List of ssh keys provided by ssh agent on a remote machine

Question

Locally keys made available by ssh agent can be listed using ssh-add -L. When connected to a remote machine through ssh, is there a way to list keys made available through ssh agent from the local machine?

Answer 1

You do forward the local agent, right? If so, then the command is the same: ssh-add -L. ssh-add connects to the socket specified by $SSH_AUTH_SOCK and if you have used ssh -A then the remote socket leads to your local agent and thus remote ssh-add (or any tool that uses the socket) will talk to the local agent.

You can even ssh-add a remote key (remote from your point of view; local from the point of view of ssh-add running on the server) and your local agent will be able to use it even after you disconnect.

^{(More complicated tricks are possible. E.g. this answer of mine describes "borrowing" keys, but in the opposite direction: a local key is added to an agent running on the server.)}

Note ssh-add -L will show you pathnames of added keys with no indication of where (what host) each key came from. You can add one key with ssh-add /foo/bar locally and you can add another key with ssh-add /foo/bar invoked on the server (when the agent is forwarded!), and ssh-add -L (locally or on the server) will show you two different keys described as /foo/bar.