OPS235 Lab 3 - CentOS7

LAB PREPARATION

Purpose / Objectives of Lab3

In this lab, you are going to help conserve disk space by learning how to compress and decompress files that are stored on your computer server. In addition, you will learn alternative methods of how to install programs.

Topics include:

1. Learning to troubleshoot some common problems after installing VMs
2. Creating and using archive files (tar and tar.gz)
3. Compiling software packages from source code
4. Install applications using various methods:

• Decompressing source code archive, and compiling source code
• Use yum utility to install software from local programs (on DVD drive)
• Use yum utility to install software from repositories (online storage areas)

4. Demonstrating the use of Bash Shell scripts to automate routine tasks

Minimum Required Materials

CentOS7 FULL DVD

Removable Hard Disk Pack (SATA)

USB key (for backups)

Lab3 Log Book

My Toolkit (CLI Reference)

Archiving / Compiling: tar gzip, gunzip make

Software Manangement: rpm yum

Commands ls more wget chmod vi

Online Linux Command Review The following links will allow you to practice Linux commands that you learned from ULI101: Bash Shell Scripting II: [ ]

INVESTIGATION 1: TROUBLESHOOTING AFTER VM INSTALLS & BACKUPS

Press e at Grub Boot Menu to edit

There are a few "classic problems" that students can encounter with their virtual machines and their host machine after performing lab2. Although all OPS235 students may not encounter these problems, it is good to be aware of them and know how to troubleshoot a problem in order to solve the problem.

A few common problems are:

• I Can't boot into Graphical Mode on my c7host
• I Forgot My Regular User Password
• I Forgot My Root Password
• I Can't Start My Virtual Machine
• I Can't start my host machine

Troubleshooting consists of 3 basic elements:

• Asking Questions (eg. what was done recently prior to problem?)
• Eliminating what the problem isn't
• Tenacity and patience (ability to focus on finding the cause of the problem)

If you cannot log graphically into your machine (first 3 common problems), there is a trick to boot your system into "single-user" mode. This mode does not provide networking, graphics, or logging in as other regular users, but can connect to a text-based interface as root. This method will only work if a GRUB (Grand Unified Boot-loader) password has not been set, or that you haven't forgotten the GRUB password.

Steps to Boot into "Single-User Mode":

Add the boot option single and then press ctrl-x to boot into single user mode

1. Boot-up your c7host. As soon as the Grub Boot menu appears, press the letter e (for "edit").
2. Using your arrow keys, scroll to next screen to linux16 command and type the word single as an argument after quiet (see diagram for reference) and then press ctrl-x to boot.
3. The system should boot into text-based mode. Enter your root password.
4. One thing to look at is partition space usage. Issue the command: df -h
5. If you notice 0% free space in the / partition, then there is a problem. This most likely is caused by not following steps to create a compressed copy of the VM image. If that is the case, locate the large image backup and remove it. Do NOT remove the image in /var/lib/libvirt/images directory!
6. You can use the passwd command to reset your regular user password (eg. passwd yourusername).
7. To restart in graphical mode, simply enter the command reboot.

Unfortunately, this method does not work if you forgot your root password (see procedure below).

Steps to Reset Root's Password:

Add word single at the end of boot options, ENTER and press b to boot

1. The procedure to reset root's password is different than shown above. Press e at the Grub boot menu.
2. Using your arrow keys, move to linux16 command and replace the argument ro with the argument rw init=/sysroot/bin/sh (see diagram for reference) and then press ctrl-x to boot.
3. The system should boot into text-based mode without prompting for root's password.
4. Issue the command: chroot /sysroot

1. Issue the command: passwd root in order to change your root password.
2. To restart in graphical mode, simply enter the command reboot.

Catastrophic Boot Problems:

Not being able to start your c7host due to Kernel Panic or some sort of "catastrophic disk failure" is not as easy to fix. You might be able to boot from your Centos LIVE DVD, open a terminal and mount the partition via command line and look for possible problems (setup files like /etc/fstab). Lab5 will discuss more about mounting and the /etc/fstab file. The "worst-case scenario" would be to purchase a new hard disk, perform lab1 completely, perform lab2 to install and set-up virtualization software, then restore your VM image and xml file backups (eg. decompressing images, issuing virsh define commands for xml files). That is why consistently performing backups of ALL of your VMS at the end of each lab is absolutely essential! You have been warned!

