命令LD_DEBUG
LD_DEBUG 是 glibc 中的 loader 设置的一个环境变量,可以方便的看到 loader 的加载过程。glibc是gnu 发布的libc库 ，即c运行库 。glibc是linux系统 中最底层的api ，几乎其它任何运行库都会依赖于glibc。
# LD_DEBUG=help ls
Valid options for the LD_DEBUG environment variable are:
libs display library search paths
reloc display relocation processing
files display progress for input file
symbols display symbol table processing
bindings display information about symbol binding
versions display version dependencies
all all previous options combined
statistics display relocation statistics
unused determined unused DSOs
help display this help message and exit
To direct the debugging output into a file instead of standard output
a filename can be specified using the LD_DEBUG_OUTPUT environment variable.
以memcached安装过程中遇到的问题为例：
命令： /usr/local/bin/memcached -p 11211 -m 64m -vv
错误：/usr/local/bin/memcached: error while loading shared libraries: libevent-2.0.so.5: cannot open shared object file: No such file or directory
使用LD_DEBUG显示库寻找信息
LD_DEBUG=libs /usr/local/bin/memcached -vv
15759: find library=libevent-2.0.so.5 [0]; searching
15759: search cache=/etc/ld.so.cache
15759: search path=/lib64/tls/x86_64:/lib64/tls:/lib64/x86_64:/lib64:/usr/lib64/tls/x86_64:/usr/lib64/tls:/usr/lib64/x86_64:/usr/lib64 (system search path)
15759: trying file=/lib64/tls/x86_64/libevent-2.0.so.5
15759: trying file=/lib64/tls/libevent-2.0.so.5
15759: trying file=/lib64/x86_64/libevent-2.0.so.5
15759: trying file=/lib64/libevent-2.0.so.5
15759: trying file=/usr/lib64/tls/x86_64/libevent-2.0.so.5
15759: trying file=/usr/lib64/tls/libevent-2.0.so.5
15759: trying file=/usr/lib64/x86_64/libevent-2.0.so.5
15759: trying file=/usr/lib64/libevent-2.0.so.5
最后一行可以看出，memcached去/usr/lib64目录下寻找libevent-2.0.so.5，先定位libevent-2.0.so.5实际目录
命令：whereis libevent-2.0.so.5
结果：libevent-2.0.so: /usr/lib/libevent-2.0.so.5
这时候需要将做一个软连接
命令：ln -s /usr/lib/libevent-2.0.so.5 /usr/lib64/libevent-2.0.so.5
如果要删除软连接
命令： rm -rf filename
到此问题解决