SSH cheatsheet

Sure! Here's a comprehensive SSH (Secure Shell) cheat sheet, covering basic to advanced features, along with tips and examples:

Basic SSH Usage

1. Connect to a Host

   ssh user@hostname
   

   Connect to hostname as user.

2. Connect with a Specific Port

   ssh -p 2222 user@hostname
   

   Connect to hostname on port 2222.

3. SSH Key Generation

   ssh-keygen
   

   Generate a new SSH key pair.

4. Copy SSH Key to a Host

   ssh-copy-id user@hostname
   

   Copy your local public key to the remote host for key-based authentication.

File Transfer

1. SCP: Copy Files Over SSH

   scp localfile.txt user@hostname:/remote/path
   scp user@hostname:/remote/path/remotefile.txt localfile.txt
   

   Copy localfile.txt to a remote host, or copy a file from a remote host to local.

2. RSync Over SSH

   rsync -avz -e ssh localfile.txt user@hostname:/remote/path
   

   Securely sync files over SSH.

Advanced SSH Features

1. SSH Tunneling (Port Forwarding)

   • Local Port Forwarding

     ssh -L localPort:remoteAddress:remotePort user@hostname
     

     Forward a local port to a remote address and port.

   • Remote Port Forwarding

     ssh -R remotePort:localAddress:localPort user@hostname
     

     Forward a remote port to a local address and port.

   • Dynamic Port Forwarding (SOCKS Proxy)

     ssh -D localPort user@hostname
     

     Create a SOCKS proxy on a local port.

2. SSH Config File

   • Create a ~/.ssh/config file for easier connection management. Example:

     Host myserver
       HostName server.example.com
       User myuser
       Port 2222
       IdentityFile ~/.ssh/mykey
     

   • Connect using the alias: ssh myserver

3. SSH Agent Forwarding

   ssh -A user@hostname
   

   Forward your SSH key agent to the host (useful for hopping between hosts).

4. X11 Forwarding

   ssh -X user@hostname
   

   Forward X11 (GUI) applications from the remote host.

SSH Tips

1. Keep SSH Sessions Alive

   • Add the following to ~/.ssh/config:

     Host *
       ServerAliveInterval 60
     

   • This sends a keepalive signal every 60 seconds to keep the connection active.

2. Use SSH Multiplexing

   • Reuse an existing SSH connection for multiple sessions to the same host.
   • Add to ~/.ssh/config:

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

3. Mount Remote Filesystem with SSHFS

   sshfs user@hostname:/remote/path /local/mount/point
   

   Mount a remote filesystem locally via SSHFS.

Security Tips

1. Disable Root Login

   • In the remote /etc/ssh/sshd_config file, ensure:

     PermitRootLogin no
     

2. Use Key-Based Authentication

   • Disable password authentication in /etc/ssh/sshd_config:

     PasswordAuthentication no
     

3. Change Default SSH Port

   • In /etc/ssh/sshd_config:

     Port 2222
     

Examples

1. Connect to a Server

   ssh [email protected]
   

2. Securely Transfer a File

   scp report.txt [email protected]:/home/myuser/
   

3. SSH Tunnel to Access a Remote Database Locally

   ssh -L 3306:localhost:3306 myuser@dbserver
   

   Access a remote MySQL server on local port 3306.