932
edits
Changes
m
→INVESTIGATION 4: USING PYTHON TO AUTOMATE MANAGING VIRTUAL MACHINES: - Providing some structure to the script.
<li>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.</li>
<li>Test your script to make sure it works. If it doesn't, go back and fix it. Do not continue until it successfully makes backups of your VMs.</li>
<li>There is a weakness to this script as written. Every time you run it, it will make a backup of all three VMs. But what if you only made a change to one of them? Do we really need to wait through a full backup cycle for two machines that didn't change? As the script is currently written, we do. But we can make it better. We've provided the scripts with some comments below.</li><li><code style="color:#3366CC;font-family:courier;font-size:.9em;">#!/usr/bin/env python3<br /># backupVM.py<br /># Purpose: Backs up virtual machines<br />#<br /># USAGE: ./backupVM.py<br />#<br /># Author: *** INSERT YOUR NAME ***<br /># Date: *** CURRENT DATE ***<br />import os<br /><br />#Make sure script is being run with elevated permissions<br />currentuser = os.popen('whoami').read().strip()<br />if currentuser != 'root':<br /> print("You must be root")<br /> exit()<br /><br />#The rest of this script identifies steps with comments 'Step <something>'.<br />#This is not a normal standard for commenting, it has been done here to link the script<br /># to the instructions on the wiki.<br /><br />#Step A: Find out if user wants to back up all VMs<br />#Step B-1:use the existing loop to back up all the VMs<br />for machine in ('centos1','centos2','centos3'):<br /> print('Backing up ' + machine)<br /> os.system('gzip < /var/lib/libvirt/images/' + machine + '.qcow2 > ~YourRegularUsername/backups/' + machine + '.qcow2.gz')<br />#Step B-2: They don't want to back up all VMs, prompt them for which VM they want to back up<br />#Step C: Prompt the user for the name of the VM they want to back up<br />#Step C-1: If the user chose Centos1, back up that machine.<br />#Step C-2: If the user chose Centos2, back up that machine.<br />#Step C-3: If the user chose Centos3, back up that machine.<br /></code></li><li>Before the for loop that backs up each machine add a prompt to ask the user if they want to back up all machines. Use an if statement to check if they said yes(See comment 'Step A').<ul><li>if they did say yes, back up all the VMs using your existing for loop(Comment step B-1).</li><li>If they didn't say yes, do nothing for now.</li></ul></li>
<li>Test your script to make sure it works. Check what happens if you say 'yes' to the prompt, and check what happens if you say things other than 'yes'.</li>
<li>Now we have a script that asks the user if they want to back up all VMS, and if they say they do it does. But if they don't want to back up every VM, it currently does nothing.</li>
<li>Add an else statement at comment Step B-2 to handle the user not wanting to back up every VM. Inside that else clause (Comment step C) ask the user which VM they would like to back up (you can even give them the names of available VMs (Centos1, Centos2, Centos3).</li><li>Now nest an if statement inside that else (Comments C-1, C-2, and C-3) so that your script can handle what your user just responded with. If they asked for Centos1, back up Centos1. If they want to back up Centos2, only back up Centos2, etc. Hint: You might want to use elif for this.</li>
<li>Test your script again. You should now have a script that:<ul><li>Makes sure the user is running the script with elevated permissions.</li><li>Asks the user if they want to back up every VM.</li><li>If they want to back up every VM, it backs up every VM.</li><li>If the user does not want to back up every VM, the script asks them which VM they do want to back up.</li><li>If the user selected a single VM, the script will back up that one VM.</li></ul></li>
</ol>
