How do I do Multihop SCP transfers?

Question

I want to copy a file from my machine A to server C, but only have access to server C through server B.

Instead of first transferring to server B, log in and then transfer to server C, Is is possible to transfer the file directly with SCP or similar programs?

(Emacs tramp-mode has this feature for editing files remotely).

Answer 1

Assuming OpenSSH, add to your SSH configuration in .ssh/config

Host distant
ProxyCommand ssh near nc distant 22

This will cause SSH to be able to connect "directly" to the machine named distant by proxying through the machine named near. It can then use applications like scp and sftp to the distant machine.

For this to work you need 'nc' aka netcat installed on the machine named near. But a lot of modern systems will have it already.

towo's tar solution is more effective for one-shot problems, assuming you've memorised tar's syntax and rules of operation.

Answer 2

You can ssh to server B using something like

ssh -L 5022:<server C IP>:22 <user_serverB>@<server B IP>

Then you can ssh to server C using

ssh -p 5022 <user_serverC>@localhost

Similarly scp would work using

scp -P 5022 <user_serverc>@localhost

Remember to use correct case of p with scp and ssh.

Answer 3

You can add -o options to scp instead of .ssh/config.

scp -o ProxyCommand="ssh $jump_host nc $host 22" $local_path $host:$destination_path

$jump_host is your "server B" in this case.

Answer 4

If you want to be really wicked, you could chain ssh and tar, something like tar c mydir | ssh server "ssh otherserver | tar x", but this can run into all hands of problems.

The easier way would be just to set up an SSH tunnel with the built-in methods of SSH; look at the -D switch in the manpage and just forward some port to the other server's ssh port.