Modifying User Accounts


Modifying User Accounts :
———————–
Modifies a user account.

1) Launch Userconf
2) Choose User Accounts & Click User Accounts
3) Modify & Press Enter
4) Modify the Fields
5) Click Accept Button

Capture

Name :
—-
usermod –> modify a user account

Usermod Command :
—————
The usermod command lets you modify an existing user account.

Syn :

usermod [options] LOGIN

Description :
———–
The usermod command modifies the system account files to reflect the changes that are specified on the command line.

Cmd :

usermod -d home
usermod -l home

Chfn Command :
————
The chfn command change the full name associated with a user account.

Cmd :

chfn user

Chsh Commands :
————-
The chsh command change the command interpreter associated with user account.

Cmd :

chsh -s shell user

usermod options

Usermod Files :
————-
/etc/group       –> Group account information.
/etc/gshadow   –> Secure group account information.
/etc/login.defs –> Shadow password suite configuration.
/etc/passwd     –> User account information.
/etc/shadow     –> Secure user account information.

Disk Space Quota


Quota :
—–
A disk quota is a limit set by a system administrator that restricts certain aspects of file system usage on modern operating systems. The function of using disk quotas is to allocate limited disk space in a reasonable way.Disk Space Quota place limits on the amount of the disk space a User (or) Group.

1) quota.user
2) quota.group

disk-quota

Types of Limits :
—————
1) Soft Limits
2) Hard Limits

Implementing Quotas :
——————-
1) Configure the kernal
2) Install quota package
3) /etc/fstab
4) Establishes quota files
5) Set quotas
6) Turn on quota checking

Installing Quota Package :
————————
The quota package is part of the redhat linux base component and generally installed.

Cmd :

rpm -qi quota

Cmd :

rpm -uvh quota*.rpm

Resides :
——-
/etc/rc.d/rc.sysinit

1) Runs quota check on root file system
2) Runs quota check on other file system
3) Runs on quota checking

Revising /etc/fstab :
——————-
To specify that a partition supports disk quotas.

/dev/hda8  /      ext2  default 1  1
/dev/hda5  /boot  ext2  default 1  2
/dev/hda6  /home  ext2  default 1  2
/dev/hda7  /usr   ext2  default 1  2

User disk quotas :
—————-
/dev/hda6  /home  ext2  default usrquota 1  2

Group disk quotas :
—————–
/dev/hda6  /home  ext2  default grpquota 1  2

User & Group quotas :
——————-
/dev/hda6  /home  ext2  default usrquota, grpquota 1  2

remount :
——–
mount -o remount /home

Quota check files :
—————–
quotacheck -arug

Kickstart Basic Information


What is Kickstart
Installing Red Hat based systems from physical or virtual media is easy enough when there is only one or two hosts to install. Beyond this, when an administrator needs to setup several Linux systems, Kickstart can provide a relatively easy way to accomplish mass deployment and can be totally automated.

kickstart_basic

Kickstart Installation
A Kickstart Installation is a special type of installation in which responce to installation dialog boxes are taken from script.

/etc/selinux/config
SELINUX=disabled

Using Kickstart
MKKickstart program is not installed by default.

Command
rpm -uvh /mnt/cdrom/redhat/rpms/kickstart*.rpm

Run MKkickstart
mkkickstart > ks.cfg

Editing Configuration File
The system to obtain its network configuration via BOOTP (or) DHCP.

Command
network –bootproto BOOTP
(or)
network –bootproto DHCP

Linux Installation Via Live CD


Make a Bootable Drive
Alternatively you can burn a DVD drive using Brasero CD/DVD burning software.

Begin Installation
click on the Install to Hard Drive icon on the desktop.

Desktop Install to Hard Drive

Select Language And KeyboardSelect Language

 Change The Installation DestinationAutomatic Partitioning

 Installation DestinationConfigure Partitioning

Select The Partitioning SchemeSelect Partitioning Scheme

Create a Swap SpaceCreate Swap Space

Create a Mount PointCreate a Mount Point

Accept ChangesAccept Changes

Set Date & TimeSet Date and Time

Begin InstallationBegin Installation

Configurationconfiguration during installation

Set Up Root PasswordSet Up Root Password

Create a User AccountCreate a User Account

Complete InstallationInstalling Bootloader

Installation is Completed

Complete Installation

CentOS 7 Installation


CentOS 7
The second CentOS-7 release. The CentOS Linux distribution is a stable, predictable, manageable and reproducible platform derived from the sources of Red Hat Enterprise Linux (RHEL)1.CentOS conforms fully with Red Hats redistribution policy and aims to have full functional compatibility with the upstream product. CentOS mainly changes packages to remove Red Hats branding and artwork.

Features
CentOS 7 uses XFS as its default file system.
OpenJDK-7 is the default JDK.
initd has been replaced by systemd.
New Linux Kernel 3.10.0, support for Linux Containers, and the inclusion of the Open VMware Tools and 3D graphics drivers out of the box.

