OPS245 Lab 2

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LAB PREPARATION

At the end of lab2, your VMware Workstation application will contain 4 virtual machines (c7host in your VMware Workstation application, and centos1, centos2, centos3 VMs in your KVM application). You will now have the option to run one virtual machine at a time, or run all machines simultaneously to learn about networking (covered in later labs)

Purpose / Objectives of Lab 2

In this lab, you will create 3 remaining virtual machines using another virtualization program called KVM that will run in your c7host VM. These VMs will be used throughout the remainder of this course to learn how to administer them (installing software, managing services, networking, etc).

While you are performing this lab, it is recommended to generally note the major differences in the different installation methods, and which method you prefer to use if you were a Linux system administrator in charge of installing many Linux distributions for an organization.

Main Objectives

  • Installing additional Virtualization Software on your c7host machine (KVM)
  • Create 3 separate VMs (virtual machines) using different installation methods:
  • centos1: Network CentOS Installation (Graphical)
  • centos2: Network CentOS Installation (minimal install - CLI only)
  • centos3: Network CentOS Installation with Kickstart configuration file (CLI only)
  • Manipulate virtual machines by CLI (virsh)
  • Properly backup VM images and backup VM configuration files
  • Create and run Bash Shell scripts to automatically create a post-install report for an installed VM.


Minimum Required Materials
Linux Command Reference
Solid State Drive
USB key
(for backups)
Lab2 Log Book

Virtualization
virt-manager
virsh
Installation Guides
Installing & Using KVM on CentOS
Using KVM (tutorial)
virsh command reference

Miscellaneous
gzip , gunzip
ip
grep
wc
pwd
ls
more
file
wget
chmod
vi

Matrix Online Tutorials:
  • Shell Scripting - Part 2 (Logic & Math Expressions):
    /home/ops235/scripting-2
  • Shell Scripting - Part 3 (Loops)
    /home/ops235/scripting-3

INVESTIGATION 1: SETUP FOR NESTED VIRTUAL MACHINES

Part 1: Install KVM Virtualization Application

We will now install the KVM package in order to create our remaining "nested" VMs. We will also be starting several services (including iptables) and disabling the firewalld service. We will learn more about managing firewalls using iptables in lab6.

Perform the following steps:
  1. Log into your c7host machine.
  2. perform a software update on your c7host VM by issuing the following command: sudo yum update
Important.png
Yum Update Hangs
If you experience yum update "hanging" around item 689 of over 1200 packages, issue the following commands (in a new terminal!):
sudo pkill systemctl
sudo yum clean all
sudo yum update
NOTE: Do NOT press <ctrl>c since it may cause your machine to cause a kernel panic when you restart your machine.
  1. Using elevated privileges, install the virtualization software by issuing the command:
    sudo yum install qemu-kvm qemu-img virt-manager libvirt libvirt-python \
    libvirt-client virt-install virt-viewer bridge-utils


  2. Restart your c7host virtual machine. If you fail to do this, you may experience virtualization network problems.
    Note.png
    About KVM
    There are actually several key programs installed for virtualization using KVM:
    • 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.
  3. Start the virtualization service: sudo systemctl start libvirtd

    NOTE: The most recent variants of CentOS and Fedora are using a service called firewalld that replaces iptables, however the iptables service is still in relatively common usage and knowing how to use it also works with firewalld. In this course we will concentrate on iptables.

  4. To disable and remove firewalld, issue the following commands:
    sudo systemctl disable firewalld
    sudo systemctl stop firewalld
    sudo yum remove firewalld

  5. To install and enable the IPTables services, issue the following commands:
    sudo yum install iptables-services
    sudo systemctl enable iptables
    sudo systemctl start iptables

Important.png
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 (without sudo!)
  2. You will be learning in the next investigation to perform several different types of CentOS Linux installs.

Part 2: Configure VMware Workstation for Nested VMs

Although we are using VMware Workstation to run our c7host VM, we will now install and configure another virtualization package called KVM in order to install the remaining VMs for this course. Since we are "nesting" VMs (i.e. running a VM inside another VM) we need to configure our c7host's Linux boot-up parameters in order to allow these VMs to run efficiently.

