Changes

<u>Main Objectives</u> :* Using '''LVM''' to '''resize partitions graphically and via commandscommand-line'''.

:* Manually Connecting connect and Disconnecting Directories disconnect directories (mount points) to existing partitions ('''mount''', '''umount''').

:* Create a Bash Shell Script script to '''monitor and report low disk size''' (run periodically in '''crontab''').

*[http://v1code.corenominaltutsplus.orgcom/howtotutorials/scheduling-setuptasks-awith-crontabcron-file/ jobs--net-8800 Using crontab]

Monitoring and ensuring adequate space for a Linux file-system is considered to be an important a critical task for a sys adminany system administrator. An application called '''LVM ''' is a very useful tool for Linux system adminstrators.administrators to easily manage file systems - even when the computer system is running!

'''LVM''' ('''Logical Volume Management''') is used to manage hard disk drives / partitions for Linux and Unix/Linux systems. LVM provides more flexibility than just working with partitioning 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.

[[Image:Ops235_lab4_1lvm1.png|thumb|500px|right|The '''system-config-lvm''' application allows the Linux system administrator to manage LVMs Graphically. Your LVM information for '''centos2''' VM should be similarly displayed.]]

# Launch your '''centos2''' VM and open a shell terminal.# CentOS provides a tool called '''system-config-lvm''' to graphically administer LVM. Install <br><br>'''NOTE:''' This tool may be replaced by a future graphical LVM management tool and is NOT currently available in the default repositories. We will now perform a "work-around" in order to make the system-config-lvm application by utility work in our system.<br><br># Issue the following command to download the system-config-lvm rpm:<br><b><code><span style="color:#3366CC;font-size:1.2em;">wget https://kojipkgs.fedoraproject.org//packages/system-config-lvm/1.1.18/1.fc19/noarch/system-config-lvm-1.1.18-1.fc19.noarch.rpm</span></code></b><br>(Although it is an rpm file for the Fedora Distribution, it will also work for Centos7).<br><br># Make certain that you are logged in as '''root'''.# Try issuing the command: <b><code><span style="color:#3366CC;font-size:1.2em;">yum install rpm -i ./system-config-lvm-1.1.18-1.fc19.noarch.rpm</span></code></b><br>You should notice an error.# Use the '''yum install''' command to resolve the following dependencies:<ul><li><b><code><span style="color:#3366CC;font-size:1.2em;">yum install gnome-python2-bonobo</span></code></b></li><li><b><code><span style="color:#3366CC;font-size:1.2em;">yum install gnome-python2-gnome</span></code></b></li><li><b><code><span style="color:#3366CC;font-size:1.2em;">yum install usermode-gtk</span></code></b></li></ul><br>

<li value="38">Open a shell as root and run Re-issue the command: <b><code><span style="color:#3366CC;font-size:1.2em;">rpm -i ./system-config-lvm-1.1.18-1.fc19.noarch.rpm</span></code></b><br>It should work this time.</li><li>Run the command: <b><code><span style="color:#3366CC;font-size:1.2em;">system-config-lvm</span></code></b></li><li>On the left-hand side, you can click on the '''Volume Group''', '''Physical Volume ''' and '''Logical Volumes ''' and view their properties on the on the right-hand side.</li><li>Determine the current LVM configuration by clicking on the appropriate element and reading the properties in the right-hand panel -- write down the answers:

<li>What is the name and size of the '''Physical Volumes'''?s</li> <li>What are the names and sizes of the '''Logical Volumes'''s?</li> <li>Is there any space in the VG which is not allocated to a LV?<br><br></li>

