Linux introduction

1. TOPIC OF DISCUSSION
• Introduction to Linux
• Linux Architecture
• File System
• Memory Management
• Ubuntu Installation
• File Commands
1

2. What is Linux?
• Linux is the software on a computer that enables applications and the
computer operator to access the devices on the computer to perform
desired functions.
• The OS relays instructions from an application to computer's processor
which performs the instructed task, then sends the results back to the
application via the operating system.
• Sounds very similar to other operating systems, such as Windows.
2

3. How its different compared to other OS?
• Something sets Linux apart from other operating systems.
• As an open operating system, Linux is developed collaboratively,
meaning no one company is solely responsible for its development or
ongoing support.
• Companies participating in the Linux economy share research and
development costs with their partners and competitors.
• Over 1,000 developers, from at least 100 different companies,
contribute to every kernel release. In the past two years alone, over
3,200 developers from 200 companies have contributed to the kernel--
which is just one small piece of a Linux distribution.
3

4. Where is Linux?
• One of the most noted properties of Linux is where it can be used.
• Windows and OS X (MAC OS) are predominantly found on
personal computing devices such as desktop and laptop computers.
• Other operating systems, such as Symbian(Mobile OS), are found
on small devices such as phones and PDAs (personal digital
assistants).
• Linux, which began its existence as a server OS and has become
useful as a desktop OS, can also be used on all of these devices.
“From wristwatches to supercomputers,” is the popular description
of Linux' capabilities.
4

5. The Future of Linux.
• Linux is being installed on the system BIOS (basic input/output system)
of laptop and notebook computers, which will enable users to turn their
devices on in a matter of seconds.
• This environment allows users to work on the Internet without having to
boot all the way into their device's primary operating system even if that
operating system is Windows.
• Linux is showing up on mobile Internet devices (MIDs) such as
smartphones and PDA.
• The growth of cloud computing is a natural fit for Linux, which already
runs many of the Internet's web servers such as Amazon's S3.
5

6. About the founder of LINUX
•Linus Benedict Torvalds (born December
28, 1969) began the development of Linux,
an operating system kernel, and today acts
as the project coordinator.
•Inspired by Minix (a kernel and operating
system developed by Andrew Tanenbaum),
he felt the need for a capable UNIX
operating system that he could run on his
home PC.
•Torvalds did the original development of
the Linux kernel primarily in his own time
and on his equipment.

7. •Torvalds originally used Minix on his
computer, a simplified kernel written by
Andrew Tanenbaum for teaching operating
system design.
•The Linux system quickly surpassed Minix in
functionality.
•The first version of the Linux kernel was
released to the Internet in September 1991. with
the second version following shortly thereafter
in October
About the founder of LINUX

8. GNU’s (GNU’s Not Unix)
• The GNU project was started in 1983 for developing a complete Unix-like
operating system, including software development tools and user application
programs, entirely of free software.
• By the release of the first version of the Linux kernel, the GNU project had
produced all the necessary components of this system except the kernel.
• Torvalds and other early Linux-kernel developers adapted their kernel to work
with the GNU components and user space programs to create a fully
functional operating system.

9. Linux Vs Windows
Open Source Development Model and
so the programmer can redesign the
OS.
It is not an open source and hence
cannot be redesigned by the
programmer.
Linux is robust and very much secure
from virus.
Windows gets affected by virus very
easily.
The Linux servers has surpassed
windows server operating system in
security.
Security is the main issue which has
made windows to think to survive.
It costs less to design and implement a
Linux Network.
It costs more to implement Windows
Network administration, when
compared to Linux.
There are 250000+ developers behind
Linux for open source deployment.
Compared to Linux, windows is
developed by few thousands of
people.

10. Linux Flavors
• Red Hat Linux (Red Hat)
• Fedora Linux
• Open Linux (Caldera)
• SuSE Linux (Novell)
• Mandrake Linux (Mandrake)
• Turbo Linux (Pacific Hi-Tech)
• Linux PPC (MAC Power PC version)
• Info magic
• Slack ware Linux Project
• Knoppix (Live CD)

11. 11
LINUX
ARCHITECTURE

12. Operating System Architectures
• Monolithic
• Layered
• Micro-kernel
• Distributed

13. Monolithic Architecture

14. Monolithic Architecture
• Monolithic operating system
– Every component contained in kernel
• direct communication among all elements
• highly efficient
– Problems:
• complexity
• new devices, emerging technologies
– enabling, protection

