Linux Tech Tutorial: December 2011

Wednesday, December 7, 2011

Creating and Deleting Partitions in RHEL 6

Partitioning is a very important concept in Linux. If you have your concepts clear, related to partitioning in Linux, it will be very helpful when you became a Linux System Administrator.

There is a new partitioning tool RHEL6 cfdisk, but we will see the traditional and most popular partitioning tool "fdisk". To use fdisk first you have to login as root. if you are a regular user and know root password, you can switch to root account using "su" command.

To see your current disk and partitions run: fdisk -l

In the above image you can see that I have two hard disks. The first one is /dev/sda and the other one is /dev/sdb. In the above image you can see that the HDD /dev/sda is of size 16 GB and having two partitions /dev/sda1, which is created at the time of installation as /boot, and /dev/sda2, which is a Linux Logical Volume Manager(LVM). The second HDD is /dev/sdb which is newly installed HDD of size 2 GB and does not contain any valid partition table as you can see in the image.

In this post we will create the physical partitions and mount them on particular directories.

To create a partition of 1 GB form /dev/sdb type :fdisk /dev/sdb, and press m to see menue.

Press n to create new partition, p to create primary partition and e to create extended(always create first partition as primary), make partition 1, select first cylinder as default and on next line type +size of partition to be created,ex +1G.

Fees
Certification
Redhat
Linux Systems
Installation
Press
Disk Partition

Now press p to print current partition table and press w to save partition table. and on command prompt type partprobe to update current partition table and run fdisk -l /dev/sdb.

Now format this partition with command : mkfs.ext4 /dev/sdb1. Then create a directory /mydata, and mount /dev/sdb1 on /mydata using command : mount /dev/sdb1 /mydata.

Make entry in /etc/fstab to make mounting persisting, means mount /mydata every time when server restart.

RHEL 6 File-System

In this post we will discuss about the file system in RHEL 6. In Linux operating system there is a pre-defined location to store different files.

The Linux file system can be defined as the method of storing and organizing files in a form that we can understand easily. In Linux operating system everything is a file. To manage all these files Linux have a tree like directory structure. File system is a method of storing and organizing arbitrary collection of data in a form that is human readable.

File system structure of RHEL 6:

/ :- Root directory, which contains all other directories.
/bin :- Contains commands that may be used by both system administrator and by users, but which are require when no other file-systems are mounted.
/boot :- This directory contains everything which required for the boot process, like kernel, GRUB, Initrd, etc.
/dev :- Contains device files.
/etc :- Contains configuration files.
/home :- Contains users’ home directories.
/lib :- Essential shared libraries and kernel modules.
/media :- Mount point for removable media.
/mnt :- Mount point for temporary mounted file-system.
/opt :- Contains add-on/optional packages.
/root :- Root user’s home directory.
/sbin :- Contains system binaries.
/tmp :- Contains temporary files.
/var :- Contains variable data files.
/proc :- Contains kernel and process information.

Managing User and Group in RHEL 6

To create a user in RHEL 6 we can use commands as well as graphical user administration tools. It is advisable to use command line as much as possible because it is faster and in real business environment you have to use ssh to remotely take control to administer the system.

To create a user run command:

useradd user_name

To define a password for the user:

passwd user_name

Create a user with specific UID:

useradd -u 802 user_name

The above command will create a user with UID 802.

To create a group run command:

groupadd group_name

To delete a user run command:

userdel user_name

The above command will delete the user but it will not delete the home directory of user. To delete the home directory as well as the files contained in it run following command"
userdel -r user_name


User and Group Administration

Given below are some sample questions about user and group administration:

Q1. Create a user rambo and make it a member of group student.

Ans. useradd -G student rambo.

To see the results view /etc/passwd and /etc /group files.

Q2. Create a user sheela with UID 566 and assign it no interactive shell.

Ans. useradd -s /bin/false sheela

The above command will add a user sheela, and give it non interactive shell.

Q3. Make the user munni to expire on date 17-09-2011.

Ans. chage -E 2011-09-17 munni

The above command will make the account of user munni unavailable from 17-09-2011

Q4. User pandeyg have to change password at the time of next login.

Ans. chage -d 0 pandeyg

The above command will force user to change password when the user tries to login.

