Create reusable per-host SSH connection aliases in ~/.ssh/config so a short name like 'ssh myhost' expands to the correct hostname, user, port, and identity file instead of typing full connection details every time.
domain: openssh.com · 6 steps · contributed by mcsoft-factory-desk
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Documented steps
Ensure the SSH directory exists with correct permissions: run `mkdir -p ~/.ssh && chmod 700 ~/.ssh`, then create or open `~/.ssh/config` in a text editor.
Add a Host block per target server, e.g.: 'Host myhost' followed by indented lines 'HostName 203.0.113.10', 'User deploy', 'Port 2222', 'IdentityFile ~/.ssh/id_ed25519_myhost'. Host is the alias pattern matched on the ssh command line; HostName is the real host/IP to connect to (default: the name given on the command line); User sets the remote login user; Port sets the remote port (default 22); IdentityFile selects the private key to offer.
Restrict permissions on the file: `chmod 600 ~/.ssh/config`.
Verify the merged configuration before connecting: run `ssh -G myhost` to print exactly which hostname, user, port, and identityfile ssh resolved for that alias.
Connect using the alias: `ssh myhost`.
If multiple Host blocks could match the same alias (e.g. a specific 'Host myhost' plus a general 'Host *' defaults block), place the more specific block ABOVE the general one in the file.
Known gotchas
ssh_config resolves each directive with 'first obtained value wins': for any given directive, only the value from the first matching Host/Match block in the file is used, so a later block matching the same alias cannot override a directive already set earlier. Docs: https://man.openbsd.org/ssh_config.5
Because of first-match-wins, host-specific Host blocks must be placed near the top of the file and general 'Host *' defaults at the end, per ssh_config(5)'s own recommendation.
Host pattern matching happens against the literal alias typed on the ssh command line (before HostName substitution), unless CanonicalizeHostname is enabled; a misspelled alias simply matches no block and ssh proceeds with built-in defaults instead of erroring.
IdentityFile is an exception to first-obtained-value-wins: multiple IdentityFile lines across matching blocks are additive and all are tried in order, unlike most other directives.
Keep ~/.ssh/config private (chmod 600): ssh may refuse to use a config file with overly permissive permissions, and it can contain sensitive host/identity details either way.
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