how to get mongodb's loaded configuration file path

Question

I want to get programmatically the path of configuration file which mongodb loaded. Is it possible to get this by running a command or something?

Answer 1

In mongo shell you can run a getCmdLineOpts command on admin database which will give you the command line options used to start the mongod or mongos:

db.runCommand({getCmdLineOpts:1})
{
    "argv" : [
        "/usr/bin/mongod",
        "--config",
        "/etc/mongodb.conf"
    ],
    "parsed" : {
        "config" : "/etc/mongodb.conf",
        "net" : {
            "port" : 27017
        },
        "storage" : {
            "dbPath" : "/var/lib/mongodb"
        },
        "systemLog" : {
            "destination" : "file",
            "logAppend" : true,
            "path" : "/var/log/mongodb/mongodb.log"
        }
    },
    "ok" : 1
}

Answer 2

On ubuntu 16 if you run systemctl status mongodb It will show you the following. At the bottom, you can see --config /etc/mongod.conf, which looks like is the location of my loaded config file

   Loaded: loaded (/etc/systemd/system/mongodb.service; enabled; vendor preset: enabled)
   Active: active (running) since Tue 2016-08-09 14:33:03 UTC; 3s ago
 Main PID: 6674 (mongod)
    Tasks: 21
   Memory: 40.1M
      CPU: 230ms
   CGroup: /system.slice/mongodb.service
           └─6674 /usr/bin/mongod --quiet --config /etc/mongod.conf

Answer 3

This is just to complement a bit the other answers. Another way, in Linux is to first run ps and check whether there is a configuration file passed-in.

$ ps axww | grep mongod | grep -v grep
14886 ?        Sl     0:00 /usr/bin/mongod -f /etc/mongod.conf

The case above is for mongod running in Fedora 32, but it would work for any Linux where mongo was started by systemd, upstart or whichever process manager.

The config file may NOT be mentioned in the command line arguments, like it happens to be the case when you start manually mongod from the command line or in the mongo docker container image:

$ docker run --name some-mongo -d mongo:latest
$ docker exec -t some-mongo bash -c "ps axww | grep mongod | grep -v grep"
  1 ?        Ssl    0:00 mongod --bind_ip_all

In these cases mongo starts with default values.

For related information, see this SO question or the reference mongo documentation.