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Peter
Asked: 2014-07-09 01:07:00 +0800 CST

Assistance with bash functionality

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I need to access data from a server that is behind a proxy. Thus, I can normally ssh to the proxy and then ssh to the destination to perform administration. However, not sure how to achieve this in bash. I do have a local ssh alias that will tunnel through the proxy automatically when i "ssh destination", but this must be in my environment or something and not used by the script.

In essence, is it possible to "ssh proxy ssh destination $commmand" in bash? I have tried the this exact command and had no success.

bash

3 Answers

  1. Not exactly what you want, but if forwarding a port is out of the question, you could set up an SSH tunnel first:

    ssh -L 2222:hostbehindproxy:22 user@proxy

    And then 

    ssh -p 2222@localhost user@hostbehindproxy "command"

    You can devise something that keeps the tunnel up at all times. A very crude way:

    while true; do
    # you need to have public key authentication for this to work on the background
    ssh -N -L 2222:hostbehindproxy:22 user@proxy
    sleep 1
done
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  2. You can try adding these lines in your ~/.ssh/config

    Host remote_server
  HostName remote_server_url_or_ip
  User remote_user 
  ProxyCommand ssh proxy_user@proxy nc %h %p

    Then you will be able to run only ssh remote_server. The ip/url and user will be the ones defined in the file. It will first ssh to proxy as user proxy_user and use nc on that session to talk to the remote server.

    • 1

  3. In order to use the command you wrote, you have to manage the authentication from the proxy server to the destination server. You can create a key pair (with ssh-keygen) on the proxy server and then put the public key in the authorized_keys file of the destination server (in .ssh/ directory of the user you use).

    After the key exchange, your "ssh proxy ssh destination $commmand" should work.

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