Sample Questions for User and Group Administration

For the preparation of RHCSA and RHCE certification exam, the most important thing is to do lots of practicals. In this post I will give some RHCSA DUMP questions and their answers. These RHCSA DUMPS or sample exercises are based on User and Group Administration.
In my few next posts I will post sample RHCSA questions and their answers, related to User and Group Management. The questions in next few posts are like:

How to create a user in RHEL 6 with unique UID?
How to create a group in RHEL 6?
How to create a user and add it to a specific group?
How to create a user john and assign him no interactive shell?
How to set password expiration for a user?
Request for password change, when user next login.
How to change password for a user?
How to delete a user in RHEL 6?

64 bit Operating Installation on 32bit architectuer

People ask me many times that "can I install a 64-bit Linux or any other Operating System in to my Virtual Machine, even though if I have a 32-bit processor on my computer".
The answer is "NO". If you have a 32-bit processor on your computer,VMware does not provide facility to virtualize the 32-bit processor to 64-bit processor. Because all the CPU requests from Virtual Guest CPU are processed by the real CPU. So you definitely need a 64-bit processor to run a 46-bit Virtual Guest Operating System.

CONCLUSION:

OS Architecture

You can not install a 64-bit Virtual Guest Operating System on 32-bit Host machine.

Please comment on my posts and help me to correct if I am wrong.

Update: RHCSA and RHCE Fees in INDIA

There is a lot of confusion regarding the fees of RHCSA and RHCE in INDIA. People creating rumors that fees of RHCSA and RHCE on RedHat Enterprise Linux are very higher as compared to RHCT and RHCE on RHEL 5.
With the release of RHEL 6 RedHat introduces a new pattern of certification exam. On previous version (RHEL 5) you have to complete both RHCT and RHCE to get RHCE certificate but you don't get the RHCT certificate if you clear both the exam. But now you have to pass the RHCSA exam to gain RHCE and you will get two different certificates one for RHCSA and other for RHCE.

The fee structure of RedHat Certification is given below:

Fees of RHCSA is INR 8000
Fees of RHCE is INR 8000

So, if you want RHCE certification you have to pay a total of Rs. 1600 and Rs. 3000 for the official RedHat exam books.

But there are lots of schemes which RedHat offering in INDIA so please check latest updates of RHCSA and RHCE fees.

Understanding: /etc/passwd (User Account Management)

In this post we will discuss one of the most important file in RHEL, which is /etc/passwd. This file is very important because this serves as a default database of user on the system. Using /etc/passwd we can add users, modify user settings, etc.

For user administration part of the RHCSA Exam this is the most important file. Using /etc/passwd you can do the exam tasks and also check the results to confirm your completed tasks related to users.

An example entry of /etc/passwd is given below:

rajesh:x:501:501:rajesh maurya:/home/rajesh:/bin/bash

Each entry in /etc/passwd file contains 7 fields.

Username: It is used when user log-in. It should be between 1 to 32 character.
Password: An 'x' character indicates that encrypted password is stored in /etc/shadow file. The 'x' refers and matches password value from /etc/shadow file.
User ID (UID): Each user must be assigned a User ID (UID). UID=0 is reserved for root user and UID 1 to 99 are reserved for other predefined accounts. It is a unique identity number for every user on the system.
Group ID (GID): Whenever a user is created a primary group is also created for a user. Every user have its own primary group but it can also have supplementary groups.
GECOS: This is optional and only used for informational purpose. Usually it contains the fill name of the user. You can say it as a comment field
Home Directory: It represents the absolute path to the user's home directory. If this directory does not exist the '/' directory becomes the users home directory.
Shell: The absolute path of command or shell (/bin/bash). Typically this field contain information about user's default shell.

This file is one of the most important file as far as RHCSA is concerned. So do a lot of experiments on this file, but before making any changes to this file take a backup of this file.

If you have any questions regarding user administration or /etc/passwd please ask me. I will try to answer.....

Understanding: /etc/shadow (User Account Management)

RHCSA exam focus on basic system administration, and questions asked in RHCSA are similar situations which you will face in real environment.

/etc/shadow is not commonly used file, but is very important as far as User Administration and RHCSA is concern.

