INTRODUCTION TO LINUX

REALLY SHORT HISTORY Before GNU/Linux there were DOS, MAC and

UNIX. All systems were proprietary. The GNU project started in the early 80s by

Richard Stallman Goal to make a free version of UNIX Developers make money by modifying and

extending existing software depending on companies needs

In the early 90s the Linux kernel appears which quickly becomes the defacto kernel for GNU

The GNU General Public License ensures that the source codes will be free for all to copy, study and to change

ADVANTAGES OVER WINDOWS It's free to relatively inexpensive Source code is available, due to GPL Bugs are fixed quickly and help is readily available

through the Internet (IRC, forums) Linux is

more stable than Windows A truly multi-user and multi-tasking

multiuser: OS that can simultaneously serve a number of users multitasking: OS that can simultaneously execute a number of

programs runs on equipment that other operating systems consider

too underpowered, e.g. 386 systems, embedded devices and smartphones.

Overall highly reliable as an operating system

DISADVANTAGES COMPARED WITH WINDOWS Not all programs exist for Linux

e.g. Office, Photoshop WINE enables you to run the majority of Windows

software in Linux Virtual machine with Windows

Isn't as popular as Windows Though this is changing as Linux distributions

develop more user friendly interfaces No specific commercial company is responsible

for Linux Typically companies maintain only their own

distribution of Linux

TYPES OF INTERFACES Typically we classify these into

GUI – Graphical user interface CLI – Console line interface

TYPES OF INTERFACES Typically we classify these into

GUI – Graphical user interface CLI – Console line interface

LINUX AND WINDOWS Linux:

From the very start it has been CLI oriented. The GUI is just an additional program that passes commands to the CLI Features accessible from the GUI also accessible from the

CLI (but not necessarily a simple command) Always possible to switch to CLI if something goes wrong

Windows Started out as a GUI focused operating system.

DOS console still available, but lacking in expressive power and user friendliness

CLI is returning to Windows – PowerShell Cygwin or MSYS - a collection of programs enabling a

Linux-like CLI in Windows

GRAPHICS USER INTERFACE IN LINUX By adopting the X-Window technology, the

graphical user interface is also available for Linux: Uses pointing devices (e.g. mouse) to control the

system, similar to Microsoft’s Windows Advantages: Tasks selectable from menus or icons.

Learning curve is very low, can do certain types of work immediately.

Disadvantages: Slow and requires certain resources to run Not an issue on modern PCs

Suitable for general users and personal computers Ubunto, Linux Mint and others

COMMAND LINE INTERFACE IN LINUX Traditional Linux (Unix also) uses command line

driven interface (or text-based interface) User needs to type command to instruct the computer

to do work (as in DOS) Advantage: fast performance. Very few resources are

required for its use. More flexible and easier automation of tasks

Disadvantages: user needs to type, making it error prone. Learning curve is higher than GUI

Suitable for advanced users and for the systems that interaction with user is not frequent, such as servers or embedded systems

LINUX SHELL Shell interprets CLI commands and

requests appropriate services from the Linux kernel

Similar to DOS but DOS has only one shell, while Linux can select from a variety shells Bourne Again shell (Bash), Debian

Almquist (dash), Z shell (Zsh)

Different shells have similar but different functionality

Bash is the default for most The GUI interface is an application

started from shell

Kernel

Bash, Tcsh, Zsh

ls pwd whoami

SOME QUICK HANDS ON TERMINAL While we are in the GUI, to get to the terminal

(CLI), we must find and open the program “Terminal”

THE TERMINAL Typically we are greeted by a window that looks like

this

andrew@production:~$ Immediately noticable:

Our user name (andrew) The computers name (production) Our security status (regular user - $ or super user - #)

THE TERMINAL - TTY As mentined, we can always access the terminal.

One mode is to switch to the virtual terminal – TeleTYpewriter - TTY

Ctrl+Alt+Fn lets us switch between12 TTY terminals Fn being F1,F2,F3…F12

The GUI in Ubuntu runs in terminal 7 – TTY7! Same as using the terminal program, only here

we are directly in the console. The terminal program in GUI is just a fancy TTY

USER MANAGEMENT As a user you can change your files, user

information and run programs Depends on your privileges

As a superuser (su) you can do any operation to anything and anyone Dangerous, try to avoid using superuser for

everything (typically named root) Anyone ever rooted their phone?

