Difference between revisions of "OPS235 Lab 2 - CentOS6"

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{{Admon/caution|THIS IS AN OLD VERSION OF THE LAB|'''This is an archived version. Do not use this in your OPS235 course.'''}}
= CentOS Installation Methods (on Virtual Machines: centos1, centos2, centos3) =
= CentOS Installation Methods (on Virtual Machines: centos1, centos2, centos3) =

Latest revision as of 12:29, 24 September 2018

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This is an archived version. Do not use this in your OPS235 course.

CentOS Installation Methods (on Virtual Machines: centos1, centos2, centos3)


A virtual machine is a software simulation of a computer which can be used as though it were actual hardware. It's possible to run multiple virtual machines on one computer, reducing hardware requirements and introducing flexibility. Some common uses of virtualization include:

  • Software testing -- Using multiple operating systems simultaneously on a single computer for testing and experimentation.
  • Network simulation -- Testing network services, protocols, and security scenarios with a small number of computers.
  • Isolation -- Protecting multiple sets of data by storing them on multiple virtual machines. If one of the virtual machines is compromised, the data on other virtual machines is still protected.
  • Server consolidation -- Reducing the number of physical servers in a network by moving physical machines to virtual machines. This saves hardware, administration, cooling, and electricity costs, and it can increase the utilization of hardware (by ensuring that the hardware is not under-loaded).
  • Load-balancing and disaster recovery -- It is possible to migrate virtual machines between different physical machines, to ensure that a workload is balanced across multiple computers, to allow routine hardware maintenance and upgrading, and to compensate for hardware failure or other disasters.

In this lab, you will create three virtual machines. This also gives you an opportunity to experiment with different ways of installing CentOS. Later in this course you will install another operating system distribution in a virtual machine.

You should already have both a CentOS installation DVD1 and a CentOS Live DVD.

In both cases, the boot media (which you used to load the installation software) and the installation source (the software that got installed) were the same: your DVD provides both. However, the CentOS (and most other Linux distributions) permits you to use any combination of boot media and installation media:

Method Boot Media Install. Source
Hard Disk
USB Flash Drive
Network (http/nfs repository)
PXE Network Boot X


  • Understand Virtualization
  • Use KVM virtualization on CentOS
  • Use a variety of installation methods:
    • Live Image Installation
    • Network Installation
    • Kickstart Installation
  • Understand the advantages and disadvantages of each type of installation, and be able to select the best installation method for a particular situation.

Required Materials (Bring to All Labs)

  • CentOS 6.5 x86_64 Live DVD
  • CentOS 6.5 x86_64 Installation DVD1
  • SATA Hard Disk (in removable disk tray)
  • USB Memory Stick
  • Lab Logbook


Linux Command Online Reference

Each Link below displays online manpages for each command (via http://linuxmanpages.com):

  • virsh (Refer to CentOS Virtualization Guide link in the "Resources on the Web" section)
  • gzip / gunzip

Resources on the Web

Virtualization: Network Installation: Kickstart Installation:

RedHat Virtualization Guide

RHEL Installation Guide

RHEL Installation Guide

Performing Lab 2

Comparison Chart

You will be learning to perform several different type of CENTOS Linux installs. As you proceed throughout this lab, you will be required to fill in the following table to be used for installation type comparison. You should try to fill out the section for the CENTOS install you performed in lab #1, and then continue with this lab.

Complete the following table (and transfer into your lab2 log-book notes):

c6host centos1 centos2 centos3
Installation Method Installation Disc Live Disc Network Installation Network Installation + Kickstart
Number of Packages Installed
Updates Installed immediately after installation
Software could be selected during installation
Disk layout could be selected during installation
Any questions asked during installation?
Total installation time (after installation questions)
Amount of disk space used
Any questions asked during first boot?
Advantages of this type of installation
Disadvantages of this type of installation
This type of installation is recommended for...

