2.2 Overview of Networking

Networks connect computers so that the different systems can share information. For users and system administrators, Unix systems have traditionally provided a set of simple but valuable network services that let you check whether systems are running, refer to files residing on remote systems, communicate via electronic mail, and so on.

For most commands to work over a network, each system must be continuously running a server process in the background, silently waiting to handle the user's request. This kind of process is called a daemon. Common examples, on which you rely for the most basic functions of your Linux system, are named (which translates between numeric IP addresses and more human-readable alphanumeric names), lpd (which sends documents to a printer, possibly over a network), and ftpd (which allows you to connect to another machine via ftp).

Most Unix networking commands are based on Internet protocols. These are standardized ways of communicating across a network on hierarchical layers. The protocols range from addressing and packet routing at a relatively low layer to finding users and executing user commands at a higher layer.

The basic user commands that most systems support over Internet protocols are generally called TCP/IP commands, named after the two most common protocols. You can use all of these commands to communicate with other Unix systems besides Linux systems. Many can also be used to communicate with non-Unix systems, as a wide variety of systems support TCP/IP.

This section also covers NFS and NIS—which allow for transparent file and information sharing across networks—and sendmail.

2.2.1 TCP/IP Administration

ftpd	Server for file transfers.
gated	Manage routing tables between networks.
host	Print host and zone information.
ifconfig	Configure network interface parameters.
named	Translate between domain names and IP addresses.
netstat	Print network status.
nslookup	Query domain name servers.
ping	Check that a remote host is online and responding.
pppd	Create PPP serial connection.
rdate	Notify time server that date has changed.
route	Manage routing tables.
routed	Dynamically keep routing tables up to date.
slattach	Attach serial lines as network interfaces.
sshd	Server for secure shell connections.
telnetd	Server for Telnet sessions from remote hosts.
tftpd	Server for restricted set of file transfers.

2.2.2 NFS and NIS Administration

domainname	Set or display name of current NIS domain.
makedbm	Rebuild NIS databases.
portmap	DARPA port to RPC program number mapper.
rpcinfo	Report RPC information.
ypbind	Connect to NIS server.
ypcat	Print values in NIS database.
ypinit	Build new NIS databases.
ypmatch	Print value of one or more NIS keys.
yppasswd	Change user password in NIS database.
yppasswdd	Update NIS database in response to yppasswd.
yppoll	Determine version of NIS map at NIS server.
yppush	Propagate NIS map.
ypserv	NIS server daemon.
ypset	Point ypbind at a specific server.
yptest	Check NIS configuration.
ypwhich	Display name of NIS server or map master.
ypxfr	Transfer NIS database from server to local host.