ITSC1407 notes

In most cases, when you obtain or "buy" software, you really do not own it. Rather, you are granted a license to use the software. The terms of the licensing agreement differ depending on the type of license accompanying the software. To understand software licensing, you should understand the following terms.

Linux is distributed as Open Source software (meeting OSI standards) under the GNU General Public License (GPL). The GNU/GPL provides that:

You should be aware that using Linux in your organization is not without cost. Although you do not pay for a license for Linux, expect to pay for the following items:

Component Facts

The Linux operating system is a modular system, which means that the components can function without affecting one another. Because of its modular nature, you can create a highly customized Linux operating system based on your individual requirements. The table below lists the modules typical to Linux. Each component (or set of components) is generally developed independently, and each component offers functionality while minimally affecting the other components.

As you can see, there are dozens of components that can be used with the Linux core. The availability of multiple components to provide a specific feature gives you a lot of choice, more than you might have with other operating system choices such as Microsoft Windows.

File Types

Most files are just files, called regular files; they contain normal data, for example text files, executable files or programs, input for or output from a program and so on.

While it is reasonably safe to suppose that everything you encounter on a Linux system is a file, there are some exceptions.

File Types

In the Linux operating system, everything (including devices and users) is a file. As the system runs, Linux opens, reads, writes to (if necessary), and closes the files it needs. The table below lists the most common types of files you'll encounter when working with Linux. (One thing to remember about working with files in Linux is that all file names are case sensitive.)

File Type		Description
Directory		A file type designed specifically to hold or point to other file types.
Normal File		Every file that is not a directory is generally a normal file.
Special Files	Hard Link	A hard link is a duplicate entry in the file system that points to a specific piece of data. Hard links are not often used. If the original entry in the file system is deleted, the hard link maintains a valid pointer to the data.
	Symbolic Link	A symbolic link is a file system entry that points to another file system entry, which in turn points to a valid piece of data. Symbolic links can work across volumes and file systems. Symbolic links are similar to shortcuts in Windows.
	Character	A file type that accepts input one character (i.e., byte) at a time. Character files often point to devices like sound cards, serial ports, or video port.
	Block	A file type that accept input in blocks (i.e., groups of bytes). Block files often point to storage devices.
	Pipe	A named pipe file allows you to send information between applications.
	Socket	A socket file is similar to a named pipe file, but a socket file allows information to be exchanged over a network.

Directory Contents

The unified file system uses a single root directory that contains various other directories. File systems from other hard drive partitions mount to directories beneath the root directory, providing access to a single directory structure. The file system hierarchy standard (FHS) governs the unified file system for Linux systems by defining a standard set of directories, subdirectories, and files. FHS is a subset of the Linux standards base (LSB) which is an organization and a set of guidelines for promoting a set of standards to increase Linux distribution compatibility.

Directory	Description
/	The / character represents the root directory of the Linux system. All directories are below the / (root directory) of the system.
/bin	The /bin directory contains binary commands that are available to all users.
/boot	The /boot directory contains the kernel and boot loader files.
/dev	The /dev directory contains device files.
/etc	The /etc directory contains configuration files specific to the system.
/home	The /home directory contains by default the user home directories.
/initrd	The /initrd directory is used during the boot process to hold the initial RAM drive image.
/lib	The /lib directory contains shared program libraries and kernel modules.
/media	The /media directory contains the /cdrom and /floppy directories. It is the point where CD-ROM and floppy drives can be mounted according to the FHS (Filesystem Hierarchy Standard) v2.3.
/mnt	The /mnt directory is an empty directory. This was the mount point for CD-ROM and floppy drives prior to FHS v2.3.
/opt	The /opt directory contains the additional programs.
/proc	The /proc directory contains information about the system state and processes.
/root	The /root directory is the root user's home directory. Do not confuse /root with the root of the system (/).
/sbin	The /sbin directory contains system binary commands.
/srv	The /srv directory contains files for services like the FTP and Web servers.
/sys	The /sys directory is new with release 2.6. It takes some of the system state date that was previously contained in /proc.
/tmp	The /tmp directory contains temporary files created by programs during system use.
/usr	The /usr directory contains system commands and utilities. /usr holds the following directories: /usr/bin /usr/lib /usr/local /usr/sbin /usr/X11R6 (for the X Window system) Depending on the implementation, the /usr directory might also include the /usr/doc subdirectory (or /usr/share/doc subdirectory) to hold documentation accessible to all users.
/var	The /var directory contains data files that change constantly. Standard subdirectories include: /var/mail (holds e-mail in boxes) /var/spool (holds files waiting for processing, such as print jobs or scheduled jobs) /var/www (holds www or proxy cache files)

Computer Roles

Before you install Linux, you should know how you'll use the system. The way the system is used will determine what kinds of components you should select to install. The table below lists common deployments for Linux systems and the components those deployments should include.

