在centos6.5 64bit上用pip安装matplotlib时候报错：

* The following required packages can not be built:
                        * freetype, pngerror: Setup script exited with 1

这是因为pip不能安装操作系统的依赖库导致的，需要用yum手动安装：

$ yum -y install freetype-devel libpng-devel

如果不知道这些库需要安装的包名，可以查一下：

$ yum search freetype | grep devel
    freetype-devel.i686 : FreeType development libraries and header files
    freetype-devel.x86_64 : FreeType development libraries and header files
$ yum search png | grep devel
    libpng-devel.i686 : Development tools for programs to manipulate PNG image
    libpng-devel.x86_64 : Development tools for programs to manipulate PNG image