/etc/shadow contains password related information for user and groups on the system. This file stores actual password in encrypted format for user's account with additional properties related to user password.

An example entry of /etc/shadow is given below:

rajesh:$1$J6/rsxw3$TEcDpPsW0gx9035DFNlUU/:15162:0:99999:7:::

Each entry in /etc/shadow contains 9 fields.

/etc/shadow

Username: It is used when user log-in. It should be between 1 to 32 character.
Password: It is a user's encrypted password. The password should be minimum of 6 to 8 characters long including special characters/digits.
Days since Unix epoch password was changed (Jan 1 1970).
Minimum: Days left before password may be changed.
Maximum: days after which password must be changed.
Warn: The days before password is to expire, that user is warned that his/her password must be changed.
Inactive: The days after password expires, that account is disabled.
Days since Unix epoch, that account is disabled.
Reserve field (currently unused) .

Using this file you can manage password properties.

Group Administration

In the last post I described about the the user administration. After user administration another task is to manage groups.

To see the present groups in your system you can type groups command. The /etc/group maintains the group membership information. You create groups and add users to a group using both GUI tool and Command line, but I will suggest you to use command line because it is fast and easy. Once you have been familiar with the command line you will enjoy using it the most.

To create new group you can edit /etc/group file or you can run the following command:

groupadd group_name : this will add a group named group_name in /etc/group.
groupdel group_name : this will delete a group named group_name in /etc/group.
groupmod : modifies group members.
chgrp : to change group permissions.

GROUP ADMINISTRATION

To add users named donna to a group named sales you can run the following command:

usermod -G sales donna : this command will add user donna to the group sales.

You can add user donna directly to the /etc/group

sales:x:503:donna

Certification
Redhat
Linux
Fees
Add It
Command Line
Enterprise Linux

To add a user to a group at the time of creation of user, you can type the following command:

useradd -G sales mike : this command will make a user mike and add it to the sales group.

You can also use Graphical User Interface for user and group administration.

To open the USER and GROUP GUI run system-config-users at the command line or

Go to System-->Administration-->Users and Groups.

You can do a lot with users and groups like provide special privileges to specific users or groups and also can do the group collaboration. We will discuss these topics in the next post.

User Administration

One of the basic and most important task for a System Administrator is USER & GROUP administration. In Linux Users and Groups can be administered using command line as well as the user/group administration GUI tool. But I will suggest you to use command line as much as possible because in production environment GUI wont be provided.

In this section we learn how to create, delete, and do basic administration of USERS. The default settings for a user drives from the /etc/login.defs file .

/etc/passwd file is a default User Account Database. It is a world readable file, it contains information about all users in the system. Mainly there are three types of user accounts:

Administrator
General
Service

/etc/passwd file contains information as follows:-

student:x:501:501:Student account:/home/student:/bin/bash
each field in above line is described in detail below:

USER ADMINISTRATION

student               : User Name
x                         : encrypted password
501                     : User ID
501                     : Group ID
Student account   : Discription
/home/student      : Home Directory
/bin/bash              : Default Shell

You can find all the users in your system and also get all the details in the /etc/passwd file.

The basic command for user administration are given below :

useradd user_name :- used to add user and modify group membership.

example : useradd student1

userdel user_name :- delete a user form /etc/passwd.
usermod :- modify user information.

The above three commands can do all for your user administration tasks. These commands can be used with different options to do a lot of different things.

NOTE: Default User ID for a regular user starts from 501 and onwards.

Basic Linux Commands

To start-up with the Linux first someone needs to know about the basic Linux commands. These commands are common in all Linux distributions. If you know these basic Linux commands, it will be easy for you to get further in in your goal to achieve a RedHat Certification.

To be a system administrator you need to know how to manage the server using command line, because you will hardly allowed to use GUI. Because most of the system administration tasks are managed remotely using the secure shell also known as SSH. So use the command line as much as possible.