15. Layered Architecture
• Groups components that perform similar
functions into layers
• Each layer communicates only with adjacent
layer
• System calls might pass through many
layers before completion

16. Layered Architecture

17. Microkernel Architecture
• Microkernel
– provides only small number of services
– attempt to keep kernel small and scalable
• High degree of modularity
• Extensible, portable and scalable
• Increased level of inter-module
communication

18. Microkernel Architecture

19. Distributed Operating Systems
• Network operating system
– Runs on one computer but allows its processes to
access remote resources
• Distributed operating system
– Single OS manages resources on more than one
computer

20. Distributed Operating Systems

21. Linux Kernel Architecture
• Monolithic kernel:
Contains modular components
– Process management
– Interprocess communication
– Memory management
– File system management
• VFS: provides a single file system interface
– I/O management
– Networking

22. Linux Kernel Architecture

23. 23
LINUX FILE
SYSTEM

24. 24
Introduction
• File system
– How are data stored in storage?
– How do users access the data?
• Data organization, files and directories
• File system types
– Disk FS: ext2, ext3, FAT, FAT32 & NTFS
– Network FS: Samba & NFS
– Flash FS: JFFS2
– Special FS: proc FS

25. 25
Introduction (cont’d)
• You should understand Linux FS
– Why?
• Everything in Linux is file, if it is NOT process
– Easy to use
• Open file, read/write and close the file
• Unlike Windows, Linux FS is standard FS
– Everyone should learn standards

26. 26
File system Hierarchy Standard
• There is not any drive C:, D:, …
• All directories are under “/”
– “/” is the root directory
• It is possible
– to have multiple partitions
– to multiple file systems

27. 27
The “/”
• The primary hierarchy in FSH
– The root of tree of file system
• All paths start form here
• There is only one “/” in file system

28. 28
The “/”

29. 29
boot
• Linux kernel
• Boot loader configuration
• If you lost boot
– You cannot boot your OS

30. 30
boot

31. 31
bin
• Essential programs
• Need for system startup
• Basic commands for
– Navigating in filesystem
– File management

32. 32
bin

33. 33
dev
• Everything is file
– Hardware components (devices) are file
• Hard disk
• Key board
• All device files are here
• Direct interaction with device driver
– Open the device file
– Read & Write

34. 34
dev

35. 35
etc
• System configuration directory
– What is done by the registry in Windows
• All configuration file are text files
– You can view and edit it manually

36. 36
etc

37. 37
home
• Home directory of user
• Each user has a directory
– /home/bahador
– /home/hamed
• All files of user are stored here

38. 38
lib
• Programs need libraries
– Dynamically linked libraries
• Programmers need libraries
• All essential libraries are here
– Needed for system startup

39. 39
lib

40. 40
proc
• Kernel’s interface
– Kernel pseudo-directory
• Special directory
– It is NOT a directory on hard disk
• Kernel Configuration
• Kernel State monitoring

41. 41
proc

42. 42
root
• Home directory of root
• Don’t confuse
– / is the “root of File system”
– root is the name of system admin
– /root is the admin

43. 43
sbin
• System configuration programs
– Format hard disk
– Manage hardware
• Only “root” can run the programs

44. 44
sbin

45. 45
tmp
• Temporary directory
• All temp files are created by programs
• Your temp files
• It is emptied regularly

46. 46
usr
• Secondary hierarchy
• Very useful programs
– We usually use them
• compiler, tools
• Are not essential for system startup

47. 47
usr

48. 48
var
• The variable directory
• All dynamic files
• User cannot change the files

49. 49
var

50. 50
Permissions
• There are 3 basic permissions
– Read (r)
– Write (w)
– Execute (x)
• How to find them
– ls -l
• How to change them
– chmod +/- r/w/x <filename>

51. 51
LINUX MEMORY
MANAGEMENT

52. Linux Memory Management
• Allocates memory space to each process
– e.g., In Intel X86, Linux allocates 1 GB of high order
memory to kernel and 3 GB of memory to executing
processes
• Address space is divided among:
– Process code
– Process data
– Code and shared library data used by process
– Stack used by process

53. Linux Memory Management
(continued)
• Linux has system calls that change size of
process data segment as required
• Offers memory protection based on type of
information stored
• When kernel needs memory space, pages are
released using LRU algorithm
• Maintains a dynamically managed area in
memory, a page cache

