Overview: FTP and FTP servers

FTP (FILETRANSFERPROTOCOL) is the abbreviation for File Transfer Protocol.

the role of FTP

As its name shows: the primary role of FTP is to have users connect to the last remote computer (which runs the FTP server program) to see what files are on the remote computer, then copy the files from the remote computer to the local computer, or send the files from the local computer to the remote computer.

The principle of FTP work

Take the file as an example, when you start FTP copy files from a remote computer, you actually started two programs: a local computer FTP client program: it to the FTP server to make copies of the file request. The other is to start the FTP server program on the remote computer, which responds to your request by transferring the files you specify to your computer. FTP takes the client/server approach, and clients install an FTP client on their local computer. The FTP client has two kinds of character interface and graphical interface. The ftp command for the character interface is complex and varied. Graphical interface of the FTP client program, the operation should be simple and convenient.

Simply put, the FTP-enabled server is the FTP server, and here's what the FTP protocol (File Transfer Protocol) is about.

Generally speaking, the primary purpose of user networking is to realize information sharing, and file transfer is one of the most important contents of information sharing. Early implementation of the Internet to transfer files, is not an easy thing, we know that the Internet is a very complex computer environment, there are PCs, workstations, there are Macs, there are large machines, according to statistics connected to the Internet on the computer has tens of millions of units, And these computers may run different operating systems, there are running UNIX servers, there are running DOS, Windows PC and running MacOS Apple, and so on, and a variety of operating systems file communication problem, need to establish a unified file transfer protocol, which is called FTP. There are different FTP applications based on different operating systems, and all of these applications adhere to the same protocol so that users can transfer their files to others or get files from other user environments.

Like most Internet services, FTP is also a client/server system. The user connects to the FTP server program on the remote host through a client program that supports the FTP protocol. The user sends a command to the server program through a client program that executes the commands issued by the user and returns the results of the execution to the client. For example, a user sends a command asking the server to send a copy of a file to the user, and the server responds to the command and sends the specified file to the user's machine. The client program receives the file on behalf of the user and stores it in the user directory.

In the use of FTP, users often encounter two concepts: "Download" (Download) and "Upload" (Upload). The download file is the copy of the file from the remote host to your computer, and the upload file is the copy of the file from your computer to the remote host. In Internet language, a user can upload (download) files to (from) a remote host through a client program.

When you use FTP, you must first log in, and you can upload or download files after you have the appropriate permissions on the remote host. That is, you must have the appropriate authorization for which computer you want to transfer files to. In other words, the file cannot be routed unless there is a user ID and password. This is contrary to the openness of the Internet, the FTP host on the internet is more than tens of millions, it is impossible to require each user on each host account. Anonymous FTP is created to solve this problem.

Anonymous FTP is a mechanism by which a user can connect to and download files from a remote host without becoming a registered user. The system administrator has established a special user ID, which can be used anywhere in the name of Anonymous,internet.

The FTP program connects anonymous FTP hosts in the same way as connecting to a normal FTP host, except that you must enter a anonymous when you require a user ID ID, and the password for that userid can be any string. It is customary to use your own e-mail address as a password to enable system maintenance programs to record who is accessing these files.

It is noteworthy that anonymous FTP does not apply to all Internet hosts, but only to those hosts that provide this service.

When a remote host provides an anonymous FTP service, certain directories are specified to be open to the public, allowing anonymous access. The rest of the directories in the system are in the hidden state. As a security measure, most anonymous FTP hosts allow users to download files from them, rather than allowing them to upload files to them, that is, users can copy all files on an anonymous FTP host to their machines, but they cannot copy any of the files on their machines to an anonymous FTP host. Even though some anonymous FTP hosts do allow users to upload files, users can only upload files to a specified upload directory. The system administrator then checks the files and moves them to another public download directory for other users to download, in which case the remote host's users are protected from uploading problematic files, such as files with viruses.

As an Internet user, you can copy files between any two Internet hosts via FTP. However, most people have only one Internet account, and FTP is primarily used to download public files, such as shareware, company technical support files, and so on. There are thousands of anonymous FTP hosts on the Internet that contain countless files for free copies. In fact, almost all types of information, all types of computer programs can be found on the Internet. This is one of the important reasons the Internet attracts us.

Anonymous FTP users have the opportunity to access the world's largest information base, the information base is cumulative, and is still growing, never closed, involving almost all topics. And all of this is free.

Anonymous FTP is a common method of publishing software on the Internet. The reason the Internet continues to this day is because people use programs that provide standard services through standard protocols. A lot of programs like this are published via anonymous FTP, and anyone can access them.

There is a huge number of anonymous FTP hosts and more files on the Internet, so how exactly do you know which directory on which anonymous FTP host a particular file is located? This is exactly what the Archie server is doing. Archie will automatically search the FTP host, construct a database containing all the file directory information, so you can find the location information of the desired file directly.