Failed to start mongod.service: Unit mongod.service not found

I follow all the steps mention in MongoDB installation [documents][1] for `Ubuntu 16.04`. [1]: https://docs.mongodb.com/getting-started/shell/tutorial/install-mongodb-on-ubuntu/ **Steps 1:** sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv 2930ADAE8CAF5059EE73BB4B58712A2291FA4AD5 **Steps 2:** echo "deb [ arch=amd64,arm64 ] https://repo.mongodb.org/apt/ubuntu xenial/mongodb-org/3.6 multiverse" | sudo tee /etc/apt/sources.list.d/mongodb-org-3.6.list **Steps 3:** sudo apt-get update **Steps 4:** sudo apt-get install -y mongodb-org **Steps 5:** sudo service mongod start when I started MongoDB got an error as: > **Failed to start mongod.service: Unit mongod.service not found.**