OPS235 Lab 5 - CentOS7

Logical Volume Management and Software Package Management

Introduction

In this lab you're going to:

• Learn how to add and remove software packages on your different Linux systems.
• Learn how to properly adjust your various Linux file systems by using and managing LVM both graphically (centos2) as well as command line (centos3).

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 2 - 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 yum rpm

Resources on the web

Additional links to tutorials and HOWTOs: Please read this page to get an overview of LVM:

• Logical Volume Management (Note: It is recommended to return to this guide as a reference when performing the next several investigations)
• Using the RPM Utility
• Using the YUM Utility

Logical Volume Management (Introduction)

Check Current LVM Information Prior to Performing Investigations

LVM (Logical Volume Management) is used to manage hard disk drives / partitions for Unix/Linux systems. LVM provides more flexibility than just working with hard disks / hard disk partitions. Volume Groups are areas used to define Physical Volumes (i.e. hard disks, disk partitions, or other forms of storage devices). Logical Volumes are then used to relate directories (mount points) to a specific physical volume or for a "range" or "span" of physical volumes.

Therefore, LVM allows more flexibility and growth potential for Linux systems (for example, having Logical volumes span multiple hard disks). CentOS uses LVM by default upon installation. Other Linux distributions may provide the capacity to install LVM, or later install and then use Logical Volume Management.

Although the concept of LVM is simple, it takes practice and preparation (or "thinking ahead") in order to correctly use this valuable tool. It is important for students to gain an understanding of LVM, and how to manage their filesystems using LVM. It is recommended for students to read the following resource prior to this lab and/or return to the following resource while performing this lab: Logical Volume Management

At this point, having completed Lab 2 you should have roughly the following disk storage setup:

(Note: These results are output from the vgs, pvs, and lvs commands that provide volume group, physical volume and logical volume information for each of the virtual machines that you created in lab2. Before proceeding, check these values with your own system to see if you are generally "on the right track".)

• centos1

 VG         #PV #LV #SN Attr   VSize VFree
 vg_centos1   1   2   0 wz--n- 9.50g    0

 PV         VG         Fmt  Attr PSize PFree
 /dev/vda3  vg_centos1 lvm2 a--  9.50g    0

 LV      VG         Attr   LSize Origin Snap%  Move Log Copy%  Convert
 lv_root vg_centos1 -wi-ao 8.03g                                     
 lv_swap vg_centos1 -wi-ao 1.47g 

• centos2

 VG         #PV #LV #SN Attr   VSize  VFree
 vg_centos2   1   3   0 wz--n- 19.51g 7.77g

 PV         VG         Fmt  Attr PSize  PFree
 /dev/vda2  vg_centos2 lvm2 a--  19.51g 7.77g

 LV      VG         Attr       LSize Pool Origin Data%  Move Log Cpy%Sync Convert
 lv_home vg_centos2 -wi-ao---- 1.95g                                            
 lv_root vg_centos2 -wi-ao---- 7.81g                                            
 lv_swap vg_centos2 -wi-ao---- 1.97g 

• centos3 (Note: This VM has no GUI installed)

 VG         #PV #LV #SN Attr   VSize VFree
 vg_centos3   1   3   0 wz--n- 14.51g 4.54g

 PV         VG         Fmt  Attr PSize PFree
 /dev/vda3  vg_centos3 lvm2 a--  14.51g 4.54g

 LV      VG         Attr   LSize   Origin Snap%  Move Log Copy%  Convert
 lv_home vg_centos3 -wi-ao----   1.00g                                            
 lv_root vg_centos3 -wi-ao----   8.00g                                            
 lv_swap vg_centos3 -wi-ao---- 992.00m                                     

• c6host (i.e. "removable hard disk" or "disk pack")

Does not use LVM. Confirm this using the same commands used above.

VM Backups and Recovery
Most of these investigations will take place in your virtual machines. If you make a significant mistake, your virtual machine may not boot. Remember that you created backups of your virtual machines in Lab 2, and you can restore them if something goes wrong.