Using the Virtual Machine Manager

Performing this Lab off the Seneca network (eg. at home)
It is recommended to perform this lab in one of Seneca College's labs. This lab uses servers which are on the Seneca network and which are not available from other locations (such as your home). If you attempt this lab from another location, adjust the belmont.senecac.on.ca URLs to point to another mirror server -- note that you may need to change the directory name as well as the server name. The installation of the centos3 virtual machine must be done at Seneca.
  1. Open a web-browser, and open the OPS235 Lab #2 WIKI.

    You need to enter your "MySeneca" username and password to obtain a "wired" Internet connection (otherwise, you will not be able to perform the "groupinstall" command in the next step). Remember to perform a "wired-connection" (logging in with your MySeneca username and password via a web-browser) every time you boot-up your host machine...

  2. Install the virtualization software (virtualization, libvirt, virt-manager) using yum install and/or yum groupinstall. This will install:
  • kvm/qemu - the hypervisor and other hardware emulation systems.
  • A system service named libvirtd that manages the VMs.
  • A graphical tool for managing virtual machines and the virsh command-line tool.
  1. Start the virtualization service: service libvirtd start
  2. The firewall configuration is altered by the addition of the virtualization software. Restart the firewall so that these changes become active: service iptables restart
  1. Start the graphical tool by selecting the menu options Applications>System Tools>Virtual Machine Manager or by typing the command virt-manager.
Run virt-manager as a regular user, not as root
Otherwise all your virtual machines will be owned by root and you won't be able to use them as a regular user.

Investigation 1: Installing from a Live Disc

Using an Image instead of a Live Disc
It is recommended that you perform this installation from your Live DVD. As a matter of interest (for future reference), it is possible to install directly from the ISO file you used to burn your Live DVD. There are many Internet tutorials that show the individual how to perform that task.


In this investigation, you will install CentOS from your live disc, and observe the differences between this type of installation and the DVD installation previously performed.

VM Details

  • Name: centos1
  • Boot media: CentOS Live DVD
  • Installation source: Live DVD
  • Memory: 768MB
  • Disk space: 10GB
  • CPUs: 1


  1. In the Virtual Machine Manger, click on the icon to Create a Virtual Machine in the upper-left corner:
  2. A window will appear with the title New VM. There are five steps to be completed; click Forward after each step:
  3. Step 1 of 5: Enter the virtual machine (called centos1) name and select Local install media
  4. Step 2 of 5: Insert the DVD containing the Centos Live Disc image. Wait a moment for the disc to be recognized, then select Use CDROM or DVD as the install media. Set the OS type to Linux and the Version to Red Hat Enterprise Linux 6 (the CentOS6 equivalent).
  5. Step 3 of 5: Set the memory to 768 MB and the number of CPUs to 1
  6. Step 4 of 5: This next step creates a disk file that will be used to simulate the virtual machine's disk drive. Select a size of 10 GB and checkmark the box labeled Allocate entire disk now
  7. Step 5 of 5: Review the options that you have selected. Make a note of the storage location. If anything needs to be changed, use the Back button to go back and edit it; otherwise, click Finish
Removing and Recreating VMs
If for some reason the user wants to remove a Virtual Machine, they can right-click the VM, and select delete in the Virtual Machine Manager. It is recommended to "delete the image file" in the remove VM dialog box when removing and then recreating a VM. Note: If you fail to properly remove the VM image file, it may affect the hard disk size for the new VM (i.e. use the old smaller size. Make certain to remove that VM image file prior to recreating the VM.
  1. The virtual machine will now start. The virtual machine is running from the live disc at this point, and no software has been installed on the hard drive of the virtual machine. The point of a live disk is to allow you to test the distribution to see whether you like it without installing to the harddrive first.
  1. Click Install to Hard Drive. The installation program, similar to the one used when installing CentOS in Lab 1, will appear. You will get a warning at one point during the installation process that the disk "May contain data" or "may need to be re-initialized" -- this is simply a warning that the virtual disk is completely blank, and it is safe to proceed with the installation.
Virtual Machine Screen Size
The virtual machine screen size will change resolution as it switches from text to graphics mode. Use the VM menu option View>Resize to VM to resize the window to show the entire VM display. If this is larger than your screen size, use View>Scale Display>Always to scale the image so it fits on your screen.
  1. During the installation process, when prompted for a storage device, first select Specialized Storage Devices, and then select the Virtio Block Device option.
  2. When prompted for the hostname, enter centos1, and when prompted for the timezone, select Toronto - Eastern Time Ontario
  3. When asked about storage, select Use All Space. Use the default values for all other fields. Notice that the installer does not ask you what software should be installed; compare the installation time to the amount of time it took to do your Lab 2 installation. Record this information in the table contained in Investigation 4.
  4. When the installation is complete, click on the reboot button at the bottom right-hand corner of the screen.
  1. Start the VM from its disk image. This can be done graphically by selecting the Virual machine name, and then clicking on the Open button, and then click the play button when the next screen appears (or by selecting Virtual Machine>Run from the virtual machine menu). You will get the Firstboot configuration questions during the boot process (asking you to create a user, set the date and time, and ignore the kdump out-of-memory warning). Make certain that the VM has a network interface connection (i.e. look at network applet on the top panel). Create a user with the same name as your Matrix account.
  2. Login using the new user account.
Network / Service Considerations
Please perform the tasks below in order allow these CentOS systems to be able to communicate with each other. Failure to properly perform these operations can cause problems in future labs.
  1. Enable SSH access to your virtual machine with these commands (semi-colon allows commands to be run in sequence):
    service sshd start; chkconfig sshd on
  2. Find out the IP address of your virtual machine: ifconfig eth0
  3. Enter the following command on your virtual machine to create a firewall exception to allow ssh traffic into the machine:
    iptables -I INPUT -p tcp -s0/0 -d0/0 --dport 22 -j ACCEPT
  4. Confirm that you can ssh to your virtual machine from the host (your main CentOS installation): ssh IPaddress