<li>Perform the following steps in Click on '''Logical View''' (i.e. above home, root, swap) and then click '''Create New Logical Volume''' button. What happens? Why do you think this application to increase the size of happened?<br><br>We will now create another partition ('''/dev/vda3''') using the '''homefdisk''' fileutility, format this newly-system to created partition so we can create another logical volume called '''4 GBarchive''':.<br><br> </li> <ol type="a"li>Quit the '''system-config-lvm''' application.</li> <li>On In the terminal as root, issue the leftcommand: <b><code><span style="color:#3366CC;font-hand sidesize:1.2em;">ls /dev/vd*</span></code></b><br><br>'''NOTE:''' If nothing displays, click on issue the command: '''Logical Volumels /dev/sd*''' containing the and use that device pathname '''home/dev/sda''' fileinstead.<br><br> <li>Issue the command: <b><code><span style="color:#3366CC;font-systemsize:1.2em;">fdisk /dev/vda</span></code></b><br>(or ''fdisk /dev/sda'' if the previous command didn't work)</li> <li>Click on At the fdisk prompt issue the command: '''Edit Propertiesp'''.What does this do?</li> <li>Change Now issue the commands '''n''' (new partition), '''p''' (primary partition), '''3''' (i.e. next available partition number). When prompted for initial block, '''press enter to accept the default beginning block size to '''4 GB, and '''type: +2G''' at ending block (create 2GB for partition) and click '''Okpress enter'''.</li> <li>Verify that At the fdisk prompt, issue the command '''p''' to review the partition information, then type '''homew''' file-system has increased in sizeto save partition table and exit (ignore WARNING message).</li> <li>You <u>'''must'''</u> restart your centos2 VM to allow changes to take effect</olli> <li>Create Open a terminal as root, and format your newly-created partition by issuing the command: <b><code><span style="color:#3366CC;font-size:1.2em;">mkfs -t ext4 /dev/vda3</span></code></b><br>(or ''mkfs -t ext4 /dev/sda3'new 3G LV')</li></ol>{| width="40%" align="right" cellpadding="10"|- valign="top"|[[Image:lvm3.png|thumb|right|500px|What '' (LV Properties: linear) containing an 'system-config-lvm''ext4'display should appear after using '' filesystem named: 'fdisk''lv_archive'to create new partition (/dev/sda3), '' and mount it at: 'formatting''/archive'partition, '' <li>Let's see what happens when we copy data over adding partition to '''lv_archiveLVM''', and then '''reduce the size of lv_archiveallocating partition'''to our default volume group. Complete the following steps below]]|[[Image:lvm4.png|thumb|right|200px|Creating a new logical volume from our newly created physical volume]]|}<ol> <ol typeli value="21">'''Restart the system-config-lvm utility'''. Do you see a"new /dev/sda3 partition under Physical Volumes?</li> <li>Issue To add the newly created partition, you need to add it into LVM to be used. '''Exit the system-config-lvm utility''' and '''issue the following commandto add the partition into LVM: '''<br><b><code><span style="color:#3366CC;font-size:1.2em;">cp -R pvcreate /etc/* dev/archive vda3</span></code></b> (or ''pvcreate /dev/sda3'' ) (enter '''y''' to proceed - ignore warning)</li> <li>Shrink the size of '''lv_archiveRestart system-config-lvm'''. You should notice a section at the bottom indicating <u>Unallocated</u> Physical Volumes. Click on the <u>unallocated</u> partition /dev/vda3 and then click ''' Add to Existing Volume Group'''1 GB(click on other button in next screen to continue). The screen should now show the partition ''/dev/vda3''contained in our default Volume Group (refer to diagram on right-side for reference). What happens?</li> <li>If you could not shrink Click on Logical View (i.e. above home, root, swap), and then click on '''Create New Logical Volume''' button and fill out the details for this new logical volume including: size of : '''1GB''', LV Properties: '''linear''', file system: '''lv_archiveext4''' file system name: '''archive''', what do you think is select '''mount''' and mount it at: '''/archive'''. Have the system create the cause directory ''/archive'' if it does not exist (Refer to diagram on right for reference).</li> <li>Confirm that this new Logical Volume now exists by changing to the problemdirectory /archive. Did you need to restart your centos2 VM to confirm that the '''/archive''' directory is now on your '''centos2''' VM?</li>  </olli>Use system-config-lvm to resize (i.e. edit) the '''archive''' logical volume to '''1.5 GB''' and verify your results.</li>

Let's say that you have run out of disk space on your '''centos3''' VM, and you need more space on the root file-system, perhaps in order to host more webpages web-pages, or to support a larger database or new software. What are your options? Getting a replacement hard-drive would probably require re-installation of the operating system and backup/restore of or backing up and restoring data on the dataold hard disk.