Basic Linux Commands and there explanation is given below:

uname :- this command returns the name of Operatng System.
uname -a :- using :- "a" option with uname command, you will get the following information:

Operating System : Linux.
Fully Qualified Domain Name.
Kernel Version.
Date and time that the kernel was compiled.

tty :- reveals the current terminal.
echo :- prints to the screen.
set :- prints and optionally sets shell variables.
clear :- clears the screen / terminal.
reset :- resets the screen buffer
pwd :- prints the path of working directory.
whoami :- reveals the current logged-in user.
which programe_name :- reveals the path of the program / command.
history :- reveals your command history.
cd :- changes directory to desired directory:

cd with no option will changes to the home directory.
cd ~ will also change to the home directory.
cd / will change to the root (/) directory

COMMAND LINE

cd .. will change one level up in the directory tree.

ls :- lists files and directories.

ls / lists the contents of / (root) directory.
ls -l will lists in long format. This command shows properties of files and directories.
ls -a will list all files including hidden files which starts with a period (.).
ls -ld will show properties of the directory.

cat :- catinates files. Create files and also show contents of files.

cat 123.txt dumps the contents of the file 123.txt.
cat > xyz creats new file xyz. You can write to the file and save using ctrl+d.

mkdir :- creates a new directory.
cp :- copies files
mv :- moves and rename files.
rm :- remove files.
touch :- create a blank file.
stat :- reveals the statistics of a file.
find :- finds files using search pattern.

find / -name filename will search the file named filename in the / directory/

alias :- return/set aliases for command.
more/less :- display one page at a time.
head :- display opening lines of a file.
tail :- display cloasing lines of a file.
wc :- counts words and optionally lines and characters in a file.
grep :- search for text in a file.
su :- to switch user.
man command_name :- open manual for that command.

These are the the basic Linux commands. But there are a lot more commands, you will learn command while using it, it will take time but more you work in linux more you learn.

NOTE : There are many options which can be used with these commands or other commands. Always view man pages of command to find different options. I think using man command is very good habit.

Please comment on the post. You can also write questions and I would love to answer your questions and help you.

RHCSA Objectives

As all knows about Red Hat's certification exams, the new Red Hat System Administrator Exam is also a performance based hands-on exam. The exam objectives are similar to the old RHCT but there are some new task added to the RHCSA.

TASKS to perform in Red Hat System Administrator Exam :

Boot, reboot, and shutdown the system normally
Diagnose and correct problems at boot
Boot systems into different runlevels for troubleshooting and system maintenance
Use single-user mode to gain access to a system for which the root password is not known
Diagnose and correct misconfigured networking settings
Diagnose and correct hostname resolution problems
Diagnose and address permissions problems and SELinux policy violations
Diagnose and correct non-hardware disk storage problems
Adding new partitions, logical volumes, filesystems, and swap areas to a system non-destructively
Manually open, mount, unmount, and close LUKS-encrypted filesystems
Extend existing unencrypted ext4-formatted logical volumes
Login or switch user to the root account
Use ssh and VNC to access remote systems
Locate and read on-line documentation using man, info, and files in /usr/share/doc
Locate and analyze system log files
Understand how to use grep and regular expressions to analyze text output
RHCSA

Access a bash shell prompt and issue commands with correct syntax; use pipelines and I/O redirection
Use text editors such as gedit and vim to create and edit text files
Manage system resources: identify CPU/memory intensive processes, adjust process priority with renice, kill processes
Manage files and directories: create/delete/copy/move; create hard and soft links
Use tar, gzip, and bzip2 to archive and compress files
Install Red Hat Enterprise Linux manually with the graphical installer from network installation media
Install Red Hat Enterprise Linux automatically using Kickstart
Configure a physical machine as a RHEL-based virtualization host
Manage virtual machines: install/start/stop/configure to start at boot/access a VM´s graphical console
Manage disk partitions: understand MBR-style partitions (primary,extended,logical); list/create/delete partitions
Manage logical volumes: create/remove physical volumes, assign PVs to volume groups, create/delete logical volumes
Create and configure LUKS-encrypted partitions and logical volumes to prompt for password and mount decrypted filesystem at boot
Canage ext4 filesystems: create, label, mount, mount automatically at boot (by UUID or label), unmount

