Transferring Files Between Windows and UNIX By David Muck At Isnare.com Ezine Articles

Unix FTP can be used to transfer files between PC's and Unix-based file servers. File transfer protocol (FTP) is the network protocol that is used to transfer the files from the PC to the Unix file server over TCP. The Unix file server will need to have an FTP server installed, and the PC will need to have an FTP client installed. The standard port for FTP communication is port 21. IETF RFC 959 outlines the specifications for FTP. With the popularity of Unix servers on the rise, Unix compatible FTP solutions are becoming increasingly commonplace and continue to expand their feature base.

Most FTP clients use an asynchronous method of communication, also referred to as non-blocking FTP. With this method, the FTP Client uses an asynchronous interface to the Windows sockets TCP/IP driver providing the fastest file transfer data rate possible while using a minimal amount of system resources.

Using FTP, Files can be uploaded and downloaded in either ASCII or binary format. Binary files are files where bytes in the file can be any 256 bit pattern. Examples of binary files include zip files, executables, images, and sound files. ASCII files are text-based binary files that can only use the 128 ASCII codes. Each ASCII character has a corresponding hex value and binary value. For example, the hex value for the letter "A" is 61, and the binary equivalent is 0110 0001.

The FTP server on the Unix server can be configured to require usernames and passwords, or to allow anonymous connections. With anonymous access configured, any and all users are able to upload files to and download files from all directories that are configured for public read and write permissions. On Unix servers, the File Manager can be used to set permissions on files and folders so that anonymous users cannot access them. Alternatively, user accounts can be created on the FTP server, assigned a username and password and access permissions applied at the user level.

Secure sockets layer (SSL) can be used for an added layer of security. With standard FTP, data that is transferred between the PC and the Unix server is not encrypted. Using FTP with SSL (FTPS) ensures that the data being transferred is protected from eavesdropping, tampering, or message forgery by encrypting the data before transferring it. IETF RFC 4217: "Securing FTP with TLS" outlines the specifications for FTP with SSL/TLS security. According to security standard for FTP, by default SSL encryption is only enabled on the command channel. This means that usernames, passwords and file locations are protected, but the transferred files remain vulnerable. To implicitly protect files that are uploaded and downloaded, the data channel also needs to be encrypted by enabling this configuration option in the FTP client.

Advanced FTP clients also provide additional productivity-enhancing features such as an intuitive GUI, the ability to save and transfer entire lists of files, and the ability to save a list of recently transferred files. A Windows GUI allows users to connect to the Unix server and manipulate the necessary files without having to become accustomed to the Unix interface. Many users transfer a specified list of files on a regular basis, or have the need to upload and download the same file multiple times. In this case, recent and custom file transfer lists can save users a lot of time.

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