ssh-agent without graphical display manager? how?

[Paul E Condon <pec@mesanetworks.net>]

I'm in the process of converting from nfs to sshfs on my home-grown
file-server/backup-server computer. This computer does not run Xwindows
or any other graphical manager. I control it mostly by logging into it
using ssh.  But when I log in this way, it appears that ssh-agent is
not started, and consequently, I cannot use ssh-add on it.  I can, of
course, use ssh-add on my desktop computer, but that is not where the
private key for the backup server is stored. Has anyone confronted
this situation and worked out a solution? Advice? 

(Please don't suggest that I use some prebuilt backup system that does
everything you want. I am special, i.e. especially unreasonable in my
goals/needs.)

TIA
-- 
Paul E Condon           
pecondon@mesanetworks.net