“Permission denied” when executing command as user? May need to execute command as superuser Append sudo to command (sudo – superuser do)

ADDING USERS Easy and straightforward

Run the following as a superuser (root or via

sudo) useradd –m USERNAME

The –m flag will create a home directory passwd USERNAME

Set the users password so he can login usermod –s /bin/bash USERNAME

Modify the users shell (-s) to use bash By default the shell is /bin/sh, a lightweight shell

LINUX FILE ACCESS PRIVILEGES Linux is a multiuser system, the files of all users

are stored in a single file structure Mechanism is required to restrict one user to

access the files of another user, if he is not supposed to

User can impose access permission to each file to restrict its access

The term “access permission” refers to read permission write permission execute permission

LINUX FILE ACCESS PRIVILEGES Access permission can also be assigned to a directory Directory is also a file that contains the attributes of

the files inside it If read permission is not given to a directory

cannot show the structure of this directory e.g. cannot use ls

If write permission is not given to a directory cannot modify anything of the directory structure e.g. cannot copy a file into this directory since it will modify

the directory structure by adding one more file If execute permission is not given to a directory

nearly nothing can be done with this directory, even cd

LINUX FILE ACCESS PRIVILEGES Use ls –l to view current directory files and

details

It is a directory

Owner policy The directory can be read, written and executed by the owner

Group policy The directory can be read and executed but not written by other users in the same group

Everyone else policy The directory can be read and executed but not written by other users in a different group

Owner Owner’s group

file size

File last modified date Hard link

no

file name

d rwx r-x r-x 2 john users 4096 July 24 2013 Autostart

POLICY PERMISSSIONS

Total value Read

Value 4

Permissions Write

Value 2

Execute Value 1

Listing

0 no read no write no execute --- 1 no read no write execute --x 2 no read write no execute -w- 3 no read write execute -wx 4 read no write no execute r-- 5 read no write execute r-x 6 read write no execute rw- 7 read write execute rwx

LINUX FILE ACCESS PRIVILAGES The access permission of a file or directory can be

changed by using the command

chmod xyz filename/directory name

660 : 110 110 000 ⇒ rw- rw- --- 545 : 101 100 101 ⇒ r-x r-- r-x

xyz refers 3 digit in octal form (cant go higher than 7) For example

421 421 421

LINUX FILE ACCESS PRIVILEGES The owner of a file or directory can be changed by

using the command

chown user:group filename/directory

user – for which user are user access privileges applied to

group – for which group are user access privileges applied to

LINUX FILE SYSTEM STRUCTURE According to the File System Standard (FSSTND)

proposed in 1994, every LINUX system should contain a set of standard files and directories

23

root /

bin

boot dev etc home

lib lost+found mnt opt

proc

root sbin

tmp usr

var

fd sd sd …

group passwd john doe bin lib local

file

directories

LISTING CONTENT OF ROOT /

THE FILESYSTEM In Linux, a file is defined as simply the thing that

deals with a sequence of bytes Hence everything are files

An ordinary file is a file; a directory is also file; a network card, a hard disk, any device are also files since they deal with a sequence of bytes

A few types of files simple/ordinary file (text file, c++ file, etc) directory symbolic (soft) link special file (device) named pipe (FIFO)

It is essetial that we know some basics on how to navigate the filesystem

SYMBOLIC LINKS AND DEVICES Symbolic (soft) link

Not a real file, just a link to another file Allow giving another name to a file without actually

duplicating it – save disk space Special file (device)

Each hardware device, e.g. keyboard, hard disk, CD-ROM, etc is associated with at least one file

Typically located in /dev directory Applications can read and write any devices by reading

and writing their associate file – hence the access method is known as device independent The drives is responsible for communicating with the actual

hardware Divide into two types: character special files, e.g. keyboard,

and block special files, e.g. hard drive

LINUX FILE SYSTEM STRUCTURE Root Directory ( / )

Top of the file system. Contains everything. /bin

Contain the binaries (executable code) of most essential Linux commands, e.g. bash, cat, cp, ln, ls, etc.

/boot Contain all the files needed to boot the Linux system,

including the binary of the Linux kernel. /dev

Contains the special files for devices, e.g. fd0, sda, etc.

