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 tutorial will allow you to learn essential shell scripting skills: Shell Scripting Basics - Part 3: N/A

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

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. Issue the command: yum info elinks
2. How can you tell if the elinks package has been installed?
3. To remove the elinks package issue the command: yum remove elinks
4. Verify that the elinks package has been removed.
5. Use the same command to remove the package called xchat and verify that the xchat package was removed.
6. Place your Centos7 Full Install DVD into the DVD drive of your hostmachine.
7. View the contents of the DVD drive using the file manager application (called nautilus). Change to the Packages subdirectory. What does this subdirectory contain?
8. Open a shell terminal and use the Linux command cd to change to the Packages subdirectory (hint: similar pathname as USB, but use "Centos 7 x86_64/Packages" and use quotes around absolute pathname 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)




9. Within the Packages subdirectory of the Centos Full Install DVD, locate the rpm file that contains the xchat application. What do you think is the purpose of the numbers also contained in the filename?
10. Issue the command: yum localinstall absolute_pathname_to_xchat_rpm_file
11. 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!)

12. Use the yum command to install the package called "x". Were you able to install the file?
13. As root, issue the following command: more /etc/yum.conf
14. 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.
15. Before adding a repository to the yum.conf file, you need to see which repositories you want to add, and obtain the appropriate URL for those repositories. View the following link to see a general listing of repositories:
    [ Available Repositories for Centos ].
16. After viewing the repository list, why should you be cautious with adding just any repository into your yum.conf file?
17. Obtain the URL for the repository: SerNet Samba Repository. You will use in the next command (see below).
18. To add the repository, issue the command: yum-config-manager --add-repo URL_of_SerNET_Samba_Repository
19. To enable the repository in yum, issue the following command: yum-config-manager --enable repository_name
20. To clean-up the repository list (including downloading new applications in added repositories), issue the command: yum clean all
21. To verify that you have added the repository, you can issue the command: yum repolist
22. Now use the yum command to install the package called "x". Were you successful, and if so, why?
23. Perform a NetSearch to compare compiling source code vs using the yum command. What are the three major features that the yum command has that compiling source code doesn't?
24. Unused and unneeded software can present a security risk and ties up disk space needlessly. Find at least 4 other packages (for example: sound & video, games, 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 Investigation 3 observations / questions in your lab log book.




INVESTIGATION 3: LOOKING AHEAD

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' <<+ I|like|weekends! + sed 's/$/\n/g' <<+ This text should be double-spaced! +


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 additional shell scripts skills, run the commands in your Matrix account:
• N/A

Perform the following steps in your c7host machine:

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

# 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


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 for the application gedit. Did it create that report? Try running the script without an argument - What did it do?
9. Use the wget command to download, study, and run the following shell scripts on-line:

   https://scs.senecac.on.ca/~murray.saul/packageInfoGraphical.bash

10. Try to understand what this Bash Shell script does.
11. #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.




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.