The Essential Guide to SSH (Secure Shell) for Linux Users

Introduction

Do you want to export data from your Linux machine to a distant server? Let’s say you need to run commands on a machine remotely but do not want to disclose your confidential data.

That’s where SSH comes into play. Using a Secure Shell, or SSH for short, will be the most appropriate solution for you to safeguard your confidential data. Firstly, learn what the SSH File Transfer Protocol is. It’s a secure method of accessing other systems and typing commands that are run on different systems.

In this guide, we are going to explore SSH as a protocol and explain what it is, how to set it up, and how to use it to its fullest. We have enlightened you on some of its basic traits, security aspects, and ways you should set up this connection to get the optimal result.

Understanding SSH For Linux

SSH is a network protocol that enables computer users to log in directly to another computer that is connected through a network. It encodes information to ensure confidentiality and requires the user to authenticate their identity for ultimate protection. 

Key Features Of SSH Include

• Encryption: Any traffic transferred through SSH is encrypted, and therefore, it is almost impossible for an intruder to intercept or tamper with; however, remember that it is a different form of SSL. To know more, read our blog: SSH vs. SSL: Know the Difference 
• Authentication: SSH supports both passwords as well as key-based authentication mechanisms to log in to the system.
• Tunneling: SSH can be termed as creating secure tunnels to the other application layers, for example, the web-based application HTTP or File Transfer Protocol FTP.

Setting Up SSH

If you are to use SSH, you will have to set up an SSH client as well as an SSH server. The SSH client is the application that is installed on your computing device, and it provides the interface to the remote system, while the SSH server is the software that is running on the remote systems, accepting the SSH connection.

1. Installation

Most of the Linux distributions, like Ubuntu, Debian, CentOS, Fedora, Arch Linux, and others available, already have SSH preinstalled for remote access. To verify, open a terminal and enter the following command:

ssh -V

If the SSH is installed, then you will be able to see the version information.

You can also install Secure Shell Protocol (SSH) on Windows, macOS, and Linux. 

2. Generating Keys

It is possible to utilize key-based authentication. To enable authentication, users need to create a public and private pair of keys. 

• Open a terminal and enter the following command:

ssh-keygen -t rsa -b 4096

It will generate a new key pair in your home directory.

• Authorize Public Key

Copy your public key to the authorized_keys file on the remote server. 

3. Connecting to a Remote Server

To connect to a remote server using SSH, you can use the following command:

ssh username@server_address

In this command, replace the username with your username on the remote server and server_address with your server’s IP address or hostname.

Common Uses of SSH

1. Remote Administration: This task involves controlling other remote systems, running commands, and setting up certain services.
2. File Transfer: It can also be used to securely transfer files between two systems, which are the SCP vs. SFTP protocol.
3. Port Forwarding: They can be used to access resources on remote machines that may not be available for access to the general public.
4. X11 Forwarding: Execute programs with a graphical user interface on a server and display the GUI on your personal computer.

Key SSH Commands

Here are some frequently used Secure Shell commands:

• scp: Transfer files from local and/or remote systems.
• sftp: Secure File Transfer Protocol, which is a file transfer protocol based on SSH.
• ssh-keygen: Shunt key pairs for the Secure Secure Shell protocol.
• ssh-add: Save the private key on one’s ssh-agent to avoid frequently entering the passphrase time after another time.
• ssh-agent: Beginning an SSH agent to aid in the management of private key resources.

Troubleshooting Common SSH Issues

If you encounter issues when using SSH, here are the solutions to the most common issues. 

1. Connection refused: Ensure that the SSH server is not running on the remote system.
2. Permission denied: Make sure that you have the right permissions when connecting to the system on the other end.
3. Key authentication failed: Verify that your public key is accepted on the distant server.
4. Disable password authentication: Do not use it at all or, at least, use key-based authentication instead.
5. Limit access: Limit the IP connection to SSH to only authenticated users.
6. Use strong encryption: A strong encryption algorithm must be established on your side as an SSH server provider.
7. Secure key management: The private keys should not be shared with anyone.