Difference between revisions of "OPS235 Lab 2 - CentOS7"

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{{Admon/caution|THIS IS AN OLD VERSION OF THE LAB|'''This is an archived version.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.'''}}

Latest revision as of 12:28, 24 September 2018

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This is an archived version.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


Purpose / Objectives of Lab2

The c7host Linux server will run virtualization software to install and run 3 virtual machines (installed in lab2).

In this lab, you will create three virtual machines. This also gives you an opportunity to experiment with different ways of installing CentOS.

Main Objectives

  • Installing Virtualization Software on your c7host machine
  • Create 3 separate VMs (virtual machines) using different installation methods:
  • Centos Live DVDInstallation
  • Network Installation without configuration file
  • Network Installation with configuration file (Kickstart)
  • Understand the advantages and disadvantages of each type of installation, and be able to select the best installation method for a particular situation.
  • Manipulate virtual machines by CLI (virsh)
  • Properly backup VMs and VM configuration in virtual manager application onto home directory and to external source (USB Key)
  • Observe how Bash Shell Scripting can be used to automate routine tasks involving VM management

What is a Virtual Machine?

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 promoting flexibility when working with multiple operating systems. 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.

Minimum Required Materials

Removable Hard Disk Pack (SATA)
USB key
(for backups)
Lab2 Log Book

My Toolkit (CLI Reference)




gzip, gunzip

Installation Guides

Installing & Using KVM on CentOS
Using KVM (tutorial)
virsh command reference
CentOS Kickstart Reference

Online Linux Command Review
The following tutorial will allow you to learn essential shell scripting skills. Login to your Matrix account, and issue the pathname to run the online tutorial in Matrix:
  • Shell Scripting - Part 2 (Logic & Math Expressions):
  • Shell Scripting - Part 3 (Loops)


Virtualization Application Setup / Comparison Chart

comparison chart in lab2 logbook.

Record VM Installation in Lab2 (Installation Comparison Chart):

You will be learning to perform several different type of CENTOS Linux installs. Lab2 already has an empty table for comparing various Linux installs. You were required in lab1 to record your observation for your c7host installation.

As you proceed throughout this lab, you will be required to fill in the comparison chart for three of the VMs (virtual machines) that you will be installing.

Complete the following steps to install and run the virtual manager application:

  1. Open a web-browser, and open the OPS235 Lab #2 WIKI.
  2. Open a shell terminal.

    WARNING: You must perform a yum update on your c7host machine before proceeding with the next steps.

  3. You will need to download an image file for the Centos7 LIVE DVD by issuing the following command (best works while at Seneca):
    wget http://belmont.senecac.on.ca/centos/7/isos/x86_64/CentOS-7-x86_64-LiveGNOME-1511.iso

  4. Install the virtualization software by issuing the command:
    yum install qemu-kvm qemu-img virt-manager libvirt libvirt-python \
    python-virtinst libvirt-client virt-install virt-viewer bridge-utils

Restart your Host Machine
You must restart your c7host machine after installing the virtualization program above. If you fail to do this, you may experience virtualization network problems!

This will install many applications (including):
  • 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 (virt-manager) 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. Centos7 uses firewalld for firewall, but we will be switching back to using iptables. Issue the following series of command to install iptables and restart the firewall:

    systemctl stop firewalld
    systemctl mask firewalld
    yum install iptables-services
    systemctl enable iptables
    systemctl start iptables
    service iptables save

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.
  1. Start the graphical tool by selecting the menu options Applications>System Tools>Virtual Machine Manager or by typing the command virt-manager

Part 1: Installing from a Downloaded Image (Centos7 LIVE CD)

Perform Downloads and Network installs at Seneca
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.
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.

Restart your Host Machine Again
You must restart your c7host machine again, prior to creating your virtual machines. If you fail to do this, you may experience virtualization network problems!
VM Details:
VM Name (and hostname): centos1
Boot media: LIVE CD Image
Installation source: Downloaded Centos7 LIVE CD image (http://belmont.senecac.on.ca/centos/7/isos/x86_64/CentOS-7-x86_64-LiveGNOME-1511.iso)
VM Image Pathname: /var/lib/libvirt/images/centos1.img
Memory: 2GB
Disk space: 10GB
File System (root partition): ext4
CPUs: 1
  1. Make certain you used the wget command to download the LiveGNOME iso file from the Belmont server (from previous instructions).
  2. In the Virtual Machine Manger, click on the icon to Create a Virtual Machine in the upper-left corner:
  3. A window will appear with the title New VM. There are five steps to be completed; click Forward after each step:
  4. Step 1 of 5:Select Local install media and click Forward.
  5. Step 2 of 5: Select Use ISO Image, click the Browse button, and then the Browse Local button. Navigate to the location of the downloaded Centos7 LIVE CD image, select the image file and click Open. When finished, click Forward to proceed.
  6. Step 3 of 5: Set the memory to 2048 MB and the number of CPUs to 1
It is extremely important to correctly specify the VM image file path-name. Double-check the spelling of the path-name before proceeding!
  1. 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. Click on
    Select managed or other existing storage and type the VM image file pathame:
    /var/lib/libvirt/images/centos1.img (make certain that the pathname is correct) and then click Forward to proceed.
  2. Step 5 of 5: Enter the virtual machine name: centos1. Review the VM information, and click Finish.

