3

I want to be able to connect to a server, start a sudo shell, then use agent forwarding to connect to another server (in order to use SCP to copy files to a protected area). But:

ubuntu@tunnelator:/var/www$ ssh -p 10022 stevebennett@localhost
Last login: Fri Apr  5 10:54:03 2013 from localhost
~ exit
Connection to localhost closed.

ubuntu@tunnelator:/var/www$ sudo ssh -p 10022 stevebennett@localhost
Password:

Presumably, starting the sudo shell is killing the agent forwarding. The difference is this:

debug1: Offering RSA public key: id_rsa
debug1: Server accepts key: pkalg ssh-rsa blen 277
debug1: Authentication succeeded (publickey).

versus:

debug1: Next authentication method: publickey
debug1: Trying private key: /root/.ssh/id_rsa
debug1: Trying private key: /root/.ssh/id_dsa
debug1: Trying private key: /root/.ssh/id_ecdsa
debug1: Next authentication method: keyboard-interactive

Is there a way to make this work? (The setup is roughly as described here: http://codysoyland.com/2010/jun/6/ssh-tip-automatic-reverse-tunnels-workflow-simplif/)

3

Thanks to user157963's suggestion, this turns out to be easy:

sudo -E ssh -p 10022 stevebennett@localhost

Or, to be a bit more selective, you can do this:

sudo su -l -c "export SSH_AUTH_SOCK=$SSH_AUTH_SOCK; ssh -p 10022 stevebennett@localhost"

(Note this only works when su'ing to the root user - it needs to be able to read the original socket file.)

I had mistakenly thought that the $SSH_AUTH_SOCK environment variable was already being preserved. Tip: the following command doesn't tell you anything useful :)

sudo echo $SSH_AUTH_SOCK

Whereas this does:

sudo bash -c 'echo $SSH_AUTH_SOCK'
  • Additionally you can just sudo -sE if you want to have a shell as root. -E preserves the current environment which includes $SSH_AUTH_SOCK which houses the forwarding agent information – Steve Tauber Jan 15 '16 at 20:03

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