Question: I've installed the mongo as part of a replicaset . The server is part of a 3 - node replicaset and I can manage through MongoDB Operations Manager. 

But when i get onto the command line and type "mongo"  , I'm getting the -bash: mongo: command not found.    

How can I fix this issue - as I'd like to be able to have the command line option

Answer: Assuming everything is running as expected - the most likely reason is that the relevant mongo binaries are not in the /usr/bin folder. I've had this problem a few times and this is the way I've resolved it 

Step 1>>>>>>>>

--Execute this command  with a user account that has enough privileges

# ps -ef | grep mongo

--resultset similar to

mongod 3890 1 0 2019 ? 14:26:05 /var/lib/mongodb-mms-automation/mongodb-linux-x86_64-4.0.11-ent/bin/mongod -f /mydir1/mongodb/myrs/automation-mongod.conf

Step2>>>>>>>>

Note:  BEFORE you run this command , ensure you've confirmed with your Linux administrator or MongoDB DBA

# cp /var/lib/mongodb-mms-automation/mongodb-linux-x86_64-4.0.11-ent/bin/* /usr/bin/

You should now be able to run the mongo command