Perform the following steps:
  1. In a terminal use elavated privileges to edit the file called: /boot/efi/EFI/centos/grub.cfg
    • If this file doesn't exist, double-check your UEFI settings in VMWare Workstation for c7host. If BIOS is selected, you MUST redo Lab 1.
  2. Search for the first occurrence of the Linux Kernel boot command. Do not make the following changes on more than one entry!
  3. Insert the boot option: kvm-intel.nested=1 at the end of the Linux kernel boot options.
    Important.png
    About the reference settings shown below
    • Only ONE of these settings might be applicable.
    • Enter JUST the text highlighted in BLUE as your kernel version, root, and LVM settings might vary slightly.


linuxefi /vmlinuz-3.10.0-1062.1.2.el7.x86_64 root=/dev/mapper/centos_c7host-root ro crashkernel=auto rd.lvm.lv=centos_c7host/root rd.lvm.lv=centos_c7host/swap rhgb quiet LANG=en_CA.UTF-8 kvm-intel.nested=1
initrdefi /initramfs-3.10.0-1062.1.2.el7.x86_64.img

OR


linuxefi /boot/vmlinuz-3.10.0-1062.el7.x86_64 root=/dev/mapper/centos_c7host-root ro crashkernel=auto rd.lvm.lv=centos_c7host/root rd.lvm.lv=centos_c7host/swap rhgb quiet LANG=en_CA.UTF-8 kvm-intel.nested=1
initrdefi /boot/initramfs-3.10.0-1062.el7.x86_64.img

  1. Save your editing changes, close the virtual machine application, and reboot your c7host VM.
  2. If you configured your c7host VM for nested VMs, then you should get the output Y when you issue the following command:
    cat /sys/module/kvm_intel/parameters/nested
    • For AMD processors, check the /sys/module/kvm_amd/parameters/nested file.
    • And if kvm_intel directory doesn't exist, double-check your Processors => Virtualization Engine (Intel VT-x/EPT...) settings in VMWare Workstation.


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

INVESTIGATION 2: INSTALL NESTED VIRTUAL MACHINES (KVM)

Important.png
Keep the root password the same for Host and VMs
In order to simplify running the lab checking scripts in future labs, using the same root password for ALL machines (c7host and virtual machines). Also use the same username and passwords for all of your machines (c7host and virtual machines).


Part 1: Installing VM from a Network (Graphical)

VM Details:
VM Name (and hostname): centos1
Boot media: Network installation
CentOS Full Network Install URL:
VM Image Pathname: /var/lib/libvirt/images/centos1.qcow2
Memory: 2048MB
Disk space: 15GB
CPUs: 2
You may see this warning when creating your first VM inside CentOS. Select Don't ask me about these directories again and click Yes.
Perform the following steps:
  1. Launch the KVM virtual machine manager by clicking Applications -> System Tools -> Virtual Machine Manager.
  2. When prompted, enter your password.
  3. Click the create a new VM icon located near the top left-corner of the application window.
  4. Select the Network Install option and click Forward.
  5. Enter (copy and paste) the URL located at the top of this section (depending whether you are at Seneca College or not) and click Forward.
  6. Set RAM size to 2048 MB and click Forward.
  7. Set Hard Disk size to 15GB and click Forward.
  8. Enter the name: centos1, AND then select the option: Customize configuration before install, and click Finish.
  9. Another dialog will appear. Click CPUs (or "processors") and on right-side under Configuration select Copy Host CPU Configuration, click Apply, and then click Begin Installation at the top left-hand side.
  10. During the install, select Gnome Desktop software selection). For partitioning, select I will configure partition settings, click done, then select Click here to create them automatically. Set the / partition for ext4 file-system type, and click Done.
  11. Set the correct Date and Time Zone, and then click on Network and Hostname. The network should be turned ON. For hostname, enter: centos1 and then click Done.
  12. Make sure that when you create your regular user account you check the box to make them an administrator.
  13. Complete the installation. Login to your regular user account, and perform a sudo yum update for the centos1 VM (reboot if required). Make certain to adjust your screen-saver settings if desired.


Important.png
Use same root password / regular username / regular user passwords for c7host and ALL VMs
To simplify the lab checking process make certain that you use the identical root password, regular username, and regular username password for VMs that you create in this labs as you did for c7host machine in lab1.


