GNU/Linux Introduction● What is UNIX & GNU/Linux?

● Pros & Cons/Which Distribution?

● Graphical/Console Interface

● Absolute Basics/Getting Help

● Files & File System/Shell

● Processes, I/O Redirection

● Networking

● System services/daemons

● References

What is UNIX?In order to understand the popularity of Linux, we need to travel back in time, about 30 years ago... Imagine computers as big as houses, even stadiums. While the sizes of those computers posed substantial problems, there was one thing that made this even worse: every computer had a different operating system. In 1969, a team of developers in the Bell Labs laboratories started working on a solution for the software problem, to address these compatibility issues. They developed a new operating system, which was

1. Simple and elegant.

2. Written in the C programming language instead of in assembly code.

3. Able to recycle code.

The Bell Labs developers named their project "UNIX."

What is Linux?By the beginning of the 90s home PCs were finally powerful enough to run a full blown UNIX. Linus Torvalds, a young man studying computer science at the university of Helsinki, thought it would be a good idea to have some sort of freely available academic version of UNIX, and promptly started to code.

From the start, it was Linus' goal to have a free system that was completely compliant with the original UNIX. That is why he asked for POSIX standards, POSIX still being the standard for UNIX.

In 1993, two years after start, there were 12000 Linux users. The project, popular with hobbyists, grew steadily, all the while staying within the bounds of the POSIX standard. All the features of UNIX were added over the next couple of years, resulting in the mature operating system Linux has become today. Linux is a full UNIX clone, fit for use on workstations as well as on middle-range and high-end servers.

What is GNU?

Linux is the name of the kernel and the trademark of Linus Torvalds. The Linux system is based on GNU tools (Gnu's Not UNIX), which provide a set of standard ways to handle and use the system. All GNU tools are open source, so the can be installed on any system.The GNU Project was launched in 1984 by Richard Stallman to develop a complete UNIX-like OS which is free software.

Pros & Cons● Linux is free

● Linux is portable to any hardware

● Linux was made to keep on running

● Linux is secure & versatile

● Linux is scalable

● Linux OS & apps have a short debug-time

● Too many distributions

● Linux is not very user friendly (but a lot of improvement recently)

● Is an open source product trustworthy?

● Games? ;-)

Which Distribution?

* DistroWatch.com hits per day as of May 12, 2009

Rank Distribution H.P.D*

1 Ubuntu 2337

2 openSUSE 1516

3 Mint 1428

4 Fedora 1369

5 Debian 1187

6 Mandriva 1013

7 PCLinuxOS 877

8 Sabayon 723

9 Puppy 712

10 MEPIS 676

11 CentOS 671

12 Arch 631

13 Slackware 523

14 FreeBSD 505

15 Damn Small 459

16 Kubuntu 452

17 Vector 449

18 Dreamlinux 411

19 KNOPPIX 407

20 gOS 379

Graphical Interface

Graphical interface for Linux exists in three separate layers: X Server (closest to OS) provides communication channel between UI & OS, Window Manager is responsible for managing the windows displayed on the screen, Desktop Environment is responsible for the content of the window. The most popular desktop environments are KDE & Gnome (now gaining popularity XFCE). Window managers with minimal DE for example: WindowMaker, BlackBox, IceWM, Sawfish, Enlightenment, FluxBox, Fvwm, etc.

GUI is out of our presentation scope.

Console Interface● There are many consoles (called Virtual

Consoles or Virtual Terminals, abbreviated VCs or VTs) that share the same screen. You can use them as independent devices, either to run independent login sessions, or just to send some output to.

● Top 10 Linux console applications according to Linux.com: Screen, Pine, Lynx, Zed, Oleo, TPP, MySQL, Midnight Commander, ZGV, Nethack. Other popular console applications: X-Chat-text, Tethereal, GNU Chess, Vlock, Halibut, Cmatrix, vifm, ncftp, antiword.

