Building Tablet PC Applications (Pro-Developer)

The File Transfer Protocol, FTP, is still in common use today. FTP is optimized for sharing files. Download speed for files is as important as ever. For example, you want to keep the time it takes to download a 650MB+ file for a Red Hat Installation CD to a minimum.

There are text-based and graphical FTP clients. While graphical clients such as gFTP are pretty, they are essentially front ends for the command-line FTP client. A substantial number of commands are available at the ftp > command prompt. It s even easy to use the FTP client to connect to the Red Hat FTP site to download the latest RPMs. One advantage to a GUI client such as gFTP is convenience; for example, it provides preconfigured bookmarks that help you connect to commonly used FTP servers.

The default Red Hat FTP server is known as Very Secure FTP, or vsFTP. Its developers believe that it is more efficient than WU-FTP, the previous default Red Hat FTP server. While it still transmits data in clear text, which can endanger passwords, it avoids the WU-FTP risks of compromising the root account. vsFTPd does this by giving its commands unprivileged status. The key configuration file is /etc/vsftpd.conf . In this file, you can configure anonymous access, messages, logging, uploading, and more.

It s common to configure an anonymous FTP server. For this purpose, you also need the anonftp-* RPM package, which configures anonymous directories in /var/ftp . This works with vsFTP and WU-FTP. Anonymous users can t go above this directory because of the concept of the chroot jail. vsFTP can be configured for anonymous access. In WU-FTP, it s fairly easy to restrict access to anonymous users and critical commands in /etc/ftpaccess .

You can also set up WU-FTP with real users, based on the user accounts in the FTP server s /etc/passwd file. Key configuration files in the /etc directory include ftpaccess , ftpconversions , and ftphosts . With the right changes, you can even configure user and time limits, as well as anonymous uploads on your FTP server. Several commands let you manage a WU-FTP server, including ftpwho , ftpcount , ftpshut , and ftprestart .

In the next chapter , we ll explore the services for a network of Linux and Unix computers. The Network File System (NFS) is optimized for sharing files between these computers. And the Network Information System (NIS) allows you to configure a single database of login and other configuration files for a network.