Failed to start mongod.service: Unit mongodb.service not found. code example

Example 1: Failed to enable unit: Unit file mongod.service does not exist.

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

Example 2: Failed to enable unit: Unit file mongod.service does not exist.

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