Because we're using LVM we can avoid this problem. We can '''add a new <u>virtual</u> hard-drive''' (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. Creating virtual hard drives is not only inexpensive, but a great way for students to learn now to simulate growing the size of the file system.

<li>Open At the '''centos3 virtual machine top of your VM window (make certain <u>Detailsnot</u>full screen mode) click the ''' view.''' menu and change view from '''Console''' to </liu> Details<li/u>Go to the '''hardware details''' view.</li> <li>Click At the bottom left-hand corner, click '''Add Hardware''' and add a new storage device of '''2GBs''', make sure itthe '''s a Bus type''' is selected as: '''VirtIO disk'''.<br><br>'''NOTE: Make certain to click "select managed or other existing storage", and fill in the pathname circled in red as shown in the diagram on the right-hand-side.<br><br>'''</li>

<li>Read the resource [ [http://tldp.org/HOWTO/Partition/fdisk_partitioning.html Partitioning with Use '''fdisk] ] ''' (''refer to learn how to properly use in Part 1'') to create a new single primary partition with for '''/dev/vdb''' that fills the entire disk, save partition table (accepting defaults prompts would work), restart your '''fdiskcentos3''' command.</li> <li>Use VM and then '''fdiskformat''' to that partition for file type: '''/dev/vdbext4''' with a Linux single partition that fills the whole disk.</li> <li>Check the messages printed when <code>fdisk</code> exits -- you may need to reboot the system in order for the new partition table to take effect. <li>Now we'll make the new device a '''physical volume''', add it to the '''volume group''', and extend '''lv_root''':</li>

:: <b><code><span style="color:#3366CC;font-size:1.2em;">pvcreate /dev/vdbvdb1</span></code></b>(enter '''y''' to proceed - ignore warning)

:: <b><code><span style="color:#3366CC;font-size:1.2em;">vgextend vg_centos3 /dev/vdbvgs</span></code></b>(to determine: ''name_of_volumegroup'')

:: <b><code><span style="color:#3366CC;font-size:1.2em;">vgextend ''name_of_volumegroup'' /dev/vdb1</span></code></b> :: <b><code><span style="color:#3366CC;font-size:1.2em;">lvextend -L +2G -r vg_centos3''name_of_volumegroup''/lv_root</span></code></b>

|{{Admon/note|LVM Safeguards When Reducing File System Size|In older versions of LVM, the system administrator had to be careful when reducing the size of Linux file-systems using LVM. This usually required to separate operations:<ul><li>Reducing the file-system to make room (''resize2fs'')</li><li>Reduce the logical volume by using the '''lvreduce''' command</li></ul><br>This used to be performed to prevent a catastrophic loss of data if the logical volume was resize smaller than the available space on the file-system.<br>The newer LVM commands have "safeguards" (eg. option '''-r''' to prevent destroying the file-system (thus making the ''resize2fs'' command <u>obsolete</u>). '''|}}

<li>Among the changes, note that your root file-system is now 2GB bigger, and you have not even rebooted your machinesince you used fdisk to create a partition!</li> <li>Reduce the size of the '''lv_root''' partition by '''1GB''' by issuing the following command:<br><b><code><span style="color:#3366CC;font-size:1.2em;">lvreduce vg_centos''name_of_volumegroup''/lv_root --size -1G</span></code></b></li>Confirm that the file system has been reduced.</li><li>Increase the size of the '''lv_root''' partition by another '''1GB''' by issuing the command:<br><b><code><span style="color:#3366CC;font-size:1.2em;">lvextend vg_centos''name_of_volumegroup''/lv_root --size +1G</span></code></b></li><Confirm that the file system can been increased.</li><li>Record the LVM Management commands in your lab log-book.</li>

We take for granted that a file-system must be mounted (for example the root partition) in order for a Linux system to be usable upon system start-up. This was create automatically for the '''/archive''' mount point automatically when we used the system-config-lvm utility in the previous investigation. We need to learn now to do this manually by editing or adding an entry in the ''/etc/fstab'' file. The '''/etc/fstab''' (file system table) contains entries to mount various file systems automatically upon start-up of the Linux system.

The Linux sys admin system administrator also has the ability to manually '''mount''' (connect) and '''un-mount''' (disconnect) partitions in order to perform maintenance on the file system (for example un-mounting the '''/home''' partition to install software and prevent users from logging in during that process).

