Mongodb not starting as normal user - mongodb

Question

My MongoDB server is not starting on command mongod
Typing sudo service mongodb status yeilds
mongodb.service - High-performance, schema-free document-oriented database
Loaded: loaded (/etc/systemd/system/mongodb.service; enabled; vendor preset: enabled)
Active: failed (Result: exit-code) since Tue 2017-11-28 20:08:25 IST; 2s ago
Process: ExecStart=/usr/bin/mongod --config /etc/mongod.conf (code=exited, status=1/FAILURE)
Main PID: 29675 (code=exited, status=1/FAILURE)
System service:
#/etc/systemd/system/mongodb.service
[Unit]
Description=High-performance, schema-free document-oriented database
After=network.target
[Service]
User=mongodb
Group=mongodb
ExecStart=/usr/bin/mongod --config /etc/mongod.conf
[Install]
WantedBy=multi-user.target
mongod conf:
#/etc/mongod.conf
storage:
dbPath: /var/lib/mongodb
journal:
enabled: true
systemLog:
destination: file
logAppend: true
path: /var/log/mongodb/mongod.log
However if i am running sudo -u mongodb mongod --config /etc/mongod.conf it runs.
Also if I run sudo mongod the server tries to start but the storage path is /data/db/ which I haven't created.
mongod --config /etc/mongod.conf gives the below error
[main] Failed global initialization: FileNotOpen: Failed to open "/var/log/mongodb/mongod.log"
I had run chown -R mongodb:mongodb /var/lib/mongodb
Permissions:
-rw-r--r-- 1 mongodb mongodb 4096 Nov 28 20:19 /var/log/mongodb/mongod.log
drwxr-xr-x 4 mongodb mongodb 20480 Nov 28 21:32 /var/lib/mongodb
Now whenever I need MongoDB server I have to run it with sudo mongod --dbpath /var/lib/mongodb/
It seems like a permission issue for me. But I cannot figure how to fix this out?