Description:

Keychain is an OpenSSH key manager, typically run from ~/.bash_profile. When
run, it will make sure ssh-agent is running; if not, it will start ssh-agent.
It will redirect ssh-agent's output to ~/.ssh-agent-[hostname], so that cron
jobs that need to use ssh-agent keys can simply source this file and make the
necessary passwordless ssh connections. In addition, when keychain runs, it
will check with ssh-agent and make sure that the ssh RSA/DSA keys that you
specified on the keychain command line have actually been added to ssh-agent.
If not, you are prompted for the appropriate passphrases so that they can be
added by keychain.