Distribution Facts

A Linux distribution is a collection of components packaged to work together as a complete system. A package is the collection of components (tools, software, utilities, devices, etc.) put together by an individual or group to make up a distribution. Each package (and therefore distribution) can use a package manager, which is a tool that installs and maintains a Linux package. For example, the RPM family of Linux distributions uses the Red Hat package manager (RPM).

The following table lists the most popular Linux distributions and their characteristics.

If you are just starting out with Linux, you should probably choose a commercial distribution to take advantage of easy setup and possibly technical support (for a fee). As you learn Linux, you likely will not need copies of the source code for the kernel and other components. Common places to get a Linux distribution include:

After you have some experience with Linux, you might then want to experiment with source code versions of Linux. A good source for information is www.tldp.org which is the community supported 'The Linux Document Project', a site full of Linux resource information.

1.4 Installing Linux

After finishing this section, you should be able to complete the following tasks:

Installation Facts

Depending on your organization and how you will deploy Linux, you have several choices of how to access the Linux source files to complete the installation. Listed below are several different methods you can use. (Before performing any installation, check the hardware compatibility list (HCL) for the Linux version you've selected to make sure your system components are supported.)

When you start the install program, you can often choose how to interact with the installation program. The following table compares various methods.

Although the installation process differs depending on the distribution, the following list represents a fairly generic installation process you will follow:

During installation, the super user account, called the root user, is created. Following installation, you can log on to Linux by typing root as the username and then supplying the password you entered during installation.

Red Hat Linux provides you with the redhat-config-language command that runs with an active X server occurrence to change the default language on your system after installation.

Licensing Type	Description
Open Source	Software that is distributed with the source files. End users can modify and recompile the software to meet their needs. Usually developed as a community project. More specifically, Open Source is a certification mark for software that adheres to the Open Source Initiative standards.
Closed Source	Software that is distributed without the source files. Many commercially available software is closed source (such as Microsoft Windows, Word, Excel).
Freeware	Software distributed without cost. The software may be open source or closed source.
Free Software	Software that is freely distributable, includes the source code, and allows the end user to modify or enhance the software. Free software may be distributed at a cost. The "free" refers to the freedom of use, not necessarily no cost.
Shareware	Software that is distributed free of cost on a trial or limited use basis. After the initial use, if you continue to use the software, you are expected to pay a fee for its use. Shareware is typically closed source software.
Artistic License	Artistic license is a type of licensing agreement that allows users to modify and distribute open source software, while still retaining some degree of copyright protection for the work being distributed. The GNU General Public License is one example of an artistic license.

Component	Description	Examples
Kernel	The kernel is the core component of the operating system. The kernel coordinates communication between the hardware and other software components. The kernel is the only component that is technically Linux. All other components are add-ons that turn the system into a fully-functional operating system.	The kernel is constantly being updated. Current and previous kernel versions can be found at www.kernel.org.
Shell	The shell is the user interface that accepts and interprets commands (either from a command prompt or a script) and forwards them to the kernel. A Linux shell is comparable to the DOS interpreter/DOS prompt.	bash (Bourne-Again Shell) is the most common (and default) Linux shell. It is an enhancement of the original Bourne shell (sh).
		tcsh is an enhanced version of the Berkeley UNIX C-shell (csh).
Graphical User Interface (GUI)	The GUI is responsible for drawing graphical elements on the computer screen. The Linux GUI was designed to work the same way regardless of the video hardware on the computer system.	XWindows is the most common GUI system. X Windows works in conjunction with an X Client to render the GUI. X Windows is capable of running as a server and sending the GUI images to separate machines running an X Client. Xfree86 is the most common X Client
Window Manager/Desktop Environment	The window manager modifies the GUI output that comes from X Windows. To change or modify the X Windows output, you can simply change the window manager. You can also use a desktop environment with a window manager. A desktop environment provides software (e.g., Web browsers and file managers) and gives users access to common tasks.	KDE (Kommon Desktop Environment), which uses the K Window Manager (kwm) and comes with the Qt toolkit for C++.
		GNOME (GNU Object Model Environment) does not specify a window manager because its design allows use of any window manager. However, it does use Metacity as a default window manager in the absence of a window manager. GNOME requires the use of the GIMP Toolkit (GTK) to render the full GNOME desktop.
Windows Emulator	A Windows emulator is an implementation of the Microsoft Windows API. The emulator lets you run Windows applications on Linux without running the Windows operating system.	Wine, available at www.winehq.com.
Boot Loader	A boot loader runs after the system executes the BIOS ROM and POST functions. It loads the Linux kernel from the boot partition on the hard disk. It is also used to boot other operating systems present on the computer.	LILO (LInux LOader) is the most common bootloader.
		GRUB (GRand Unified Bootloader) is a new bootloader that offers extra functionality.
Applications and Utilities	Utilities are special programs that help you manage the system. Applications are programs that let you use the computer for specific tasks (such as word processing, listening to music, or managing data).	Text Editors (command-line based)	Vi
			Nano
		File Managers	Nautilus (used with GNOME)
			Konqueror (used with KDE)
		Office Applications (similar to Word, Excel, etc.)	OpenOffice KOffice (for KDE)
		Graphic Editor (like PhotoShop)	GIMP
Daemons (Services)	Daemons are programs that run in the background, providing additional functionality to a system. The Windows equivalent of a daemon is a service.	File/Print Services	SMB/Samba NFS
		Print services	LPR CUPS
		Web Server	Apache Tomcat
		Domain Name Service (DNS)	BIND
		E-mail	Sendmail Postfix
		Firewall	ipchains Smoothwall Astaro Security Linux
		Proxy Server	Squid