  1. Repeat the steps as you did in the previous investigation (Investigation1 Part 1) to stop and disable firewalld, install iptables-services, start and enable iptables for this newly-created VM.
  2. Repeat the steps as you did with c7host post-install to turn off SELinux and perform a yum update.
  3. Issue the following command to obtain the IPADDR for your centos1 VM to record in your lab2 logbook: ip address show
  4. Record the time taken to install, and compare this to the time taken by the previous installations in your lab2 logbook.

Part 2: Installing from a Network (Minimal install - CLI)

VM Details:
VM Name (and hostname): centos2
Boot media: Network installation
CentOS Full Network Install URL:
VM Image Pathname: /var/lib/libvirt/images/centos2.qcow2
Memory: 2048MB
Disk space: 20GB
CPUs: 1
Perform the following steps:
  1. Create the VM (called centos2) as you did with the centos1 machine.
  2. Make certain to enter the name: centos2, AND then select the option: Customize configuration before install, and select Copy Host CPU Configuration, click Apply, and then click Begin Installation.
  3. When selecting the install options for centos2, do the same operation that you did in centos1 (but with Minimal Install software selection instead), but after automatically creating the partitions, reduce the size of the root logical volume to 8 GiB and add a logical volume with a size of 2 GiB (mount point: /home, name: home, and make certain root and /home logical volumes have ext4 file system).

  4. Complete the installation. Login to your regular user account.
  5. Repeat the steps as you did in the previous investigation (Investigation1 Part 1) to stop and disable firewalld, install iptables-services, start and enable iptables for this newly-created VM.
  6. Repeat the steps as you did with c7host post-install to turn off (permissive) SELinux (using the command 'vi' instead of 'vim') and perform a yum update.
  7. Issue the following command to obtain and record your centos2 IPADDR in your lab2 logbook: ip address show
  8. Record the time taken to install, and compare this to the time taken by the previous installations in your lab2 logbook.

Part 3: Installing from a Network using a Kickstart File

VM Details:
VM Name (and hostname): centos3
Boot media: Network installation
CentOS 7 Full Install Network URL:
Kickstart File URL (Kernel options):
VM Image Pathname: /var/lib/libvirt/images/centos3.qcow2
Memory: 2048MB (IMPORTANT Do not use less than 2048MB during installation.)
Disk space: 15GB
CPUs: 2


Important.png
Include ks= in the URL options field!
When using a kickstart file, make sure you include the ks= portion of the link. If done correctly, you should not be able to select partitions or any other settings.


Perform the following steps:
  1. Create the VM (called centos3)
  2. During the install, copy the network URL, then click the URL options to expand the kernel options input textbox. Type the following in the kernel options textbox:
  3. Then click the forward button to proceed. Make certain to select the correct Memory Size and Disk Space size shown in the VM Details above
  4. Make certain to enter the name: centos3, AND then select the option: Customize configuration before install, and select Copy Host CPU Configuration, click Apply, and then click Begin Installation.
  5. Observe the installation. How is it different from booting from a downloaded image?
  6. Record the time taken to install, and compare this to the time taken by the previous installations.

    If 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.

  7. What happens when the installation is finished?
  8. In a web browser, click the kickstart (KS) link above. This link is a text file. Read through it to find the following information (pay attention to lines starting with #) and record it in your Lab Logbook:
    • Regular-user account name
    • Regular-user account password
    • Root Password
  9. Boot the virtual machine and log in (use the user ID and password information from the previous step to gain access to this VM).
  10. Compare the experience to the first time you booted the other virtual machines.
  11. Repeat the steps as you did in the previous investigation (Investigation1 Part 1) to stop and disable firewalld, install iptables-services, start and enable iptables for this newly-created VM.
  12. Repeat the steps as you did with c7host post-install to turn off SELinux and perform a yum update.
You'll notice something when you go to set SElinux to permissive. The kickstart file already did that for you. It could even have performed the switch from firewalld to iptables for you (but it didn't).
  1. Issue the following command to obtain and record your centos2 IPADDR in your lab2 logbook: ip address
  2. 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.
  3. Record the time taken to install, and compare this to the time taken by the previous installations in your lab2 logbook.


