Question

For example, I want to know the database directory that is used by mongodb to run what it is?

The documentation said that the default data is in /data/db however, there is no such directory

I wonder if there is a mongodb command to get that simple info. I look through the web and could not find it.

Answer 1

You can see the Configuration Parameters used with:

> db.serverCmdLineOpts()

For example:

{
    "argv" : [
        "mongod",
        "--dbpath",
        "/usr/local/db"
    ],
    "parsed" : {
        "dbpath" : "/usr/local/db"
    },
    "ok" : 1
}

Any parameters not specifically listed will be using their default values.