Login Services

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

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.Security issues surround both Telnet and FTP. See Chapter 12, "Security," for ways