Copy files via a complex ssh connection?

Question

Suppose I have host A from which I ssh to host B, where I sudo -U some_role and from under it ssh to host C. My goal is an interactive shell on C.

Assume that from C I cannot ssh back to A.

What is the best way to copy a file from A to C using the connection built above? What preparations / changes should I introduce into the chain to make infrequent, simple file copying possible?

Of course I can run cat > target_file inside the interactive shell and copy-paste via the terminal, but for large binary files this is not exactly convenient.

Answer 1

I take it host B is e.g. a gateway in an intranet and can connect to host A and C, e.g. like this:

                                                                       -----------------------------------------------------------
                                                                      |                                                           |
                                                                      |                                                           |
                       ---------                                -----------                    --------------                     |
                      |A        |------------------------------|   B       |------------------|              |                    |
                       ---------                               |           |                  | C            |                    |
                                                                -----------                    --------------                     |
                                                                      |                                                           |
                                                                       -----------------------------------------------------------

In this case the best solution is ssh port forwarding. I describe it at http://www.linuxintro.org/wiki/Tunneling_with_OpenSSH

First, on A, you tunnel B's port 2222 to C's port 22 with the command:

ssh -L 2222:C:22 B

then you copy to C's port 22, by connecting to port 2222 on A (localhost) with the command:

scp -P 2222 file root@localhost:

Answer 2

The quickest way to transfer files is to launch a temporary web server in the directory containing the files you want to copy. So run the following command on host A:

python -m SimpleHTTPServer 4000

Then on host C:

wget http://hostA.local:4000/myfile.txt

or with IP address:

wget http://192.168.1.135:4000/myfile.txt

You can also see the files in a browser if the target host has a GUI.

To stop the web server on host A, use CTRL-C.

If you use this solution often, you may want to use gnu screen (https://ss64.com/bash/screen.html) so that you can continue to work while the web server is running.