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

INVESTIGATION 3: MANAGING VIRTUAL MACHINES (KVM)

Important.png
Root Privileges
As part of this investigation you will learn how to switch over to the root account in order to run several privileged commands in sequence. It can be tempting to just use this technique all the time, and never have to worrry about sudo, but do not do so. It undermines the security of your system. Use it only when you need it.
Important.png
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!

Part 1: Backing Up Virtual Machines

Perform the following steps:
  1. Shut down your centos1, centos2, and centos3 VMs. For centos2 and centos3, which are CLI-only, you can issue the following command to shutdown: sudo shutdown -h. Please be patient, the VMs will shut down!
  2. In your c7host VM, open a new Terminal window.
  3. Use elevated privileges to list the size and names of files in/var/lib/libvirt/images/
    • What do these files contain?
  4. Use the command sudo -i and enter your password if prompted. You are now root until you use the command exit to return to your normal user account.
  5. Change to the images directory by issuing the following command: cd /var/lib/libvirt/images/. Note that you did not need to use sudo, as you are already using elevated permissions.
  6. Make a compressed backup of your centos1.qcow2, centos2.qcow2, and centos3.qcow2 files to your regular user's home directory by issuing each command - one at a time (create backups directory before running these commands):
    gzip < centos1.qcow2 > ~YourRegularUsername/backups/centos1.qcow2.gz
    gzip < centos2.qcow2 > ~YourRegularUsername/backups/centos2.qcow2.gz
    gzip < centos3.qcow2 > ~YourRegularUsername/backups/centos3.qcow2.gz
      NOTE: Make certain to use the redirection signs "<" and ">" properly in the command!
Important.png
Please be patient
It may look like the command prompt is stuck but it could take a while for gzip to compress an entire operating system. NOTE: Do NOT press <ctrl>c to cancel this process. If you do, your archive will become incomplete and your recovery will be corrupt.
  1. 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!
  2. Once you are sure you have all three VMs backed up, use the exit command to revert back to your normal user.
  3. Start the centos3 VM.
  4. Make certain that you are in your VM and not in your main system!
  5. Wreck only your centos3 system! Try this command inside the centos3 virtual machine:sudo rm -rf /* (ignore error messages).
  6. Shut down and restart the centos3 VM (you may need to use the Force Reset option to do so).
  7. When the machine restarts it will not boot since all system files have been removed!
  8. Use the Force Off option to turn centos3 back off.
  9. Restore the original image from the backup from your home directory to your images directory by typing sudo -i command first [do not forget to exit when you are done], then this command:
    gunzip < ~YourRegularUsername/backups/centos3.qcow2.gz > /var/lib/libvirt/images/centos3.qcow2
  10. Restart the VM. Is it working normally?
  11. You should also make a copy of the XML configuration file for each VM 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:
  12. Execute the following command: sudo virsh dumpxml centos3 > centos3.xml
  13. Examine the file centos3.xml. What does it contain? What format is it in?

Part 2: Restoring Virtual Machines

Click on the cog icon to select different installed desktop environments.
  1. We will now learn how to download a compressed image file and XML configuration file and add it as a VM to the Virtual Machine Manager menu.
  2. Issue the following commands:
  3. Use gunzip with elevated privileges to decompress the qcow2 image file into the /var/lib/libvirt/images directory.
  4. Issue the command: sudo virsh define centos4.xml
  5. What happened in the virtual manager window? In order to remove a VM entry in the Virtual Manager window, simply issue the command virsh undefine VM_name without the .xml file extension
  6. Start up your new centos4 VM.
  7. Click on the user OPS235, and click the cog icon.
  8. Notice Cinnamon (Software Rendering) is selected. The Cinnamon desktop environment has been installed on this VM. From this menu, you can select other installed desktop environments. This is how you switch between them. Write it down.
  9. Login with the password ops235. Feel free to explore the new environment.
  10. Prior to your practical test, you will be required to perform a similar operation to download, unzip and run a VM image for your practical test.
Important.png
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. Note that it is better to shut down the VMs prior to shutting down the host
  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?

Part 3: Using Shell Scripts for VM Backup & Management

Idea.png
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.

