LINUX

1. Learning Linux

2. Linux Overview
Its a elongated version of UNIX where UNIX is
developed from a useless OS to Advance OS

Invented by LINUS , trying to make UNIX to
have a free system that completely compatible
with UNIX following the POSIK standards

It can be modified to the users need and can
be developed too and work on embedded
system

Many software engineers are using Linux for
there extensional need which are not provided
by the version of windows and Macintosh

3. Linux versions
Some Linux versions as
•
SUSE Linux
•
Ubuntu 1.0.10,Linux essential
•
Cent OS 5,6 essential
•
Fedora User,Desktop essential
•
Caldera open Linux
•
Slackware Linux

4. Linux advantages and
disadvantages
Advantage of Linux

Its free of cost

Its portable to any
hardware

Made to keep on running

Its secure and versatile

Its scalable

Has short debugging time
Disadvantages of Linux

There are far too many
distributions

Not very user friendly

Confusing for beginners

Changing versions

Frequent updated

Sometimes complicated

5. Booting process

Booting is a process or set of operations that loads and hence starts the
operating system starting from the point where the system is powered on

initially when the system is powered on a a relatively small program stored
in read-only memory (ROM) along with a small amount of needed data, to
access the nonvolatile device or devices from which the operating system
programs and data can be loaded into RAM.

all the other devices are not activated so booting is the process which
connect the hardware by launching a boot loader and connects to the
operating system of the RAM

6. Booting in windows

Turn on the power

CPU pins are reset and registers are set to
specific values

CPU jumps to address of bios

Bios runs the post and necessary checks

Bios runs the jump to MBR(MASTER BOOT
RECORD)

Primary boot loader runs from MBR and jumps to
secondary boot loader

Secondary boot loader loads operation system

7. Booting in Linux
Booting in Linux is done by following steps

BIOS is set up it loads and perform some checks and
gives control to MBR

MBR loads and it contains the info of the GRUB and
executes it

GRUB loads the kernel and has knowledge of the file
system and init images

KERNEL executes and runs /bin/init initial program of
RAM disk

INIT initiates the run level by selecting mode of run
level

RUN LEVEL runs and gives control to operating
system

8. Installation of Linux Cent OS 5

INSERT DISK-->POWER THE SYSTER ON-->
RUN BIOS SETUP--> CHANGE BOOT PRIORITY TO DVD--> EXIT

Select the install or updated existing system option

Skip installation media checks

Click next on welcome window

Choose language

Choose keyboard formate

Select the instilation device type (basic or specific
storage drive)

Specify host name if necessary


9. Partitioning , package selection
and rebooting

Select network device and edit

Click on connect automatically or on DNV or enter
manually

Select network setting and apply

Select time zone

Type the password which is to be the root password and
confirm password and click next

Select partition of the system as needed or customize

Select the required package of software

installation will start once done click on reboot

Initialization is done now start using the system

10. File system of Linux

11. File system

12. • /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
• /home - Home directories of the common users

13. • /initrd- (on some distributions) Information for
booting.
• /lib- Library files, includes files for all kinds of
programs needed by the system and the users.
• /lost+found- Files that were saved during failures
are here.
• /misc- For miscellaneous purposes.
• /mnt - Standard mount point for external file
systems,
• /net - Standard mount point for entire remote file
systems
• /opt - contains extra and third party software.

14. • /proc - containing information about system
resources.
• /root - The administrative user's home
directory.
• /sbin - Programs for use by the system and
the system administrator.
• /tmp - Temporary space for use by the system,
cleaned upon reboot
• /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

15. Linux File Permissions
These read, write, and execute permissions are
defined for:
• user - the user that owners the file
• group - users in the files group
other - every other user
There are also three other components when it
comes to file mode bits, namely
• the setuid bit
• the setgid bit
• the sticky bit.

16. Read write execute
The repeated rwx sequences represent the notion of
read (r), write (w), and execute (x)
permissions for user, group, and other (in that order). The
possible file types
• - = Regular File
• d = Directory
• l = Symbolic Link
• b = Block Special Device
• c = Character Device
• s = Unix Socket (local domain socket)
• p = Named Pipe

17. Special modes
Setuid - Set User ID When the setuid bit is set for a
program, on execution the process's effective user ID
gets set to that of the program file itself the lower case
"s" where the "x" was. If however, the file didn't have the
"x" permissions for the user, and then had the setuid bit
set to S
Setgid - Set Group ID When the setgid bit is set for a
program, on execution the process's effective group ID
gets set to that of the program file the setgid bit is
shown as either an "S" or "s".
Sticky Bit -When a directory has the sticky bit set, only
root or the file's owner has permission to change files in
that directory. The letter's "T" and "t" are used to indicate