# Perform this Part part in your '''centos2''' VM.# As you may recall in Part 1 of Investigation 1, we created another logical volume called lv_archive '''archive''' using the graphical application '''system-config-lvm'''. This logical volume should be mounted (connected) to our existing file-system (2GB).

# What is the purposed of issuing this command without arguments? Can you see the lv_archive partition'''/archive''' mount point?# Create a new Confirm that the directory called named '''/archive'''is mounted.# You can use the '''umount''' command to unmount a file-system (eg. for maintenance purposes). Note the the name of the command is umount, <u>not</u> unmount.# Issue Make certain you are not located in the /archive directory, and issue the following commandto unmount the /archive directory: <br><b><code><span style="color:#3366CC;font-size:1.2em;">mount /dev/vdb -t ext4 umount /archive </span></code></b># Issue the '''mount''' command (without arguments) to verify that the '''lv_archive''' logical volume is mountedconfirm it has been unmounted.# Without changing to the '''/archive''', list View the contents of that directory.# Issue the file-system table /etc/fstab by issuing the following command: <br><b><code><span style="color:#3366CC;font-size:1.2em;">umount cat /etc/archive fstab</span></code></b># Issue Note the line that automatically mounts a file-system (''/dev/sda3'', type 'mount'ext4'' command ) to verify that lv_archive logical volume has been unmounted'''/archive'''.# Although This was automatically performed for you might have been successful unvia the '''system-mounting the lv_archive logical volume, can you think of any reasons why you might not be able to unconfig-mount that logical volume? lvm''' utility.# Quickly view View and record the tutorial about fields for the <b>[http:'''//man7.org/linux/man-pages/man5/fstab.5.html /etc/fstab]</b> file to understand the purpose of this file archive''' mount in your lab logbook, and the major elements contain in this file.# Issue then issue the following commandto reconnect or mount '''/archive''': <br><b><code><span style="color:#3366CC;font-size:1.2em;">echo "mount &nbsp; -t ext4 &nbsp; /dev/vdb centos_centos2/archive ext4 defaults 1 1" >> &nbsp; /etc/fstabarchive</span></code></b><br><br>'''NOTE:''' If you are having problem mounting, use the /dev pathname listing in your /etc/fstab file.<br><br># Confirm that those contents this file-system has been properly mounted. Note: You could have been added also issued the command: '''mount -a''' to <u>automatically</u> mount the file-systems contained in the bottom of '''/etc/fstab'''file.# Issue <br><br>Tip: If you had to do manually configure /etc/fstab (eg. only in text-based mode - centos3), you could have issued the command(as root): <br> <b><code><span style="color:#3366CC;font-size:1.2em;">mount -aecho "/dev/centos_centos2/archive /archive ext4 defaults 1 2" >> /etc/fstab</span></code></b><br>(although we don't need to do this, since it was already done).<br><br># Check to see if '''/archiveA curious question''' is now mounted. What do you think : If root needs to unmount the above operation did? Confirm by rebooting your VM to see if '''/archivehome''' is mounteddirectory for maintenance but we had to first login in graphically as a regular user, then su to "root", isn't our regular user still logged in so we can't un-mount the /home directory?!? How can we as a Linux System Administrator get around the problem (hint: you already learned it somewhere in lab3!!! Wow, using what we already taught can pay-off in the future ... lol!).  

Monitoring disk space activity helps provide Linux system administrators information to help take corrective actionbefore problems can occur.

# The methods to monitor potential penetration to a Linux system are too numerous, and are taught in other coures (for example: SEC520). On method of monitoring potential penetration is to look for abnormally large files. Issue the command:<br><b><code><span style="color:#3366CC;font-size:1.2em;"> find -P / -size +10000k –print100000k</span></code></b>

|{{Admon/tip|Bash Shell Scripting Tips:|<br><ul><li>'''Using awk to Manipulate Text:'''<br><br>Legend has it that the '''awk''' command was invented by three C programmers that wanted to create a utility in Unix that had programming syntax more like C programming (awk stands for the first letter in each person's name). People started to use the command and found it very useful for report generation and file repair or manipulation.<br><br>The command mimics a C program, with braces '''{ }''' that surround the action to perform based on records from a database file matching either test conditions, regular expressions, etc. Fields appear as numbers appear surprisingly similar to positional parameters (eg. with $1, $2, ... etc).<br><br>'''<u>Examples</u>:'''<br><br>''awk '{print}' data-file.txt''<br><br>'''<br><br>''awk -F";" '{print $5,$3}' data-file.txt''<br><br>''awk -F"," '$4 &gt;&#61; 10000 {print $1, $2}' employee-incomesalary.txt''</li></ul>}}

