Linux Introduction

Unix

Development started on 1969 in AT&T's Bell Labs
Written in PDP-11 Assembly, released on 1971
Re-written in a new, dedicated programming language named C, 1972
Became the first portable operating system
Due to legal limitations, source code was available for anyone who asked for it, and quickly became favorite in academic institutes as well as commercial vendors.

GNU

"Printer Drivers Crisis"
started in 1983 by Richard Stallman, with the goal of creating a "complete Unix-compatible software system" composed entirely of free software.

GNU

Stallman wanted computer users to be "free", as most were in the 1960s and 1970s – free to study the source code of the software they use, free to share the software with other people, free to modify the behavior of the software, and free to publish their modified versions of the software.
The GNU philosophy was later published as the GNU Manifesto in March 1985.

Linux

Hello everybody out there using minix -

I'm doing a (free) operating system (just a hobby, won't be big and professional like gnu) for 386(486) AT clones. This has been brewing since april, and is starting to get ready. I'd like any feedback on things people like/dislike in minix, as my OS resembles it somewhat (same physical layout of the file-system (due to practical reasons) among other things).

Linus Benedict Torvalds, comp.os.minix Newsgroup, August 25th 1991

Linux kernel + GNU software =

GNU/Linux

Linux

Linux is not a whole operating system, but only a kernel.
The operating system consists of a kernel, and a large set of applications.
Collecting applications is a mess, and people started building software collections called Distributions.

GNU/Linux Distributions

GNU/Linux is everywhere

Servers and supercomputers — more than 90% of today's 500 fastest supercomputers run Linux
Desktop computers
Mobile phones — Android, Bada, Tizen, Firefox OS, Mobilin, MeeGo
Network equipments — Routers, Access Points, Modems
Smart TVs, Printers, PDAs, Home entertainment systems, ATMs, etc.

Linux GUI

Linux has few different display managers — X [Windows], XOrg, WayLand etc.
Linux has multiple graphical environments — GNOME, KDE, Unity, XFCE, Cinnamon etc.

Linux software

Linux has large collection of software running natively, such as web browsers, productivity suits, etc.
If something is missing, there is good chance it has alternatives, sometimes even better than the original software.
Linux has software compatibility layer for running most of Windows software (WINE).
It is possible to run emulated operating system using Xen, Qemu, DosBox, VirtualBox, VMWare, etc.

Linux software repositories

In Linux you should never install software directly from the web.
Instead, there are download servers called Repositories.
Later on, some operating systems started to serve software in Application Stores, but these are yet incomplete comparing to the rich software collections available on mainstream Linux.

Linux user permissions

Linux is a multi-user operating system.
Groups consists users. Each user can be listed in several groups.
Only the first user, named root has the administration rights.

Linux user policy

Users can become root by logging-in as root (not recommended!),
become root using the su root command,
Modern Linux can run commands as root using the sudo command, which requires the user to be in the sudoers group.

Linux file permissions

In normal Linux filesystems, there are three kinds of permissions to each file or directory; Read, Write, Execute
Each permission can be given to exact one user (the file owner), one group, and everyone else.
rw- r-- --- user group filename
… means that the user has read/write permissions, the group can read the file, and the file is inaccessible to others.

Linux filesystem structure

In Linux, everything lives in a logical filesystem…

/ — The Filesystem root
/boot — System's boot loader
/dev — The location of every hardware device
/proc — Every process represents a file
/home/<user> — User directories

Linux filesystem structure

/etc — Applications configurations
/lib — Shared libraries
/bin — System binaries
/usr — Non-critical files
/var — Variable files; Files that change periodically
/tmp – Temporary storage; empty on boot time
/mnt – Custom mount points; Also /media

Why CLI?

Most operating systems have Command Line Interface in addition to the Graphical UI.

Linux isn't different. In fact, almost everything in Linux can be done from the command line.

Local and remote

It is possible to open command line from the Terminal application, or from any of the attached Virtual Terminals.
Remote access possible using SSH, which stands for Secure SHell, and can transfer files, execute commands, and drop the remote user into local shell.
PuTTY is a great SSH client for Windows, WinSCP is great client for SCP/SFTP/FTP for Windows.

Filesystem commands

ls – Show content of current directory (similar to DOS dir command)
cd – Change directory (similar to DOS cd command)
pwd – Show current directory (again, similar to DOS cd command)
mkdir – Create directory (similar to DOS mkdir/md commands)
cat – Print file content (Similar to DOS type command)
rmdir – Remove directory (similar to DOS rmdir/rd commands)
rm – Remove file(s) (similar to DOS del command)

Permissions commands

chmod – Change file permissions (similar to Windows cacl command)
chown – Change file owner
chgrp – Change file group

Miscellaneous commands

ps – Show list of processes (similar to Windows tasklist command)
kill – Terminate a running process
man – Provide documentation for a given command (Very handy! ☺)
touch – Create an empty file/Set file modification time to now
sort – Sort a given text file
grep – Find given patterns in text stream
sed – Manipulate text streams

Standard Streams

Linux contain three different streams:

STDIN – Standard Input
STDOUT – Standard Output
STDERR – A stream dedicated to print error messages

Stream Redirection

ls > filename – Redirect command output to file
cat foo >> filename – Append command output to file
cat < filename – Read input from file
ls &> filename – Redirect both STDOUT and STDERR to a file

Linux Plumbering

The pipe operator | use the output of one command as the input to the second command.

It allow us run few commands in a batch so each command will process the output of the previous command.

Single Line scripting

$ date # Show current time/date
	Wed Mar 20 23:18:55 IST 2013
	$ date | grep -o ..:..:.. # Extract the time pattern
	23:18:55
	$ ls | grep [א-ת] > list.txt # Find files contains Hebrew letters and write these to a file

Scripting

You already know [almost] everything!
Save commands to a file using your favorite text editor or cat > filename
Give execute permission to your script by chmod +x filename
Execute! ./filename

Thanks!

Tomer Cohen, http://tomercohen.com

Presentation slides available online: http://tomer.github.com/linux101

Linux introduction