  • 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.

  • Examples

    var1=5;var2=10
    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 (for / while / until)
  • 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).

  • Conditional statements && (run if previous command or test is true) and || (run is previous command or test is false) can also be used when testing multiple conditions.

  • Examples:
    set ops235 is fun
    for x
    do
     echo "argument is $x"
    done

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

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

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

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.

Perform the following steps:
  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:
sudo virsh list
sudo virsh list --all
sudo virsh list --inactive
  1. Now, shut-down your centos1 VM normally, and close the centos1 VM window.
  2. Switch to your terminal and issue the command: sudo 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?
Important.png
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. Open a Bash shell terminal.
  2. Use a text editor (such as vi or nano) to create a Bash Shell script called: backupVM.bash in your bin directory.
  3. Enter the following text content into your text-editing session:


#!/bin/bash


# backupVM.bash
# Purpose: Backs up pre-defined virtual machines
#
# USAGE: ./backupVM.bash
#
# Author: *** INSERT YOUR NAME ***
# Date: *** CURRENT DATE ***


if [ $(whoami) != "root" ] # only runs if root
then
 echo "You must be root" >&2
 exit 1
fi

  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 [ "$answer" = "y" ] # Backup all VMs if answer is yes
then
 for num in 1 2 3 # Determinant loop for 3 arguments: 1, 2, and 3
 do
  echo "Backing up VM #$num"
  gzip < /var/lib/libvirt/images/centos$num.qcow2 > ~/backups/centos$num.qcow2.gz

  echo "VM #$num BACKUP DONE"
 done

elif [ "$answer" = "n" ]
then
 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
 do
  read -p "Invalid Selection. Select 1, 2, or 3: " numanswer
 done
 echo "Backing up VM #$numanswer"
 gzip < /var/lib/libvirt/images/centos$numanswer.qcow2 > ~/backups/centos$numanswer.qcow2.gz

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


  1. Save, set permissions, and then run that shell script to backup centos1. Since that script will only work if you are have root permissions, you will need to use the technique you learned earlier in this lab to run the command with elevated privileges. Confirm that this script did backup this image to your home directory
  2. Use the wget command to download, study, and run the following shell scripts on-line:
    https://ict.senecacollege.ca/~ops245/labs/vm-start-text.bash
    https://ict.senecacollege.ca/~ops245/labs/vm-stop-text.bash

    https://ict.senecacollege.ca/~ops245/labs/vm-start.bash
    https://ict.senecacollege.ca/~ops245/labs/vm-stop.bash
  3. Try to understand what these Bash Shell scripts do.


Answer INVESTIGATION 3 observations / questions in your lab log book.

INVESTIGATION 4: USING PYTHON TO AUTOMATE MANAGING VIRTUAL MACHINES

Idea.png
Python Scripting Tips:

String Methods
  • The string data type has a number of methods that we can use on it to get a modified version of the data a string variable holds.
  • Note that these don't change the existing string, just return a copy of it with some change. You can store this updated copy in a variable, or use it in a command.
  • Some examples include:
    • find() - locates a value (e.g. another string) if it is in this string.
    • lower() - convert the entire string to lower-case
    • replace() - finds a value in the string, and replaces it with a different value.
    • split() - breaks the string up on a value, and returns a list.
    • strip() - removes leading and trailing whitespace
    • upper() - convert the entire string to upper-case
  • There are many more options than this, but you will get a lot of utility out of these.

Methods in General
  • Python is an object oriented programming language. In this course, that won't actually affect us much, but it does change how you run some commands.
  • In bash, every command ran on its own (while you might provide the command some arguments, or pipe different data into it). In python, the modules we import, and the types of variables we use can (will) have commands built into them. For example: converting all letters in a string to UPPER CASE).
  • While you could write a command in bash that would do that and pass it a variable holding a series of letters as an argument, in python that behaviour (and more) is built into the string type of variable.
  • The actions that are built into types are called methods. To use a method on a variable just add .methodname() to the end of the variable. Instead of getting back the value, you'll get something else (based on what that method does). Suppose we had a variable called course that currently had the value 'ops245'. Course codes are usually written in ALL-CAPS, so instead of just saying print(course), we could say print(course.upper())

This week you have added some significant capabilities to your python scripting. The ability to run loops and make decisions makes your scripts much more powerful. In this investigation you will write a python script that backs up the centos1, centos2, and centos3 VMs, or lets the user to specify which VMs they want backed up.

