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Auto SSH Agent

(2019-09-04)

Notes that probably won't make any sense to anyone other than myself. This is borderline incoherent and probably mostly wrong

~/bin/agent, everywhere:

This is a generic script for launching the agent on the keyhost. I'm using kageant on Windows right now as my keyhost so I don't actually use this.

#!/bin/bash
HOST=`hostname`
AGENT="ssh-agent -s"
if [ ! -d $HOME/.ssh/agent ]; then
        mkdir -p $HOME/.ssh/agent
fi
pid=`ps -u$LOGNAME | grep ssh-age | awk '{print $1}'`
if [ -z "$pid" ]; then
        $AGENT | grep -v echo > $HOME/.ssh/agent/$HOST & pid=$!
        sleep 1 # Let it fork and stuff
fi

On The Keyhost

in .profile or .bash_profile:

~/bin/agent
. ~/.ssh/agent/`uname -n`

On the systems you are going to ssh from

(This can be the source and/or target systems if you are going to be stringing chains of ssh sessions together)

In .ssh/config:

ForwardAgent yes

On The Targets

In .bashrc:

if [ -S "$SSH_AUTH_SOCK" ] && [ ! -h "$SSH_AUTH_SOCK" ]; then
  ln -sf "$SSH_AUTH_SOCK" ~/.ssh/agent/$(hostname)_ssh_auth_sock
fi
export SSH_AUTH_SOCK=~/.ssh/agent/$(hostname)_ssh_auth_sock

Use

  • log into keyhost, ssh-agent starts
  • use ssh-add to install your key into the running agent
  • ssh as desired
  • when you disconnect, any forwarded agent sockets become useless (while you are disconnected)
  • when you return, ssh back in to the target, all agent forwarders on that host become active again

Commentary

As noted above, I'm using my Windows system(s) as keyhosts, so I use kageant with kitty for my initial ssh session. From there I land on hosts where screen sessions are run, and can ssh from there without requiring passwords (for the most part).

Credit

I started with this Superuser.com question.

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