At this point, Linux is installed and the network interface is running. Now we begin configuring network services for the users. This chapter covers two traditional services that have been part of TCP/IP networking since the beginning: Telnet and FTP.

The Telnet daemon (telnetd) allows users to log in and run any available applications directly on a Linux server. Some would say this turns the Linux system into a compute server because the remote system has access to the computer power of the server. However, the term compute server is confusing because most people think it relates solely to scientific, number-crunching applications. Others would say that remote login access turns the Linux server into a terminal server because the remote systems act like terminals connected to the server. However, this terminology is also confusing because many people think of the hardware adapters that increase the number of terminals that can connect to a server when they hear the words terminal server. In this book, we say that services such as Telnet turn the Linux server into a network login server because it allows a user to log in and run applications directly on the Linux system. Telnet extends to the TCP/IP network the same login service that was described for serial ports in Chapter 2, "The Network Interface."

The other service covered in this chapter is the File Transfer Protocol (FTP). It allows users to transfer files to and from the server. Like Telnet, FTP requires a user to log in before using the service.

Telnet and FTP services are usually installed during the initial Linux installation. The system administrator then needs to ensure the following:

• The server daemons are started when they are needed

• The users have valid accounts to log in to the servers

Properly performing both of these tasks to configure network login services is the topic of this chapter.

FTP requires the two configuration steps described previously, but it can require additional configuration in order to provide special services, such as anonymous FTP. (Anonymous FTP allows people who don't have a valid user account to log in to the system.) This chapter covers the configuration of optional FTP services with examples drawn from Red Hat Linux.

Note Security issues surround both Telnet and FTP. See Chapter 12, "Security," for ways to secure these services.

The chapter begins by looking at how telnetd, ftpd, and various other network services are started when they are needed. Two techniques for starting services on-demand are examined: the Extended Internet Services daemon (xinetd) used by Red Hat and the Internet Services daemon (inetd) used by several other Linux distributions. We start with the fundamentals of why and how services are started on-demand.

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