INVESTIGATION 2: ARCHIVING FILES

Part 1: Creating a File Archive

1. Perform this part on your centos3 machine.
2. Boot up your centos3 VM.
3. Change your working directory to /usr/share/doc/sudo*
4. Use the tar (tape archiver) command to create an archive file named /tmp/archive1.tar
   • tar cvf /tmp/archive1.tar .

Warning! Don't miss the . at the end of the tar commands below! It specifies what should go into the archive: the contents of the current directory.

4. What do the options c, v, and f mean?
5. Record the archive file size.
6. Compress the file using gzip:
   • gzip /tmp/archive1.tar
7. Record the archive file size after compression.
8. Make sure you're still in /usr/share/doc/sudo* and then create a compressed archive:
   • tar cvzf /tmp/archive2.tgz .
9. What does the z option do?
10. Compare the sizes of /tmp/archive1.tar.gz and /tmp/archive2.tgz</code></b>. Why are they so close in size?

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

Part 2: Restoring Files From an Archive

1. This section is to be performed in your centos3 VM.
2. Create the directory /tmp/extract1
3. Change to the /tmp/extract1 directory.
4. Move the file archive1.tar.gz to your current directory.
5. Unzip the first archive you created:
   • gunzip archive1.tar.gz
6. Extract the files from the first archive:
   • tar xvf archive1.tar
7. Are all the files there?
8. Compare /tmp/extract1/README and /usr/share/doc/sudo*/README</code></b>. Are they exactly the same? Why?
9. Create the directory /tmp/extract2
10. Move the file archive2.tgz to the /tmp/extract2 directory.
11. Extract the files from the second archive:
    • tar xvzf /tmp/extract2/archive2.tgz
12. Note that this time a separate gunzip command was not needed. Why?
13. Repeat the previous command, leaving out the option "z". Does it work? Why?
14. Compare the README file in this directory with the original file. Are they exactly the same?

Answer Part 2 observations / questions in your lab log book.




Part 3: Practical Application - Compiling Source Code from Archive File

Now that you know how to create and decompress "zipped tarball archives", we will demonstrate how to install applications from websites containing these types of archives. Although this method is not as "user-friendly" as using the yum or rpm command, this method is useful if the application is NOT contained in regular software repositories...


In order to build software from source code, you must have the appropriate software development tools (such as make and gcc) and libraries (such as GTK) installed. The required tools will vary depending on the computer languages used in the software being built.

1. Part is to be performed in your centos2 VM.
2. Issue the following command to install a basic set of development tools and libraries:
   yum groupinstall "Development Tools" "Development Libraries"




Installing Development Libraries In the future, remember the above procedure whenever installing software from source. Sometimes, you need to install additional tools or libraries in order to compile a particular software package

3. Go to the directory /tmp
4. Use the wget command to download the "tar ball" that contains the source code for the NLED text editor. wget is a command-line tool to download files from the web using the http or ftp protocols.
   • wget http://cdot.senecac.on.ca/software/nled/nled_2_52_src.tgz
5. Extract the files. Change to the newly-extracted directory (/tmp/nled-2.52)
6. Check to see if there is a file named configure. If so, run it; if not, skip this step. (Most but not all source code archives contain this file)
7. Check to see if there is a file named Makefile or makefile. If so, type the command:
   • make
   • Did the command work? Why? Use the yum command to install the package gcc. What do you think the package gcc does?
8. Reissue the make command. Where you successful? What does make do?
9. Issue the command as root: yum list ncurses. What do you see? Issue the command at root: yum search ncurses. What do you observe?
10. In this case, you need to install the ncurses development libraries as well. Issue the following command as root: yum install ncurses-devel.x86_64. Now issue the command: make
11. Some software distributed as source code can automatically install itself. Try this command:
    • make install
12. Most but not all source code archives include the capability of installing themselves this way.
13. If the command make install does not work (how can you tell? What command did you learn from ULI101 to confirm that this command cannot be run from the command line?), copy the nled program manually:
    • cp nled /usr/local/bin
14. Test nled to make sure it works.
15. Why did copying the nled executable to /usr/local/bin allow the nled command to be run by name anywhere in the command prompt?

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

INVESTIGATION 3: Using the Yum Command for Local & Repository Installs

Part 1: Install and Remove Software with Yum

Internet Connection In order for yum to work you require a connection to the Internet. Establish this connection by using the browser to log into SeneNET

1. Change to your home directory.
2. Issue the command: yum install elinks and answer y to the question about installation.
   1. Where did yum get the elinks software?
   2. Why could yum install elinks when rpm couldn't?
3. Issue an RPM query to verify that elinks is installed. Record this command in your lab log-book.
4. Issue the command: yum remove elinks
5. Issue an RPM query to verify that elinks is no longer installed. Record this command in your lab log-book.
6. Issue this command: yum info cups

• Based on the result, do you think that cups is a useful package for your system? If not, try removing it.

