TopolearnA good config file replaces long command lines and is used by every SSH-based tool, from scp to Git to VS Code.
~/.ssh/config stores per-host settings. A Host line starts a block that applies to matching host names (patterns with * and ? work):
HostNameis the real address; theHostname becomes an alias.User,Port,IdentityFileset the login name, port and key.IdentitiesOnly yesoffers only the listed key, avoiding "Too many authentication failures" when the agent holds many keys.ServerAliveInterval 60sends keepalives so idle connections through NAT or firewalls do not drop.
The crucial rule: for each option, the first value found wins. ssh reads the file top to bottom and keeps the first match, so put specific Host blocks first and general defaults (Host *) at the end. Command-line -o options beat everything in the file.
Every tool that uses OpenSSH honours this file: scp web:file ., rsync, git clone git@github-work:org/repo.git and editors' remote features all use the alias.
To see what ssh will actually use for a host, run ssh -G web; it prints the fully resolved configuration. Include ~/.ssh/config.d/* lets you split a large config into files (put it near the top).
Example
# ~/.ssh/config
Host web
HostName 203.0.113.10
User deploy
IdentityFile ~/.ssh/work_ed25519
IdentitiesOnly yes
Host github-work
HostName github.com
User git
IdentityFile ~/.ssh/work_ed25519
Host *
ServerAliveInterval 60
AddKeysToAgent yes
# usage: ssh web scp app.tgz web:/tmp/ git clone git@github-work:acme/api.git
# check: ssh -G web | grep -E '^(user|hostname|port) 'Remember
- Host blocks define aliases with HostName, User, Port, IdentityFile
- First obtained value wins: specific blocks first, Host * last
- ssh -G host prints the effective settings
Watch out for
- Putting Host * with a User at the top; it then overrides every later block's User.