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The `ftp` Command in Linux: Dive into Classic FTP

File Transfer Protocol (FTP) is one of the oldest and most commonly used protocols to transfer files between computers over a TCP/IP-based network, like the internet. The ftp command in Linux provides an interface to interact with FTP servers.

Understanding FTP (File Transfer Protocol)

FTP, which stands for File Transfer Protocol, is a standard network protocol used to transfer files between a client and server over a computer network. Originally developed in the 1970s, FTP is one of the oldest protocols still in widespread use today.

Theoretical Explanation:

  1. Protocol: At its core, FTP is a set of rules that dictate how files are exchanged over the Internet. This set of conventions ensures that different computing systems, irrespective of their underlying architectures, can communicate and transfer data seamlessly.

  2. Client-Server Model: FTP operates on a client-server model. The 'client' is typically a user's personal computer or device that requests files, and the 'server' is the machine that stores the files and responds to requests.

  3. Channels: FTP uses two separate communication channels:

    • Control Channel: Used for exchanging command and control information. Typically, it operates on port 21.
    • Data Channel: Used for transferring the actual file data. It usually operates on port 20.
  4. Use Cases: FTP is widely used for:

    • Website Management: Web developers often use FTP to upload and download files from their web hosting accounts.
    • File Sharing: It allows for the sharing of large files that might not be feasible through email.
    • Backup: Many organizations back up data to remote servers using FTP.
    • Software Updates: Some software applications retrieve updates using FTP.

In the modern digital environment, while FTP remains an essential tool, it's crucial to understand its security limitations and opt for more secure variants like SFTP or FTPS when transmitting sensitive data.

FTP Data Flow


  1. FTP Client: The source of the FTP connection, typically your computer or another device trying to access the server.

  2. Client Process: Represents the FTP software or application you're using to initiate the FTP connection on the client side.

  3. Ephemeral port: This is a temporary, random port the client uses to establish the initial connection. It communicates directly with the control connection on the server.

  4. Control Connection: Once the client makes contact with the server, they establish a control connection, typically through the server's well-known port 21. This connection is used to send FTP commands and receive responses.

  5. Data Connections: Unlike the control connection that communicates commands, the data connection is used to transfer actual file data. This typically uses the server's port 20.

  6. FTP Server: The destination of the FTP connection. This is the machine storing the files you want to access.

  7. Service Process: Represents the server-side FTP software or application that's listening for incoming connections and managing file transfers.

  8. Well Known 21 Port: The standard port FTP servers listen on for incoming control connections.

  9. Data Port (usually 20): The standard port FTP servers use to send and receive file data.

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