Answer the Investigation 1 observations / questions in your lab log book.

Investigation 2: Installing from the Network

Authenticate to the network
The rest of this lab uses network access. Be sure to authenticate to the network using your browser before proceeding.


It is possible to install CentOS entirely from the network. In this investigation, you will install CentOS from a webserver on the internet.

VM details


  1. Create the VM (called centos2) as you did with the centos1 virtual machine, except select network installation using the installation source url displayed above.
  2. Observe the boot process. How is it different from booting from an optical disc (DVD)?
  3. Start the installation process (make certain to use information in the VM Details section above).
  4. When you get to the disk partitioning step, select Use All Space and enable the checkbox labelled Review and modify partition layout. If an dialog box displays a permissions problem, then click yes to proceed. On the next screen, change the logical volumes as follows:
    • Reduce the size of the root LV to 8000 MB.
    • Add a logical volume with a size of 2000 MB and a mountpoint of /home (you can name it whatever you want, and use ext4 as the file-system type).
  5. On the software selection screen, select Desktop.
  6. Complete the installation. Record the time taken to install, and compare this to the time taken by the previous installations.Record this information in the table contained in Investigation 4.

Answer the Investigation 2 observations / questions in your lab log book.

Investigation 3: Installing from the Network using Kickstart


When CentOS is installed using the techniques you have used so far, the user is asked a number of questions. In some situations, it is better to provide the answers to these questions in a file rather than answer them individually. This type of file is called a kickstart file.

In this investigation, a kickstart file is provided for you. You can also create or modify a kickstart file using a regular text editor or a graphical tool.

VM details


  1. Create the VM as you did with the centos2 virtual machine, specifying a network install as before, but specify the kickstart location under the "options section" for network install. What do you think is the purpose of this kickstart file?
  2. Observe the installation. How is it different from booting from an optical disc?
  3. Complete the installation. Record the time taken to install, and compare this to the time taken by the previous installations.
  4. What happens when the installation is finished?
  5. Take a look at the kickstart file (eg. view url in a webj-browser) to determine the root password as well as the name and password for the first user account.
  6. Boot the virtual machine and log in (use the user ID and password information from the previous step). Compare the experience to the first time you booted the other virtual machines. Record this information in the table contained in Investigation 4.

