Remote login OS X

This enables logging into the Mac from a remote computer.
The steps are:
On the Mac (as server):
1. System Preferences >> Sharing : Here check the box Remote Login and select who you want to use this facility in the "Allow access for" box. Note the remote login command. In my case it's

ssh paul@192.168.1.5

In my case, this didn't work unless I used

sudo ssh paul@192.168.1.5

Without sudo I got a lot of stuff about unknown keys after which it went back to the command prompt.
With sudo, on the other hand, I was given the option to accept, or not, the authenticity of the host. After typing "yes", the connection was made.
Now I could delve into whatever directory on the Mac from Ubuntu on the Dell and use scp (without sudo) a file to the Desktop of the Dell with

scp file.ext 192.168.1.12:~/Desktop

This caused me to be asked again to accept or not the authenticity of the host (this time the Dell was the server or host).