Absolute Basics

Quick-start commands:Command Meaning

ls Displays a list of files in the current working directory, like the dir command in DOS

cd directory change directories

passwd change the password for the current userfile filename display file type of file with name filename

cat textfile throws content of textfile on the screen

pwd display present working directoryexit or logout leave this sessionman command read man pages on command

info command read Info pages on command

apropos string search the whatis database for strings

Getting Help

● There are two main sources: man & info pages and online communities (or ask google)

● man pages very structured, overwhelming source of documentation.

● info pages contain more recent information and are easier to use then man pages.

● many commands have built-in –help page.● Online: Google.com, help.Ubuntu.com,

LinuxQuestions.org and many many others.

Files & File System

● A simple description of the UNIX system, also applicable to Linux, is this:

“On a UNIX system everything is a file; if something is not a file, it is a process.”

● Sorts of files: regular, directories, special (devices) files – character & block, links, (domain) sockets, named pipes.

● There are two partition types: data (0x83) & swap (0x82); Data: ext2/3/4, reiser 3/4, xfs, jfs, gpfs, psfs, lustre, gfs/2, ocfs/2, nilfs, btrfs, etc.

Files & File System: Partition

● Linux generally counts on having twice the amount of physical memory in the form of swap space on the hard disk.

● All partitions are attached to the system via a mount point. The mount point defines the place of a particular data set in the file system. Usually, all partitions are connected through the root partition.Filesystem Size Used Avail Use% Mounted on/dev/md0 89G 4.2G 81G 5% //dev/md1 92G 189M 87G 1% /home/projects/dev/md2 46G 42G 1.9G 96% /home/file_share

Files & File System: Layout

Files & File System: Subdirectories

Directory Content

/bin Common programs, shared by the system, the system administrator and the users.

/boot The startup files and the kernel, vmlinuz. In some recent distributions also grub data. Grub is the GRand Unified Boot loader and is an attempt to get rid of the many different boot-loaders we know today.

/dev Contains references to all the CPU peripheral hardware, which are represented as files with special properties.

/etc Most important system configuration files are in /etc, this directory contains data similar to those in the Control Panel in Windows

/home Home directories of the common users.

/initrd (on some distributions) Information for booting. Do not remove!

/lib Library files, includes files for all kinds of programs needed by the system and the users.

/lost+found Every partition has a lost+found in its upper directory. Files that were saved during failures are here.

Files & FS: Subdirectories cont./misc For miscellaneous purposes.

/mnt Standard mount point for external file systems, e.g. a CD-ROM or a digital camera.

/net Standard mount point for entire remote file systems

/opt Typically contains extra and third party software.

/proc A virtual file system containing information about system resources. More information about the meaning of the files in proc is obtained by entering the command man proc in a terminal window. The file proc.txt discusses the virtual file system in detail.

/root The administrative user's home directory. Mind the difference between /, the root directory and /root, the home directory of the root user.

/sbin Programs for use by the system and the system administrator.

/tmp Temporary space for use by the system, cleaned upon reboot, so don't use this for saving any work!

/usr Programs, libraries, documentation etc. for all user-related programs.

/var Storage for all variable files and temporary files created by users, such as log files, the mail queue, the print spooler area, databases, etc.

Files & File System: Files● For Example:

This table gives an overview of file types:

jaime:~/Documents> ls -ltotal 80-rw-rw-r-- 1 jaime jaime 31744 Feb 21 17:56 intro Linux.doc-rw-rw-r-- 1 jaime jaime 41472 Feb 21 17:56 Linux.docdrwxrwxr-x 2 jaime jaime 4096 Feb 25 11:50 course

Symbol Meaning

- Regular file

d Directory

l Link

c Special file

s Socket

p Named pipe

b Block device

Files & File System: PermissionsThe Linux security model is based on the one used on UNIX systems. On a Linux system, every file is owned by a user and a group user. There is also a third category of users, those that are not the user owner and don't belong to the group owning the file. For each category of users, read, write and execute permissions can be granted or denied.

Code Meaning

u user permissions

g group permissions

o permissions for others

Code Meaning

0 or - The access right that is supposed to be on this place is not granted.