18. Permissions: Octal
Representation
• Permissions In Plain English Symbolic Octal
• read,write,and execute rwx 7
• read and write rw- 6
• read and execute r-x 5
• read r-- 4
• write and execute -wx 3
• write -w- 2
• execute --x 1
• no permissions --- 0

19. The command takes the general form:
chmod MODE file There are two ways to represent the
MODE:
(1) Using symbolic modes (letters to indicate the categories
and permission)
(2) Using numeric modes (An octal (base 8) number that
represents the mode)
In order to change the permissions of a file using symbolic
permissions, use the command format:
chmod SYMBOLIC/NUMERIC­MODE FILENAME
Chmod (changing permission)

20. NUMERICAL MODE
• chmod 400 file To protect a file against accidental overwriting.
• chmod 500 directory To protect yourself from accidentally removing,
renaming or moving files from this directory.
• chmod 600 file A private file only changeable by the user who
entered this command.
• chmod 644 file A publicly readable file that can only be changed by
the issuing user.
• chmod 660 file Users belonging to your group can change this file,
others don't have any access to it at all.
• chmod 700 file Protects a file against any access from other users,
while the issuing user still has full access.
• chmod 755 directory For files that should be readable and executable
by others, but only changeable by the issuing user.
• chmod 775 file Standard file sharing mode for a group.
•

21. SYMBOLIC MODE
• chmod a=rwx filename the a means all and rwx means set
read,write, and execute. chmod ugo=rwx filename or chmod
ugo+=rwx filenameRegarding just the symbolic mode part of
the command, here are a few more examples:
• To add read permission for all:a+r To remove permissions for
all:a-r
• To add execute permissions for all:a+x To remove execute
permissions for all:a-x
• To remove execute permissions from group and other (i.e from
all users except the file's owner): go-x To remove permissions
to do anything from all users except the owner: go=
• The setuid bit can be set using: u+s The setuid bit can be
removed using: u-s
• setgid can be set using: g+s and removed using: g-s
• The sticky bit can be set by using: +t and removed using: -t

22. • To assign read, write permissions only for user and group:ug=rw
• To add read, write permissions to user and group to the
permissions that already exist:ug+=rw
• To remove execute permissions from group and other (i.e from all
users except the file's owner):go-x
• To remove permissions for all: a-r To add execute permissions for
all: a+x remove execute permissions for all: a-x
• To assign read, write permissions only for user and group: ug=rw To
add read, write permissions to user and group to the permissions
that already exist: ug+=rw To add read, write permissions to user and
group to the permissions that already exist: ug+=rw
• To remove execute permissions from group and other (i.e from all
users except the file's owner): go-x To remove permissions to do
anything from all users except the owner: go=
• The setuid bit can be set using: u+S The setuid bit can be removed
using: u-s
• setgid can be set using: g+s removed using: g-s
• set by using: +t removed using: -t

23. UNMASK
• octal numbers are preceded by a 0 (in the same way
hex would be preceded by 0x), so the umask value
itself is actually 002.
• This value is an octal (base 8, digits 0-7) value which
is subtracted from a base value of 777 for directories,
or subtracted from a base value of 666 for files.
• A umask of 002 basically means don't remove any
permissions from the base value for "user" or "group",
but "other" is not allowed write permission (write
permission is octal 2, or binary 010 meaning -w-).

24. Chown and Chgrp command
• The chown command can be applied to
change both user and group ownership of a
file, while chgrp only changes group
ownership. Of course the system will check if
the user issuing one of these commands has
sufficient permissions on the file(s) she wants
to change.
• In order to only change the user ownership of
a file, use this syntax:
chown/chgrp newuser file

25. Commands till now
• bash ­GNU shell program.
• cat file(s)­Send content of file(s) to standard output.
• cd directory or root­ Enter directory or cd is a bash built­
in command.
• chgrp newgroup file(s)­ Change the group ownership of
file(s) to newgroup
• chmod mode file(s)­ Change access permissions on
file(s)
• chown newowner[:[newgroup]] file(s)­ Change file
owner and group ownership.
• df file­Reports on used disk space on the partition
containing file.

26. • fdisk­to know hard disk size
• echo string­Display a line of text export Part of bash that
announces variables and their values to the system.
• find path expression­find files in the file system
hierarchy
• locate searchstring­Print all accessible files matching the
search pattern.
• ls file(s)­Prints directory content.
• man command­Format and display online (system)
manual pages for command.
• Pwd ­Print the present or current working directory.
• umask [value] ­Show or change new file creation mode.