How to allow ssh access on linux?

Secure Shell (SSH) is a critical tool for managing and accessing remote servers securely. It provides an encrypted communication channel, ensuring data privacy and integrity while allowing users to execute commands, transfer files, and manage systems over a network. Widely used by system administrators, developers, and IT professionals, SSH is the backbone of secure server management in Linux environments.

Configuring SSH access in Linux not only involves enabling the service but also optimizing its security. From setting up authentication methods to restricting user access, a well-configured SSH service ensures robust protection against unauthorized access while maintaining efficient system operations. Understanding how to configure and secure SSH access is essential for both beginners and experienced users.

Preparing Your System

To allow SSH access, the first step is to ensure your Linux system is properly prepared. This involves checking for the presence of an SSH server, installing it if necessary, and verifying its configuration. Here’s how to prepare your system effectively:

1. Installing SSH Server on Popular Linux Distros

• Ubuntu/Debian-based Systems: Use the apt package manager to install OpenSSH server. For example:

  sudo apt update
  sudo apt install openssh-server
  

  CentOS/Red Hat-based Systems: Use the dnf or yum package manager:

  sudo dnf install openssh-server
  

  Fedora: Install the OpenSSH server package:

  sudo dnf install openssh-server

2. Enabling and Starting the SSH Service

• After installation, enable the SSH service to start automatically on boot:

  sudo systemctl enable sshd

• Start the SSH service if it’s not already running:

  sudo systemctl start sshd

3. Verifying SSH Installation and Version

• Confirm that SSH is installed and running:

  sudo systemctl status sshd
  

   

• Check the installed version of SSH to ensure compatibility:

  ssh -V
  

4. Updating System Packages

• Before setting up SSH, update your system to ensure all dependencies are up-to-date:

  sudo apt update && sudo apt upgrade -y
  

Configuring SSH Access

After ensuring the SSH server is installed and running, configuring it properly is crucial for both functionality and security. Here are the key steps involved in configuring SSH access on a Linux system:

1. Editing the SSH Configuration File (/etc/ssh/sshd_config)

• Open the SSH configuration file using a text editor like nano or vi:

  sudo nano /etc/ssh/sshd_config

• Look for options like PermitRootLogin, PasswordAuthentication, and Port, and adjust them based on your requirements.

2. Changing the Default SSH Port

• By default, SSH uses port 22. Changing it to a non-standard port can help reduce brute force attacks:

  Port 2222
  

  Save the file and restart the SSH service:

  sudo systemctl restart sshd
  

3. Allowing Specific Users or Groups

• To restrict SSH access to specific users or groups, add the following lines to the configuration file:

  AllowUsers user1 user2
  AllowGroups sshusers

4. Disabling Root Login

• For enhanced security, prevent root login by setting:

  PermitRootLogin no

5. Enabling Key-Based Authentication

• Disable password authentication:

  PasswordAuthentication no
  

• Generate an SSH key pair on your client and copy the public key to the server using:

  ssh-copy-id user@hostname

6. Enabling Two-Factor Authentication (Optional)

• Install and configure tools like Google Authenticator to enable two-factor authentication for added security.

7. Applying Changes and Restarting SSH

• Restart the SSH service to apply the new settings:

  sudo systemctl restart sshd