Full Config Block

Anatomy of a complete Host block

Every directive you'll commonly use, in one place. Most blocks need only a subset, but knowing what's available prevents reinventing wheels.

The directives that matter most day-to-day

Directive	Purpose
`HostName`	Actual address (IP or FQDN)
`User`	Remote username
`Port`	SSH port (default 22)
`IdentityFile`	Path to the private key
`IdentitiesOnly`	Don't try every key in agent — only IdentityFile
`ForwardAgent`	Forward your agent (default: no, keep it that way)
`ProxyJump`	Hop through this host first (next lessons)
`Compression`	Compress on slow links (off on fast LAN)
`ServerAliveInterval`	Keepalive every N seconds
`ServerAliveCountMax`	Disconnect after N missed keepalives
`AddKeysToAgent`	Auto-add used keys to agent
`UseKeychain`	macOS — pull passphrase from Keychain
`ControlMaster / Path / Persist`	Multiplex connections (later lesson)

Indentation is convention, not rule

SSH parses the file fine without indentation, but indented blocks are dramatically more readable when you have 20 hosts. Pick a style and stick with it.

Code

A fully-loaded block·ssh-config

Host office
    HostName 192.168.1.100      # IP or FQDN
    User you_username                  # remote username
    Port 22                      # SSH port
    IdentityFile ~/.ssh/id_ed25519_office
    IdentitiesOnly yes           # only try this key
    ForwardAgent no              # keep agent here, not forwarded
    Compression no               # fast LAN, no compression
    ServerAliveInterval 60       # keepalive every 60s
    ServerAliveCountMax 3        # disconnect after 3 misses (3 min total)
    AddKeysToAgent yes
    UseKeychain yes              # macOS only

Exercise

Pick your most-used host alias. Open the block and verify it has at least: HostName, User, IdentityFile, ServerAliveInterval, AddKeysToAgent. Add what's missing. Then run ssh -G that-host and skim the resolved settings — you'll see all the inherited defaults from Host * plus your block's overrides.