SSH Server Setup and Connection Guide

This guide covers the basic steps to install an SSH server, configure it for security, and connect to it from a client.

1. Server-Side Installation

On Ubuntu/Debian-based systems:

sudo apt update
sudo apt install openssh-server

Verify Status

sudo systemctl status ssh

2. Basic Configuration

The main configuration file is located at /etc/ssh/sshd_config.

Common Security Hardening

Before making changes, back up the original file:

sudo cp /etc/ssh/sshd_config /etc/ssh/sshd_config.bak

Edit the file:

sudo nano /etc/ssh/sshd_config

Recommended changes:

• Change Default Port: Port 2222 (Reduces automated script attacks)
• Disable Root Login: PermitRootLogin no
• Key-Based Auth Only: PasswordAuthentication no

Apply Changes

sudo systemctl restart ssh

3. Firewall Configuration (UFW)

If using UFW, allow the SSH port:

sudo ufw allow ssh
# OR if you changed the port:
sudo ufw allow 2222/tcp

4. Connecting to the Server

Basic Password Connection

ssh username@server_ip_address

Connection with Custom Port

ssh -p 2222 username@server_ip_address

5. SSH Key Authentication (Recommended)

Generate Keys on Client

ssh-keygen -t ed25519

Copy Key to Server

ssh-copy-id -i ~/.ssh/id_ed25519.pub username@server_ip_address

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6. Common SSH Commands and Usages

Execute a Remote Command (Without Logging In)

ssh username@server_ip_address "df -h"

Copy Files (SCP)

• Local to Server:

  scp local_file.txt username@server_ip_address:/home/username/
  

• Server to Local:

  scp username@server_ip_address:/path/to/remote_file.txt /local/path/
  

• Directory (Recursive):

  scp -r local_dir username@server_ip_address:/remote/path/
  

SSH Config File (~/.ssh/config)

Avoid typing the full IP and port every time by creating an alias on your client machine:

nano ~/.ssh/config

Add an entry:

Host myserver
    HostName 192.168.1.50
    User colton
    Port 2222
    IdentityFile ~/.ssh/id_ed25519

Now you can connect simply with: ssh myserver

SSH Port Forwarding (SSH Tunnel)

Expose a remote service (like a Web UI on port 8080) to your local machine:

ssh -L 9000:localhost:8080 username@server_ip_address

Now you can visit http://localhost:9000 in your browser to access the remote service.

List Active SSH Sessions (On Server)

who
# OR
w

Terminate All Other SSH Sessions

sudo pkill -u username -t pts/1