Answer the Investigation 3 observations / questions in your lab log book.

Investigation 4: Updating the VMs

Check that your graphical VMs are connected to Network
It is recommended when starting a graphical VM, check the network icon to see if the system is connected. If it is NOT connected, select auto eth.

  1. In each VM, run this command: yum update
  2. Record the answers to these questions in your log book:
    • How long did it take to run on each VM? How many packages were updated?
    • Why does it take longer in some VMs than others?

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Never Shutdown Computer During Upgrade
Your computer (host, vms) are at their most vulnerable when you perform an update. Always plan ahead for appropriate time prior to performing an update. Shutting down your computer while performing an update may cause your computer not to boot! You have been warned!!!

Investigation 5: Managing Virtual Machines from the Command Line

Manage virtual machines from the host
The commands used to manage virtual machines must be executed on the host (your disk pack) and not inside a virtual machine.
  1. Start the centos1 virtual machine, and stop the centos2 and centos3 virtual machines.
  2. Switch to the c6host machine, and open a shell terminal.
  3. Enter these commands into your c6host machine and note the result:
    • virsh list
    • virsh list --all
    • virsh list --inactive
  4. Now, shut-down your centos1 VM normally, and close the centos1 VM window.
  5. Switch to your terminal and issue the command: virsh start centos1
  6. Using the appropriate command check to see if your centos1 VM is now running.
  7. There are other commands that can be used (such as suspend, or shutdown). The "shutdown" command may not always work since it relies on the guest handling a particular ACPI event. Why do you think it is useful to have commands to manipulate VMs?
Virtual Machine Does not Shutdown from Command
If the Virtual machine fails to shutdown from the virsh shutdown command, then you can go to the Virtual Machine manager and halt or shutdown within the VM itself, then you can click the PowerOff button in the VM window. You'll want to avoid a forced shutdown since those are equivalent to yanking the power cord out of the wall on a physical machine!

Answer the Investigation 5 observations / questions in your lab log book.

Investigation 6: How do I backup a virtual machine?

Backing up VMs
There are two general processes in order to back up your images:
  1. Compressing your images (also recommended to backup up to external storage USB Key) using the gzip command.
  2. Backup the VM xml configuration file (preferably to USB key) using virsh shell command to add VM to virtual machine manager list (in the event that the HOST machine is "wiped" and re-installed, but VM images and xml configuration files have been backed up external storage).