Role	Description	Common Components
Desktop	A desktop implementation is targeted to the end-user in environments such as home-based computers (for gaming, multi-media, or Web surfing) or home offices.	Graphical desktop Web browser (like Mozilla) E-mail client Productivity tools (an office productivity suite like GNOME Office, for example) Sound, graphics, and video support Gaming support
Workstation	A workstation implementation is for large corporate installation, system administrators, or developers. Office workstations often have more business productivity applications while workstations for software developers and system administrators have tools for creating and compiling software and administering network resources.	Word processor Database editor Desktop publishing applications Spreadsheet applications E-mail applications Development tools System administration tools
Server	A server provides networking services to multiple users or to other computers. Because end users do not typically log on to a server directly, graphical and multimedia components are often not installed on servers to conserve system resources and eliminate sources of problems. Linux can provide many different services (e.g., file, email, and Web services) on one machine unless it is being accessed by a very large number of people.	Mail services Routing Proxy service FTP service Web services (to allow users to access information, like an online catalog for example, through a Web browser) Network file system (NFS) (for file sharing) Storage (e.g., an appliance server) Database services (for storing client information, for example)

Distribution	Characteristics	Examples
RPM	An RPM distribution uses the Red Hat package manager (RPM). RPM distributions are the most common commercially-available distributions.	Red Hat (most common in the United States) SUSE (most common in Europe) Mandrake
Debian	Debian distributions use the Debian package manager. The Debian family contains the largest number of packages (software and tools) because it is the most open of the Linux families.	Xandros Linspire (formerly Lindows)
.tar.gz/.tgz/Slackware	This Linux family doesn't use a package manager; rather, its installation and management is done through tarball or gzip tarball files.	CollegeLinux VectorLinux SLAX BuffaloLinux
Source-based distributions	The distributions in this family are designed to work from source code. The user compiles the kernel and software from source code prior to installing the software.	Gentoo

Installation File Location	Description
CD-ROM or removable media	Installation source files are on a disk or other removable media such as: USB, Firewire devices Floppy, Zip disk (multiple disks might be required) CD-ROM Use this method if you have access to portable installation source files.
Network	Installation files are located on a shared directory on the network. To complete the installation, you must: Copy the source files to a shared network location. Boot the computer to a limited version operating system with networking support (typically from a boot floppy). Make sure the computer uses the appropriate protocols to connect to the network share (FTP, SMB, NFS). Connect to the network share and start the installation. Using this method, the computer does not need a drive for accessing the installation files, and you can start multiple installs with a single source.
Disk imaging	Using disk imaging, you install Linux on one system. You then use imaging tools (or even backup/restore utilities) to replicate the installation to other computers. Use this method to install Linux quickly on multiple systems. In most cases, the hardware in each system must be identical.

Installation Method	Description
GUI install	With the GUI method, you make installation choices using the mouse and keyboard from graphical installation screens. The GUI install is the default install for most distributions.
Text install	A text install bypasses the GUI screens, giving you basic text screens instead. Use the text install if the system has video card problems or low video support.
Scripted	In a scripted installation, you answer all installation questions ahead of time. Your responses are stored in a file that is then read by the install program. The installation progresses without interaction. Use this system for a fully automated install and to quickly install on multiple systems.