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OPS235 Lab 2 - CentOS7 - SSD

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{{Admon/important|Remember to Backup your VM to USB Key!|Remember that you need to backup your '''centos2''' VM to your USB key before you leave your Seneca lab, or you will lose your work!}}

=INVESTIGATION 2: COMMON POST-INSTALL TASKS=

===Part 1: Perform Software Updates===

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This will download and install all of the packages that have been updated since the installation DVD image was created. If you complete this command at Seneca, it should run quite fast as Seneca College hosts a CentOS Repository mirror (a copy of all of the current CentOS packages, on a local web server). You will be reminded at the end of each of the remaining labs to perform software updates on ALL of your VMs.

=== Part 2: Managing Virtual Machines from the Command Line ===

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|colspan="2"|{{Admon/note|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.}}

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# Start the '''centos1''' virtual machine, and stop the '''centos2''' and '''centos3''' virtual machines.

# Switch to the '''c7host''' machine, and open a shell terminal.

# Enter these admin commands into your '''c7host''' machine and note the result:

:: <code>virsh list</code>

:: <code>virsh list --all</code>

:: <code>virsh list --inactive</code>

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|colspan="2"|{{Admon/note|Virtual Machine Does not Shutdown from Command|If the Virtual machine fails to shutdown from the <code>virsh shutdown</code> 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!|}}

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<ol><li value="4">Now, shut-down your centos1 VM normally, and close the centos1 VM window.</li><li>Switch to your terminal and issue the command: <code>virsh start centos1</code></li><li>Using the appropriate command check to see if your centos1 VM is now running.</li><li>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?</li><li>Since this is a text-based version of Linux, you do not need to turn off the screen-saver.</li></ol>

=== Part 3: Backing Up Virtual Machines ===

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|colspan="2"|{{Admon/important|Backing up VMs|There are two general processes in order to back up your images:<ol><li>'''Compressing your images''' (also recommended to backup up to external storage USB Key) using the '''gzip''' command.</li><li>'''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).</li></ol> 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!|}}

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# Shut down all of the virtual machines.

# Change to the directory <code>/var/lib/libvirt/images/</code>. Note the size of the files in this directory. What do these files contain?

# Make a compressed backup of the '''centos3.img''' file to your home directory with this command: <code>gzip < centos3.img > ~YourUserId/centos3.img.backup.gz</code> (Note: Make certain to use the redirection signs "<" and ">" properly in the command!)

# 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!

# Start the '''''centos3''''' VM.

# '''Make certain that you are in your VM and not in your main system!'''

# Wreck only your centos3 system! Try this command inside the centos3 virtual machine:<code>rm -rf /*</code> (ignore error messages).

# Shut down the centos3 VM. If you tried to start the centos3 VM, it would not boot since all system files have been removed!

# Restore the original image from the backup in your home directory by typing this command: <code>gunzip < ~YourUserId/centos3.img.backup.gz > centos3.img'''</code>

# Restart the VM. Is it working normally?

# Create compressed backups of your other virtual machines (ie. '''centos1''' and '''centos2''').

# 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:

# Execute the following command: <code>virsh dumpxml centos3 > centos3.xml</code>

# Examine the file <code>centos3.xml</code>. What does it contain? What format is it in?

# 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.

# Issue the following commands:<ul><li><code>wget http://cs.senecac.on.ca/~murray.saul/ops235/practical1.img.gz</code></li><li><code>wget https://scs.senecac.on.ca/~murray.saul/ops235/practical1.xml</code> </li></ul>

<ol><li value="17">Copy these files to the '''/var/lib/libvirt/images''' directory and decompress the image</li><li>Make certain your present working directory is: '''/var/lib/libvirt/images'''</li><li>Issue the command: <code>virsh define practical1.xml</code></li><li>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)</li><li> Launch the VM to see if it boots-up</li><li>Can you log into this VM? Perhaps your instructor will give you a clue in week #7... >;p </li></ol>

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|colspan="2"|{{Admon/tip|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.}}

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<ol>

<li value="22">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...</li>

<li>Answer this question in your log book:</li>

</ol>

::* In order to fully back up a virtual machine, what information should be saved in addition to the virtual machine image?

<ol><li value="24">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: <code>wget http://matrix.senecac.on.ca/~murray.saul/ops235/lab2check2.bash</code> 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'''. </li></ol>

===Part 4: Automating Routine Tasks (Shell Scripting)===

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{{Admon/tip|Bash Shell Scripting Tips:| <ul><li>'''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'''. </li><li>'''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) </li><li>'''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'' ''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'' </li></ul>}}

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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: <ul><li>'''/home/murray.saul/scripting-2'''</li><li>'''/home/murray.saul/scripting-3'''</li></ul>

Perform the following steps in your c7host machine:

# Open a Bash shell terminal and login as root.

# Use a text editor (such as <code>vi</code> or <code>nano</code>) to create a Bash Shell script called: <code>backupVM.bash</code> in /root's home directory.

# Enter the following text content into your text-editing session:

#!/bin/bash

# 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

then  echo "You must be located in /root" >&2

exit 1

fi

</code>

<ol><li value="4">Save your editing session, but remain in the text editor.</li><li>This shell script is designed particularly for your centos1, centos2, and centos3 VMS.</li><li>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</li></ol>

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$num.img > /root/centos$num.img.backup.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$numanswer.img > /root/centos$numanswer.img.backup.gz

echo "VM #$numanswer BACKUP DONE":

else

echo "Invalid Selection... Aborting program"

exit 2

fi

</code>

<ol>

<li value="7">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</li><li>Use the <code>wget</code> command to download, study, and run the following shell scripts on-line:<blockquote><code>https://scs.senecac.on.ca/~murray.saul/vm-start-text.bash https://scs.senecac.on.ca/~murray.saul/vm-stop-text.bash</code> <code>https://scs.senecac.on.ca/~murray.saul/vm-start.bash https://scs.senecac.on.ca/~murray.saul/vm-stop.bash</code></blockquote></li><li>Try to understand what these Bash Shell scripts do.</li><li>You have completed lab2. Proceed to Completing The Lab, and follow the instructions for "lab sign-off".</li></ol>

'''Answer all observations / questions in your lab log book.'''

Msaul

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OPS235 Lab 2 - CentOS7 - SSD

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