8. Unused and unneeded software can present a security risk and ties up disk space needlessly. Find at least 4 other packages (for example: games, sound & video, etc) that you're not using on your system, and remove them. Be careful to ensure that removing those packages does not also remove other software that you do need.

Answer Part 1 observations / questions in your lab log book.

Part 2: Managing Repositories with Yum

ADD THIS SECTION


Answer Part 2 observations / questions in your lab log book.

INVESTIGATION 3: LOOKING AHEAD

Automating Routine Tasks (Shell Scripting)

Bash Shell Scripting Tips: Manipulating Text: Examples (try in a shell script)


We will continue with using shell scripts to create a Software Information Report that manipulates output generated by the rpm command. The sed and awk commands are very useful tools in shell scripting to manipulate text. In this lab, we will be using sed to allow the user to select certain portions from the rpm command (options -qi).

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:




#!/bin/bash

# packageInfo.bash

# Purpose: Generates a report to displaying specified information of installed software

#
# USAGE: ./packageInfo.bash

#

# Author: *** INSERT YOUR NAME ***

# Date: *** CURRENT DATE ***

if [ $HOME != "root" ] # only runs if logged in as root

then
 echo "You must be logged in as root." >&2

 exit 1

fi




4. Save your editing session, but remain in the text editor.
5. The code displayed below will require the user to include only one argument after the command (script) which will be the application name. The following code will also generate the report title and current date. Add the following code




if [ $# -ne 1 ]

then

  echo "Your command must have a application-name as argument" >&2

  echo "USAGE: $0 [application-name]" >&2

  exit 1

fi



# Creates report title (echo with -e option allows newline \n character to be used)



echo -e "\nSOFTWARE PACKAGE INFORMATION REPORT" > /root/package-info.txt

echo -e "Date: $(date +'%A %B %d, %Y (%H:%M:%p)')\n\n " >> /root/package-info.txt

6. Save your editing session, but remain in the text editor.
7. The code displayed below uses a trick called the "Here Document" to redirect stdin from within the command (a quick way to display output on the screen). The read command will store the different information report items as words (separated by a space). The sed command used to convert the spaces to pipes (|) and stored into another variable. This allows the sed command to use extended regular expressions to print rpm elements that match those various patterns to be added to the report. Add the following code







# Clear screen and use Here Document to display select on report items to read into variable



cat <<+

Available Package Information Items:

Name

Summary

Version

License

Source

URL

+

read -p "Enter word(s) shown above separated by spaces: " choice



# Convert spaces to pipe symbol (|)

processedChoice=$(echo $choice | sed 's/ /|/g')



# Use sed with extended regular expressions to only print those matching report elements

rpm -qi $1 | sed -r -n "/($processedChoice)/ p" >> /root/package-info.txt



cat <<+

File "/root/package-info.txt" can been created

+

8. 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
9. Use the wget command to download, study, and run the following shell scripts on-line:

   https://scs.senecac.on.ca/~murray.saul/vm-start-text.bash
https://scs.senecac.on.ca/~murray.saul/vm-stop-text.bash
https://scs.senecac.on.ca/~murray.saul/vm-start.bash
https://scs.senecac.on.ca/~murray.saul/vm-stop.bash

10. Try to understand what these Bash Shell scripts do.
11. #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.

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

LAB 3 SIGN-OFF (SHOW INSTRUCTOR)


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

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:

✓ Archived files created

✓ Unnecessary/unused packages have been deleted (list at least 4, and show that they are no longer installed).

✓ 2 packages installed with yum command

✓ 1 repository added for yum

✓ License of the nautilus package




Preparing for Quizzes

1. What is the purpose of booting into single-user mode?
2. List steps in order to boot into single-user mode
3. What is the difference between a .tgz file and a .tar.gz file? What do these stand for?
4. What is the purpose of a repository?
5. What is source code?
6. How do you build software from source code?
7. Which is preferred: installing from an RPM file, or installing from source code? Why?
8. What does yum do that rpm does not?
9. List the steps to install a package via rpm command.
10. List the steps to determine detailed information regarding an install package via rpm and yum commands.
11. List the steps to remove a package via rpm command.
12. List the steps to install a package using the yum command.
13. List the steps to remove a package using the yum command.