OPS235 Lab 3 - CentOS7 - VMware

From CDOT Wiki
Revision as of 09:52, 16 May 2016 by Msaul (talk | contribs) (Created page with 'Category:OPS235Category:OPS235 Labs = LAB PREPARATION = == Purpose / Objectives of Lab3== [[Image:software.png|thumb|right|300px|Installing software is an important ta…')
(diff) ← Older revision | Latest revision (diff) | Newer revision → (diff)
Jump to: navigation, search


Purpose / Objectives of Lab3

Installing software is an important task for computer system administrators.

In this lab, you are going to identify potential problems such as not properly compressing VM image files when backing up VMs, or forgetting your root password. You will also learn to conserve hard 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 applications (i.e. programs).

Main Objectives

  • Learn to troubleshoot some common problems after installing VMs
  • Create and extract archive files (tar and tar.gz)
  • Install applications using various methods:
  • Download, decompress and archive file from the Internet, then compile source code in order to install an application.
  • Use yum utility to install software from local source programs (on DVD drive)
  • Use yum utility to install software from repositories (online storage areas)
  • Learn how to add repositories (online software storage areas) to install less common applications.
  • Demonstrate the use of Bash Shell scripts to automate routine tasks (generate a customized software report)

Minimum Required Materials

Removable Hard Disk Pack (SATA)
USB key
(for backups)
Lab3 Log Book

My Toolkit (CLI Reference)

Archiving / Compiling:

gzip, gunzip

Software Manangement:




Online Linux Command Review
The following tutorial will allow you to learn essential shell scripting skills:
  • Shell Scripting Basics - Part 4 (The sed Utility):


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 what a potential problem may look like, and know how to solve that problem.

A few common problems are:

  • I Can't boot into Graphical Mode on my c7host machine
  • 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 IS NOT
  • 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 the root user. 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 centos1 VM. when the Grub Boot menu appears, press the letter e (for "edit").
  2. Using your arrow keys, scroll to next screen to linux or linux-efi 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 regularuserid). You can press ctrl-c if you wish to abort (i.e. not change password).
  7. To restart in graphical mode, simply enter the command reboot.
Unfortunately, this method does not work if you forgot your root password (To reset your root password, refer to procedure below).

Steps to Reset Root's Password:

Add rw init=/sysroot/bin/sh as shown and then press ctrl-x to boot into single user no root password mode
  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 linux or linux-efi 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

  5. Issue the command: passwd root in order to change your root password (press ctrl-c if you wish to abort - i.e. not change password).
  6. 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!


Part 1: Creating a File Archive

  1. Boot up your centos3 VM.
  2. Change your working directory to /usr/share/doc/sudo*
  3. Use the tar (tape archiver) command to create an archive file named /tmp/archive1.tar
    • tar cvf /tmp/archive1.tar .
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.
  1. What do the options c, v, and f mean?
  2. Record the archive file size.
  3. Compress the file using gzip:
    • gzip /tmp/archive1.tar
  4. Record the archive file size after compression.
  5. Make sure you're still in /usr/share/doc/sudo* and then create a compressed archive:
    • tar cvzf /tmp/archive2.tgz .
  6. What does the z option do?
  7. Compare the sizes of /tmp/archive1.tar.gz and /tmp/archive2.tgz. Why are they so close in size?

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

Part 2: Restoring Files From an Archive

  1. Remain 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. 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

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

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"

  1. Go to the directory /tmp
  2. 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.
  3. Extract the files. Change to the newly-extracted directory (/tmp/nled-2.52)
  4. 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)
  5. 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?
  6. Reissue the make command. Where you successful? What does make do?
  7. Issue the command as root: yum list ncurses. What do you see? Issue the command at root: yum search ncurses. What do you observe?
  8. 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
  9. Some software distributed as source code can automatically install itself. Try this command:
    • make install
  10. Most but not all source code archives include the capability of installing themselves this way.
  11. 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
  12. Run nled from the current directory to make sure that it works. To exit this application, press ESC, then type the letter q at the command prompt as the bottom left-hand corner and then press ENTER.
  13. 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

Manage Software and Repositories 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. Perform this section in your c7host machine.
  2. Issue the command: yum install elinks
  3. Now issue the command: yum info elinks
  4. How can you tell if the elinks package has been installed?
  5. To remove the elinks package issue the command: yum remove elinks
  6. Verify that the elinks package has been removed. Also verify that the application called: xchat is not installed.
  7. Place your Centos7 Full Install DVD into the DVD drive of your hostmachine.
  8. View the contents of the DVD drive using the file manager application (called nautilus). Change to the Packages subdirectory. What does this subdirectory contain?
  9. Use a graphical file manager to view the contents of the DVD in your machine.

    TIP: If you are having problems locating pathname to your DVD, open a terminal, login as root, issue the command: mount, and look for a path-name containing your Centos Install DVD and use that path-name when required later in this section.

  10. Open a shell terminal and use the Linux command cd to change to the Packages sub-directory (hint: similar path-name as USB, but use Centos 7 x86_64/Packages and use quotes " " around full path-name since there are spaces within the pathname).
A Note about Repositories
Since software repositories are on-line storage areas for software for particular Linux distributions, the Linux administrator can enable (add) or disable (remove) additional software repositories. Usually only the basic or "base" repositories are enabled upon Linux installation.

