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SSH: Access Servers from Anywhere

SSH is how you connect to Linux servers remotely. It's encrypted. It's secure. It's essential.

Here's the thing: You'll SSH into servers constantly. Learn it well.

What SSH Actually Does​

SSH (Secure Shell) gives you encrypted remote access. You can:

  • Run commands on remote servers
  • Transfer files securely
  • Tunnel traffic
  • Access servers from anywhere

That's it. But that's everything.

Basic Connection​

ssh username@hostname
ssh username@192.168.1.100       # With IP
ssh -p 2222 username@hostname    # Custom port

Real examples:

ssh ubuntu@54.123.45.67
ssh -p 2222 admin@server.example.com

The format: ssh user@host. Simple.

Exiting: Type exit or press Ctrl+D. That's it.

Running Commands Remotely​

ssh user@host "command"

Real examples:

ssh ubuntu@server "df -h"        # Check disk usage
ssh ubuntu@server "sudo systemctl status nginx"

My take: Useful for quick commands. Don't need to log in fully.

SSH Keys (The Right Way)​

Passwords are annoying. Keys are better.

Why keys:

  • More secure
  • No password typing
  • Required for automation
  • Works with CI/CD

My take: Use keys. Always. Passwords are for beginners.

Generating Keys​

ssh-keygen -t ed25519            # Modern (recommended)
ssh-keygen -t rsa -b 4096        # RSA (older, but works)

With email:

ssh-keygen -t ed25519 -C "your_email@example.com"

Files created:

  • ~/.ssh/id_ed25519 = Private key (keep secret!)
  • ~/.ssh/id_ed25519.pub = Public key (share this)

My take: Use ed25519. It's modern. It's secure. RSA works, but ed25519 is better.

Copying Key to Server​

# Easy way
ssh-copy-id username@hostname

# Manual way
cat ~/.ssh/id_ed25519.pub | ssh username@hostname "mkdir -p ~/.ssh && cat >> ~/.ssh/authorized_keys"

The easy way: ssh-copy-id does everything. Use it.

The manual way: Copy the public key, add it to ~/.ssh/authorized_keys on the server.

My take: Use ssh-copy-id. It's easier. Less error-prone.

Testing Keys​

ssh username@hostname

If it works without a password, keys are set up correctly.

My take: Test it. Make sure it works. Then you're set.

SSH Config (Make Life Easier)​

Create ~/.ssh/config:

Host myserver
    HostName 54.123.45.67
    User ubuntu
    Port 22
    IdentityFile ~/.ssh/id_ed25519

Then connect:

ssh myserver                     # Instead of ssh ubuntu@54.123.45.67

My take: Use SSH config. Saves typing. Makes life easier.

Common Options​

ssh -v user@host                 # Verbose (debugging)
ssh -X user@host                 # X11 forwarding
ssh -L 8080:localhost:80 user@host  # Port forwarding

My take: You'll rarely use these. But they're useful when you need them.

SCP: Copy Files Over SSH​

# Copy to server
scp file.txt user@host:/path/

# Copy from server
scp user@host:/path/file.txt ./

# Copy directory
scp -r directory/ user@host:/path/

Real examples:

scp config.txt ubuntu@server:/etc/nginx/
scp ubuntu@server:/var/log/nginx/access.log ./

My take: SCP is simple. Use it for file transfers.

SFTP: Interactive File Transfer​

sftp user@host

Commands:

  • put file.txt - Upload
  • get file.txt - Download
  • ls - List remote
  • lls - List local
  • exit - Quit

My take: SCP is easier for single files. SFTP is better for multiple files.

SSH Tunneling (Port Forwarding)​

# Local forwarding
ssh -L 8080:localhost:80 user@host

# Remote forwarding
ssh -R 8080:localhost:80 user@host

What it does: Forwards ports through SSH. Useful for accessing services.

My take: Advanced. You'll use it rarely. But useful when you need it.

Security Best Practices​

Disable Password Authentication​

Edit /etc/ssh/sshd_config:

PasswordAuthentication no

My take: Once keys work, disable passwords. More secure.

Change Default Port​

Edit /etc/ssh/sshd_config:

Port 2222

My take: Reduces automated attacks. Not essential, but helps.

Disable Root Login​

Edit /etc/ssh/sshd_config:

PermitRootLogin no

My take: Always do this. Root shouldn't SSH directly.

Common Mistakes (I've Made These)​

  1. Wrong key permissions: Private keys should be 600. chmod 600 ~/.ssh/id_ed25519

  2. Forgetting to restart SSH: After changing config, restart: sudo systemctl restart sshd

  3. Wrong username: Make sure you're using the right username. ubuntu on Ubuntu, ec2-user on Amazon Linux, etc.

  4. Firewall blocking: Make sure port 22 (or your custom port) is open.

  5. Key in wrong place: Public key goes in ~/.ssh/authorized_keys on the server, not locally.

What's Next?​

Now that you can SSH into servers, you can manage them remotely. Or learn about Networking Fundamentals to understand how networks work.

Personal note: When I started, I'd type passwords constantly. Then I learned SSH keys. Now I never type passwords. Keys are the way. Learn them. Use them. Your future self will thank you.