SSH Cheatsheet

Basic Connection

  • Connect to remote server
ssh user@hostname
  • Connect with specific port
ssh -p <port> user@hostname
  • Connect with specific identity file
ssh -i <private-key> user@hostname
  • Connect with verbose output
ssh -v user@hostname
  • Connect and execute command
ssh user@hostname 'command'

SSH Key Management

  • Generate SSH key pair
ssh-keygen -t rsa -b 4096 -C "your-email@example.com"
  • Generate Ed25519 key (recommended)
ssh-keygen -t ed25519 -C "your-email@example.com"
  • Copy public key to remote server
ssh-copy-id user@hostname
  • Copy public key with specific key file
ssh-copy-id -i ~/.ssh/id_rsa.pub user@hostname
  • Add SSH key to ssh-agent
ssh-add ~/.ssh/id_rsa
  • List keys in ssh-agent
ssh-add -l
  • Remove all keys from ssh-agent
ssh-add -D

File Transfer

  • Copy file to remote server
scp local-file user@hostname:/remote/path/
  • Copy file from remote server
scp user@hostname:/remote/file /local/path/
  • Copy directory recursively
scp -r local-directory user@hostname:/remote/path/
  • Copy with specific port
scp -P <port> local-file user@hostname:/remote/path/
  • Sync directories with rsync
rsync -avz local-directory/ user@hostname:/remote/path/
  • Sync with delete (mirror)
rsync -avz --delete local-directory/ user@hostname:/remote/path/

Port Forwarding and Tunneling

  • Local port forwarding
ssh -L <local-port>:<remote-host>:<remote-port> user@hostname
  • Remote port forwarding
ssh -R <remote-port>:<local-host>:<local-port> user@hostname
  • Dynamic port forwarding (SOCKS proxy)
ssh -D <local-port> user@hostname
  • Background tunnel
ssh -f -N -L <local-port>:<remote-host>:<remote-port> user@hostname
  • Keep tunnel alive
ssh -o ServerAliveInterval=60 -o ServerAliveCountMax=3 user@hostname

SSH Configuration

  • Edit SSH config file
vim ~/.ssh/config
  • Example SSH config entry
Host myserver
    HostName example.com
    User username
    Port 2222
    IdentityFile ~/.ssh/id_rsa
    ServerAliveInterval 60
  • Connect using config alias
ssh myserver
  • Test SSH config
ssh -T git@github.com

Security and Authentication

  • Disable password authentication (server-side)
# In /etc/ssh/sshd_config
PasswordAuthentication no
PubkeyAuthentication yes
  • Change SSH key passphrase
ssh-keygen -p -f ~/.ssh/id_rsa
  • View SSH key fingerprint
ssh-keygen -lf ~/.ssh/id_rsa.pub
  • Connect with specific cipher
ssh -c aes256-ctr user@hostname
  • Disable host key checking (not recommended for production)
ssh -o StrictHostKeyChecking=no user@hostname

Session Management

  • Run command in background
ssh user@hostname 'nohup command &'
  • Keep session alive after disconnect
ssh user@hostname
screen -S session-name
# or
tmux new-session -s session-name
  • Reconnect to screen session
ssh user@hostname
screen -r session-name
  • Reconnect to tmux session
ssh user@hostname
tmux attach-session -t session-name

Troubleshooting

  • Debug connection issues
ssh -vvv user@hostname
  • Check SSH service status
systemctl status ssh
# or
service ssh status
  • View SSH logs
tail -f /var/log/auth.log
# or
journalctl -u ssh -f
  • Test specific SSH version
ssh -o Protocol=2 user@hostname
  • Escape sequences (when connected)
~.  # Disconnect
~^Z # Background SSH
~#  # List forwarded connections
~?  # Help

Common Use Cases

  • Jump host / bastion server
ssh -J jump-host target-host
  • Multiple jump hosts
ssh -J host1,host2 target-host
  • X11 forwarding for GUI applications
ssh -X user@hostname
  • Compress data transfer
ssh -C user@hostname
  • Run local script on remote server
ssh user@hostname 'bash -s' < local-script.sh
  • Mount remote filesystem with SSHFS
sshfs user@hostname:/remote/path /local/mount/point

Quick File Operations

  • Edit remote file directly
ssh user@hostname 'vim /path/to/file'
  • Create remote directory
ssh user@hostname 'mkdir -p /path/to/directory'
  • Check disk space on remote server
ssh user@hostname 'df -h'
  • View remote file content
ssh user@hostname 'cat /path/to/file'
  • Tail remote log file
ssh user@hostname 'tail -f /var/log/application.log'