  1. In your bin directory, create the file backupVM.py, and populate with our standard beginning
    #!/usr/bin/env python3
    # backupVM.py
    # Purpose: Backs up virtual machines
    #
    # USAGE: ./backupVM.py
    #
    # Author: *** INSERT YOUR NAME ***
    # Date: *** CURRENT DATE ***
    import os
    currentuser = os.popen('whoami')
    if currentuser.read() != 'root':
      print("You must be root")
      exit()
    else:
      for machine in {'centos1','centos2','centos3'}:
        print('Backing up' + machine)
        os.system('gzip < /var/lib/libvirt/images/' + machine + '.qcow2 > ~YourRegularUsername/backups/' + machine + '.qcow2.gz')
  2. Try to run that script. You'll notice it does not work. No matter what you do, it always says you are not root.
  3. Modify the print statement that tells the user they must be root to also include the current username, then run the program again.
  4. It should print out root, but with an extra new-line. You may have noticed this in your other python scripts so far: the data we get from os.popen() has an extra new-line on the end. We will need to modify the string(s) it gives us a bit. See the side-bar for hints on how to do so.
  5. Modify the if statement so it is just getting the current username, not the username and a newline. You can do this using several steps and several variables, but it can also be done in a single line.
  6. Now that the script recognizes you as being root (or at least running the script with root permissions), it should work. Notice how we've used the + to combine several strings together to pass to the os.system command. We did this because this script needs the python variable to be evaluated before the whole line gets handed over to os.system. If you left the variable names inside the quotes, python will ignore them as just being part of a string. By putting them outside of a string, and concatenating their value to that string, we can evaluate them and feed them into that command.
  7. Convert the rest of the bash script above into python, then test your python version to make sure it works.

LAB 2 SIGN-OFF (SHOW INSTRUCTOR)

Follow the submission instructions for lab 2 on Blackboard.

Important.png
Backup ALL of your VMs!
If you have successfully completed this lab, make a new backup of all of your virtual machines onto your USB Key.
Perform the Following Steps:
  1. Use the virsh start command to launch all the VMs (centos1, centos2, and centos3).
  2. Inside each virtual machine, run ip a on the command line. Open a Terminal window in centos1 to do so. You'll need the IP address of each machine for the next steps.
  3. Switch to your c7host VM, open a terminal, login as root, and change directory to /root/bin.
  4. Issue the Linux command: wget https://ict.senecacollege.ca/~ops245/labs/lab2-check.bash
  5. Give the lab2-check.bash file execute permissions (for the file owner).
  6. Run the shell script and if any warnings, make fixes and re-run shell script until you receive "congratulations" message.
  7. Arrange proof of the following on the screen:
All VMs:
  • All 4 VMs created and running
  • Proof of yum updates on ALL VMs (i.e. results from yum update command)
c7host VM:
  • Run the lab2-check.bash script in front of your instructor (must have all  OK  messages)
Lab2 logbook notes completed.
  1. Upload a screenshot of the proof listed above, the output file generated by the lab2-check.bash script, your log book, and your backupVM.py to blackboard.

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. List the steps to install a VM from:
    • Downloaded iso file
    • Network install (without kickstart file)
    • Network install (with kickstart file)
  9. What is the purpose of the virsh command?
  10. How to start and stop VMs using the virsh command?
  11. List the steps to correctly backup your VMs to a USB disk
  12. List the steps to correctly restore your VMs from a USB disk to your c7host VM.
  13. How can you prompt the user for data and store into a variable?
  14. How do you perform mathematical operations in the Bash shell and within a Bash shell script?
  15. What is the difference between a determinant loop and an in-determinant loop?
  16. Show a few examples how loops can be used to error-check when prompting the user for data.
  17. What is the purpose of the && and || symbols when used with logic?'
  18. What does the command rpm -qi centos-release do and why is it important?
  19. What is the difference between rpm -q centos-release and uname -a?