MongoDB not starting in Ubuntu 16.04 after turning on Authorization - mongodb

Question

I was trying to add password to my mongodb but after changing authorization to enabled but mongodb doesn't start after that while trying with sudo service mongod start. I followed this tutorial to do the same. I even turned my firewall off. The result of sudo service mongod status is as follows:
● mongod.service - High-performance, schema-free document-oriented database
Loaded: loaded (/lib/systemd/system/mongod.service; disabled; vendor preset: enabled)
Active: failed (Result: exit-code) since Wed 2018-10-03 16:56:31 IST; 1s ago
Docs: https://docs.mongodb.org/manual
Process: 17641 ExecStart=/usr/bin/mongod --config /etc/mongod.conf (code=exited, status=2) Main PID: 17641 (code=exited, status=2)
Oct 03 16:56:31 dev-76 systemd[1]: Started High-performance, schema-free document-oriented database.
Oct 03 16:56:31 dev-76 systemd[1]: mongod.service: Main process exited, code=exited, status=2/INVALIDARGUMENT
Oct 03 16:56:31 dev-76 systemd[1]: mongod.service: Unit entered failed state.
Oct 03 16:56:31 dev-76 systemd[1]: mongod.service: Failed with result 'exit-code'.
ANd if i try to login then i get the following:
sam#dev-76:/etc$ mongo -u admin -p mongoadmin admin
MongoDB shell version v3.6.8
connecting to: mongodb://127.0.0.1:27017/admin
2018-10-03T17:06:09.418+0530 W NETWORK [thread1] Failed to connect to 127.0.0.1:27017, in(checking socket for error after poll), reason: Connection refused
2018-10-03T17:06:09.418+0530 E QUERY [thread1] Error: couldn't connect to server 127.0.0.1:27017, connection attempt failed :
connect#src/mongo/shell/mongo.js:251:13
#(connect):1:6
exception: connect failed
UPDATE
My mongod.conf is as follows:
# mongod.conf
# for documentation of all options, see:
# http://docs.mongodb.org/manual/reference/configuration-options/
# Where and how to store data.
storage:
dbPath: /var/lib/mongodb
journal:
enabled: true
# engine:
# mmapv1:
# wiredTiger:
# where to write logging data.
systemLog:
destination: file
logAppend: true
path: /var/log/mongodb/mongod.log
# network interfaces
net:
port: 27017
bindIp: 127.0.0.1
# how the process runs
processManagement:
timeZoneInfo: /usr/share/zoneinfo
#security:
authorization: enabled
#operationProfiling:
#replication:
#sharding:
## Enterprise-Only Options:
#auditLog:
#snmp:

Answer 1

I forgot to uncomment the line
#security:
authorization: enabled
After uncommenting the line it works,
security:
authorization: enabled
Also to use mongodb for persistence from my application i changed my uri like below,
mongodb://username:password#localhost:27017/mycollection?authSource=admin&authMechanism=SCRAM-SHA-1