  3. The virtual machine will now start - start timing your installation and making notes for centos1 virtual machine in the installation comparison chart in lab2 logbook. 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 hard-drive first.
  4. Double-click Install to Hard Drive. The installation program, similar to the one used when installing CentOS in Lab 1, will appear. You basically perform the same installation operations for this VM including for Date & Time, Network & Hostname, and Installation Destination. Make certain to use the hostname: centos1 as opposed to c7host) for this installation. (with a few slight differences).
  5. For Installation Destination, select the destination option: I will configure partitioning and then click Done. Make certain that the Partition Scheme is set to LVM and then click on the link: Click to Create Automatically. Done. Check to make certain that the root partition has file system type: ext4.
  6. Accept the changes and then click Begin Installation.
    1. You will be required to make selections very similar to what you did in lab1.
    2. While the system is installing, take a few minutes to record your observations (including slight differences with centos1 install as opposed to c7host install).
    3. When the installation process is complete, note the time required to install this system and record in the installation comparison chart of your lab2 logbook.

  7. Power-off your Centos7 LIVE system.
  8. You should notice that the Centos7 boot menu appears. Either press ENTER to start or wait for it to start automatically.
  9. Finish the final steps in the setup process (like you did in lab1).
  10. #You may want to turn off the screen-saver (like you did in Lab1): How to Turn-off Screen Saver (lab1)
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 and the name of your Ethernet network adaptor: ifconfig
  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. If you are logged in as root, logout to your regular user account.
  5. Confirm that you can ssh to your virtual machine from the host (your main CentOS installation): ssh regularuserid@IPaddress (where regularuserid is your regular user login id, and IPaddress is the IP_ADDRESS of your centos1 VM!).
  6. Make certain to disable SELinux for centos1 (refer to lab1)
  7. Adjust your screen-saver settings and run a yum update on your centos1 VM before proceeding to Part 2

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

Part 2: Installing from a 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.
VM Details:
VM Name (and hostname): centos2
Boot media: Network installation
Installation source URL: http://belmont.senecac.on.ca/centos/7/os/x86_64/
VM Image Pathname: /var/lib/libvirt/images/centos2.img
Memory: 2048MB
Disk space: 20GB
CPUs: 1

  1. Create the VM (called centos2) as you did with the c7host machine, except for the following differences:

    1. Select Network Installation using the installation source URL displayed above.
    2. When customizing your partitions, do the same operation that you did in centos1, but after automatically creating the partitions, reduce the size of the root LVM partition to 8000 MB and add an LVM partition with a size of 2000 MB (mount point: /home, name: home, and make certain root and /home partitions have ext4 file system).
    3. Don't forget to install the GNOME desktop here as you will need a GUI for Centos2

  2. Complete the installation. Login to your regular user account, and perform a yum update for the centos2 VM (reboot if required). Make certain to adjust your screen-saver settings if desired.
  3. Repeat the steps as you did to start the SSH service, set iptables to accept connections via ssh, test connections between centos2 and c7host, and disable SELinux (refer to lab1).
  4. Record the time taken to install, and compare this to the time taken by the previous installations. Record your findings in the Installation Comparison chart in lab2 logbook.

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

Part 3: Installing from a Network using a Kickstart File

VM Details:
VM Name (and hostname): centos3
Boot media: Network installation
Installation source URL: http://belmont.senecac.on.ca/centos/7/os/x86_64/
Kickstart File URL: http://matrix.senecac.on.ca/~andrew.smith/ops235/centos7-kickstart-v01.cfg
VM Image Pathname: /var/lib/libvirt/images/centos3.img
Memory: 2048MB
Disk space: 15GB
CPUs: 1

  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 a downloaded image?
  3. Complete the installation. Record the time taken to install, and compare this to the time taken by the previous installations.

