nginx中的lua执行错误，哪位朋友见过？

    location /test_lua {

      default_type 'text/plain';

      content_by_lua 'ngx.say("hello, lua")';

    }

    能执行并在页面中输入hello,lua

    但是在日志中会提示如下：

    2019/03/13 12:38:01 [alert] 13305#0: detected a LuaJIT version which is not OpenResty's; many optimizations will be disabled and performance will be compromised (see https://github.com/openresty/luajit2 for OpenResty's LuaJIT or, even better, consider using the OpenResty releases from https://openresty.org/en/download.html)

       

    执行这部分时

    access_by_lua_block {

    local command = "gm convert /home/img/test_o.jpg -thumbnail 300x425 /home/img/test_lua.jpg";

    os.execute(command);

    }

    则日志中出现以下错误，并且根本不执行gm这行，gm这行单独在linux命令行下是能执行成功的

2019/03/13 12:38:08 [alert] 13305#0: detected a LuaJIT version which is not OpenResty's; many optimizations will be disabled and performance will be compromised (see https://github.com/openresty/luajit2 for OpenResty's LuaJIT or, even better, consider using the OpenResty releases from https://openresty.org/en/download.html)

sh: gm: command not found