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OPS235 Lab 3 - CentOS6

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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

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:

Resources on the web

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

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. Move to the appropriate sub-directory for packages that begin with the letter b.
  7. Issue the following command: rpm -i elinks-0.12-0.21.pre5.el6_3.x86_64.rpm and note the result

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.
  1. 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?
  2. Issue an RPM query to verify that elinks is installed. Record this command in your lab log-book.
  3. Issue the command: yum remove elinks
  4. Issue an RPM query to verify that elinks is no longer installed. Record this command in your lab log-book.
  5. 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.
  1. 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.

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 centos33:

Steps:

  1. Run the following commands and make note of the output:
  2.  ls /dev/vd*
     pvs
     vgs
     lvs
     df -h
    
  3. Open the centos3 virtual machine console
  4. Go to the hardware details view
  5. Click "Add Hardware" and add a new storage device of 2GBs, make sure it's a VirtIO disk.
  6. Go back to the console view
  7. Run the same ls command (performed in step 1), what's changed?
  8. Now we'll make the new device as a physical volume, add it to the volume group, and extend lv_root:
  9.  pvcreate /dev/vdb
    
     vgextend vg_centos3 /dev/vdb
    
     lvextend -l +100%FREE -r vg_centos3/lv_root
    
  10. Now rerun the ls/pvs/vgs/lvs/df commands. What has changed and what caused those changes?
  11. 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).
  1. 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?
  2. 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.
  3. Create a new 3G LV (LV Properties: linear) containing an ext4 filesystem named lv_archive and mount it at /archive
  4. 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).
  1. Shrink the size of lv_archive to 1 GB.
  2. Try shrinking the home file-system. What happens? Why?

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

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.

Completing the lab

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

Notes:

  1. rpm command options
  2. yum command options
  3. How to use pvs/vgs/lvs/df/pvcreate/vgextend/lvextend
  4. Answer to this question "What is the license of the nautilus package?"

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:

  1. elinks installed on the host (disk pack - main system c6host).
  2. Unnecessary/unused packages have been deleted (list at least 4, and show that they are no longer installed).
  3. Fresh backup of the virtual machines.

Preparing for Quizzes

  1. What is a VG? PV? LV?
  2. What commands are used to determine VG / PV / LV information?
  3. What does yum do that rpm does not?
  4. List the steps to install a package via rpm command.
  5. List the steps to determine detailed information regarding an install package.
  6. List the steps to remove a package via rpm command.
  7. List the steps to install a package using the yum command.
  8. List the steps to remove a package using the yum command.
  9. What is the total size of the "main" VG on your system?
  10. How do you create a LV?
  11. How do you delete an LV?
  12. How would you increase the size of the root filesystem by 50 MB?