24.8 Networking Services

24.8.1 Objective 1: Configure and Manage inetd and Related Services

• inetd is the Internet super daemon; it listens on multiple inbound ports and launches the appropriate child daemon to service the requests.

• inetd uses TCP Wrappers (tcpd) to add access security to services.

• inetd is configured in /etc/inetd.conf.

• You can eliminate an inbound service managed by inetd simply by commenting out its declaration in /etc/inetd.conf and restarting or signaling inetd.

• TCP Wrappers allow the administrator to define access rules for hosts. The configuration files are /etc/hosts.allow and /etc/hosts.deny.

24.8.2 Objective 2: Operate and Perform Basic Configuration of sendmail

• sendmail is a Mail Transfer Agent (MTA).

• sendmail is configured in /etc/sendmail.cf. This file is generally regarded as difficult to configure.

• The "smart host" parameter is used to configure a local sendmail daemon to transfer mail to a site's official mail system.

• /etc/aliases is a file that stores aliases for inbound mail addresses; it can redirect mail to one or more users.

• Whenever /etc/aliases is modified, newaliases must be executed.

• Each user can forward her own mail using a .forward file, containing the forwarding email address, in her home directory.

• Outbound mail that is trapped due to a network or other problem will remain queued; it can be examined using the mailq command.

24.8.3 Objective 3: Operate and Perform Basic Configuration of Apache

• Apache is configured using httpd.conf, srm.conf, and access.conf. On some installations, these may all be combined into httpd.conf.

• The configuration files contain configuration directives, one per line, consisting of a keyword and an argument list. For example:

  DocumentRoot /home/httpd/html

  sets the root directory for HTML files on the system.

• Apache is typically started at boot time using the system's startup methods.

24.8.4 Objective 4: Properly Manage the NFS, smb, and nmb Daemons

24.8.4.1 NFS

• Traditional Unix file sharing is done with NFS, originally developed by Sun Microsystems.

• NFS is a client-server package, and any system can hold both roles simultaneously.

• Exporting (sharing) a local filesystem with NFS is done by including a line in the /etc/exports file, consisting of a directory and list of allowed systems, along with NFS options. For example:

  /usr    (ro) orion.mydomain.com(rw)
  /home   *.mydomain.com(rw)

• Remote NFS filesystems are mounted using the mount command:

  # mount -t nfs server1:/home /mnt/server1 

• NFS is typically started at boot time using the system's startup methods.

24.8.4.2 Samba

• The Samba suite implements Server Message Block (SMB) protocols used on Microsoft and IBM LANs.

• smbd handles file and printer sharing and authentication.

• nmbd implements the WINS service.

• Samba is configured in /etc/smb.conf. The file consists of sections, each with a series of keyword = value pairs.

• Samba 2.0 and later comes with a web-based configuration tool called SWAT; it is usually configured to be monitored by inetd.

24.8.5 Objective 5: Set Up and Configure Basic DNS Services

• DNS is the distributed database of name-to-IP-address translations.

24.8.5.1 The resolver

• The resolver is a library used by networked applications when a domain name needs to be translated into an IP address.

• The resolver uses local files, NIS, and DNS to resolve hostnames as directed by /etc/resolv.conf.

24.8.5.2 Domain registration

• Domain names are assigned through a registration process with one of the domain name registrars on the Internet.

• The DNS server daemon is named, part of the BIND package.

• named can be configured to speed up a local system by acting as a non-authoritative caching-only name server.

• named is configured using /etc/named.conf.

• The nslookup , host, and dig utilities can be used to retrieve information from DNS servers.

• BIND Version 4 and Version 8 have significantly different configuration file formats, although the information contained in the files is similar.