Linux is a great platform to act as an Intranet / Internet server. The term Intranet refers to the application of Internet technologies inside an organisation mainly for the purpose of distributing and making available information inside the company. Internet and Intranet services offered by Linux include mail, news, WWW servers and many more that will be outlined in the next sections.
Sendmail is the de facto standard mail server program (called an MTA, or Mail Transport Agent) for Unix platforms. It is robust, scalable, and properly configured and with the necessary hardware, can handle loads of thousands of users without blinking. Alternative mail servers, such as smail and qmail, are also available.
In an organisation or ISP, users will likely access their mail remotely from their desktops. Several alternatives exist in Linux, including POP (Post Office Protocol) and IMAP (Internet Message Access Protocol) servers. The POP protocol is usually used to transfer messages from the server to the client. IMAP permits also manipulation of the messages in the server, remote creation and deletion of folders in the server, concurrent access to shared mail folders, etc.
There are a number of MUA (Mail User Agents) in Linux, both graphical and text mode. The most widely used ones include: pine, elm, mutt and Netscape.
There are many MLM (Mail List Management) programs available for Unix in general and for Linux in particular.
One userful mail-related utility is fetchmail. Fetchmail is a free, full-featured, robust, well-documented remote-mail retrieval and forwarding utility intended to be used over on-demand TCP/IP links (such as SLIP or PPP connections). It supports every remote-mail protocol now in use on the Internet. It can even support IPv6 and IPSEC.
Fetchmail retrieves mail from remote mail servers and forwards it via SMTP, so it can then be read by normal mail user agents such as mutt, elm or BSD Mail. It allows all the system MTA's filtering, forwarding, and aliasing facilities to work just as they would on normal mail.
Fetchmail can be used as a POP/IMAP-to-SMTP gateway for an entire DNS domain, collecting mail from a single drop box on an ISP and SMTP-forwarding it based on header addresses.
A small company may centralise its mail in a single mailbox, configure fetchmail to collect all outgoing mail, send it via a single mailbox at their ISP and retrieve all incoming mail from the same mailbox.
Most Linux distributions include Apache. Apache is the number one server on the internet according to http://www.netcraft.co.uk/survey/ . More than a half of all internet sites are running Apache or one of it derivatives. Apache's advantages include its modular design, stability and speed. Given the appropriate hardware and configuration it can support the highest loads: Yahoo, Altavista, GeoCities, and Hotmail are based on customized versions of this server.
Optional support for SSL (which enables secure transactions) is also available at:
A number of web browsers exist for the Linux platform. Netscape Navigator has been one of the choices from the very beginning and the upcoming Mozilla (http://www.mozilla.org) will have a Linux version. Another popular text based web browser is lynx. It is fast and handy when no graphical environment is available.
FTP stands for File Transfer Protocol. An FTP server allows clients to connect to it and retrieve (download) files. Many ftp servers and clients exist for Linux and are included with most distributions. There are text-based clients as well as GUI based ones. FTP related software (servers and clients) for Linux may be found at: http://metalab.unc.edu/pub/Linux/system/network/file-transfer/
Usenet (also known as news) is a big bulletin board system that covers all kinds of topics and it is organised hierarchically. A network of computers across the internet (Usenet) exchange articles through the NNTP protocol. Several implementations exist for Linux, either for heavily loaded sites or for small sites receiving only a few newsgroups.
A DNS server has the job of translating names (readable by humans) to IP addresses. A DNS server does not know all the IP addresses in the world; rather, it is able to request other servers for the unknown addresses. The DNS server will either return the wanted IP address to the user or report that the name cannot be found in the tables.
Name serving on Unix (and on the vast majority of the Internet) is done by a program called named. This is a part of the bind package of The Internet Software Consortium.
DHCP and bootp are protocols that allow a client machine to obtain network information (such as their IP number) from a server. Many organisations are starting to use it because it eases network administration, especially in large networks or networks which have lots of mobile users.
The Network Information Service (NIS) provides a simple network lookup service consisting of databases and processes. Its purpose is to provide information that has to be known throughout the network to all machines on the network. For example, it enables an administrator to allow users access to any machine in a network running NIS without a password entry existing on each machine; only the main database needs to be maintained.
There are also various ways of authenticating users in mixed networks.