Remember: if you did not create backups for all of your VMs, then you don't have any restoration points to fall-back to!

Investigation 4: Extend the size of lv_root using command-line tools

Perform this investigation in centos3.

Let's say that you have run out of disk space on your computer (centos3), you need more space on the root filesystem, perhaps to host more webpages or a larger database or new software. What are your options? Getting a replacement harddrive would probably require reinstallation of the operating system and backup/restore of the data.

Because we're using LVM though - we can avoid that. We can add a new harddrive (which will serve as a physical volume) to the volume group, and extend the root logical volume to make use of the new available space.

Perform the following operations to increase the size of lv_root in centos3:

Steps:

1. Run the following commands and make note of the output:

 ls /dev/vd*
 pvs
 vgs
 lvs
 df -h

2. Open the centos3 virtual machine console
3. Go to the hardware details view
4. Click "Add Hardware" and add a new storage device of 2GBs, make sure it's a VirtIO disk.
5. Go back to the console view
6. Run the same ls command (performed in step 1), what's changed?
7. Now we'll make the new device as a physical volume, add it to the volume group, and extend lv_root:

 pvcreate /dev/vdb

 vgextend vg_centos3 /dev/vdb

 lvextend -L +2G -r vg_centos3/lv_root

8. Now rerun the ls/pvs/vgs/lvs/df commands. What has changed and what caused those changes?
9. Among the changes, note that your root filesystem is now 2GB bigger - and you have not even rebooted your machine!

Answer the Investigation 4 observations / questions in your lab log book.

Investigation 5: How is LVM managed using system-config-lvm?

Perform this investigation on the VM named centos2.

Screenshot of system-config-lvm in CentOS. Click to enlarge.

1. Let's learn to administer (manage) our LVM graphically for our centos2 Virtual Machine.
   CentOS provides a tool called system-config-lvm to graphically administer LVM. The package is not installed by default, so you will need to install it by issuing: (yum install system-config-lvm).

2. Use this tool to determine the current LVM configuration by clicking on the appropriate element and reading the properties in the right-hand panel -- write down the answers:
   1. What are the names and sizes of the PVs?
   2. What is the name and size of the VG?
   3. What are the names and sizes of the LVs?
   4. Is there any space in the VG which is not allocated to a LV?
3. Increase the size of the home file-system to 4 GB:
   1. Click on the LV containing the home filesystem.
   2. Click on Edit Properties.
   3. Change the size to 4 GB and click Ok.
4. Create a new 3G LV (LV Properties: linear) containing an ext4 filesystem named lv_archive and mount it at /archive
5. Backup /etc into /archive

• Copy the files in /etc into the filesystem mounted at /archive
  (use the graphical tools or the command line. If using cp, remember to use the -R option).

6. Shrink the size of lv_archive to 1 GB.
7. Try shrinking the home file-system. What happens? Why?

Answer the Investigation 5 observations / questions in your lab log book.

Storage Setup (prior to starting Lab 4)

At this point, having completed Lab 3 you should have roughly the following disk storage setup:
(Note: These results are output from the vgs, lvs, and pvs commands within each virtual machine. You will be using these commands in the following lab investigations)

• centos1

 This VM has a GUI and no free space in the VG.

 VG         #PV #LV #SN Attr   VSize VFree
 vg_centos1   1   2   0 wz--n- 9.80G    0

 LV      VG         Attr   LSize  
 lv_root vg_centos1 -wi-ao   8.83G                                     
 lv_swap vg_centos1 -wi-ao 992.00M                                     

 PV         VG         Fmt  Attr PSize PFree
 /dev/vda2  vg_centos1 lvm2 a-   9.80G    0

• centos2

 This VM has a GUI and free space in the VG.