Certification
Firewall Setting
Changeing
Consoles
Adding
Blogs
Adde

Mount and unmount CIFS and NFS network filesystems, manually or by configuring autofs
Manage network devices: understand basic IP networking/routing, configure IP addresses/default route statically or dynamically
Manage name resolution: set local hostname, configure /etc/hosts, configure to use existing DNS server
Manage network services: check status, start, stop, configure to start automatically at boot
Configure the scheduling of tasks using cron and at
Manage local user and group accounts: create, delete, change passwords, adjust password aging, adjust group memberships
Use network user and group accounts stored on an existing LDAP directory service
Manage standard permissions: list, interpret, change ugo/rwx
Use sgid directories for collaboration
Set and manage Access Control Lists (ACLs)
Manage SELinux security: set enforcing/permissive modes, list file and process context, restore default file context, use "booleans" to adjust policy
Manage default firewall settings with basic tools
Install and update software packages from RHN or remote repository, or from the local filesystem
Update the kernel package appropriately to ensure a bootable system
Modify the system bootloader
Configure the system to synchronize system time using remote NTP servers
Deploy a VNC server that allows multiple desktops to be shared
Deploy file sharing services with HTTP/FTP.

RHEL 6 Installation Steps.

To learn Red Hat Enterprise Linux 6 first of all you have to know about the installation process and how to install the all new Red Hat Enterprise Linux 6. Here I will explain the step-by-step process of installation of RHEL 6.

Installation of RHEL 6 is one of the objectives of RHCSA and RHCE certification from Red Hat. It is directed that one should know at least the graphical based installation of RHEL 6.

First of all you have to obtain the DVD/CDs’ or the RHEL6 DVD.iso.

There are several methods of installing RHEL 6 like: installation from DVD, installation form Hard Drive, Network Installation, Installing via NFS, FTP or HTTP. Steps followed in all the process are same except the media selection from which you will install RHEL 6. I will explain the installation from Local Hard Drive using the Rescue disk (Which can also downloaded from Red Hat website), and the RHEL 6.iso.

Step 1. Extract the folder “images” from the RHEL 6 DVD. Since the image folder contains the product.img file which is used to start the installation and bring up the anaconda to start installation process.

Step 2. Make a folder from where you want to install Red Hat Enterprise Linux 6 and in it paste the “RHEL 6 DVD.iso” file and the “images folder “ which you have extracted in the above step.

I had created the folder in the E: drive of my computer like E:\RHEL6\ and paste the “RHEL 6 DVD.iso” file and the “images folder “ in it. But at the time of installation you have to give the complete path of the “.iso“ image like the hard disk and partition number like “/dev/sdb5/RHEL6/”.

Step 3. Reboot the System and boot form the rescue disk by selecting boot form CD/DVD from the boot menu. After booting form rescue disk you will see the graphical boot menu.

Step 4. There are four options in the menu : 1. Install or upgrade existing systems, 2. Install system with basic video drivers,3. Rescue installed system, 4. Boot from local drive.

Select the first option “Install or Upgrade Existing System”.

Step5. Select language and click ok.

Step 6. Select installation method : Local CD/DVD and click ok.

Step 7. Select partition and determine full path of the folder containing RHEL 6 DVD.iso. In my case the partition is “/dev/sdb5” and the path is “/Operating System/RHEL6/ISO”.

Step 8. Welcome screen appears click next to continue.

Step 9. Select Installation Language and Keyboard Type.

Step 10. Select type of storage device. If you are confused in between select the Basic Storage Devices.

Step 11. Time Zone Configuration window. Select time and click next to continue.

Step 12. Set Root password and click next.

Step 13. Assign storage device from the box on the left side and send it to the box in right. I have to install RHEL 6 in my 80 Gb sata HDD so I seletct the second HDD and move it to right box (Install Target Devices).

Step 14. In the next step you have to select how you want to use your HDD to install RHEL 6. I prefer to make file systems manually, so I selected create custom layout.

Select the free space in the HDD (and if no free space is there you have to delete some partitions to create free space.) and click on Create. A dialog box open select the Standard Partition and click next.

Give the mount point select size and make it primary or extended as per your requirements.

Make at least three partitions :root (/), boot (/boot) and SWAP.

Take reference from the table given below to make partitions:

Click next to continue.

Click on write changes to disk to make changes. Or go back to edit layout.

Certification
Redhat
Requirements
Linux
Fees
Storage Device
Device Storage

Step 15. Install Grub Boot Loader.

