OPS235 Lab 4 - CentOS7

Logical Volume Management (Continued) and User / Group Management

Introduction

In this lab you're going to learn how to:

• Add a virtual hard disk and expand your vm's existing file system using LVM
• Administer (add, remove, modify) users on a Linux system.
• Save time while adding new users using a template of start-up files.
• Create and manage groups on a Linux system.

Required Materials (Bring to All Labs)

• CentOS 6.5 x86_64 Live DVD
• CentOS 6.5 x86_64 Installation DVD1
• SATA Hard Disk (in removable disk tray)
• USB Memory Stick
• Lab Logbook

Prerequisites

• Completion and Instructor "Sign-off" of Lab 2: OPS235 Lab 3 - CentOS6

Linux Command Online Reference

Each Link below displays online manpages for each command (via http://linuxmanpages.com):

LVM Information Utilities:	LVM Management Utilities:	Additional Utilities:
vgs lvs pvs vgdisplay lvdisplay pvdisplay	system-config-lvm (Tutorial) lvextend resize2fs lvcreate lvreduce pvcreate vgextend	mount umount useradd userdel usermod groupadd groupdel

Resources on the web

Additional links to tutorials and HOWTOs:

• Logical Volume Management (Note: It is recommended to return to this guide as a reference when performing the next several investigations)
• Linux File Systems (ext2/ext3/ext4)
• Partitioning with fdisk
• Mounting / Unmounting File-systems
• UID and GID explained

Software Package Management

Investigation 1: How do you query the RPM database?

RPM maintains a database of installed software. This information is very useful to system administrators. In the previous lab you queried that database using RPM with the -q argument. When you query the RPM database, you can separately specify:

• Do an operational task on one or more packages (like installing or removing a package), using a select-option
• What information you want about those packages, using a query-option

Perform the following steps:

(Perform investigations 1 - 3 in your host machine (c6host)

1. Using information from the man page for rpm, fill in this information:

Option	Meaning	Select or query option?	Example command
-a	Select all packages	select-option
-l
-i	Show the package information.
-f filename
packagename	Select just this package	select-option

Answer the Investigation 1 observations / table contents in your lab log book.

Investigation 2: How do you install and remove software with RPM?

1. Use the graphical file manager (Nautilus) to change to the directory on your Installation DVD. Go to the sub-directory called Packages. It should contain a file called: lynx-2.8.6-27.el6.x86_64.rpm
2. Execute the following command: rpm -i lynx-2.8.6-27.el6.x86_64.rpm
3. Issue an RPM query to check that lynx is installed. Record this command in your lab log-book.
4. Issue the following command: rpm -e lynx
5. Issue an RPM query to verify that lynx is no longer installed. Record this command in your lab log-book.
6. Issue the following command: rpm -i elinks-0.12.rpm. Did it work? Explain in your lab log-book why this command may not have worked.

Answer the Investigation 2 observations / questions in your lab log book.

Investigation 3: How do you 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 the Investigation 3 observations / questions in your lab log book.

Archiving Files / Compiling Software from Source Code

Archive files are often used to contain source code for software; in this lab you will also be compiling software from a source code archive.

Do not Shut-Down VMs Until Instructed
You will be running all 3 VMs eventually when performing this tutorial, Leave all VMs running until you are instructed to shut them down at the end of this lab.

Investigation 1: How do you create an archive file?

Use centos3
Perform these steps in the centos3 virtual machine.

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 .

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. Why are they so close in size?

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

Investigation 2: How do you restore files from an archive?

Remain in your centos3 VM
Perform these steps in the centos3 virtual machine.

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

Answer the Investigation 2 observations / questions in your lab log book.

Investigation 3: How do you build software from source code?

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...

Use centos2
Perform these steps in the centos2 virtual machine.

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

User/Group Management

Investigation 4: The /etc/passwd file

1. Look at the /etc/passwd file.
2. Make note of the contents of that file.
3. Read about the file: http://linux.die.net/man/5/passwd
4. Make sure you know what information each field contains.
5. Why do you think there are so many users?
6. Look at the names of the users. What do you think these user names represent? Are they people?
7. What is the numeric user ID (UID) of the root user?
8. The user IDs of real users (people) are different from the user IDs of system accounts. What is the pattern?