 VG         #PV #LV #SN Attr   VSize VFree
 vg_centos2   1   4   0 wz--n- 19.51g 4.73g

 LV      VG         Attr   LSize   
 lv_archive vg_centos2 -wi-ao---- 1.00g                                            
 lv_home    vg_centos2 -wi-ao---- 4.00g                                            
 lv_root    vg_centos2 -wi-ao---- 7.81g                                            
 lv_swap    vg_centos2 -wi-ao---- 1.97g                                  

 PV         VG         Fmt  Attr PSize PFree
 /dev/vda2  vg_centos2 lvm2 a--  19.51g 4.73g

• centos3

 This VM has no GUI installed.

 VG         #PV #LV #SN Attr   VSize VFree
 vg_centos3   2   3   0 wz--n- 16.50g    0 

 LV      VG         Attr   LSize  
 lv_home vg_centos3 -wi-ao----   1.00g                                            
 lv_root vg_centos3 -wi-ao----  10.00g                                            
 lv_swap vg_centos3 -wi-ao---- 992.00m                                    

 PV         VG         Fmt  Attr PSize  PFree
 /dev/vda3  vg_centos3 lvm2 a--  14.51g 2.54g
 /dev/vdb   vg_centos3 lvm2 a--   2.00g 2.00g

• c6host (i.e. "disk pack")

 /dev/sdc3        20G  3.7G   15G  20% /
 /dev/sdc2        29G  4.7G   23G  18% /home
 /dev/sdc1        97G   48G   45G  52% /var/lib/libvirt/images

Logical Volume Management (Continued)

Recovering VMs
Most of these investigations will take place in you virtual machines. If you make a significant mistake, your virtual machine may not boot. Remember that you created backups of your virtual machines in Lab 3, and you can restore them if something goes wrong.

Resources

Please read this page to get an overview of LVM: Logical Volume Management

It is recommended to open another window(eg. right-click, open in new tab or window) to make reference to view LVM commands as you perform investigations 1 to 3.

Investigation 1: How are LVMs are managed using Command-Line Tools

1. You are going to repeat the same LVM management operations (as your did with the centos2 VM in lab3), but you will using command-line tools in the centos3 VM. Since the centos3 VM only operates in command-line mode, you will need to refer to the "Logical Volume Management" link above.
2. Write down the exact commands used at each step, and record appropriate command output:

a. Determine the current LVM configuration using the pvs, vgs, and lvs commands.

b.Grow the home filesystem to 2G using the command lvextend and resize2fs.

c.Create a new 2G LV containing an ext4 filesystem and mount it at /archive (use mkdir, lvcreate, mkfs, mount, edit the file /etc/fstab (read the resource: https://wiki.archlinux.org/index.php/fstab ), and then reboot to confirm automatic mount).

d.Copy the contents of /etc into /archive.

e.Shrink lv_archive to 1G (use umount, resize2fs, lvreduce, and mount)

Investigation 2: How can a PV be added to an existing VG using Command-Line Tools?

1. Add an additional 2 GB virtual disk to your centos1 system, we will use it as an additional physical volume.
2. Do the rest of this investigation in the command line.
3. You should now have both /dev/vda and /dev/vdb.
4. Record the size of the volume group and the amount of free space (Hint: use a command that you learned in a previous lab).
5. Read the resource Partitioning with fdisk to learn how to properly create a partition with the fdisk command.
6. Use fdisk to partition /dev/vdb with a Linux single partition that fills the whole disk.
7. Check the messages printed when fdisk exits -- you may need to reboot the system in order for the new partition table to take effect.
8. Mark vdb1 as a physical volume usable by LVM.
9. Add the new physical volume to the existing volume group.
10. Verify that the volume group is larger and has more free space.

Think!
The next part of this investigation requires some research, thought, and creativity.

Using that additional space, create a separate filesystem for /home:

1. Create the logical volume lv_home (1G ext4)
2. Find a way to move the contents of /home onto it.
3. Change your system configuration so that the new filesystem is mounted on /home from now on.

