Answers for "Failed to start mongodb.service: Unit not found."

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

$service mongodb start
$service mongodb status

Failed to enable unit: Unit file mongod.service does not exist.

> systemctl list-unit-files --type=service
...
mongodb.service             disabled
...

Failed to enable unit: Unit file mongod.service does not exist.

> systemctl list-unit-files --type=service 
...
mongodb.service             enabled
...