54. Linux Memory Management
(continued)
• If any pages marked for deletion have been
modified, they’re rewritten to disk
– Page corresponding to file mapped into memory is
rewritten to file
– Page corresponding to data is saved on swap
device
• Linux uses system of page table to keep track
of free and busy pages
• Uses virtual memory mechanism

55. 55
UBUNTU
INSTALLATION

57. Login screen
Enter the user
name

58. PWD
• PWD
• Present working Directory
• Display the absolute path of the current
directory.

59. The absolute path of
the root directory is
displayed.
PWD

60. ls
• ls :
• List the Files and Directories within the current directory.
• Syntax:
• ls [options]
• Options:
• -l List file with permission.
• -a List hidden file.
• -i List files and inode number.
• -R List directories , sub directories

61. ls
Lists the files and
directories in the present
directory.

62. ls -l
l option lists the long
listing of Files and
directory.

63. l l command
File or directory
names.
Time stamp
Size of the files or
directories
The name of the group which has
the permissions over the files or
directories
Owner name, the user
who created the
directory.
No of links to the directory
It defines the permissions
assigned to the owners,
groups and other users

64. ls -a
[a] option lists all files and
directories including hidden files

65. ls -al
al option lists all files and
directories including hidden files
in long listin format.

66. ls -R
[R] option lists working directory
as well as contents in the
directory.

67. mkdir
• mkdir :
• Make directory (or) To create a
directory
• Syntax : mkdir <dirname>

68. cd
• cd
• Change directories
• Syntax : cd <directory name>
• cd .. To a directory one level up (parent
directory)
• cd - To your previous working directory
• cd / To the / (slash) directory

69. cd –
cd -
command will take you to
the previous working
directory
Here the current directory is
newdir when we enter cd -, it
takes to the previously worked
directory.
Again cd - is given as shown.
Now it will take to the
previously worked directory
i.e., (newdir)

70. cat
• cat
– it is the command to create and view files
• Syntax:
• cat [options] [filename]
cat > [filename] → To create a file
cat [filename] → To view a file
cat >> [filename] → To append text to a file

71. cat
As mentioned in the
previous slide. cat is
used to create a file
The file is saved
through ctrl -d after
typing the text

72. cat
Enter
cat <filename> to
view the content of
file.

73. cat
To append the text in a
file,
Cat >> (symbol) and
file name.

74. cat
The screen shows
the appended file

75. The -s option trims
multiple adjacent
blank lines into single
blank line
cat

76. The –b option
numbers the each
text line of the
output

77. cat
The –A option shows all
characters including control
and non printing characters
Here the $ represents the end of
the line

78. touch
• touch command is used to update the time stamps of a file.
• touch is also used to create new empty file.
– Syntax : touch [filename]
• touch can create multiple empty file too.
– Syntax : touch [filename1] [filename2]

79. touch
Here the empty file
is created

80. Multiple files are
created using touch
command
touch

81. Copy Command
• cp : cp command is known for copying files and
directories.
Syntax : cp [options] source destination
Options :
-r recursively copy an entire directory tree
-p preserve permissions, ownership, and time stamps
– Example :
cp File1 File2

82. There is a file
named ‘a’ in the
directory test .
Copy Command

83. Here we notice that test1 is a
empty directory. Let us copy
the file ‘a’ into this directory.
Copy Command

84. Cp copies the file ‘a’ from the
directory test to the directory
test1.
Copy Command

85. Thus the file ‘a’ is
copied to the test1
directory.
Copy Command

86. Directories new and
old are listed with
their contents.
Copy Command

87. -r option copy the
entire directory tree
‘old’
Copy Command

88. Copy Command
Thus the contents
of old directory is
copied to new
directory.

89. Copy Command
Command l l shows the
permission of the file

90. Copy Command
Using chmod,
permission of the file is
changed

91. Copy Command
Now, we copy the
file one to the
directory old

92. Copy Command
See the comparison
of the file one
shown above in the
new and old
directory

93. Copy Command
Now using command cp along with
–p option the permission is
preserved.

94. •mv : This command is used to move and renaming
files and directories
•Syntax:
mv <source> <destination>
Example
mv file1 file2 (now the file1 is changed to file2)
Move Command

