Different ways to START/SHUTDOWN  mongod

1.FROM Service command:

sudo systemctl start mongod.service
service mongod start/stop/status

2.Run mongodb without service command

mongod --dbpath /var/lib/mongo/ --fork --logpath /var/log/mongodb/mongod.log

mongod --auth --dbpath /var/lib/mongo/ --fork --logpath /var/log/mongodb/mongod.log

mongod : command to start mongo
dbpath : database directory
fork : run service/terminal in background (always work with –logpath)
logpath : mongo log path

SHUTDOWN MongoDB (If started manually)

mongod --dbpath /var/lib/mongo/ --shutdown

3. RUN MONGODB WITH mongod.conf 

mongod.conf  is a configuration file which used by mongod.service to run, this file having all parameters which defines log path , database path, port , authentication etc.
In spite of giving all parameters to command pass only mongod.conf

mongod.conf locates at /etc/mongod.conf

mongod -f /etc/mongod.conf
mongod -f /etc/mongod.conf --shutdown