---

SSH (Secure Shell) is a protocol for secure remote login and command execution. Essential for managing remote servers, secure file transfer, and tunneling.

---

Basic Connection

• ssh user@hostname - Connect to remote host

• ssh user@hostname -p 2222 - Connect on custom port

• ssh -i ~/.ssh/key.pem user@hostname - Use specific key file

• ssh -v user@hostname - Verbose output (debugging)

---

Port Forwarding

• ssh -L 8080:localhost:80 user@hostname - Local port forward

• ssh -R 8080:localhost:80 user@hostname - Remote port forward

• ssh -D 1080 user@hostname - Dynamic SOCKS proxy

• ssh -L 8080:remote:80 -N user@hostname - Forward without shell

---

File Transfer

• scp file.txt user@hostname:/path/ - Copy file to remote

• scp user@hostname:/path/file.txt . - Copy file from remote

• scp -r dir/ user@hostname:/path/ - Copy directory recursively

• rsync -avz dir/ user@hostname:/path/ - Sync with rsync

---

Remote Execution

• ssh user@hostname "command" - Execute command remotely

• ssh user@hostname "cat file.txt" - Read remote file

• cat file.txt | ssh user@hostname "cat > remote.txt" - Pipe to remote

---

Configuration

• ~/.ssh/config - SSH client configuration file

• Host alias - Define host alias

• HostName real.hostname.com - Set hostname

• User username - Set default user

• IdentityFile ~/.ssh/key - Specify key file

• Port 2222 - Set port

---

Common Examples

Basic Connection

ssh user@example.com

Connect to remote server.

Port Forwarding

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

Forward local port 8080 to remote port 80.

Copy File

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

Copy file to remote server.

Execute Command

ssh user@example.com "ls -la"

Run command on remote server.

SSH Config

Host myserver
    HostName example.com
    User myuser
    IdentityFile ~/.ssh/id_ed25519
    Port 2222

Configure SSH alias in ~/.ssh/config.

---

Tips

• Use key-based authentication instead of passwords

• Configure ~/.ssh/config for easier connections

• Use -N flag for port forwarding without shell

• rsync is often faster than scp for large transfers

• Use ControlMaster for connection multiplexing

• Keep SSH keys secure and use passphrases

• Disable password authentication on servers when possible