Introduction To Linux

Introduction to Linux

What is an Operating System? • An operating system (OS) is a resource manager. It takes the form of a set of software routines that allow users and application programs to access system resources (e.g. the CPU, memory, disks, modems, printers network cards etc.) in a safe, efficient and abstract way.

A Brief History of UNIX

A Brief History of UNIX

Architecture of the Linux Operating System • Kernel The operating system kernel is in direct control of the underlying hardware. The kernel provides low-level device, memory and processor management functions (e.g. dealing with interrupts from hardware devices, sharing the processor among multiple programs, allocating memory for programs etc.) .

• The kernel (in raw binary form that is loaded directly into memory at system startup time) is typically found in the file /boot/vmlinuz, while the source files can usually be found in /usr/src/linux. The latest version of the Linux kernel sources can be downloaded from http:// www.kernel.org.

Shells and GUIs • Linux supports two forms of command input: through textual command line shells similar to those found on most UNIX systems (e.g. sh - the Bourne shell, bash - the Bourne again shell and csh - the C shell) and through graphical interfaces (GUIs) such as the KDE and GNOME window managers. If you are connecting remotely to a server your access will typically be through a command line shell.

System Utilities • Virtually every system utility that you would expect to find on standard implementations of UNIX has been ported to Linux. This includes commands such as ls, cp, grep, awk, sed, bc, wc, more, and so on. These system utilities are designed to be powerful tools that do a single task extremely well (e.g. grep finds text inside files while wc counts the number of words, lines and bytes inside a file). Users can often solve problems by interconnecting these tools instead of writing a large monolithic application program.

Application programs • Linux distributions typically come with several useful application programs as standard. Examples include the emacs editor, xv (an image viewer), gcc (a C compiler), g++ (a C++ compiler), xfig (a drawing package), latex (a powerful typesetting language) and soffice (StarOffice, which is an MS-Office style clone that can read and write Word, Excel and PowerPoint files).

Why Not Red Hat? Red Hat is in a tough spot. Most of their revenue streams are based on sales, support, and training while the open nature of Linux has resulted in thousands of freely-available Linux resources on the Web. Their survival depends on having a product that is proprietary enough to make you dependent upon them for upgrades and support. And now that they are a publically-held company they are under pressure to meet the expectations of Wall Street analysts for revenue growth and cash flows every quarter. (Did you think it was just a coincidence that they churned out new versions at an average of two a year?) In time, Red Hat's dominance will likely kill off smaller commercial distributions like Mandrake (France) and TurboLinux (Japan) and dealing with Red Hat will be no different than dealing with Microsoft.

Why Debian ? Debian is the world's leading non-commercial totally free Linux distribution. Remaining loyal to the concept upon which Linux was created, it is produced by hundreds of volunteer developers around the world. Contrary to a common misconception, Debian is not for Linux gurus only. As a matter of fact, as you will see on the guide pages, its advanced package management system makes it one of the easier distributions for new Linux users to work with. Here are just a few of its advantages:

· Non-Proprietary: Debian is a true GNU/Linux distribution using the standard UNIX style commands. This ensures that what you learn today won't be obsolete in two years and makes it easier to also learn how to work with UNIX systems. · Easy Maintenance: A seamless, totally-integrated package management system makes it easy to keep your system up to date and free of orphan files and incompatible products. Most dependent packages are handled automatically so you don't get the "Failed dependencies" error commonly encountered when trying to add software on RPM-based systems like Red Hat and Suse. · Automated Patching: The Debian package system also allows you to use a single command to update your entire system (operating system and installed packages) over the Internet. This allows you to use a scheduler to routinely run a shell script to automatically update your system with the latest program, OS,

Extensive: Only free software packages (applications, utilities, etc.) are allowed to be included in the official Debian distributions, and the current binary distribution comes on 14 CDs because there are over 10,000 of them. With Debian, you don't have different "server“ and "workstation" or "personal" editions. It's everything all in one. · Support Options: Peer support is available through a community of listservs (mailing lists) and chat rooms. Replies to messages may even be from those who helped develop the product. And since you're likely not the first person to encounter a given issue, there are also searchable archives of listserv messages. If your company requires commercial support contracts fear not. Numerous for-profit support operations offer a variety of technical support options. With Debian, you don't have to worry about forced upgrades due to vendors dropping support for older versions.

Minimal Investment: Debian's peformance is excellent even with the modest hardware requirements Linux is famous for. While most OSs require newer, faster, bigger hardware, Debian allows you to utilize those old Pentium systems instead of throwing them into a landfill. This, along with the fact that you can load a single copy of Debian on as many systems as you want, means you can set up a full-blown enterprise at very little cost. · Reliable: Debian's focus on stability and reliability results in servers that you may have to reboot once a year, rather than once a month. · User-centric: New versions of Debian are developed when major changes warrant one, not to generate revenues from upgrades. (You need only look at the version numbers of the various distributions to verify this.)

Simplicity = Limitations Complexity = Capabilities

Debian

/etc/network/interfaces

Red Hat

/etc/sysconfig/network-scripts/ifcfg-eth0 (A separate file for each interface)

Suse

For versions >= 8.0 /etc/sysconfig/network/ifcfg-eth0 (A separate file for each interface) For versions < 8.0 /etc/rc.config

Using Linux You can use your Debian Linux software to set up the following types of systems: •Web servers for external (Internet) or internal (Intranet) use. •Mail servers to handle both internal and Internet e-mail. •Other Internet-type application servers such as FTP, news, IRC (chat), etc. • Web cam servers to keep an eye on your home or business operations from a remote location. •Proxy/NAT servers that allow all the systems on a network to share a single broadband Internet •connection at home or the office.

•Packet-filtering firewalls which allow you to control what traffic goes out of and comes in to your network (while also performing the proxy/NAT function). •Internal LAN servers for file and print sharing much like Novell or NT/2000. There's even a Linux software package available called Samba that makes a Linux server appear as an NT server to Windows workstations. •DNS servers to resolve Internet and/or internal LAN host/domain names. •Database servers running MaxDB - formerly SAPDB (free), MySQL (free), or Oracle ($$$$) database software.

•Fax servers running HylaFax and utilizing old faxmodems allow all users on your network to send faxes from their desktops rather than printing out a hard-copy to stuff in a fax machine. •LAN and WAN routers which offer an inexpensive alternative to those $5,000 Cisco boxes. •Syslog servers which allow you to centralize the monitoring of your network and systems operations. •IDS (Intrusion Detection Systems) to monitor your Internet address space for hacking and attack activity.