Investigation 5: Adding users

Use centos1
Perform these steps in the centos1 system.

1. Read the man page for the useradd command.
2. Create a new user account for each of your pod mates, using their learn account name as a user name. Give each user a password.
3. Grep the /etc/passwd file for each of the new users.
   • What is the home directory of each user?
   • What group is each user in?
   • What else do you know about each user?
   • Where are the passwords stored?
4. Look at the man page for /etc/shadow using the command man 5 shadow
   • Grep the /etc/shadow file for each of the new users.
   • Make note of this information.
5. Create two new dummy users, ops235_1 and ops235_2.
6. Investigate the home directory of one of your new users.
   • What files are there? Be sure to include hidden files.
   • What do you think these files are used for?
   • How does the operating system determine which files are created in a new home account? The answer can be found here: http://www.linuxhowtos.org/Tips%20and%20Tricks/using_skel.htm
   • Look at the files (including hidden files) in the template directory referred to in the article. Compare them to what is in a home directory for a new user. What do you notice?
   • Create a new file in this directory with the following command: touch foo
   • Create a new user named foobar, with the option to automatically create a home directory.
   • Look at the contents of foobar's home directory. What do you notice?
7. Be sure to record your observations in your lab notes.

Use centos3
Perform these steps in the centos3 virtual machine.

1. Add your matrix account user to centos3.

Investigation 6: Managing Groups

Use centos1
Perform these steps in the centos1 virtual machine.

1. Read the man page for the groupadd and groupdel commands.
2. Note which option allows you to set the Group ID number (GID) when you create a new group.
3. Examine the file /etc/group
   • Which values of GID are reserved for system accounts?
   • Which values of GID are reserved for non-system user accounts?
   • What is the lowest available GID number for non-system users?
   • What is the default group name of a new user?
   • Add a new group named ops235 with a GID of 600.
   • You are angry at some irresponsible users on your system.
     • Add a new group named idiots.
     • Look at /etc/group and note the GID of idiots.
     • What GID is given to a new group if if you do not specify it?
     • Your anger has subsided. Delete the idiots group.
     • Look at /etc/group again and note the change.

Be sure to record your observations in your lab notes.

Investigation 7: Deleting users

Use centos1
Perform these steps in the centos1 virtual machine.

1. Read the man page for the userdel command. Note which option automatically removes the users home directory when that user is deleted.

1. Delete the user ops235_1 using the command userdel ops235_1
2. Delete the user ops235_2 using the same command with the option which removes the home directory of the user.
3. Check the contents of the /home directory. What do you notice?
4. Check the contents of the /etc/group file. What do you notice?

Be sure to record your observations in your lab notes.

Investigation 8: Modifying users

Use centos1
Perform these steps in the centos1 virtual machine.

1. Read the man page for the usermod command. Note which options change the user's full name, primary group, supplementary groups, and shell.

1. Add each of your new users to the group ops235 (in other words, add ops235 to each user as a supplementary group).
2. Examine /etc/group. What has changed?
3. Use the usermod command to associate each of your pod mates' full name to their user name. With each change, examine their entries in the /etc/passwd file. What has changed?
4. Be sure to record your observations in your lab notes.

Completing the lab

Time for a new backup!
If you have successfully completed this lab, make a new backup of your virtual machines. Remember to also make a backup of the new second virtual disk drive on centos1 -- you now have two virtual disks on centos1, and therefore two image files, and therefore will need two backup files.

Arrange proof of the following on the screen:

1. Two PVs on centos1.
2. Separate /home filesystem (on an LV) in centos1.
3. Account created on centos3 matching your Matrix account.
4. List contents of /etc/group file (ops235 group).
5. List contents of /etc/passwd file (created accounts).
6. Fresh backup of the virtual machines.

Preparing for the Quizzes

1. What is a VG? PV? LV?
2. What is the total size of the "main" VG on your system?
3. How do you create a LV?
4. How do you delete an LV?
5. How would you add the disk partition /dev/sdb7 to your volume group "main"?
6. How would you increase the size of the root filesystem by 50 MB?
7. What is the purpose of /etc/fstab?
8. What is the purpose of /etc/shadow?