~/.ssh/config: Host, HostName, User, Port and IdentityFile

~/.ssh/config lets you type ssh prod instead of ssh -i ~/.ssh/prod_key -p 2222 deploy@203.0.113.10. Each Host block starts with one or more patterns, and the keywords below it apply when the name you type matches. For each keyword the first value found wins, so put specific hosts above Host *.

Example and the resolved result

ssh -G prints the configuration ssh would use for a host, without connecting:

cat > config <<'EOF'
Host prod
    HostName 203.0.113.10
    User deploy
    Port 2222
    IdentityFile ~/.ssh/prod_ed25519
    IdentitiesOnly yes

Host *
    ServerAliveInterval 60
EOF
ssh -G -T -F config prod | grep -E '^(hostname|user|port|identityfile|identitiesonly|serveraliveinterval) '

user deploy
hostname 203.0.113.10
port 2222
identitiesonly yes
serveraliveinterval 60
identityfile ~/.ssh/prod_ed25519

Keywords you use most

Pitfalls

• Order matters: the first matching value is used. A User under Host * at the top overrides every later block.
• Permissions: on Linux and macOS ssh refuses a config file that other users can write.
• Too many keys: with many keys in the agent, servers may disconnect after too many failed attempts. IdentitiesOnly yes avoids it.