUDNN "Build Caffe with cuDNN library support" ON IF NOT CPU_ONLY)
  caffe_option(BUILD_SHARED_LIBS "Build shared libraries" ON)
  caffe_option(BUILD_python "Build Python wrapper" ON)
  set(python_version "2" CACHE STRING "Specify which Python version to use")
  caffe_option(BUILD_matlab "Build Matlab wrapper" OFF IF UNIX OR APPLE)
  caffe_option(BUILD_docs   "Build documentation" ON IF UNIX OR APPLE)
  caffe_option(BUILD_python_layer "Build the Caffe Python layer" ON)
  caffe_option(USE_OPENCV "Build with OpenCV support" ON)
  caffe_option(USE_LEVELDB "Build with levelDB" ON)
  caffe_option(USE_LMDB "Build with lmdb" ON)
  caffe_option(ALLOW_LMDB_NOLOCK "Allow MDB_NOLOCK when reading LMDB files (only if necessary)" OFF)
  
  # ---[ Dependencies
  include(cmake/Dependencies.cmake)
  
  # ---[ Flags
  if(UNIX OR APPLE)
    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fPIC -Wall")
  endif()
  
  if(USE_libstdcpp)
    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -stdlib=libstdc++")
    message("-- Warning: forcing libstdc++ (controlled by USE_libstdcpp option in cmake)")
  endif()
  
  add_definitions(-DGTEST_USE_OWN_TR1_TUPLE)
  
  # ---[ Warnings
  caffe_warnings_disable(CMAKE_CXX_FLAGS -Wno-sign-compare -Wno-uninitialized)
  
  # ---[ Config generation
  configure_file(cmake/Templates/caffe_config.h.in "${PROJECT_BINARY_DIR}/caffe_config.h")
  
  # ---[ Includes
  set(Caffe_INCLUDE_DIR ${PROJECT_SOURCE_DIR}/include)
  set(THIRDPARTY_DIR ${PROJECT_SOURCE_DIR}/3rdparty)
  include_directories(${Caffe_INCLUDE_DIR} ${PROJECT_BINARY_DIR} ${THIRDPARTY_DIR})
  include_directories(BEFORE src) # This is needed for gtest.
  
  # ---[ Subdirectories
  add_subdirectory(src/gtest)
  add_subdirectory(src/caffe)
  add_subdirectory(tools)
  add_subdirectory(examples)
  add_subdirectory(python)
  add_subdirectory(matlab)
  add_subdirectory(docs)
  
  # ---[ Linter target
  add_custom_target(lint COMMAND ${CMAKE_COMMAND} -P ${PROJECT_SOURCE_DIR}/cmake/lint.cmake)
  
  # ---[ pytest target
  add_custom_target(pytest COMMAND python${python_version} -m unittest discover -s caffe/test WORKING_DIRECTORY ${PROJECT_SOURCE_DIR}/python )
  add_dependencies(pytest pycaffe)
  
  # ---[ Configuration summary
  caffe_print_configuration_summary()
  
  # ---[ Export configs generation
  caffe_generate_export_configs()
  </code></pre>
  
  <p>What do I have to install? Does libphreads exist or I have to use libphread?</p>