Ubuntu 16.04 ssh-add without ssh-agent?

Question

I have configured ssh-agent on many older Ubuntu installations, but today, on my new Ubuntu 16.04 setup, I realized that ssh-add has been working, but I never configured my system to run ssh-agent!

Edit: It's not just that I haven't configured it, it is not even running:

ps aux | grep ssh
root       976  0.0  0.0  65520  5384 ?        Ss   16:04   0:00 /usr/sbin/sshd -D
user123+  6121  0.0  0.0  21292  1016 pts/1    S+   16:50   0:00 grep --color=auto ssh

How is ssh-add working without ssh-agent? What is this magic? I see there is a gnome-keyring-daemon running on my system, but open-ssh isn't integrated with gnome is it?

Answer 1

Ubuntu uses the gnome-keyring-daemon as an alternative (compatible) implementation of an SSH agent.

It is installed through the package gnome-keyring and started automatically through /etc/xdg/autostart/gnome-keyring-ssh.desktop.

You can see that which process is your SSH agent with sudo lsof $SSH_AUTH_SOCK.

Answer 2

The environment variable SSH_AGENT_LAUNCHER expands to the process that launches the ssh-agent.

On my 14.04, by default, after start:

% echo "$SSH_AGENT_LAUNCHER"
upstart

while after killing, and unset-ing the variable(s), and then spawning ssh-agent again:

% echo "$SSH_AGENT_LAUNCHER"
## Nothing, not being set

So at the startup the init process spawns ssh-agent directly or indirectly, and the environment variable SSH_AGENT_LAUNCHER is set accordingly.