Linux Network Services

You can activate many basic networks services on a Linux computer. Several are controlled by the xinetd daemon. Many administrators set up their own DNS servers so they don t have to maintain /etc/ hosts on every computer on their networks. Others set up their own DHCP servers; this frees them from having to maintain IP address information on every computer on their networks. Commands are also available to help you set up and configure printers, as well as configure the sendmail server.

This section addresses just the commands that you might run at the command-line interface; no GUI tools are discussed. For more information on the services in this section, refer to Chapters 23 “ 26 .

Commands for xinetd Services

As we mentioned, many services, including the Remote Shell and Telnet, are controlled through the Extended Internet Services Daemon, xinetd . This daemon listens for requests and starts network services on demand.

You can start the Remote Shell from a client using a number of different commands, which appear in Table A.24.

Table A.24: Remote Shell Commands

Command	Description
rlogin     hostname	Logs into a remote computer with a Remote Shell server; uses the current username.
rlogin -l username hostname	Logs into the remote hostname computer with a different username .
rsh hostname	Logs into a remote computer with a Remote Shell server; uses the current username.
rsh -l username hostname	Logs into the remote hostname computer with a different username .
rexec hostname command	Logs into the remote computer hostname and executes the command .

Variations on the telnet command are quite rich, but many cover very special situations. Since telnet provides a straightforward remote login interface, not many variations are required. A few useful options are shown in Table A.25.

Table A.25: telnet Commands

Command	Description
telnet hostname	Opens a console login interface on hostname .
telnet -a hostname	Sends the current USER as the username for the telnet login process.
telnet -f hostname	Supports the use of Kerberos on the Telnet server.
telnet -l username hostname	Attempts to log into the hostname computer as username .

DNS and DHCP

There aren t a lot of commands related to the DNS or DHCP servers or clients . Chapter 24 explains the configuration of these systems; the commands in their main configuration files, /etc/named.conf and /etc/dhcpd.conf , are addressed in detail in that chapter. Table A.26 describes a few basic commands.

Table A.26: DNS and DHCP Commands

Command	Description
named	DNS server daemon.
dhcpd	DHCP server daemon.
dhclient	DHCP client daemon; can also be used as a command to refresh IP address data. In previous Red Hat distributions, this command was called dhcpcd or pump .

Printer Commands

Associated with the CUPS and LPD print systems are several basic commands, some of which apply to both systems. For example, with the cups-lpd service, which is part of xinetd , LPD commands are automatically translated for a CUPS system. Basic print commands are described in Table A.27.

Table A.27: Basic Print Commands

Command	Description
lpr file	Prints the file; this is the basic LPD print command.
lpc	Manages LPD print queues and active printers.
lpq	Examines the print spool; you can specify the printer with the -P switch.
lprm job	Removes a print job with job number.
cupsaddsmb	Allows you to share a CUPS printer via Samba.
cupsconfig	Opens the CUPS configuration utility in the Lynx text browser.
cups-lpd	Starts the CUPS LPD xinetd service that allows CUPS to read LPD commands.
filter	Adds a new CUPS filter.
lp file	Prints the file using CUPS.
lppasswd	Controls access to the CUPS configuration.
lpoptions	Sets CUPS printer options/defaults.
lpstatus	Prints CUPS status (queue) information.

Mail Management Commands

Linux offers commands that help you manage the sendmail mail server. The most important of these commands, the m4 macro processor, just processes the sendmail configuration file. Other commands allow you to manage aliases, databases, and more. These commands are described in Table A.28. For more information on sendmail, read Chapter 26 .

Table A.28: sendmail Commands

Command	Description
m4	Processes the sendmail macro file, normally /etc/mail/sendmail.mc, into a format suitable for the sendmail configuration file, normally /etc/mail/sendmail.cf .
mailq	Sends a summary of queued mail message headers to the printer; sendmail -bp performs the same task.
makemap	Creates sendmail database maps from /etc/mail configuration files.
mailstats	Returns mail statistics ” numbers of messages, total sizes, and more.
newaliases	When you change /etc/aliases , this command updates the sendmail database.
praliases	Shows current aliases from the database.
rmail	Reads UUCP-based mail.
smrsh	Enters the sendmail shell.