[GTALUG] for multi-hop ssh/scp: option "ProxyJump"

[D. Hugh Redelmeier]

I'm away from home, regularly accessing my computers at home.
Easy: ssh into a gateway machine and ssh from there into the internal 
machine of my choice.  Nested ssh sessions.
It gets a little more annoying when I want to transfer a file.

The new-to-me ssh/scp option "ProxyJump" handles this conveniently.

Consider the example of transferring a file "f" from machine "home"
through machine "gw" to machine "away", all done from an xterm on
"away".

Note: because "away" is behind NAT, "gw" cannot scp to it.
Note: -A enables ssh-agent to avoid some manual authentication
Note: things become more complicated if f has slashes.

[away] $ ssh -A gw
[gw] $ scp -p home:f .
[gw] $ exit
[away] $ scp -p gw:f .
[away] $ ssh -A gw
[gw] $ rm f
[gw] $ exit

This can be simplified because the ssh command allows shell commands
as arguments.  That's not a habit I've developed.

[away] $ ssh -A gw scp -p home:f .
[away] $ scp -p gw:f .
[away] $ ssh -A gw rm f

The ProxyJump option makes this a lot simpler:

[away] $ scp -p -o 'ProxyJump gw' home:f .

I have no need for more than one intermediate hop so I haven't figured out 
how that would work.