System Requirements
512MB RAM – 32Bit OS
1024MB RAM – 64BIT OS
1GB+More – RAM
Supports i386 Systems (32-bit Pentium, AMD)
Supports x86_64 systems (AMD64/EM64T)
Maximum logical CPUs10 – 32
Maximum memory – 16GB
Disk Space – 8GB
Free Memory – 1GB

64 Bit ISO
http://mirrors.usc.edu/pub/linux/distributions/centos/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.iso
http://mirrors.usc.edu/pub/linux/distributions/centos/7/isos/x86_64/CentOS-7-x86_64-LiveKDE-1511.iso
http://mirrors.usc.edu/pub/linux/distributions/centos/7/isos/x86_64/CentOS-7-x86_64-Minimal-1511.iso
http://mirrors.usc.edu/pub/linux/distributions/centos/7/isos/x86_64/CentOS-7-x86_64-Everything-1511.iso
http://mirrors.usc.edu/pub/linux/distributions/centos/7/isos/x86_64/CentOS-7-x86_64-LiveGNOME-1511.iso

64 Bit Torrent
http://mirrors.usc.edu/pub/linux/distributions/centos/7/isos/x86_64/CentOS-7-x86_64-DVD-1511.torrent
http://mirrors.usc.edu/pub/linux/distributions/centos/7/isos/x86_64/CentOS-7-x86_64-LiveKDE-1511.torrent
http://mirrors.usc.edu/pub/linux/distributions/centos/7/isos/x86_64/CentOS-7-x86_64-Minimal-1511.torrent
http://mirrors.usc.edu/pub/linux/distributions/centos/7/isos/x86_64/CentOS-7-x86_64-LiveGNOME-1511.torrent
http://mirrors.usc.edu/pub/linux/distributions/centos/7/isos/x86_64/CentOS-7-x86_64-Everything-1511.torrent

CentOS 7 Installation
Installation of CentOS 7

CentOS-Welcome-screen

Choose your language

choose-lanuage-1

Change the Installation Destination

installation-summary-1

Change partition & Click done

device-selection-1

Create a partition table

partition-table-1

Click on accept changes

accept-chnages-1

Select Time Zone

time-zone-1

Configure Networking and Set the hostname

Network-hostname-1

Click on software selection

software-selection-1

Click on begin installation

begin-installation-1

Set root password

set-root-password-1

Create a user

user-creation-1

Installation is in progress

during-installation-1

Installation is completed

reboot-after-installation-1

Accept the EULA agreement

Centos-7-License-info

CentOS 7 Screen

Centos-7-screen-after-login-1

File System Structure


Linux-Directory-Structure

File System Structure
/Bin
It contains binaries are basic command line utilities. These commands only can execute by both root as well as the normal user.

/Boot
It contains boot loader files, image of the kernel and init.rd information.
Boot Loader contains bootable files and commands which are required to boot the Operating System. There are two different types of Linux boot loaders are there.
LILO (Linux Loader)
GRUB (Grand Unified Bootable Loader) 

/Dev
It contains Hardware Devices information.

/Etc
It contains Operating System main configuration files.

/Home
It contains normal users home directories information.

/Lib
It Contains library files that supports the binaries located under /bin and /sbin

/Media
It Displays mount point for Removable Devices.

/Mnt
It contains temporary mount points for the Hardware Devices.

/Opt
It contains third party applications information.

/SBin
It contains Super Users binary information.

/Srv
Contains server specific services related data.

/Tmp
It contains temporary files and downloaded files information.

/Usr
Majority of the Operating System will be loaded into the Sub Directory and it Contains binaries, libraries, documentation, and source-code for second level programs.

/Var
It contains Variable data information (Ex: – Log Files, Mail Spool Information).

/Root
It contains Super Users home directories information.

/Proc
It contains all kernel related running process information.

 

Concepts of Kernal & Shell


Linux_Kernel_2

Kernal
The kernel is a program that constitutes the central core of a computer operating system. It has complete control over everything that occurs in the system. A kernel can be contrasted with a shell (such as bash, csh or ksh in Unix-like operating systems), which is the outermost part of an operating system and a program that interacts with user commands. The kernel itself does not interact directly with the user, but rather interacts with the shell and other programs as well as with the hardware devices on the system, including the processor (also called the central processing unit or CPU), memory and disk drives.

Interacts with the hardware
First program to get loaded when the system starts and runs till the session gets terminated
Different from BIOS which is hardware dependent.
Kernel is software dependent

Types of Kernals
Monolithic
All OS related code are stuffed in a single module
Available as a single file
Faster functioning

Micro
OS components are isolated and run in their own address space
Device drivers, programs and system services run outside kernel memory space
Supports modularity
Lesser in size

Shell
Shell is a UNIX term for the interactive user interface with an operating system. The shell is the layer of programming that understands and executes the commands a user enters. In some systems, the shell is called a command interpreter.

Program that interacts with kernel
Bridge between kernel and the user
Command interpreter
User can type command and the command is conveyed to the kernel and it will be executed

Types of Shells
Sh

simple shell

BASH
Bourne Again Shell

KSH
Korne Shell

CSH
C Shell

SSH
Secure Shell