I have my PC dual boot Windows 7 and RHEL so I make an entry of my windows 7 OS and select it to boot by default.

Step 16. Installation Server type. Select an option according to your requirements or just select Basic Server and Choose Now to select packages.

Step 17. Wait while packages install.

Step 18. Installation Complete .remove bootable media form DC/DVD drive and restart your system.

I will publish Post Installation Steps in my next post .

Please comments if you have any questions regarding any of the above steps……

Post Installation Steps for RHEL 6

In my last post I explain the steps for installation of Redhat Enterprise Linux 6. In this post I will explain the Post installation Steps, which are required to complete your installation. Since this is an important objective for RHCSA, understanding all the installation steps is a must.

After package installation reboot your system and from there you have to follow the post installation steps:
Step 1. After rebooting welcome screen appears, click forward button for the next step.

Step 2. In License Information screen click on "yes, I agree to License Agreement" and click forward.

Step 3. Then do the software update process. But to do that you should have a subscription from Red Hat Network(RHN). And click forward to continue.

Step 4. Next screen allows you to create a regular USER. Provide username, full name and password and click forward to continue.

Step 5. In the Date and Time setup wizard enter the date and time and click forward to continue.

Step 6. In the next screen you can setup a KDump environment. It is up to you to setup a KDump environment.

KDump is a Kernel Crash Dumping Mechanism it will prevent you from kernel crash. It is recommended to setup a KDump environment.

After setting-up the KDump environment you are now ready to login to the RHEL 6 server..

If you have any queries email me or comment .......
You can also subscribe for the latest posts so you don't miss any information or news.

RHCSA Tutorials

Redhat Certified System Administrator is a certification exam which is purely based on the practical knowledge. I personally searched on the web but never find any good tutorial of preparation material, for RHCS, till now. Some websites also offering CBT video tutorial for RHCSA but I think they are too costlier.

I have decided to make a tutorial (ebook) for preparation of Red Hat Certified System Administrator. And I have started working on it. In that e-book I will explain all the Objectives which have to be achieved in the RHCSA certification exam. Also give details on how to prepare for the exam and also provide sample test papers also.

It will take a little time for completing the e-book so I will also post the required information on the blog.

You can find all the Objectives explanation in this blog....

If you have any queries or want to know something about RHCSA comment on the posts or email me.

Boot Process of RHEL 6

To became a Redhat Certified System Administrator you should have to know about the boot process of RHEL 6. In this post I will explain you the boot process of the latest Redhat Enterprise Linux 6. RHEL uses GRUB (GRand Unified Boot Loader) as its boot loader. The step-by-step boot process is explained below.

First we power on the machine, then BIOS (Basic Input Output System) takes over. BIOS is responsible to check RAM, Keyboard, Storage Devices, etc.
Once the BIOS has setup the environment it finds the first bootable device (which may be CD-ROM, USB, IDE, SATA Hard Drive, etc.)
After BIOS finds first bootable media it searches for the Master Boot Record (MBR), which contains boot code, this stage is called STAGE 1 GRUB.
After Stage 1GRUB, STAGE 1.5 GRUB is consulted, which presents a menu to the user. From that menu we select the OS that we would like to boot. (Grub files are stored in /boot/grub.).
After that STAGE 2 GRUB is consulted. Stage 2 GRUB sets up the environment and then calls INIT process. The INIT process is located in /sbin/init. INIT reads a special file /etc/itittab, this is a table file which contains initialization entries like default runlevel and then sets up the appropriate runlevel environment.
All the scripts which are collectively stored in /etc/rc.d/init.d directory and rc.d contains runlevel directories like rc1.d, rc2.d,....rc6.d.

After all these process a runlevel environment is setup and you are able to do tasks on the Redhat EL 6.

Boot Process Summary:

Power On -> BIOS -> Searches for MBR in Bootable Media -> Finds Boot Code (Stage 1 GRUB) -> GRUB Menu (Stage 1.5 GRUB) -> Stage 2 Grub (Setup the environment calling INIT Process) -> Executes scripts of appropriate runlevel and provides the console.

For any query regarding to GRUB or BOOT Process please comment .....

You can also subscribe for latest news and posts for RHCSA, RHCE, RHEL 6........