If you’re a developer or SysAdmin, you're probably familiar with SSH as an efficient way to communicate with servers remotely.
Briefly, SSH is a protocol that helps you access servers remotely from anywhere. This allows you to get your work done faster while keeping your data more secure.
So, if you're new to the world of development and servers, SSH is definitely something you should get familiar with.
So, what exactly is SSH? When do you need it, and how do you use it?
Let's go through it step by step in this article.
What Is SSH?
SSH stands for Secure Shell, a protocol used to manage and access servers remotely over an encrypted network connection.
SSH is a commonly used standard for server administration because it can encrypt connections and provide authentication mechanisms.
SSH works by establishing a secure connection between your device (client) and the target server. Once connected, you can access the shell on the server to run commands, change configurations, monitor the system, and perform other administrative tasks.
Besides shell access, SSH also supports various needs such as file transfer and tunneling. The protocol generally uses TCP port 22 as its default port, although administrators can change it according to their security needs and server configuration.
If SSH is a new term for you, let's go over some related terms to avoid any misconceptions. When discussing SSH, you need to understand what a Shell, Terminal, and OpenSSH are.
Here's a quick explanation:
- Shell: An interface used to give commands to the operating system.
- Terminal: The place where you open and use a shell.
- SSH: A protocol for remotely accessing a shell on another computer or server.
- OpenSSH: Software/tools that implement SSH.
Here's a simple example: you open a terminal and run the SSH. This connects you to the shell on the server, where you can run commands.
Key Components of SSH
Now that you understand the basic terms, let's look at some of the components involved when you establish an SSH connection.
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SSH Client
SSH Client is software used to establish a connection to an SSH Server. You usually run it through a terminal on your laptop or computer. OpenSSH is one example of software that provides an SSH Client.
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SSH Server
SSH Server is a service running on the server that accepts connections from an SSH Client. Once a connection is received, the server processes the login request and provides access according to the user's permissions.
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Public Key
A Public Key is one part of an SSH Key pair used for authentication. The Public Key can be stored on the server to help verify the user's identity.
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Private Key
A Private Key is the counterpart to the Public Key and is stored on the user's device. This key must be kept secret because it is used to prove the user's identity during authentication.
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SSH Daemon (sshd)
The SSH Daemon, or sshd, is a program running on the server that accepts and handles SSH connections. On Linux systems, sshd runs as a service and makes the server ready to accept connections from SSH Clients.
SSH Functions
To better understand what SSH can do, let's go through its main functions one by one:
1. Remote Server
The most common function of SSH is accessing a server remotely. As a developer or administrator, you can log in to a VPS, cloud server, or dedicated server from your laptop without having to be physically present where the server is located. Once logged in, you can manage the system from anywhere, just as if you were working directly from the server terminal.
2. File Transfer
SSH can also be used to transfer files securely. Technologies such as SCP (Secure Copy Protocol) and SFTP (SSH File Transfer Protocol) use SSH connections to send or retrieve files from a server. This is useful for application deployment, backups, and file transfers that require protection during transmission.
3. Remote Command
Not every task requires an interactive terminal session. SSH can execute specific commands directly from the client. For example, an administrator can check disk usage, run scripts, or restart services without having to open a long shell session.
4. Port Forwarding
This feature allows you to forward a connection from one port to another through an SSH connection. This means you can access internal services without making them publicly accessible. This approach can help keep your server more secure.
5. Tunneling
With SSH tunneling, you can create a secure path between your device and a server through an SSH connection. Through this path, you can access resources or services that are not publicly accessible more securely. This feature is commonly used for troubleshooting, accessing databases, or accessing internal services.
How Does SSH Work?
The SSH process can be illustrated as follows:
Client → Internet → SSH Server → Authentication → Encryption → Shell
As the client, you access the SSH Server through the internet. The client then communicates with the SSH Server to establish a secure connection, including encryption and authentication processes. Once these processes are complete, you can access the shell on the server.
To make it clearer, let's look at each part of the process:
1. SSH Client
The SSH Client connects you to the server through SSH. You can run it through a terminal on a device such as a laptop or computer. One commonly used example of an SSH Client is OpenSSH.
2. SSH Server
SSH Server is a service running on the server that accepts connections from an SSH Client. When you try to connect, the SSH Server receives the request and processes it.
3. Default Port 22
By default, SSH uses TCP port 22 to receive connections. So, when you run SSH without specifying another port, the connection is automatically directed to port 22.
4. Authentication Process
After connecting, the server needs to make sure that you have permission to access it. This process is called authentication and can use a password, an SSH key, or additional methods such as MFA.
5. Data Encryption
Once the connection is established, SSH encrypts the data sent between your device and the server. This means that someone trying to intercept the connection cannot easily read the information being transmitted.
