📂 SCP Tutorial: Understanding, Installing, and Using SCP on Linux

In this tutorial, we'll explore SCP (Secure Copy Protocol), compare it with FTP (File Transfer Protocol), and guide you through the process of installing and configuring SCP on a Linux server and client. We'll also provide examples of using SCP for file transfers.

📑 Table of Contents

📄 What is SCP?
🔍 SCP vs. FTP: A Comparison
🔢 What is the Default SCP Port?
🛠️ Installing and Configuring SCP on a Remote Server and Client
📁 Examples: Using SCP for File Transfers

📄 What is SCP?

SCP (Secure Copy Protocol) is a network protocol that securely transfers files between a local and a remote host or between two remote hosts. SCP is based on SSH (Secure Shell), providing strong encryption and authentication, making it more secure than FTP.

SCP operates over SSH, using port 22 by default. It ensures that both the authentication and data transfer are encrypted, protecting sensitive information from being intercepted during transmission.

🔍 SCP vs. FTP: A Comparison

Feature	SCP	FTP
Security	High (Encrypted via SSH)	Low (Data is not encrypted)
Default Port	22	21
Authentication	SSH Keys, Password	Username, Password
File Transfer Modes	Secure (SCP over SSH)	Active, Passive
Ease of Use	Command-line based, simple syntax	GUI and command-line options
Transfer Speed	Fast (minimal overhead due to encryption)	Can be slower (depending on mode and settings)
Firewall Compatibility	Works well with firewalls	May require additional ports (especially in passive mode)
Use Case	Secure file transfer between trusted systems	General-purpose file transfer

🔢 What is the Default SCP Port?

The Default SCP Port 22 is the same as the default SSH port. SCP operates over SSH, so when you initiate an SCP connection, it uses port 22 by default to establish a secure, encrypted communication channel.

🛠️ Installing and Configuring SCP on a Remote Server and Client

📡 On the SCP Server:

Ensure SSH is Installed:

On a Debian/Ubuntu server:

sudo apt update
sudo apt install openssh-server

On a CentOS/RHEL server:
```
sudo yum install openssh-server
```
Start and Enable the SSH Service:

sudo systemctl start sshd
sudo systemctl enable sshd

Configure the SSH Server (Optional):
Open the configuration file:
```
sudo nano /etc/ssh/sshd_config
```
Modify the following settings as needed:
- To change the default port (from 22 to another), add or modify:
```
Port 2222
```
- Ensure PermitRootLogin is set to no for security:
```
PermitRootLogin no
```
- Save and close the file.
Restart the SSH Service:
```
sudo systemctl restart sshd
```

💻 On the SCP Client:

Ensure SCP is Installed:
On a Debian/Ubuntu client:
```
sudo apt install openssh-client
```
On a CentOS/RHEL client:
```
sudo yum install openssh-clients
```
Connect to the Remote Server Using SCP:
SCP is ready to use with the SSH service running on the server. You can start transferring files as needed.

📁 Examples: Using SCP for File Transfers

Example 1: Easy - Copying a Single File from Local to Remote

scp /path/to/local/file.txt username@remote_host:/path/to/remote/directory/

This command copies file.txt from your local machine to the specified directory on the remote host.

Example 2: Mid - Copying a Directory Recursively from Remote to Local

scp -r username@remote_host:/path/to/remote/directory/ /path/to/local/directory/

The -r option is used to copy a directory and its contents recursively from the remote server to your local machine.

Example 3: Mid - Copying Files Between Two Remote Servers

scp username1@remote_host1:/path/to/remote/file.txt username2@remote_host2:/path/to/destination/

This command copies a file from one remote server to another, using your local machine as a relay.

Example 4: Hard - Using a Non-Default Port and SSH Key Authentication

scp -P 2222 -i /path/to/private_key username@remote_host:/path/to/remote/file.txt /path/to/local/directory/

The -P 2222 option specifies a non-default port (2222).
The -i option specifies the path to your private SSH key for authentication.
This command securely copies a file from a remote server to your local machine.

This tutorial provides a comprehensive overview of SCP, its installation, configuration, and basic usage for secure file transfers between Linux systems. Happy file transferring! 📂🔐