ssh-agent-switcher is a daemon that proxies SSH agent connections to any valid forwarded agent provided by sshd. This allows long-lived processes such as terminal multiplexers like tmux or screen to access the connection-specific forwarded agents.

More specifically, ssh-agent-switcher can be used to fix the problem that arises in the following sequence of events:

1. Connect to an SSH server with SSH agent forwarding.
2. Start a tmux session in the SSH server.
3. Detach the tmux session.
4. Log out of the SSH server.
5. Reconnect to the SSH server with SSH agent forwarding.
6. Attach to the existing tmux session.
7. Run an SSH command.
8. See the command fail to communicate with the forwarded agent.

The ssh-agent-switcher daemon solves this problem by exposing an SSH agent socket at a well-known location, allowing you to set SSH_AUTH_SOCK to a path that does not change across different connections. The daemon then looks for a valid socket every time it receives a request and forwards the request to the real forwarded agent.

Related blog posts

• 2025-12-26: ssh-agent broken in tmux? I've got you!
• 2023-11-17: SSH agent forwarding and tmux done right