    If the during the installation, you see the message at the bottom Pane is Dead, click the Virtual Machine menu at the top, select Shut Down -> Force Off, right-click on centos3 in the virtual manager window and select Delete. Redo the VM setup for a new instance of the centos3 VM.
  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.
  7. Repeat the steps as you did to start the SSH service, set iptables to accept connections via ssh, test connections between centos3 and c7host, and disable SELinux (refer to lab1).
  8. Remember that centos3 is text-based interface only (no graphics). To recover from a blank screen, press a key (like the SPACE key) to return to the screen display.
  9. Record the time taken to install, and compare this to the time taken by the previous installations. Record your findings in the Installation Comparison chart in lab2 logbook.


Part 1: 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 c7host machine, and open a shell terminal.
  3. Enter these admin commands into your c7host machine and note the result:
virsh list
virsh list --all
virsh list --inactive
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!
  1. Now, shut-down your centos1 VM normally, and close the centos1 VM window.
  2. Switch to your terminal and issue the command: virsh start centos1
  3. Using the appropriate command check to see if your centos1 VM is now running.
  4. 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?
  5. Since this is a text-based version of Linux, you do not need to turn off the screen-saver.

Answer all observations / questions in your lab log book.

Part 2: Backing Up Virtual Machines

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!)
  4. Compare the size of the compressed and original files (hint: use ls -lh). If file is very large (like 15GB), you didn't compress it and you need to remove that file and perform the previous step until you get it right!
  5. Start the centos3 VM.
  6. Make certain that you are in your VM and not in your main system!
  7. Wreck only your centos3 system! Try this command inside the centos3 virtual machine:rm -rf /* (ignore error messages).
  8. Shut down the centos3 VM. If you tried to start the centos3 VM, it would not boot since all system files have been removed!
  9. Restore the original image from the backup in your home directory by typing this command: gunzip < ~YourUserId/centos3.img.backup.gz > centos3.img
  10. Restart the VM. Is it working normally?
  11. Create compressed backups of your other virtual machines (ie. centos1 and centos2).
  12. 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:
  13. Execute the following command: virsh dumpxml centos3 > centos3.xml
  14. Examine the file centos3.xml. What does it contain? What format is it in?

  15. We will now learn how to download a compressed image file and xml configuration file and add it as a VM to the virtual manager menu.
  16. Issue the following commands:
  1. Copy these files to the /var/lib/libvirt/images directory and decompress the image
  2. Make certain your present working directory is: /var/lib/libvirt/images
  3. Issue the command: virsh define practical1.xml
  4. What happened in the virtual manager window? To remove a VM entry in the Virtual Manager window, simply issue the command: virsh undefine vm_name (without the .xml file extension)
  5. Launch the VM to see if it boots-up
  6. Can you log into this VM? Perhaps your instructor will give you a clue in week #7... >;p

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.
  1. 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...
  2. 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?
  1. A previous OPS235 student graciously created a shell script that you can download and run to check to see how you performed this lab (to see if you are on the right track).
    Simply issue the command: wget http://matrix.senecac.on.ca/~murray.saul/ops235/lab2check2.bash and run on your c7host machine.

    If the shell script indicates any major errors, please inform your OPS235 instructor or lab assistant to advise what to do.

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


Part 1: Automating Routine Tasks (Shell Scripting)

Bash Shell Scripting Tips:

  • Data Input:

    A shell script can obtain data from a number of methods: reading input files, using arguments when issuing command (positional parameters), or prompting for data to store in a variable. The later method can be accomplished by using the read command, for example: read -p "Enter your name: " userName.

  • Mathematical Expressions:

    In shell scripting, data is stored in variable as text, not other data types (ints, floats, chars, etc) like in compiled programs like C or Java. In order to have a shell script perform mathematical operations, number or variable need to be surrounded by two sets of parenthesis ((..)) in order to convert a number stored as text to a binary number.


    echo "$var1 + $var2 = $((var1+var2))"

    Note: shell does not perform floating point calculations (like 5/10). Instead, other commands like awk or bc would be required for floating point calculations (decimals)

  • Loops (iteration):

    Loops and logic are a very important elements of shell scripting (not to mention programming as well). Determinant loops (such as for loops) usually repeat for a preset number of times (eg. counts, positional parameters stored). In-determinant loops (such as while or until loops) may repeat based on unknown conditions (like waiting for user to enter correct data). Test conditions can be used with in-determinant loops, or even commands! If a command runs successfully (eg ls, cd, grep matching a pattern), zero (true) value is returned, otherwise a non-zero (false) value is returned. Command options or redirection to /dev/null can be used to just test if command runs, but not display stdout or stderr. Conditional statements "and" (&&) / "or" (||) can also be used when testing multiple conditions.

