Keeping the Agent Around

I answered an interesting question on the Suse Forums today, and I thought I would log my answer here too. Teresa wanted to know how to have ssh-agent remember her passkey across multiple shell logins and the like. I answered the question here for how to do it when you are using X, but she was doing everything from the console and so didn't have the luxury of an overarching environment.

When you run 'ssh-agent', it starts up a process that listens on a local socket, and prints out some info you can use to set environment variables with, which then tell other programs where to ask it for info:

$ ssh-agent -s
SSH_AUTH_SOCK=/tmp/ssh-CzngL4914/agent.4914; export SSH_AUTH_SOCK;
SSH_AGENT_PID=4915; export SSH_AGENT_PID;
echo Agent pid 4915;

So normally you "eval" the results of this to actually create the environment variables, so you put something like this in your .bashrc:

eval `ssh-agent -s`

But if instead you dump that to a file, you can now use this in any other virtual terminal, say, or another screen session, rather than killing the old one, starting up a new ssh-agent, and adding the key again.

$ ssh-agent -s > sshx
$ cat sshx
SSH_AUTH_SOCK=/tmp/ssh-CzngL4914/agent.4914; export SSH_AUTH_SOCK;
SSH_AGENT_PID=4915; export SSH_AGENT_PID;
echo Agent pid 4915;
$ eval `cat sshx`
Agent pid 4915
$ printenv |grep SSH_
SSH_AUTH_SOCK=/tmp/ssh-CzngL4914/agent.4914
SSH_AGENT_PID=4915

Now any keys you ssh-add to this ssh-agent will be effective in any other shell. It doesn't look like you need to use the nohup command with ssh-agent, as it automagically works as a daemon already, so as long as you use the correct environment variables, you should be communicated with that one no matter what.