This document provides an overview of the Linux operating system. It discusses key Linux concepts like the kernel, shell, file system structure, permissions, users and groups. It also summarizes important commands for navigating and managing files, directories, users, software and services in Linux. These include commands like ls, cd, mkdir, chmod, useradd, yum, service and chkconfig. The document outlines the directory structure in Linux and describes important directories like /bin, /home, /etc. It also covers processes, pipes, redirection and Linux file systems & partitions.

1. LINUX
Presentation by Kallam Srinivas Reddy
(K00316758)
Operating Systems CSEN5322_002_201410
Instructor- Young lee

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Overview of Linux System
Vi editor
Basic Commands
Redirect, Append, and Pipe
Relative & Absolute Path
File System & Partitions
Permissions
Process Management
User Management
Group
Software Management
Backup and restore
Managing installed services
Outline

3. Overview of Linux System
Linux is an Operating system (OS).
Linux system is described as kernel & shell.
Kernel is the main program of Linux system. It controls
hardware, CPU, memory, hard disk, network card etc.
Shell is an interface between user and kernel. Shell interprets your
input as commands and pass them to kernel.

4. Overview of Linux System
Multiuser & Multiprocess:
Many people can use one machine at the same time.
File & Process:
Data, directory, process, hard disk etc (almost everything) are
expressed as a file.
Process is an running program identified by a unique id (PID).

5. Overview of Linux System
Directory Structure
Files are put in a directory.
All directories are in a hierarchical structure (tree structure).
User can create and remove any directories on the tree.
Top directory is “/”, which is called slash or root.
Users have the own directory. (home directory)

6. Overview of Linux System
Directory Structure

7. Overview of Linux System
Important Directories:/bin- This contains files that are essential for correct operation of the
system. These are available for all users to use.
/mnt- Provides a location for mounting devices, such as remote file
systems and removable media
/home- This is where user home directories are stored.
/var- This directory is used to store files which change frequently, and
must be available to be written to.
/etc- Various system configuration files are stored here.

8. Overview of Linux System
/dev- This contains various devices as files, e.g. harddisk, CDROM drive,
etc.
/root- This is the root (administrator) user's home directory
/sbin- Binaries which are only expected to be used by the super user.
/tmp- Temporary files.
/boot Has the bootable Linux kernel and bootloader configuration
files(GRUB)
/usr- Contains user documentation, games, graphical files,
libraries(lib),etc..

9. Overview of Linux System
Normal user and Super user
In Linux system, there is one special user for administration, who can
do anything. This special user is called root or superuser.
Case Sensitivity
Linux operating system is case sensitive.

10. Overview of Linux System
Run levels in Linux- refers to the mode of operation in the Linux
operating systems
Following are the run levels of some popular Linux versions
Following are the seven run levels in Ubuntu
 0 ->halt
 1 ->Single user mode
 2 ->Graphical multi-user with networking
3 – 5 -> Unused but configured the same as runlevel 2
6 -> Reboot

11. Overview of Linux System
Following are the seven run levels in Red Hat Linux and Fedora
 0 ->halt
 1 ->Single user text mode(without networking)
 2 ->Not used (user definable)
 3 -> Full multi-user text mode
 4 -> Not used (user definable)
 5 -> Full multi-user graphical mode (with an X-based login screen)
 6 -> Reboot

12. VI Editor
• Programs & configuration files are text files.
• There are two popular text editors vi and Emacs.
• vi is a screen-oriented text editor originally created for
the Unix operating system.

13. Basic Commands
How to run commands
When you log on Linux machine, you will see,
[cseos@hyperion001 srinu]$
 start typing the command next to the $ symbol
 One command consists of three parts, i.e. command name, options,
arguments.
Between command name, options and arguments, space is necessary.
For Example
[srinu~]$ command-name optionA optionB argument1 argument2

14. Basic Commands
Options always start with “ - ”.
For Example
• cd ..
• ls –l .bashrc
• mv fileA fileB

15. Basic Commands
Basic useful Commands
 ls - show files in current position
 cd - change directory
 cp - copy file or directory
 mv - move file or directory
 rm - remove file or directory
 pwd - show current position
 mkdir - create directory
 rmdir - remove directory
 cat - display file contents
less - display file contents pagewise

16. Basic Commands
man - display online manual
su - switch user
 passwd - change password
 useradd - create new user account
 userdel - delete user account
 mount - mount a file system
 umount - unmount a mounted file system
 df - show disk space usage
 shutdown - reboot or turn off machine

17. Redirect, Append and Pipe
Redirect and append
 Output of command is displayed on screen by redirecting to a file.
 Using “>”, you can redirect the output from screen to a file.
 Using “>>” you can append the output to the bottom of the file.
Pipe
 Some commands require input from a file or other commands.
 Using “|”, you can use output from other command as input to the
command.

