Caching ssh private keys using openssh on GNU/Linux

You probably use ssh on a daily basis, I know I do.  I find that many people I talk to don't know that typical ssh installations have the ability to cache their private keys, so they wind up having to type their private key passphrase several times a day.  Some people actually get frustrated enough with this process that they remove the passphrase from their private key file entirely.  Don't do that!  Trust me, there is a safer and better way.

In this article I discuss how to setup GNU/Linux (using openssh) hosts to cache your private keys on startup.  I will discuss how to configure Microsoft Windows hosts using Simon Tatham's excellent PuTTY applications in another article.