[nmglug] ssh confusion

[Tom Ashcraft]

Can anyone give me some basic pointers and tips on ssh?  (Specific 
questions at end.)

Background.  In the process of trying to compare and contrast the 
configuration differences across three different Linux laptops in my 
home--this in order to try to figure why one of them consistently fails 
to connect to imap.comcast.net (continuing saga; not what I wish to 
address here)--it occurred to me that I might be able to ssh from one 
computer into the others in order to see and copy certain portions of 
the different directory structures into a text file on my desktop.  This 
so that I could study everything in a convenient, organized fashion in 
one place (again not the topic at issue; but, yes, I'm not the kind of 
person who can memorize a phone book.)

Sure enough! I can ssh into Debian machine from Kubuntu machine.  I can 
ssh into Debian machine from Ubuntu Mate machine.  But connections are 
refused from Debian machine into Kubuntu and Ubuntu Mate and between 
Kubuntu and Ubuntu Mate machines.

If I remember correctly, when I setup the Debian machine I opted to 
install a server.  But that was months ago and I haven't thought it 
about since, nor do I even know where to find it.  Does it boot with the 
machine and make itself available so that I can ssh into it? I don't 
know.  Old as I am I'm still a server-side noob, barely a twinkle in my 
Daddy's eye.

All I know about servers is that I've watched some videos and installed 
a couple of Ubuntu Server virtual machines for trying to learn some 
basics about understanding and managing networks and servers (became 
interested mostly because of the longtime foggy notion that I'd like to 
someday get a Raspberry Pi and setup a PiHole to work with our router; 
again, not the issue at hand, just more background for those of you who 
know me.)  I've used ssh at the most basic level about half a dozen 
times in my life.

So my questions are:

1.  Is it not possible to ssh from the machine you are typing at into 
the target/host machine without having a server installed and running on 
the target machine?  Are there permissions or shares or ports or whatnot 
that need to be configured on the target machines? To the best of my 
knowledge there are no firewalls running on the machines.

2.  Where might general ssh learning time be best spent first?  Any good 
cheat sheets or overviews to recommend?  (Yes, I know what man pages 
are, and even how to use them passably well if I have a clear concept of 
what it is I'm supposed to be looking for.)

Thanks,
Tom