Lab: The log file already exist

After I run the command
vagrant@m103:~$ mongod -f /shared/mongod.conf

As a result I have:
2019-03-17T23:27:06.343+0000 I CONTROL [main] log file "/var/mongodb/db/mongod.log" exists; moved to "/var/mongodb/db/mongod.log.2019-03-17T23-27-06".

And I am not able to run my mongod.

That is a warning only. That does not stop mongod from running.

Yeah, I have just figured out. Thank you @steevej-1495 !