keychain
Re-use ssh-agent and/or gpg-agent between logins.
TLDR
Check for a running ssh-agent, and start one if needed
$ keychain
Also check for gpg-agent
$ keychain --agents "[gpg,ssh]"
List signatures of all active keys
$ keychain --list
List fingerprints of all active keys
$ keychain --list-fp
Add a timeout for identities added to the agent, in minutes
$ keychain --timeout [minutes]