Cheat Sheet #day37 - SSH

SSH Cheatsheet

Basic Usage

• Connect to a Remote Host

    ssh username@hostname
  

  Example:

    ssh user@example.com
  

• Connect with a Specific Port

    ssh -p port_number username@hostname
  

  Example:

    ssh -p 2222 user@example.com
  

• Run a Command on a Remote Host

    ssh username@hostname command
  

  Example:

    ssh user@example.com 'ls -l /var/www'
  

Key-Based Authentication

• Generate SSH Key Pair

    ssh-keygen -t rsa -b 4096 -C "your_email@example.com"
  

  • Add SSH Key to SSH-Agent

    eval "$(ssh-agent -s)"
    ssh-add ~/.ssh/id_rsa

• Copy Public Key to Remote Host

    ssh-copy-id username@hostname
  

  Example:

    ssh-copy-id user@example.com
  

Configuration

• Edit SSH Config File

  • Path: ~/.ssh/config

    nano ~/.ssh/config

Example Config File:

    Host example
        HostName example.com
        User user
        Port 22
        IdentityFile ~/.ssh/id_rsa

• Connect Using Config Alias

    ssh example
  

Port Forwarding

• Local Port Forwarding

    ssh -L local_port:destination_host:destination_port username@hostname
  

  Example:

    ssh -L 8080:localhost:80 user@example.com
  

• Remote Port Forwarding

    ssh -R remote_port:destination_host:destination_port username@hostname
  

  Example:

    ssh -R 8080:localhost:80 user@example.com
  

• Dynamic Port Forwarding (SOCKS Proxy)

    ssh -D local_port username@hostname
  

  Example:

    ssh -D 1080 user@example.com
  

File Transfer

• SCP (Secure Copy)

  • Copy Local to Remote

    scp local_file username@hostname:/remote/directory

Example:

    scp file.txt user@example.com:/home/user/

• Copy Remote to Local

    scp username@hostname:/remote/file /local/directory

Example:

    scp user@example.com:/home/user/file.txt /local/directory

• SFTP (SSH File Transfer Protocol)

    sftp username@hostname
  

  • Common SFTP Commands

    sftp> get remote_file
    sftp> put local_file
    sftp> ls
    sftp> cd directory
    sftp> pwd
    sftp> exit

Tunneling and Proxying

• SSH Tunnel for All Traffic

    ssh -D 8080 -C -q -N username@hostname
  

  • Use the tunnel as a SOCKS proxy in your browser or application.

• ProxyCommand

  • Use another SSH server as a proxy.

    Host internal
        HostName internal.example.com
        User user
        ProxyCommand ssh -q -W %h:%p gateway.example.com

Advanced Options

• Enable X11 Forwarding

    ssh -X username@hostname
  

• Enable Compression

    ssh -C username@hostname
  

• Increase Verbosity

    ssh -v username@hostname
  

• Multiple Levels of Verbosity

    ssh -vvv username@hostname
  

SSH Agent Forwarding

• Enable Agent Forwarding

    ssh -A username@hostname
  

Managing SSH Keys

• List Loaded Keys

    ssh-add -l
  

• Remove All Loaded Keys

    ssh-add -D
  

SSH Security

• Disable Root Login

  • Edit /etc/ssh/sshd_config on the remote server:

    PermitRootLogin no

• Change Default SSH Port

  • Edit /etc/ssh/sshd_config on the remote server:

    Port 2222

• Restrict User Logins

  • Edit /etc/ssh/sshd_config on the remote server:

    AllowUsers user1 user2

Additional Tips

• Use SSH Escape Sequences

  • ~.: Disconnect

  • ~C: Open command line

  • Type escape sequences after pressing Enter.

• SSHFS (SSH Filesystem)

  • Mount a remote filesystem via SSH:

    sshfs username@hostname:/remote/directory /local/mount/point

This cheatsheet covers essential commands and configurations for using SSH effectively, from basic connections to advanced tunneling and security practices. Adjust commands and paths according to your specific setup and needs.