Introduction to Linux

© 2010-15 SysPlay Workshops <workshop@sysplay.in
All Rights Reserved.
Introduction to Linux

2© 2010-15 SysPlay Workshops <workshop@sysplay.in
What to Expect?
Introduction to OS & OSS
Linux System Overview
Linux Usage Basics

OS Fundamentals
What is an OS?
Infinitely Running Program
Why do we need an OS?
Processor/Time Management
Memory Management
Storage Management
Network Management
I/O management

Open Source Software
Fundamentals
Originally Free Software
Freedom to Run, Change and Redistribute
Licenses – GNU GPL (Code) and GNU FDL (Doc)
The Freedom provides openness
Hence, also referred as Open Source Software
Over time FS & OSS have differed
But still largely same
Latest Complete Definitions
FS: http://www.gnu.org/philosophy/free-sw.html
OSS: http://www.opensource.org/osd.html

OSS: Industry Advantage
Stable Software – Less Development Cycle
Whole Community Support
Time to Market
And most of all, today OSS provides almost a complete set
of software required for any kind of software development
Applications, GUIs, Utilities, … - All GPL or LGPL stuff
Languages – Whole set from the world :)
C Compiler – gcc & friends
Debuggers – gdb & friends
Profilers, Tracers, ...
and the list goes on

And finally the most important one
OS + OSS = Linux

Why to choose OSS & Linux?
Quality and Reliability of Code
Availability of Code
Extensive Hardware Support
Communication Protocols and Software Standards
Available Tools
Community Support
Licensing
Vendor Independence
Cost
And, a wide range of Architecture Support

Linux on Architectures
x86
Started with this
Mainly intended for PCs
Power PC
Intended for PC
Have become popular in embedded
Strong ARM
Faster CPU – Higher Performance
PDAs, Setup box etc.
ARM
Suits well for Embedded
Include THUMB – reduce code bandwidth
High density code than PPC, x86
Many More
Alpha, H8, MIPS, Sparc, SuperH, ...

The Complete Software System
Operating System
“Kernel Space”
OS Services
Applications
“User Space”
Hardware

Linux Kernel Subsystem
The Process Scheduler (SCHED)
The Memory Manager (MM)
The Virtual File System (VFS)
The Network Interface (NET)
The Input/Output System (IO)
Additionally,
the Inter-Process Communication (IPC)

Linux OS Services
System Call Interface
X Window System

Linux Applications
Shell
Terminal / Console
Window Manager
Editor
Compiler
...

Linux Usage Basics

Topics
Root & System Directories
Shell Basics & the 'bash' Shell
File Basics & related Commands
User Basics & related Commands
File Access Permissions
System & Help Information
Standard I/O, Redirection and Pipes

/
the Root of an inverted tree
The top-most or super-parent directory
The container of your computer
Type: ls /

System Directories
/bin, /sbin - system binaries/applications
/var - logs, mails
/proc, /sys - “virtual” windows into the kernel
/etc - configuration files
/lib - shared system libraries
/dev - device files
/boot - Linux kernel and boot related binary files
/opt - for third-party packages
/root, /home - home directory for super user & other users
/usr - user space related files and dirs (binaries, libraries, ...)
/tmp - scratch pad
/mnt - mount points

Shell Basics
What is a Shell?
Various types of Shells
Bourne Shell (sh)
C Shell (csh)
Korn Shell (ksh)
Bourne Again Shell (bash)
TENEX csh (tcsh)
Z Shell (zsh)
Busybox (busybox) – Embedded Systems

Bourne Again SHell
env - shell environment variables
export [var_name] - export a shell variable
HOME - path to user’s home directory
PATH - executable search path
PWD - present user directory
PS1 - command prompt
which - shows executable path
history - command recall

Bourne Again SHell ...
alias - create shortcuts to commands
file - shows the information about a file
type - shows information about a command
Scripts
/etc/profile - System wide startup script
~/.bash_profile – User specific startup script
~/.bashrc – Shell specific startup script
~/.bash_logout – User specific shutdown script

File Basics
Every thing is viewed as a file in Linux
A file under the /
Seven Types
Regular (-)
Directory (d)
Character Device (c)
Block Device (b)
Named Pipe (p)
Socket (s)
Symbolic Link (l)

File related Shell Commands
ls - list directory/file contents
cd - change directory
pwd - print working directory
df - disk free
du - disk usage
cp - copy
mv - move, rename
rm – remove
mkdir - make directory
rmdir - remove directory
cat, less, head, tail - used to
view text files
vi, vim - editors
touch - create and update
files
grep - search in files
find, locate - search for files
gzip, gunzip, bzip2, bunzip2,
xz, unxz - compression
tar - archive
sed, awk - file manipulation

User Basics
All Accesses into a Linux System are through a
User with a Password
Super User – root
Normal Users - <user_name>
Files: /etc/passwd, /etc/shadow
Users can be categorized into groups
root, bin, sys, adm, …
File: /etc/group

User related Shell Commands
useradd - create user
userdel - delete user
usermod - modify user
su - <username> - start new shell as different
user
finger - user information lookup
passwd - change or create user password
who, w, user - to find out who is logged in

User & File Access
All Files have User specific ownerships & access
permissions
Type: ls -l
–rw–r––r––
Symbol Name Number Position
r read 4 r--
w write 2 -w-
x execute 1 --x
type user group other
user (anil) group (anil)

Related Shell Commands
chmod – Change file permissions
chown – Change file owner
chgrp – Change file group

Few “Help”ful Shell Commands
uname - print system information
man <topic> - manual pages
info <topic> - information pages

Linux Manuals
Divided into sections
1 Shell commands e.g. mv, ls, cat
2 System calls e.g. _exit, read, write
3 Library calls e.g. exit, printf
4 Device and network specific info e.g. mouse, ttyS, null
5 File formats e.g. passwd, termcap
6 Games and demos e.g. fortune, worms
7 Miscellaneous e.g. ascii, fifo, pthreads
8 Administrative commands e.g. fsck, network daemons
9 POSIX Programmer Manual
Info pages are also available

Standard Input & Outputs
Standard Input – 0 (default: keyboard)
Standard Output – 1 (default: monitor)
Standard Error – 2 (default: monitor)
Examples
read
echo
q

Redirections & Pipes
command < file - reads standard input from file
command > file - directs standard output to file
command >> file - appends standard output to file
command 2> file - directs standard error to file
command 2>> file - appends standard error to file
command > file 2>&1 - both standard output &
error to file
cmd1 | cmd2 - transfer o/p of cmd1 as i/p to cmd2

What all have we learnt?
Introduction to OS & OSS
The 3 software layers
The hardware core
Linux Usage Basics
Root & System Directories
Shell, File, User Basics
System & Help Information
Standard I/O, Redirection and Pipes

Any Queries?

Introduction to Linux

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