18. Redirect, Append and Pipe
Commands
head - show first several lines and omit other lines.
tail - show last several lines and omit other lines.
grep - show lines matching a pattern
Working with commands:
In home directory, type
->ls .bash_profile
->cp .bash_profile sample.txt
->less sample.txt

19. Redirect, Append and Pipe
Using redirect.
->head 3 sample.txt
->head 3 sample.txt > redirect.txt
Using append.
->tail 3 sample.txt tail 3
->sample.txt >> redirect.txt less redirect.txt
Using pipe.
less redirect.txt
grep PATH redirect.txt
tail redirect.txt | grep PATH
rm sample.txt
rm redirect.txt

20. Relative & Absolute Path
Path means a position in the directory tree.
 To express a path, you can use relative path or absolute path.
In relative path expression, the path is not defined uniquely, it
depends on your current path.
 In absolute path expression, the path is defined uniquely, it does not
depend on your current path.

21. File System & Partitions
Everything is a file in linux.
Mounting
Files related to mounting in linux
/etc/mtab(Current files mounted)
/etc/fstab(info about permanent mounting points)

22. File System & Partitions
Partitions
Commands to view existing partitions
 fdisk –l
 parted –l
Partition administration using fdisk
fdisk <partition name with location> eg:- fdisk /dev/sda.
Various options for fdisk are n,p,q,t,v,w,etc..
Updating the partition without restarting :partrobe /dev/sda or partx /dev/sda
Formatting a partition with file systems(eg- ext4 system)
mkfs.<file system type> <partition name>
Eg - mkfs.ext4 /dev/sda
Note:-After formatting the partition must me mounted in ordered to use

23. File System & Partitions
Mounting Partitions:-
Temporary mounting
mount <device name> <directory name(mount point)>
Eg:- mount /dev/sda oslab
Permanent mounting
Add the parameters for mounting point in the file /etc/fstab as follows
Umounting the partition
umount <mount point directory>
Eg:- umount /oslab
To view mount points use the command mount
Assigning label to the partition(giving some name to partition)
e2label <partition name> <label>
Eg:- e2label </dev/sda> <os>

24. File System & Partitions
Mounting a partition using label
mount LABEL=<label name> <partition name>
Eg:- mount LABEL=os /oslab
LVM(Logical volume management)

25. File System & Partitions
Components of LVM
Physical volume (PV)
Physical Extend (PE)
Volume Group (VG)
Logical Volume (LV)
Logical Extend (LE)
Commands in LVM
pvs, vgs, lvs – displays all PVs, VGs, and LVs in the system
Display detailed information
pvdisplay, vgdisplay, lvdisplay
 creating PVs, VGs, LVs
pvcreate, vgcreate, and lvcreate

26. File System & Partitions
lvresize – resizes a logical volume
lvreduce – reduces a logical volume
vgreduce – reduces a volume group
Removing/deleting PVs, VGs, LVs
pvremove, vgremove, lvremove

27. Permissions
All the files and directories have the permissions and owner assigned
to them.
There are three types of permission readable, writeable and
executable.
Permissions are given to three kinds of groups namely owner, group
member and others.
Example[cswug@hyperion001 cswug]$ ls l .bash_profile
-rw-r--r-- 1 cswug cswug 191 Jan 4 13:11 .bash_profile
Note-r : readable, w:writable, x: executable

28. Permissions
Commandschmod- change file mode, add or remove permission
chown- change owner of the file
Examplechmod a+w filename - add writable permission to all users
chmod o-x filename - remove executable permission from others
Note- u: user (owner), g: group, o: others a: all

29. Permissions
acl- access control lists
More secure way to secure the files.
The file system have to be mounted with the option acl in /etc/fstab
file.
Files with acls can be read only using the getfacl command.
Writing or changing acls can be done with setfacl or /usr/bin/setfacl.
To remove an acl of a file system use –x option for setfacl command.