    Examples (try in a shell script)

    set ops235 is fun
    for x
     echo "argument is $x"

    for x in $(ls)
     echo "Filename: $x"

    read -p "enter a whole number: " num
    until echo $num | grep -q "^[0-9][0-9]*$"
     read -p "Incorrect. Please enter WHOLE NUMBER: " num

    read -p "pick a number between 1 and 10: " num
    while [ $num -lt 1 ] || [ $num -gt 10 ]
    read -p "Incorrect. Please pick number between 1 and 10: " num

You will continue our use of Bash Shell scripting by first creating a Bash Shell script that will allow the Linux sysadmin to select their created VMs for backup to root's home directory. Afterwards you will download, view and run a couple Bash Shell scripts that use the virsh command to start and stop your virtual machines.

If you require additional practice in creating shell scripts using logic, loops and mathematical operations, run the commands in your Matrix account:
  • /home/murray.saul/scripting-2
  • /home/murray.saul/scripting-3

Perform the following steps in your c7host machine:

  1. Open a Bash shell terminal and login as root.
  2. Use a text editor (such as vi or nano) to create a Bash Shell script called: backupVM.bash in /root's home directory.
  3. Enter the following text content into your text-editing session:


# backupVM.bash
# Purpose: Creates system info report
# USAGE: ./report.bash
# Author: *** INSERT YOUR NAME ***
# Date: *** CURRENT DATE ***

if [ $PWD != "/root" ] # only runs if in root's directory
 echo "You must be located in /root" >&2
 exit 1

  1. Save your editing session, but remain in the text editor.
  2. This shell script is designed particularly for your centos1, centos2, and centos3 VMS.
  3. The code displayed below will prompt the user if they wish for all VMs to be backed-up; otherwise, allow the user the option of specifying which VMs to be backed-up. Add the following code

read -p "Backup all VMs? (y|n):" answer # prompt if all VMs to be backed-up

if [ "$answer" = "y" ] # Backup all VMs if answer is yes
 for num in 1 2 3 # Determinant loop for 3 arguments: 1, 2, and 3
  echo "Backing up VM #$num"
  gzip < /var/lib/libvirt/images/centos$num.img > /root/centos$num.img.backup.gz

  echo "VM #$num BACKUP DONE"

elif [ "$answer" = "n" ]
 read -p "Which VM should be backed up? (1/2/3): " numanswer
 until echo $numanswer | grep "^[123]$" >> /dev/null # Look for match of single digit: 1,2, or 3
  read -p "Invalid Selection. Select 1, 2, or 3: " numanswer
 echo "Backing up VM #$numanswer"
 gzip < /var/lib/libvirt/images/centos$numanswer.img > /root/centos$numanswer.img.backup.gz

 echo "VM #$numanswer BACKUP DONE":
 echo "Invalid Selection... Aborting program"
 exit 2

  1. Save, set permissions, and then run that shell script to backup centos1. Confirm that this script did backup this image to root's home directory
  2. Use the wget command to download, study, and run the following shell scripts on-line:

  3. Try to understand what these Bash Shell scripts do.
  4. You have completed lab2. Proceed to Completing The Lab, and follow the instructions for "lab sign-off".

Answer all observations / questions in your lab log book.


Time for a new backup!
If you have successfully completed this lab, make a new backup of your virtual machines as well as your host machine.

Arrange proof of the following on the screen:

  1. All VMs:
    • Working virtual machines created and running
    • Disk layout and size correct on all virtual machines
    • Proof of yum updates
    • All virtual machines backed-up (eg. usb stick and/or home directory)
  2. c7host machine:
    • Correct VM image filenames contained in /var/lib/libvirt/images directory
    • Creation of your bash shell script called backupVM.bash
    • A list of your iptables rules (command: iptables -L)
  3. Lab2 logbook notes and Installation Comparison chart completed

Practice For Quizzes, Tests, Midterm & Final Exam

  1. What is the name of the CentOS installation program?
  2. What is the name of the file created by the CentOS installation program?
  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. How can you reduce the number of software updates required immediately after installation?
  6. How do you start and stop virtual machines?
  7. How do you SSH into your virtual machines?
  8. What is procedure to backup your VM images (and XML config files) to your USB key?
  9. The kickstart installation (centos3) was a network installation. Can a kickstart file be used with a DVD installation?
  10. The kickstart installation (centos3) was fairly fast. Why? Under what circumstances would it take a long time, even on a fast network?