4 or r read access is granted to the user category defined in this place

2 or w write permission is granted to the user category defined in this place

1 or x execute permission is granted to the user category defined in this place

Tools: id, chmod, chown, chgrp, umask, etc.

Shell

The shell is an advanced way of communicating with the system, because it allows for two-way conversation and taking initiative. Both partners in the communication are equal, so new ideas can be tested. The shell allows the user to handle a system in a very flexible way. An additional asset is that the shell allows for task automation. A shell can best be compared with a way of talking to the computer, a language. Most users do know that other language, the point-and-click language of the desktop. But in that language the computer is leading the conversation, while the user has the passive role of picking tasks from the ones presented. It is very difficult for a programmer to include all options and possible uses of a command in the GUI-format. Thus, GUIs are almost always less capable than the command or commands that form the backend.

Shell cont.sh or Bourne Shell: the original shell still used on UNIX systems and in UNIX

related environments. This is the basic shell, a small program with few features. When in POSIX-compatible mode, bash will emulate this shell.

bash or Bourne Again SHell: the standard GNU shell, intuitive and flexible. Probably most advisable for beginning users while being at the same time a powerful tool for the advanced and professional user. On Linux, bash is the standard shell for common users. This shell is a so-called superset of the Bourne shell, a set of add-ons and plug-ins. This means that the Bourne Again SHell is compatible with the Bourne shell: commands that work in sh, also work in bash. However, the reverse is not always the case. All examples and exercises in this book use bash.

csh or C Shell: the syntax of this shell resembles that of the C programming language. Sometimes asked for by programmers.

tcsh or Turbo C Shell: a superset of the common C Shell, enhancing user-friendliness and speed.

ksh or the Korn shell: sometimes appreciated by people with a UNIX background. A superset of the Bourne shell; with standard configuration a nightmare for beginning users.

ProcessesThere are several process types: interactive (initialized & controlled through a terminal session), automatic processes (not connected to terminal), daemons (server processes).Command Meaning

command Runs this command in the foreground.

command & Run this command in the background (release the terminal)

jobs Show commands running in the background.

Ctrl+Z Suspend (stop, but not quit) a process running in the foreground (suspend).

Ctrl+C Interrupt(terminate and quit) a process running in the foreground.%n Every process running in the background gets a number assigned

to it. By using the % expression a job can be referred to using its number, for instance fg %2.

bg Reactivate a suspended program in the background.

fg Puts the job back in the foreground.

kill End a process

I/O RedirectionMost Linux commands read input, such as a file or another attribute for the command, and write output. By default, input is being given with the keyboard, and output is displayed on your screen. Your keyboard is your standard input (stdin) device, and the screen or a particular terminal window is the standard output (stdout) device.

However, since Linux is a flexible system, these default settings don't necessarily have to be applied. The standard output, for example, on a heavily monitored server in a large environment may be a printer.

Output redirection is done with >, >>, 2>&1, tee and |

Input redirection is done with <

Filtering is done with grep, sort, uniq, (sed, awk - streams)

Networking

Simplified OSI model:

/etc/hosts

/etc/resolv.conf

ip, ifconfig, route, netstat, host, ping, traceroute, whois

Layer name Layer Protocols

Application layer HTTP, DNS, SMTP, POP, ...

Transport layer TCP, UDP

Network layer IP, IPv6

Network access layer PPP, PPPoE, Ethernet

System Services/Daemons

● Daemons are non-interactive processes that provide particular service (see /etc/services)

● Daemons could be self-contained or run from the helper like X/InetD or TCPD.

● Most common services/applications: www/apache, ftp/(proftpd, vsftpd), smtp/(sendmail, postfix), pop&imap/dovecot, smb/samba, dns/bind, java/tomcat, ldap/slapd, ssh&sftp/openssh, scheduler/(atd, crond), MySQL, PostgreSQL, dhcp/dhcpd, etc.

References

● Introduction to Linux http://tldp.org/LDP/intro-linux/html/index.html

● GNU Operating System http://www.gnu.org/● The Linux Foundation http://www.linux.com● http://en.wikipedia.org/wiki/Comparison_of_file_systems