AddKeysToAgent

When using an agent, you might like the SSH config file option AddKeysToAgent, which will automatically add used keys to your ssh-agent for future use.

Consider the following; we're starting with no keys in our agent:

[vagrant@centos1 ~]$ ssh CentOS2-V4
Enter passphrase for key '/home/vagrant/.ssh/id_ed25519': 
Last login: Thu Aug  9 15:58:01 2018 from 192.168.33.10
[vagrant@centos2 ~]$ logout
Connection to 192.168.33.11 closed.
[vagrant@centos1 ~]$ ssh CentOS2-V4
Last login: Thu Aug  9 16:12:04 2018 from 192.168.33.10
[vagrant@centos2 ~]$ 

Note that the first time, we're prompted for our key's passphrase. The second time, we're not.

It is now loaded into our agent:

[vagrant@centos1 ~]$ ssh-add -l
256 SHA256:P7FdkmbQQFoy37avbKBfzMpEhVUaBY0TljwYJyNxzUI vagrant@centos1 (ED25519)

This is all handled by one config option:

[vagrant@centos1 ~]$ cat .ssh/config 
Host *
 Port 22
 AddKeysToAgent yes