LINUX FILE SYSTEM STRUCTURE /etc

Contain host-specific files and directories, e.g. information about system configuration

/home Contain the home directories of every user in the

system, e.g. dlun, guest, etc /lib

Store all essential libraries for different language compilers

/lost+found Contain all the files on the system not connected to

any directory. System administrator should determine the fate of

the files in this directory

LINUX FILE SYSTEM STRUCTURE /mnt Ubunto will typically mount to /media!

Used by system administrator to mount file systems temporarily by using the ‘mount’ command

Before using any devices (located in /dev), they have to be mounted to the system for registration

For example, after mounting a CD-ROM, the file system in it will be mapped to /mnt/cdrom directory Ubunto maps to /media/CD_name

User can then read and write files in the CD-ROM by accessing this directory

Similar to mapping a drive letter to a CD-ROM in Windows

Different from the special file in /dev. The special file is only a place where data of the CD-ROM is transferred or stored. No file system concept.

LINUX FILE SYSTEM STRUCTURE /opt

Use to install optional, add-on software packages, e.g. LibreOffice and such

/proc Contains process and system information

/root Home directory of the user root, usually the

administrator /sbin

The directories /sbin, /usr/sbin, and /usr/local/sbin contain system administration tools, utilities and general root only commands, such as halt, reboot and shutdown

LINUX FILE SYSTEM STRUCTURE /tmp

Contain temporary files. Usually files in this directory will be deleted from time to time to avoid the system fills with temp files

/usr One of the largest sections of the Linux file system Contain read-only data that are shared between

various users /var

Contain (variable) data that keeps on changing as the system is running.

FREQUENTLY USED COMMANDS TO NAVIGATE AND MANIPULATE THE FILESYSTEM

pwd : show the name of the current directory ls : to show the names of the file in the current

directory cd : change directory

cd / change to the root directory cd .. change to the parent of that directory

cp : copy one file to another cp abc.txt xyz.txt copy abc.txt to xyz.txt

rm : remove file rmdir : remove (empty) folder man : ask for the manual (or help) of a command

man cd ask for the manual of the command cd

FREQUENTLY USED COMMANDS TO NAVIGATE AND MANIPULATE THE FILESYSTEM

touch: create an empty file touch abc.txt create empty file with name abc.txt

cat : show the content of a text file cat abc.txt show the content of abc.txt

nano: simple text editor (one of many) vi : advanced text editor (read manual and tutorials!) man : ask for the manual (or help) of a command

man cd ask for the manual of the command cd

PROCESS MANAGEMENT Linux is a multitasking system Multiple programs can be executed at the same

time Ultimately, a program needs to be executed by a

CPU If there is only one CPU, how are multiple

programs executed at the same time? They are not, they share the CPU time CPU sharing happens so fast it feels like all

programs are executing in parallel

VIEW PROCESSES One can easily see the system status of

executables with command top

VIEW PROCESSES Or using ps -a

KILLING PROCESSES

If a process becomes unresponsive, one way to end it is to use signals; the command kill -ID PID ID what kill signal to send PID proces ID, can be found in top command and

elsewhere

Common kill signal IDs 1 – Hang up, safest way to ask a process to stop 2 – Kill program, same as pressing Ctrl + C 9 – Forces termination, last resort 15 – Ask process to end itself

INSTALLING APPLICATIONS Using apt-get

Typically recommended to do apt-get update Will fetch an up to date list of applications

Install package with apt-get install PACKAGE Search through the list of applications with apt-cache search NAME

Update all installed packages with apt-get upgrade

HINTS Always use TAB

It will auto-complete what we are typing by looking at available executables and files

If more than one option is available, press TAB multiple times to switch between them

Available executables are determined by PATH and files are determined by our location in the filesystem

EXERCISE ONE Position yourself to the home directory

cd ~ Using the wget command, download these slides

from http://gemma.uni-mb.si/ros2014/slides.pdf Syntax is wget URL

wget http://gemma.uni-mb.si/ros2014/slides.pdf

Open the slides and go to the next page

EXERCISE TWO Again using the wget command, download more

exercises from http://gemma.uni-mb.si/ros2014/exercises.txt

You can open them with any text editor (gedit)

HELPFUL LINKS Expanded cheat sheet for command line

http://www.cheatography.com/davechild/cheat-sheets/linux-command-line/

Introduction to Linux command line http://www.phas.ubc.ca/~mbelab/computer/linux-

intro/html/ Writing Bash scripts

Scripts are typically non compiled programs http://mywiki.wooledge.org/BashGuide