If you manage servers all day, SSH becomes muscle memory. But even muscle memory has friction — typing ssh -A hostname hundreds of times per week adds up. Fortunately, macOS and zsh give us a clean, elegant way to eliminate that overhead entirely.
In this blog post, we will configure your Mac so typing only the hostname automatically initiates an SSH session, while still maintaining strict control over SSH agent forwarding.
- The Goal
- Why This Is Not Built Into SSH
- Step 1: Configure Agent Forwarding the Right Way
- Step 2: Teach zsh to Auto-SSH Unknown Commands
- How It Works Behind the Scenes
- Verifying Agent Forwarding
- Why This Setup Is Ideal for Administrators
- Final Thoughts
The Goal
Instead of typing:
ssh -A server1
You simply type:
server1
…and you are immediately connected via SSH.
No aliases. No wrappers. No bad habits.
Why This Is Not Built Into SSH
SSH itself is just a command-line tool. It executes only when explicitly called. Your shell (zsh on modern macOS) is responsible for deciding what happens when you type a word and press Enter.
By default, zsh follows this logic:
- If the word matches a command in your PATH, it executes it
- If it does not, zsh throws a “command not found” error
We are going to intercept that failure case and reinterpret it as:
“This is probably a hostname — initiate SSH.”
Step 1: Configure Agent Forwarding the Right Way
Before automating anything, we define where SSH agent forwarding is allowed. This ensures speed without sacrificing security.
Edit your SSH configuration:
vi ~/.ssh/config
Add the following:
Host server1 server2 server3
ForwardAgent yes
This setup enforces:
- Agent forwarding disabled by default
- Explicit opt-in for trusted hosts
- Compatibility with bastions, jump hosts, Git, Ansible, and scp
Step 2: Teach zsh to Auto-SSH Unknown Commands
Now we configure zsh to treat unknown commands as SSH targets.
Edit your shell configuration:
vi ~/.zshrc
Add the following function:
ssh() {
command ssh -A "$@"
}
function command_not_found_handler() {
command ssh -A "$1"
}
Reload your shell:
source ~/.zshrc
How It Works Behind the Scenes
When you type:
server1
zsh attempts to locate a command named server1.
- No executable is found
- zsh invokes
command_not_found_handler - The handler runs ssh server1
- SSH applies per-host configuration from
~/.ssh/config
The result is a seamless SSH experience with zero extra typing.
Verifying Agent Forwarding
Once connected, verify forwarding with:
ssh-add -l
- Keys listed: forwarding active
- Authentication agent error: forwarding disabled
This validation is critical when working across multiple trust boundaries.
Why This Setup Is Ideal for Administrators
- Zero keystroke overhead
- No fragile shell aliases
- Security-first defaults
- Works cleanly with jump hosts
- Scales across laptops and long-lived admin environments
This approach balances speed and discipline — exactly what experienced administrators need.
Final Thoughts
This is a small change that delivers an outsized productivity gain. Once your muscle memory adapts to typing only hostnames, it becomes difficult to imagine going back.
By combining zsh’s extensibility with SSH’s configuration model, you get a fast, elegant, and secure workflow — one that scales with both your environment and your responsibilities.
