Ssh:key, agent, Keychain

Previously encountered a problem, in the use of some Linux distribution, with Ssh-keygen generated a good key pair and uploaded to the target server, but each login to re-enter.

This is related to Ssh-agent, see the following man ssh-agent output:

Ssh-agent is a program to hold private keys used for public key authentication (RSA, DSA). The idea is
That Ssh-agent was started in the beginning of a x-session or a login session, and all other windows or
Programs is started as clients to the Ssh-agent program. Through use of environment variables the agent
Can is located and automatically used for authentication when logging on to other machines using SSH(1).

Ssh:key, agent, Keychain