There are a few ways for yum to install applications:
  • yum localinstall (install rpm files located from the machine via downloads to hard-drive, DVD, etc)
  • yum install (install applications from an online repository)

  1. Within the Packages subdirectory of the Centos7 Full Install DVD, locate the rpm file that contains the xchat application (note the full path-name of the file). What do you think is the purpose of the numbers also contained in the filename?
  2. Issue the command: yum localinstall "full_pathname_to_xchat_rpm_file"
  3. Verify that the xchat command has been installed.
IRCs: A Great Tool for Linux Administrators
Although Search Engines (like Google) are a system administrator's good friend, Internet Relay Chats (IRCs) are also a great tool for system administrators to help obtain information. Many website offer information on how to connect to IRCs (both nodes (eg. FreeNode) and irc channel (eg. #linux).

A few tips to consider with IRCs:
  • Do your Homework (read docs first!)
  • Ask specific questions
  • Not all chats are friendly
  • Be patient when asking questions (use courtesy)
  • The advise is free (you get what you pay for!)
  1. We will now look at how we can add different repositories to our c7host machine.
  2. As root, issue the following command: yum repolist
  3. Take a few moments to view the contents of the file. Do you see which repositories are used by the yum command? Write down the repositories in your lab logbook.
  4. View the following link to see a general listing of repositories:
    [ Available Repositories for Centos ].
  5. To add this repository, issue the command:
    wget https://dl.fedoraproject.org/pub/epel/7/x86_64/e/epel-release-7-5.noarch.rpm
  6. To enable the repository in yum, issue the following command:
    yum install epel-release-7-5.noarch.rpm
  7. To clean-up the repository list (including downloading new applications in added repositories), issue the command: yum clean all
  8. To verify that you have added the repository, you can issue the command: yum repolist
  9. Unused and unneeded software can present a security risk and ties up disk space needlessly. Find at least 4 other packages to remove on your c7host machine(for example: sound & video, games, etc) that you're not using on your system. Be careful to ensure that removing those packages does not also remove other software that you do need.

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


Automating Routine Tasks (Shell Scripting)

Bash Shell Scripting Tips:

  • The Here Document

    A neat little trick involving a special type of redirection of stdin ( << ) that allows input to be redirected to a command from within the command. The name relates to where the stdin is contained: not in a file, but "here in the command itself". A character (like +) is used to mark the boundary of stdin. It is important that the ending boundary only contains a line with that matching character (eg +); otherwise the stdin will continue to be read! This command is a convenience way to display multiple lines on that screen, but this command can be used with any Linux command that accept stdin.

    Examples (try at the shell prompt)

    cat <<+
    This is a test message
    This is the second line

    mail -s "test message" youremailaddr <<+
    This is a test message
    I hope you like it.


    tr [a-z] [A-Z] <<+
    i like ops235
    i love scripting.

  • Using sed to Manipulate Text

    The Linux command sed stands for Streaming Editor which is an effective way to manipulate a text file, output sent from a command, or from within a "here document". This command can manipulate matching text on a variety of criteria (such as line number, regular expression match, etc). Commands can then be used for manipulation such as omitting, printing, substituting, adding, inserting, etc. The sed option -n suppresses display of text so the print (p) command can be used; otherwise, the text will be displayed (with edits via the sed command instructions). Results of text manipulation with sed can be stored in a variable using command substitution, or redirected to a file. NEVER redirect the stdout from a sed command to the same input file (or the input file will be destroyed)!

  • Examples (try at the shell prompt)

    sed 's/|/ /g' <<+

    sed 's/$/\n/g' <<+
    This text
    should be


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).

If you require additional practice in creating shell scripts using the "sed" utility, run the following command in your Matrix account:

  1. Perform the following steps in your c7host machine for this section.
  2. Open a Bash shell terminal and login as root.
  3. Use a text editor (such as vi or nano) to create a Bash Shell script called: packageInfo.bash in root's home directory.
  4. Enter the following text content into your text-editing session:


# packageInfo.bash
# Purpose: Generates a report to displaying specified information of installed software
# USAGE: ./packageInfo.bash [application-name]
# Author: *** INSERT YOUR NAME ***
# Date: *** CURRENT DATE ***

if [ $HOME != "/root" ] # only runs if logged in as root
 echo "You must be logged in as root." >&2
 exit 1

  1. Save your editing session, but remain in the text editor.
  2. 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 ]
  echo "Your command must have a application-name as argument" >&2
  echo "USAGE: $0 [application-name]" >&2
  exit 1

# Create 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

  1. Save your editing session, but remain in the text editor.
  2. 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:

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" has been created

  1. Save, set permissions, and then run that shell script for the application gedit. Did it create that report? Try running the script without an argument - What did it do?
  2. Use the wget command to download, study, and run the following shell scripts on-line:
  3. Try to understand what this Bash Shell script does.
  4. You have completed lab3. Proceed to Completing The Lab, and follow the instructions for "lab sign-off".

Answer Investigation 3 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. centos3 VM:
    • Archived files created
  2. c7host Machine:
    • Four unnecessary packages removed
    • xchat package installed
    • One repository added for yum
    • Creation of your bash shell script called packageInfo.bash
  3. Lab3 log-book filled out.

Practice For Quizzes, Tests, Midterm & Final Exam

  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.