How to use rsync with a remote remote host

Question

I am a happy user of rsync -e ssh and use it to synchronize data between my machine and a remote host using

rsync -avz -e ssh me@hostA:~/folder ~/folder

And this did what I needed until now.

I am now working with a configuration where the access is a bit more complicated. Suppose now ~/folder is on hostB, but hostB is not directly accessible from my machine, but only indirectly via hostA.

So if I only want to see the folder on hostB. I first need to ssh to hostA, then to hostB after which I can see my files in ~/folder on the remote host.

My question now is, what is the (best) method to use rsync directly between my machine and hostB?

Unfortunately this is the configuration I need to work with. Assume there is no possibility to temporarily store the data on hostA itself.

Answer 1

Have a look at How do I connect to a pc through another pc using ssh

You create a new ~/.ssh/config entry with the name tunnelb:

Host tunnelb
HostName hostB
User user
ProxyCommand ssh user@hostA nc %h %p

If you have a recent version of ssh you can use Proxycommand ssh user@hostA -W %h:%p instead. This is preferred as it does not rely on nc

Now you can just use rsync -e ssh tunnelb:~/folder ~/folder as it will use the defined entry in ~/.ssh/config.

Answer 2

Variant 1:

First, start ssh on hostA permanently with local port forwarding in another terminal. E.g.:

ssh -N -v -L 22022:hostB:22 hostA

Then, "feed" rsync with ssh to localhost:22022. One variant is to write to ~/.ssh/config:

Host hostB
HostName localhost
Port 22022

Variant 2:

Replace -e ssh with -e to some script which contains:

ssh hostA 'ssh hostB' "$@"

I didn't try it so some details would be elaborated additionally.