# SSH Configuration

**SSH configuration files** control connection defaults and options. The main file is `~/.ssh/config`, which lets you define host aliases, authentication options, and forwarding rules without typing them on every command.

Basic syntax:

```
Host work
    HostName work.example.com
    User alice
    Port 2222
    IdentityFile ~/.ssh/id_ed25519

Host *
    AddKeysToAgent yes
    StrictHostKeyChecking accept-new
```

Then connect with `ssh work` instead of `ssh -p 2222 alice@work.example.com`.

Host patterns:

- `Host work` — matches exactly "work"
- `Host *.example.com` — matches all subdomains
- `Host *` — matches all hosts (set defaults here)

Common options:

```
HostName              actual hostname or IP
User                  username on remote
Port                  SSH port (default 22)
IdentityFile          path to private key
ProxyJump             jump host (see ssh-jump-hosts)
AddKeysToAgent        add keys to SSH agent (yes/no)
StrictHostKeyChecking ask/accept-new/no (host key verification)
ServerAliveInterval   idle timeout in seconds
Compression           enable compression (yes/no)
ForwardAgent          forward SSH agent to remote (yes/no)
LocalForward          local port forwarding
RemoteForward         remote port forwarding
```

SSH reads config top-to-bottom and uses the first matching value. More specific hosts should appear before `Host *`.

View effective config for a host: `ssh -G work` (shows merged settings).

Check syntax: `ssh -G hostname` (errors show invalid config).