30. Process Management
Process is a unit of running program.
Each process has some information, like process ID, owner, priority, etc.
CommandsKill - Sends specified signal to specified process .The process is specified by
process ID.
Killall – kills all the process with a particular name. The program is
specified by command name.
ps - Show process status
top - Show system usage statistics

31. Process Management
Check your process.
ps
ps –u
Check process of all users.
top (To quit top, press “q”)
ps –e
ps –ef
Find your process.
ps –ef | grep cseos

32. Process Management
Output of “ top” command

33. User Management
Commands to know
whoami – Gives the current Username.
 who – gives the information about who is logged on the system.
 who am i – gives the details about current session in a line.
 w – shows you who is logged on and what they are doing.
 id – gives the user id, primary group id, and a list of the groups that
you belong to.

34. User Management
Root user-The root user is also called the superuser is the most
powerful account on the Linux system(userid 0)
User management on any Unix can be done in three ways.
1. Graphical
2. Command line tools
3. Edit the local configuration files

35. User Management
Important files in user management/etc/shadow- User passwords are encrypted and kept in /etc/shadow
/etc/passwd –Contains the local user database on Linux
/etc/default/useradd - contains some default user options.
Home directories(Two ways of creating home directories)
1. useradd –m to create a home directory for user.
2. Create a directory using mkdir and setting the owner as user using
chmod and restricting the permissions.

36. User Management
Commands for user management
useradd- to add a user
usermod – to modify the properties of a user
gpasswd – to manage the users
userdel – to delete a user
passwd – to manage passwords for users).
chage – to change the attributes of the passwords of users
su – allows a user to run a shell of other users
Sudo-The sudo program allows a user to start a program with the credentials
of another user.

37. Group
Users can be listed in groups.
Groups allows you to set permissions on the group level instead of having to
set permissions for every individual user.
/etc/group – file in which group membership is defined.
Commands for group management
group – to view the list of groups to which user belongs to.
groupadd – to add new groups
usermod - Group membership can be modified
groupmod – to change the group name
groupdel – to remove a group permanently

38. Software Management
RPM utility is used to manage soft wares in linux
RPM – Red Hat Package Manager
Tool used for installing, uninstalling, verifying, querying, and updating software packages.
Commands for RPM
 rpm –qa (q- query and a- all) > gives all the installed packages on the system
 rpm –q <package name>
> to check whether a package is installed or not.
 rpm –ivh <package name> > to install a package(i-install, v- verbose view, hhash progress)
Note:- to install a package, first navigate to the directory in which packages are
stored
 rpm –e <package name> >to uninstall/ remove a package(e- erase)

39. Software Management
 rpm –qf <package directory> > to install the package forcefully
 rpm –qlc <packager name>
> to see the configuration files of installed
package(q-query, l-local, c-configuration)
 rpm –qld <package name>
> to see which directory is associated with a
particular package (q-query, l- local, d- directory)
Dependency- some packages requires some other packages to be installed
before it can be installed.
 rpm -ivh <package name> --nodeps > to install packages without dependicies.
 rpm -uvh <package name>
> to update a package(u- update, v-verbose, h-hash
progress)

40. Backup and restore
Backup using tar
 tar – cvf <destination and name to be> <source file>
>creating a tar backup
for source file (note: c-create, v-verbose, f-name of tar file)
eg:- tar – cvf /opt/etc.tar /etc
 gzip <file name> >applying gzip on the tar file
eg:- gzip /opt/etc.tar
 scp <gzip file> <destination address> > transferring the file to another system
using secure copy (scr) (destination address is the IP address of the target system
followed by the target directory)
eg:- scp /opt/etc.tar.gz 192.XXX.XX.X/root/
 gunzip <file name> > to unzip the file
 tar – xvf <file name> > to untar the file (x-remove)
eg:- tar – xvf etc.tar

41. Managing installed services
Services/programs
Two commands to control the services
1. Service
Temporary control(changes only for current session / after booting the
changes will be erased from the service)
Commands
 service <name of the service> status -> used to check the status of the service
service <name of the service> start -> used to start the service
service <name of the service> stop -> used to stop the service
service <name of the service> reload -> used to reload the service
service <name of the service> restart -> used to restart the service

42. Managing installed services
2. Chkconfig
Permanent control(changes are carried until they are changed again no
matter of booting).
Commands
 chkconfig - - list >to check the availability of the service
chkconfig <service> on > to make the service available after restart
chkconfig <service> off > to make the service unavailable after restart