给 tengine 加 waf 出错

用./nginx -t 检查配置时，提示一下信息
nginx: the configuration file /usr/local/src/tengine/conf/nginx.conf syntax is ok
nginx: [error] init_by_lua_file error: /usr/local/src/tengine/waf/init.lua:16: module 'cjson' not found:
no field package.preload['cjson']
no file '/usr/local/src/luajit/cjson.lua'
no file './cjson.so'
no file '/usr/lib64/lua/5.1/cjson.so'
no file '/usr/lib64/lua/5.1/loadall.so'
stack traceback:
[C]: in function 'require'
/usr/local/src/tengine/waf/init.lua:16: in main chunk
nginx: configuration file /usr/local/src/tengine/conf/nginx.conf test failed
已经把 lua-cjson 编译安装上了，怎么还回报错，不是太明白