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==LVM Tools==
[[Image:lvm1.png|thumb|300px400px|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.]]
* There are is a choice for managing LVM: Graphically or via Command-Line.
* A graphic program is called: '''system-config-lvm'''. This graphical application is useful, but may be deprecated (i.e. "being phased out").
* There are various commands to manage LVM (some include):
:*'''pvs'''
:*'''lvs'''
== Any Simple Comparisons for LVM !?! ==
'''Certainly... Think of Using LVM like "building a cake":'''
* A cake needs to rest on a '''platter'''.
'''Need a Bigger Cake? Add More Layersfor the unexpected guests!'''
* We can grow a larger cake by adding more <u>layers</u>.
'''Logical Volumes are like the "Hungry Unexpected Guests" at the Party (ai.ke.a the "cake inhalers"larger number of guests that expected)'''
* As hungry guests sample some can and want more, they can grab more layers of cake.
==Additional File System Maintenance==
[[Image:mount.png|thumb|400px700px|right|Using the '''mount''' command with no arguments displays file-systems that are already mounted. The Linux system administrator can use the '''mount''' and '''umount''' commands to connect and disconnect different partitions from the file-system to perform maintenance.]]
'''<u>Mounting and Un-Mounting File-Systems</u>'''
The Linux 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). Those command are called: '''mount''' and '''umount''' (that is NOT a typo)!
A useful example of un-mounting and mounting manually would be if a software update is to be performed, and users are not allowed to access the system. In this case, the system administrator could send an alert for the users to log-off the system due to system maintenance, un-mount the '''/home''' directory to prevent any regular users to login, and then update the software. Once the software has been updated, then mount the '''/home''' directory to allow user access.
[[Image:disk_usage.png|thumb|700px|right|The '''df''' and '''du''' commands are useful tools for Linux system administrators to flag disk space issues and investigate their causes.]]
Since administrators may need to log into the system with their regular user accounts, and then issue the '''su''' command to connect into the '''root''' account, there is a dilemma: How can /home be unmounted when you are logged in as a regular user. The solution would be to reboot the machine and boot into single-user mode (demonstrated in '''lab3'''). This allows the system administrator to connect into the system in a text-based system automatically logged in as root. Remember that '''the root account has its own home directory''' (i.e.'''/root''') which is not associated with the ''/home'' directory (which can now be un-mounted and mounted for system maintenance).
'''<u>Monitoring File System Space</u>'''
Another essential duty of a Linux system administrator is to anticipate problems and take preventative measures to avoid computer system problems <u>before</u> that occur.
'''crontab -r''' (remove crontab file)
<pre style="font-size:14pt">
.---------------- minute (0 - 59)
* * * * * command to be executed
</pre>
(NOTE: The asterisk (*) indicate to run for that unit of time. Below is an example ) <u>'''Example of crontab entriesentry (using the ''crontab'' command to edit the '''/etc/crontab''' file)'''</u> <pre style="font-size:14pt;font-family:courier;"># Check every minute for logins by user “elvis”* * * * * who | grep 'elvis'
# Run a script called "ascript.bash" every odd hour (1,3 5...) during the week
# Run "ascript.bash" every half hour during the week
# Same... just doing it a different way
</pre>
# What is a VG? PV? LV?
# What is the total size of the "main" VG on your system?
# How do you create a an LV?# How do you delete resize an LV?
# How would you add the disk partition '''/dev/sdb7''' to your volume group "main"?
# How would you increase the size of the root filesystem by 50 MB?
