[NTLUG:Discuss] Keychain question

[Dennis]

I have set up RSA, ssh-agent, can ssh from Server A to Server B
OK, and only need to give the passphrase once during a login
session.

I have this code from Jeremy Zawodny's article on keychains:

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if [ -n "$PS1" ]; then
  /usr/local/bin/ ~/.ssh/identity ~/.ssh/id_rsa
  . ~/.ssh-agent-`uname -n`
else
  /usr/local/bin/keychain --quiet ~/.ssh/identity ~/.ssh/id_rsa
  . ~/.ssh-agent-`uname -n
fi

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MY QUESTIONS:

I have ~/.ssh/id_rsa and ~/.ssh/id_rsa.pub, but do not have a
~/.ssh/identity. How do I get one of those, or is that an out-
of-date-filename, or do I make one from a copy of my private 
key or public key, or..., or...?

I'm not completely certain what the statement does:

  /usr/local/bin/keychain --quiet ~/.ssh/identity ~/.ssh/id_rsa
  . ~/.ssh-agent-`uname -n

I get that it calls keychain in quiet mode, good for cronjobs,
but the list of ~/.ssh/identity followed by ~/.ssh/id_rsa
goes over my head. Can someone help me understand that?

Thanks big!

/dennis