SSH Configuration

SSH config file location

~/.ssh/config

Basic host configuration

Host myserver
    HostName 192.168.1.100
    User admin
    Port 22

Connect using alias

ssh myserver

Multiple hosts

Host server1
    HostName 192.168.1.100
    User admin

Host server2
    HostName 192.168.1.101
    User root

Use specific key

Host myserver
    HostName example.com
    User admin
    IdentityFile ~/.ssh/id_rsa_myserver

Jump host (bastion)

Host internal-server
    HostName 10.0.0.50
    User admin
    ProxyJump bastion

Host bastion
    HostName bastion.example.com
    User jump-user

Alternative jump syntax

Host internal-server
    HostName 10.0.0.50
    User admin
    ProxyCommand ssh -W %h:%p bastion

Wildcard patterns

Host *.example.com
    User admin
    IdentityFile ~/.ssh/company_key

Host 192.168.1.*
    User root
    Port 2222

Keep connection alive

Host *
    ServerAliveInterval 60
    ServerAliveCountMax 3

Connection multiplexing

Host *
    ControlMaster auto
    ControlPath ~/.ssh/sockets/%r@%h-%p
    ControlPersist 600

Disable host key checking (unsafe!)

Host dev-server
    HostName dev.example.com
    StrictHostKeyChecking no
    UserKnownHostsFile /dev/null

Forward agent

Host myserver
    HostName example.com
    ForwardAgent yes

Local port forwarding

Host myserver
    HostName example.com
    LocalForward 8080 localhost:80

Remote port forwarding

Host myserver
    HostName example.com
    RemoteForward 9000 localhost:3000

Dynamic forwarding (SOCKS)

Host myserver
    HostName example.com
    DynamicForward 1080

X11 forwarding

Host myserver
    HostName example.com
    ForwardX11 yes

Compression

Host slow-connection
    HostName remote.example.com
    Compression yes

Connection timeout

Host *
    ConnectTimeout 30

Multiple identities

Host github-work
    HostName github.com
    User git
    IdentityFile ~/.ssh/id_rsa_work

Host github-personal
    HostName github.com
    User git
    IdentityFile ~/.ssh/id_rsa_personal

Logging

Host myserver
    HostName example.com
    LogLevel DEBUG

IPv4 only

Host myserver
    HostName example.com
    AddressFamily inet

Preferred authentication

Host myserver
    HostName example.com
    PreferredAuthentications publickey,password

Disable password auth

Host myserver
    HostName example.com
    PasswordAuthentication no

Send environment variables

Host myserver
    HostName example.com
    SendEnv LANG LC_*

Request TTY

Host myserver
    HostName example.com
    RequestTTY yes

Include other configs

Include ~/.ssh/configs/*

Complete example

# Default settings
Host *
    ServerAliveInterval 60
    ServerAliveCountMax 3
    ControlMaster auto
    ControlPath ~/.ssh/sockets/%r@%h-%p
    ControlPersist 600

# Production servers
Host prod-*
    User deployer
    IdentityFile ~/.ssh/id_rsa_prod
    StrictHostKeyChecking yes

# Development servers
Host dev-*
    User developer
    IdentityFile ~/.ssh/id_rsa_dev
    StrictHostKeyChecking no

# Specific server
Host webapp
    HostName prod-web-01.example.com
    User admin
    Port 2222
    LocalForward 3306 localhost:3306

SSH key generation

# RSA key
ssh-keygen -t rsa -b 4096 -C "email@example.com"

# Ed25519 key (recommended)
ssh-keygen -t ed25519 -C "email@example.com"

# With custom filename
ssh-keygen -t ed25519 -f ~/.ssh/id_ed25519_work

Copy key to server

ssh-copy-id user@hostname

# With specific key
ssh-copy-id -i ~/.ssh/id_rsa_work.pub user@hostname

Test SSH config

ssh -T git@github.com
ssh -vvv user@hostname

View effective config

ssh -G hostname