How to start mongo v4.2.0 : <p>I have successfully installed Mongo v4.2.0.</p>

<pre><code>mongo --version
MongoDB shell version v4.2.0
git version: a4b751dcf51dd249c5865812b390cfd1c0129c30
OpenSSL version: OpenSSL 1.1.1c  28 May 2019
allocator: tcmalloc
modules: none
build environment:
    distmod: ubuntu1804
    distarch: x86_64
    target_arch: x86_64
</code></pre>

<p>But when i start mongo, it is showing error.  Kindly help me out. I am using ubuntu 18.04.
mongo</p>

<pre><code>MongoDB shell version v4.2.0
connecting to: mongodb://127.0.0.1:27017/?compressors=disabled&amp;gssapiServiceName=mongodb
2019-10-07T11:35:13.915+0530 E  QUERY    [js] Error: couldn't connect to server 127.0.0.1:27017, connection attempt failed: SocketException: Error connecting to 127.0.0.1:27017 :: caused by :: Connection refused :
connect@src/mongo/shell/mongo.js:341:17
@(connect):2:6
2019-10-07T11:35:13.916+0530 F  -        [main] exception: connect failed
2019-10-07T11:35:13.916+0530 E  -        [main] exiting with code 1
</code></pre>
