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Network+ TechNote: UNIX/LINUX Networking


UNIX is a multi-tasking, multi-user, server and client operating system. It is text-based, meaning it does not have a graphical user interface. In a typical old fashion UNIX network, dumb terminals are connected to a centralized server running UNIX, which is like connecting several monitors and keyboards to the same computer. In modern network environments, UNIX systems often coexist with other operating systems and then clients use a terminal emulator (e.g. as a TELNET client), or other specialized as well as standard client software (e.g. a web browser) to access the server. Every user executes programs and stores files on the same system, allowing them to share resources in real-time.

Even though UNIX is often looked at as an old-timer, it is still a popular OS for critical and reliable services. There are many different UNIX variants (Linux, Solaris, SunOS, HP-UX, Digital UNIX, SCO Open Server, DG-UX, UNIXWARE, AIX, BSDI, NetBSD, NEXTSTEP, A/UX, to name a ‘few’), which run on various types of hardware, from regular PCs to large mainframes. UNIX is an operating system "developed by programmers for programmers", making it rather complex to manage. Nevertheless, because it is powerful and stable, UNIX and its variants are used in many different types of environments such as hospitals, telecommunication systems, academia and many corporate networks.

TCP/IP is the native protocol for UNIX networks. The HOSTS file, DNS and many other TCP/IP protocols and utilities now common on other operating systems originated on UNIX. Even the location of the HOSTS file on Windows NT/2000/XP systems is the same as on UNIX systems (the etc directory). Some other relevant from origin UNIX services and protocols are described below the Linux section.


Linux is an open source operating system that is somewhat similar to UNIX. Open source means that its source code is publicly available, allowing everyone to create extensions, utilities, GUIs, software, etc. Partly because of this, there are many different distributions of Linux, of which many are free. Linux is very popular for web hosting; many of the web servers on the Internet today run a Linux or a Linux-like OS. Besides acting as a HTTP, FTP or mail server, Linux is also often used for firewalls and caching proxy servers. One of the advantages of Linux over Windows for example is that Linux can be stripped down to run on older and/or slower hardware. Besides using Linux as a server, Linux has become more popular as a client OS as well. A variety of GUIs are available to make it all a bit more user-friendly, as Linux is originally a text-based only OS like UNIX.

Security in Linux is also very similar to security in UNIX. Users and groups can be configured and assigned Read, Write, and/or Execute permissions for files and folders. The owners/creators of files can assign these permissions for their own files and folders, the user ‘root’ (equivalent to Administrator on Windows systems) The National Security Agency (NSA) developed a more advanced security system for Linux, called Security-Enhanced Linux (SELinux), which implements mandatory access controls that allow an administrator to define a wide range of security policies. These policies allow applications, services, and data to be made available based on their context regardless of user and group permissions.

Because TCP/IP is the standard protocol in Linux and UNIX systems, connecting it to a network, regardless of other operating systems in the network, usually requires only a basic IP address configuration (IP address, subnet mask, default gateway, and DNS servers). For a more advanced integration in Microsoft networks you can use other services such as the ones below.

Some of the following services and protocols have already been mentioned in the Network Services chapter in regards to different operating systems accessing and sharing the same Network Attached Storage (NAS). These services and protocols can also be used to allow Microsoft, Linux, Mac OS X and other operating systems to coexist in a network and share additional services such as printer sharing, name resolution, and authentication.


Network File System (NFS) is a remote file access service that allows a UNIX machine to mount a directory (share) on a remote computer and treat it as part of the local file system. The main drawback of NFS is that it is not a very secure technology. Besides UNIX and Linux systems, NFS is also supported by other operating systems including MAC OS, Windows, and Netware. The latter each have there own similar services and protocols to provide seemingly local access to remote files. Examples of similar technologies covered in other section of these TechNotes are SMB/CIFS, Apple Filing Protocol (AFP), and Netware Core Protocol (NCP).


SAMBA is a collection of services and protocols that allows UNIX, Linux and Max OS computers to participate in Microsoft networks. Its initial purpose was to provide UNIX file and print services to Microsoft clients, by making shared folders and shared printers appear as they were located on a Microsoft Windows server. SAMBA essentially allowed UNIX to understand the SMB and NETBIOS protocol.

Nowadays, SAMBA goes beyond providing file and print services and allows UNIX and the formerly mentioned operating systems to fully participate in a Microsoft Windows domain. This includes logging on to the domain and participating in Active Directory services by using a modified version of Kerberos and LDAP and name resolution through WINS and Dynamic DNS. Above all, SAMBA is available as a free download from www.samba.org.


UNIX provides advanced printer sharing services through the Line Printer Daemon (LPD) service. With LPD/LPR you can print from a UNIX, MAC, or Windows workstation to a print server. The Line Printer Remote (LPR) protocol allows clients to connect to printers shared on a server running the Line Printer Daemon (LPD) service. This server is typically a UNIX server, but LPR/LPD is available in other operating systems running TCP/IP. Additionally, every network printer attached directly to a TCP/IP network supports client through the LPR protocol.


Current related exam objectives for the Network+ exam:

2.13 Identify the purpose of network services and protocols (For example: NFS (Network File System), LPD (Line Printer Daemon) and Samba).

3.1 Identify the basic capabilities (For example: client support, interoperability, authentication, file and print services, application support and security) of the following server operating systems to access network resources:

- UNIX/Linux

3.2 Identify the basic capabilities needed for client workstations to connect to and use network resources (For example: media, network protocols and peer and server services).

3.4 Given a remote connectivity scenario comprised of a protocol, an authentication scheme, and physical connectivity, configure the connection. Includes connections to the following servers:
- UNIX/Linux

4.5 Given a troubleshooting scenario between a client and the following server environments, identify the cause of a stated problem:
- UNIX/Linux

Click here for the complete list of exam objectives.

Discuss this TechNote here Author: Johan Hiemstra


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