95. Move Command
A file is available in
the name of one in
the directory old

96. Move Command
Here we see that using
mv command the file is
moved from old to
new directory.

97. Move Command
Now check into the old
directory where the file one
is moved. Hence the
directory is empty

98. Move Command
The file one is shown above in
the new directory

99. Move Command
Here a file is
created test in the
old directory

100. Move Command
This example shows
how to rename a file
test to tested

101. Move Command
Using the l l command, the
above screen shows the
renamed file

102. rm and rmdir command
• rm : This command is used to remove files
Syntax: rm <filename>
Example :
rm file1
• rmdir : This command is used to remove directories.
• Syntax: rmdir <directory name>
Example :
rmdir linux

103. This screen shows the
contents of the new
directory
rm command
The above rm command
is used to remove the
file k

104. Here the file named k is
removed from the directory
rm command

105. Here a directory is created named
donic which is removed through the
command rmdir
rmdir command

106. The above screen
shows that directory
donic is removed
rmdir command

107. In the above screen we
see that directory tomy
is unable to remove
rmdir command

108. Using rm with option – r,
the directory along with
contents can be removed
rm command

109. Now the above
screen shows that
the directory is
removed
rm -r command

110. The above screen shows
the contents of
directory jerry
rm command

111. The rm with –ri
command is used to
remove the contents
interactively.
rm -ri command

112. We can see that the file for which
we have given ‘y’ is removed and
‘n’ is preserved
rm -ri command

113. • The file command is used to check the file content.
• Syntax : file <filename>
• Example: file f1 (f1 is a file. File will show the
format)
• file /dev/fd0 (The output shows that the
fd0 is a block special file)
File command

114. File format
The file along with file name
(ss) shows the file format

115. This shows the
format of the
file cat as
executable file
File format

116. more
l l command shows
the contents at once.

117. more
l l lists the content
quickly, which makes
the viewer to see
only last page

118. more
More is used to
lists the contents
one screen at a
time

119. more
More is been
prompted after
listing one by one

120. more
Here it is the
same process
listing more
contents, shown
as above

121. more
Here it is the
same process
listing more
contents, shown
as above

122. more
Now the more
command is over
and we are in
the end of the
page

123. vi & vim editor
➢Vi is known as the visual editor.
➢It is a standard editor under Linux and Unix system.
➢Vim is the improved version of vi editor
➢Vi have three modes of operation
Command mode
Insert mode
Esc mode

124. vi Modes
• Command mode:
• Operations such as cut, copy, paste, delete, undo,
redo etc., are done in this mode.
• Insert mode:
• Type in new text
• Ex-mode :
• Extended commands for saving, exiting, search-and-
replace can executed here

125. Working with vi editor
exam is a file
created or
opened with the
vi editor.

126. Command Mode
Press ‘i’ to get
into the insert
mode

127. Insert Mode
This is the insert
mode

128. After typing the
data’s hit escape to
get into command
mode
Insert Mode

129. Ex- Mode
Press :wq to
write and
quit

130. Ex- Mode
Press q! to
quit without
saving the
data

131. Yank
Hit escape and type 3yy to
yank three lines from the
cursor position
Like this example, you can
copy any number of lines
by typing numbers of lines
and yy

132. In the previous slide, we
saw how to yank the text.
After yanking we see the
message as below
Text yanked

133. Now the yanked text is
pasted from the cursor
position by hitting the ‘p‘
Text put

134. delete
To delete text, place the
cursor in the beginning of the
line and give the total number
and dd

135. Now 3 lines are
deleted and message
get displayed as 3
fewer lines as shown
below
delete

136. cut and put
To cut a line after curser
position hit 1cc.

137. Get into insert mode and place
the cursor where the data should
be pasted. Press esc to get in to
command mode
cut and put

138. Now hit p to paste the
data.
cut and put

139. Search
Get into ex mode type /
followed by data to be
searched and press enter

140. When we press enter it shows
the first found match from
bottom to top.
Search

141. Then if we press ‘n’ it will shows the
second match for that data.If we continue
pressing n it will show successive
matches.
Search

142. Find command
• Find: To search files and directories in a
specified path.
• Syntax: find <directory> [conditions] [action]
• Condition: -name <file name> - to search a
particular file
• -user <user name> - lists the files owned by
user.
• -perm <mode> - search a file depending
on permission.

