Answer by Patrick Walter for scp'ing using key file as a parameter, How can I do that if possible?

This might help another noob.

[I know this is a redundant circular example but its good to illustrate] Scenario:

1. ssh from Mac -> Ubuntu
2. scp files from Mac -> Ubuntu
3. close ssh and scp files from Ubuntu -> Mac

I had only created ssh keys on my Mac (via ssh-keygen) and shared them with the machine running Ubuntu via (ssh-copy-id). So I could copy files, while logged into my Mac from the machine running Ubuntu, but not the other way around.

Solution: I had to create ssh keys on the Ubuntu Machine and share them with my Mac. then I could successfully run the following command on the Ubuntu Machine

Mac IP: 192.168.1.40
Ubuntu IP: 192.168.1.38

On Mac

ssh-keygen
ssh-copy-id ubuntu@192.168.1.38

ssh ubuntu@192.168.1.38

# Now on Ubuntu
ssh-keygen
ssh-copy-id MAC@192.168.1.40

And now the following command should copy the file without asking for password to MAC

sudo scp -i /home/ubuntu/.ssh/id_rsa MAC@192.168.1.40:~/Documents/Fluff/Version-Control/tools/pull.sh .