SELinux relabelling may be required
Your system may report that the files are not present in the new /home filesystem when they are clearly there. This is due to the Security-Enhanced Linux system (SELinux) preventing access to the files, because the files were tampered with (moved) and are no longer recognized as home directory content. You can fix this problem by restoring the file context labels so that SELinux accepts the files as valid home directory content: restorecon -r /home

Investigation 3: How can I use fdisk to manage storage on my disk pack?

On your c6host (i.e. "disk pack"), using your choice of the GUI and/or command-line tools:

1. Create a new partition or logical drive (NOT a logical volume!) - minimum 5G, leaving at least 10G free space in the extended partition.
2. Format that partition (i.e. put a filesystem on it).
3. Make sure it's mounted automatically on a mountpoint of your choosing (easiest is to create a new directory for a mountpoint).

Updated backup instructions

If you completed this lab correctly - please make sure you are still making full backups of your virtual machines.

Remember adding a new harddrive to centos3? You will need to back up that drive as well. If you don't - you will only have half of your machine backed up, which is of no use for a recovery.

Resources on the web

Additional links to tutorials and HOWTOs:

• archiving with tar, gzip, gunzip
• init vs systemd
• init vs systemd vs upstart
• Runlevels

Managing Run-Levels and System Services

Investigation 4: How do we Manage Runlevels?

Use centos2 and centos3
Perform these steps in both of these virtual machines.

The runlevel command is now deprecated in Fedora, and will likely be deprecated in RHEL/CentOS at some point as well, but for now this is what the industry is using.

1. Issue the following Linux command:
   • runlevel
2. Note the difference in output between centos2 and centos3.
3. You can use the init command to change the current runlevel. See a list of runlevels here. Use the man command to learn how to use the init command. Use this command to change the current runlevel in centos2 to 3. What happened? What happens after your reboot?
4. Change the default runlevel on centos2 to 3. What happens now after you reboot?
5. Issue the following Linux command:
   • startx
6. What happens?
7. Log-off your graphical system. You should return to your shell prompt.
8. Change the default runlevel for centos2 back to 5 and reboot to make sure it works.

Answer the Investigation 4 observations / questions in your lab log book.

Investigation 5: How do we Manage System Services?

Remain in your centos2 VM
Perform these steps in the centos2 virtual machine.

We have seen that maintaining unneeded packages can be a security risk due to the unnecessary increase in the complexity of your system. Similarly, it is also unnecessarily hazardous, and even more so, to leave unneeded services running. In this investigation, we will learn how to control services, and turn off those services that we think are not necessary to help reduce security risks.}}

1. Issue the following Linux command:
   • service --status-all
2. Note the services that are currently running.
3. Use the service command to stop the service named iptables
4. Issue the service command to verify that this service has stopped.
5. If you reboot now - the iptables service will be turned back on. We don't want it on though, it causes students headaches. To turn it off permanently we need to use the chkconfig command: chkconfig iptables off
6. Reboot and confirm that it's no longer running.

Answer the Investigation 5 observations / questions in your lab log book.

Completing the Lab

Arrange evidence for each of these items on your screen, then ask your instructor to check each item:

1. Compressed files: /tmp/archive1.tar.gz and /tmp/archive2.tgz
2. nled application is installed
3. Lab5 notes how to use service/chkconfig commands
4. VMs backed-up

Preparing for Quizzes

1. What is the advantage of disabling services such as bluetooth?
2. What is the difference between a .tgz file and a .tar.gz file? What do these stand for?
3. What is the purpose of a repository?
4. What is source code?
5. How do you build software from source code?
6. Which is preferred: installing from an RPM file, or installing from source code? Why?
7. How do you use service/init/chkconfig to:
   • show/set current runlevel
   • list services
   • stop a service
   • start a service
   • Why is it important to learn how to manage services?
   • Why is it important to stop certain services?

Backup your work
Backup your disk images for centos2 and centos3 Virtual Machines.