143. This command searches
the password file from /
directory.
Find command

144. The above screen shows
the execution of
command
Find command

145. Locate command
• Locate:
• To search or locate files and directories
from the database.
• It locate the files faster than the find
command
• Syntax:
• locate [pattern]

146. To search file named
test1 from database.
Locate command

147. All the files and directories
named test1 is located and
displayed.
Locate command

148. • man : Display helpful information about
commands.
• Syntax:
• man [option] command
• Option:
• –k - search by command description
rather than command name.
Man command

149. Man command
It displays manual pages for
ls command.

150. Man command
The manual page of ls
command is displayed here.
Enter q to exit from manual
page.

151. • useradd :
• To create a new user account and login
directory for that new account.
• Useradd will create new entries in system
files.
• Syntax : useradd [options] [user]
• Options
• -c Comment field.
-d Home directory
• -e Account expiration date.
useradd command

152. useradd command
User named
abdulkalam is created.
To set password for
abdulkalam.

153. useradd command
Enter the
password.

154. User home directory
When new user account is
created ,a login directory for
the user is created in /home
dir.

155. User configuration files
• When a new user account is created, its entries
updates the following system files.
• - /etc/passwd
• - /etc/group
• - /etc/shadow

156. Passwd file
To view password
configuration file.

157. Passwd file
First field represent
username.
x represents encrypted
password is available in
shadow file.
User id.
Group id.
User home
directory.
User login shell.

158. Group id for the
user abdulkalam.
Groups file

159. User login
Abdulkalam
logging in .

160. User login
User home dir
or login dir

161. User account can be deleted
through userdel command
userdel command

162. Creating groups
• New group is created by hand-editing the file
/etc/group or by using groupadd command.
• Syntax: groupadd groupname
• groupdel command is used to remove the group.
• Syntax groupdel groupname
• Groupmod is used to rename the existing
groupname.
• Syntax: groupmod –n newname oldname

163. Groupadd command
A group is added in the name
of india by using the command
groupadd.

164. Usermod command
Using usermod command
the user abdulkalam is
added to group India

165. Groups file
To view group file

166. The last field shows the user
abdulkalam added in India group
Groups file
The id number assigned to the
group india is 501

167. Groupdel command
Groupdel command deletes
window group.

168. Group Administration
Create a directory named
product and group named
sales.

169. User’s are added in the sales
group using usermod
command.
Group Administration

170. Open the group
file.
Group Administration

171. This shows that the three
users are added in the sales
group.
Group Administration

172. Change the group name sales to product
directory using chgrp command.
Group Administration

173. The screen shows that the
changes been made in the
group field.
Group Administration

174. Three files created under product
directory.
Group Administration

175. The permission for the
product directory is
changed.
Group Administration

176. The user tom is not a member of
the group. So the permission is
restricted.
Group Administration

177. suresh logs in terminal. As he is the
member of the group, he have the
privilege to access the file.
Group Administration

178. rajesh logs in terminal. As he is the
member of the group, he have the
privilege to access the file.
Group Administration

179. tom logs in terminal. he is not the
member of the group so does not have
the privilege to access the file.
Group Administration

180. The above screen shows the
permission been restricted to the
user tom.
Group Administration

181. Changing owner
The chown command
change the file or
directory owner.
After giving the chown
command the owner is
changed from root to
suresh.

182. Changing owner
The owner and group name
can be change using chown
command.

183. User administration
Chage –l : lists the
account and password
information of user tom.
This field sets the
password for the
maximum valid days
given.
Inactive period is used to
give grace time to change
the password.

184. User administration
The –M command with
100 sets as the maximum
days.
The password expires
field is updated by +100
days from user creation
date.

185. User administration
Allowable account
inactivity period after
which password will
expire.

186. User administration
The -W option shows the
warning message before
expiration.

187. User administration
The -m option for
minimum number of
days a user can exists
with password.

188. The -E option is for
specific expiration date
for an account.
User administration

189. Set userID
• It allows an executable file to run under the
user or group security context with the
permission of its owner.
• SUID can be set as follows:
• chmod u+s [filename]
(or)
• chmod 4xxx [filename]

190. The above screen shows file
shadow and password along with
the set user id permission.
The passwd is the command which
updates the password in the shadow
file, instead of not having the execute
permission.
Set userID

191. Tom changes the password
using passwd command.
Set userID

192. The set userid permission
is removed from the
/usr/bin/passwd file.
Set userID

193. Now we can view that tom
user cannot change the
password.
Set userID

194. Set GroupID
The user suresh logs get
into the product directory
and create a file.
The user suresh who create a
file, the group name is
assigned as suresh.

195. The groupid is set to
the product directory.
Note: the group sales is added
to the product directory.
Set GroupID

196. After setting the group id, user
suresh creates a file win98. Using
the command ls –l shows that the
file is created under the group
sales.
Set GroupID