Taking the time to backup the image of the Operating System's file system allows the user to return to a "restoration point" using the gunzip command in case something bad occurs to the OS during a lab.
Failure to take the time to make and confirm backups can result in loss of lab work for the student!
  1. Shut down all of the virtual machines.
  2. Change to the directory /var/lib/libvirt/images/. Note the size of the files in this directory. What do these files contain?
  3. Make a compressed backup of the centos3.img file to your home directory with this command: gzip < centos3.img > ~YourUserId/centos3.img.backup.gz
    (Note: Make certain to use the redirection signs "<" and ">" properly in the command!)
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Make sure the backup is successful!
If there are any error messages, DO NOT proceed past this point. You're going to destroy your centos3 virtual machine and restore it using the backup you have created -- if there are any problems with the backup, you will not have a working virtual machine, and will have to re-install it.
  1. Compare the size of the compressed and original files.
  2. Start the centos3 VM.
  3. Make certain that you are in your VM and not in your main system!
  4. Wreck only your centos3 system! Try this command inside the centos3 virtual machine: rm -rf /*
  5. Shut down the VM. If you tried to start the centos3 VM, it would not boot since all system files have been removed!
  6. Restore the original image from the backup in your home directory by typing this command: gunzip < ~YourUserId/centos3.img.backup.gz > centos3.img
  7. Restart the VM. Is it working normally?
  8. Create compressed backups of your other virtual machines.
  1. You should make a copy of the xml configuration file in case you "wipe" and re-install the host machine, and want to add a restored VM backups to the virtual machine manager list. We will demonstrate using the centos3 xml configuration file, and prove that a "clone" can be added to your list.Please perform the following step:
    1. Execute the following command: virsh dumpxml centos3 >centos3.xml
    2. Examine the file centos3.xml. What does it contain? What format is it in?
    3. Make a copy of centos3.xml called centos3a.xml.
    4. Edit the file centos3a.xml, making the following changes:
    • Change the name (in the file, not the file name) to centos3a
    • Change at least one of the hexadecimal characters in the UUID. Do not change the length of the UUID. Valid hexadecimal characters are 0-9 and a-f.
    1. Issue this command: virsh define centos3a.xml
    2. Issue the command virsh list --all and record any changes.
    3. Issue the command: virsh undefine centos3a
    4. List all of the virtual machines again, and note any changes.
  2. For the remainder of these labs, it is assumed that you will backup both the images and xml configuration files for all Virtual machines, when asked to backup your virtual machines. It is also highly recommended to backup these files to an external storage device (eg. USB key) in case the host machine gets "wiped" and you need to rebuild your HOST machine and then restore your Virtual Machines...
  3. Answer this question in your log book:
  • In order to fully back up a virtual machine, what information should be saved in addition to the virtual machine image?
Backing up VMs
It is essential to back up your VMs at the end of each lab, so you can easily restore them if something goes wrong in the next lab.
Shutting Down the Host while Virtual Machines are Running
If you shut down your host system while virtual machines are running, they will be suspended, and will resume the next time you boot your host system.

Answer the Investigation 6 observations / questions in your lab log book.

Investigation 7: Kickstart Files

Even when you perform a non-Kickstart installation, the installation program creates a Kickstart file in the /root directory for reference.

  1. Obtain the kickstart files for all four of your installations (your disk pack c6host, plus the centos1, centos2, and centos3 virtual machines).
  2. To prevent confusion, copy your kickstart files to kickstart filenames that describe their purpose (eg. kickstart_host, kickstart_centos1, kickstart_centos2, etc...)
  3. Copy them all to your c6host system (tip: use scp, webmail, or command-line mail. Refer to the manpages for help).
  4. Compare these files. What are the differences? Similarities? (Tip: you may want to use tools such as sdiff to help with the comparison).
  5. How could you use the kickstart file produced by the installation program to perform additional, identical installations?

Answer the Investigation 7 observations / questions in your lab log book.

Completing the Lab

Arrange evidence for each of these items on your screen, then ask your instructor to review them and sign off on the lab's completion:

  1. Three working virtual machines created.
  2. Disk layout and size correct on all virtual machines
  3. Use virsh to list the status of all vms.
  4. Four kickstart files.
  5. All virtual machines fully updated.
  6. All virtual machines backed up to a usb stick.
  7. Installation comparison table filled in.
  8. Lab Logbook (lab2) notes filled-in.

Preparing for Quizzes

  1. What is the name of the CentOS installation program?
  2. Which factors recorded in your table (above) were due to the type of installation performed, and which factors were due to the amount of software installed?
  3. Which type of installation works best for confirming compatibility with hardware before installation? Why?
  4. Which type of installation works best for installing large numbers of computers? Why?
  5. What factors affect installation time?
  6. How can you reduce the number of software updates required immediately after installation?
  7. Why would you enable additional repositories during installation?
  8. What does the file /root/anaconda-ks.cfg contain, and how is it created?
  9. How do you start and stop virtual machines?
  10. How do you SSH into your virtual machines?
  11. What is the purpose of and relationship between these pieces of software?
    • libvirt
    • libvirtd
    • virsh
    • virt-manager
    • virt-install
    • kvm
  12. The kickstart installation (centos3) was a network installation. Can a kickstart file be used with a DVD installation?
  13. The kickstart installation (centos3) was fairly fast. Why? Under what circumstances would it take a long time, even on a fast network?
  14. What other types of installation sources are possible (besides Live Disc, Installation Disc, and Network?)