LIBRARY_PATH 和 LD_LIBRARY_PATH 的关系

LIBRARY_PATH
The value of LIBRARY_PATH is a colon-separated list of directories, much like PATH.
When configured as a native compiler, GCC tries the directories thus specified when searching for special linker files, if it can't find them using GCC_EXEC_PREFIX.
Linking using GCC also uses these directories when searching for ordinary libraries for the -l option (but directories specified with -L come first). 

LD_LIBRARY_PATH
A colon-separated list of directories in which to search for
ELF libraries at execution-time.  Similar to the PATH
environment variable.  Ignored in set-user-ID and set-group-ID
programs.

LIBRARY_PATH is used by gcc before compilation to search for directories containing libraries that need to be linked to your program.

LD_LIBRARY_PATH is used by your program to search for directories containing the libraries after it has been successfully compiled and linked.

Linux gcc编译链接时的动态库搜索路径

GCC编译、链接生成可执行文件时，动态库的搜索路径顺序如下（注意不会递归性地在其子目录下搜索）：

1、gcc编译、链接命令中的-L选项；
2、gcc的环境变量的LIBRARY_PATH（多个路径用冒号分割）；
3、gcc默认动态库目录：/lib:/usr/lib:usr/lib64:/usr/local/lib。

执行二进制文件时的动态库搜索路径

链接生成二进制可执行文件后，在运行程序加载动态库文件时，搜索的路径顺序如下：

1、编译目标代码时指定的动态库搜索路径：用选项-Wl,rpath和include指定的动态库的搜索路径，比如gcc -Wl,-rpath,include -L. -ldltest hello.c，在执行文件时会搜索路径`./include`；
2、环境变量LD_LIBRARY_PATH（多个路径用冒号分割）；
3、在 /etc/ld.so.conf.d/ 目录下的配置文件指定的动态库绝对路径（通过ldconfig生效，一般是非root用户时使用）；
4、gcc默认动态库目录：/lib:/usr/lib:usr/lib64:/usr/local/lib等。

其中，Linux GCC默认的动态库搜索路径可以通过 ld --verbose 命令查看：

[root@typecodes tcpmsg]# ld --verbose
	............
	SEARCH_DIR("/usr/x86_64-redhat-linux/lib64");
	SEARCH_DIR("/usr/local/lib64");
	SEARCH_DIR("/lib64");
	SEARCH_DIR("/usr/lib64");			   ##### 64位系统
	SEARCH_DIR("/usr/x86_64-redhat-linux/lib");
	SEARCH_DIR("/usr/local/lib");
	SEARCH_DIR("/lib");
	SEARCH_DIR("/usr/lib");