6. Session Creation
After the authentication process is complete, SSH creates a session between your device and the server. From there, you can access the shell and run various commands on the server. The session ends when you log out or the connection is closed.
SSH Authentication Methods
To establish a secure connection, you can use several authentication methods with SSH:
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Password Authentication
This method uses a username and password to verify the user. It is easy to implement but using a weak or reused password can increase the risk of attacks such as brute-force attacks.
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SSH Key Authentication
This method uses a pair of public key and private key. The public key is stored on the server, while the private key remains on the user's device. This is a strong option for authentication because the private key does not need to be sent to the server during the login process.
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Multi-Factor Authentication (MFA)
MFA adds another authentication factor after the primary credentials have been verified. For example, you may be asked to enter a code from an authenticator app. With this additional layer, compromising a single factor does not automatically provide access to the server.
SSH vs Telnet
Telnet is another protocol that can be used to remotely access a server. It was developed in the early days of the internet and was commonly used in more limited network environments. Because of this, Telnet does not provide network encryption like SSH. At the time, server networks could still be considered relatively secure because they were often treated as internal networks.
However, as the internet developed rapidly and cyber threats became more complex, SSH emerged as a more secure solution.
The most important difference between the two lies in how data is transmitted. Telnet sends data without encryption, so usernames, passwords, and commands sent through the connection could be exposed if the traffic is intercepted. SSH, on the other hand, encrypts communication between the client and server, providing better protection for transmitted information.
Besides encryption, SSH also provides several authentication methods, such as passwords and SSH keys. SSH also has mechanisms to maintain data integrity during communication.
To make the differences between SSH and Telnet clearer, take a look at the comparison below:
| Feature | SSH | Telnet |
| Encryption | Data is encrypted | Data is sent without encryption |
| Authentication | Password, key, and additional methods | Generally, username and password |
| Security | More secure with proper configuration | More vulnerable to interception |
| Data Integrity | Provides data integrity protection | Does not provide equivalent protection |
What Makes SSH More Secure?
In summary, several things make SSH more secure:
- Encryption: SSH encrypts communication between the client and server, making transmitted data difficult to read if the connection is intercepted.
- Authentication: SSH supports several authentication methods, such as passwords and SSH keys, to ensure that only authorized users can log in.
- Security: SSH can be strengthened through configurations such as firewalls, access restrictions, and disabling root login.
- Data Integrity: SSH helps ensure that data sent between the client and server is not modified by another party during communication.
How to Use SSH
Using SSH is relatively easy. Linux and macOS usually come with an SSH Client, so you can open the Terminal and start using it.
If you're using Windows, you can use PowerShell or Windows Terminal with OpenSSH.
Use the following format:
ssh user@ip-server
Replace user with the username on the server and ip-server with the IP address of the target server. If the server uses a port other than 22, add the -p option, for example:
ssh -p 2222 user@ip-server
How to Install an SSH Server
If you're using a Linux server and want to access it through SSH, you need to install an SSH Server first. The process varies slightly depending on the Linux distribution you use.
1. Ubuntu and Debian
On Ubuntu and Debian, you can install the SSH Server using the openssh-server package.
sudo apt update sudo apt install openssh-server
2. Rocky Linux and CentOS
For Rocky Linux and CentOS, you can use dnf to install the SSH Server:
sudo dnf install openssh-server
3. Check SSH Status
After the installation is complete, you can check whether the SSH Server is running with:
sudo systemctl status ssh
If the SSH service is not running, use:
sudo systemctl start ssh
To restart the SSH service:
sudo systemctl restart ssh
To make the SSH Server start automatically when the server boots:
sudo systemctl enable ssh
On some distributions, especially Rocky Linux and CentOS, the SSH service is named sshd. In that case, replace ssh with sshd in the systemctl commands. For example:
sudo systemctl status sshd
When Should You Use SSH?
SSH is the go-to choice when you need to manage a server remotely, especially in the following environments:
- VPS (Virtual Private Server): Manage applications, services, databases, and system configurations.
- Dedicated Server: Administer physical servers without having to be at the data center.
- Cloud Server: Access instances for deployment, troubleshooting, and maintenance.
- Private Cloud: Manage internal resources with more controlled access.
- Data Center: Perform infrastructure administration from an administrator's workstation.
As long as the server can be reached over a network and the SSH Server is properly configured, administrators can perform many tasks without needing direct physical access.
Conclusion
SSH is an important protocol for securely accessing and managing servers remotely. With encryption, authentication, file transfer, and tunneling, SSH helps administrators keep their infrastructure secure.
For secure and reliable server needs, you can choose a VPS or cloud server service that provides SSH access, such as CloudRaya. This allows you to access your server whenever and wherever you need it with ease. Sign up for CloudRaya now!