We will now use This emphasis on this section focuses on how to run useful shell scripting scripts or shell script that we have created at specific dates/times. It would be silly to expect a system administrator to stay up late (eg. 2 a.m.) to help automate the task for manually run a shell script to terminate processes or to re-boot Linux administrator servers. Database files (tables) are used to provide instructions on how frequent shell scripts or commands can be notified run. The '''cron''' daemon is used to refer to these files and to run them on a pre-determined basis. The term '''cron''' comes from the old word '''chronograph''' meaning a special type of potential disk space issueswatch (actually a ''stop-watch'') to help monitor and schedule routine tasks.

#Try to understand what these this Bash Shell scripts doscript does (refer to man pages for the '''awk''' command), and then run the script as root.

<li value="45">Quickly view the tutorial about the <b>[http://v1code.corenominaltutsplus.orgcom/howtotutorials/scheduling-setuptasks-awith-crontabcron-file/ jobs--net-8800 Using crontab]</b> file to understand the purpose of this

<li>Issue the following command to setup a crontab entry for root:<br><b><code><span style=" pointer-events:none;cursor:default;color:#3366CC;font-size:1.2em;">crontab -e</span></code></b></li><li>Enter the following line in order to run at 6:00 on the first day of every month:<br><b><code><span style=" pointer-events:none;cursor:default;color:#3366CC;font-size:1.2em;">0 6 1 * * /root/monitor-disk-space.bash #Runs at first day of each month (6:00 am on the first day of every month)</span></code></b></li><li>'''Save ''' the file crontab entry.</li><li>Confirm that the entry was properly saved by issuing the following command:<br><b><code><span style=" pointer-events:none;cursor:default;color:#3366CC;font-size:1.2em;">crontab -l</span></code></b></li></ol>

{{Admon/important|Time for a new backup, INCLUDING YOUR VIRTUAL HARD DRIVE!|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 <br><br>''centos1'' Virtual hard-- you now have two virtual disks on ''centos1'', and therefore two drives created in this lab are image files, and therefore will now need two backup filesto be backed up as well!'''.}}

::<ol><li><span style="color:green;font-size:1.5em;">&#x2713;</span> x:'''centos2''' VM:<blockquote><ul><li>'''Logical Volume''', '''Physical Volume''', and '''Volume Group''' information </li><li>Contents of '''/etc/fstab''' file</li><li>Proof that '''/archive''' has been mounted</li></ul></blockquote><li><span style="color:green;font-size:1.5em;">&#x2713;</span> x:'''centos3''' VM:<blockquote><ul><li>Proof of virtual hard disk creation</li><li>'''Logical Volume''', '''Physical Volume''', and '''Volume Group''' information </li></ul></blockquote></li><li><span style="color:green;font-size:1.5em;">&#x2713;</span> x:'''c7host''' Machine:<span style="colorblockquote><ul><li>Proof of creation of the shell script:green;font'''monitor-disk-size:1space.5em;"bash'''</li><li>Crontab entry for '''root''' account</li></ul>&#x2713;</spanblockquote><li> x::<span style="color:green;font-size:1.5em;">&#x2713;</span> x'''Lab5''' log-book filled out.</li></ol> 

= Preparing for the = Practice For Quizzes , Tests, Midterm &amp; Final Exam ==

# How do you create a an LV?# How do you delete resize an LV?

# How can you determine if a partition has been mounted onto a system?# How can you unmount an existing partition from the file-system?# How can you temporarily mount a partition on a file-system?# How can you permanently mount a partition on a file-system upon boot-up?# What is are the purpose separate elements (fields) of the '''/etc/fstab'''file?# Describe the tools that a Linux system administrator have to monitor disk space usage.