[CentOS] Live CD boot for KVM guest. How?

Ljubomir Ljubojevic office at plnet.rs
Thu Oct 20 17:36:32 EDT 2011


Vreme: 10/20/2011 10:22 AM, Müfit Eribol piše:
> On 19.10.2011 21:07, Ljubomir Ljubojevic wrote:
>> Vreme: 10/19/2011 06:34 PM, Müfit Eribol piše:
>>> Hi,
>>>
>>> My host and guest are CentOS 6. The guest is going to be a web server in
>>> production. I am trying to resize (extend) of the base partition of my
>>> guest.  But I can of course start the installation of CentOS 6 guest all
>>> over again with a larger image size. However, just for the sake of
>>> better understanding I an trying to solve things not to be end up in a
>>> dead end after some years.
>>>
>>> 1. I created a guest CentOS 6 with 12G total disk (on a iscsi drive). No
>>> Desktop, just for terminal use. No LVM, just a simple basic partitioning.
>>> 2. Later I wanted to increase the size of total image to 200G.
>>> 3. I managed to resize the image to 200G on my iscsi drive. So, there is
>>> 188G unallocated/unformatted volume within the guest image.
>>>
>>> Now, the hardest part. I have to resize the partition. I have been
>>> trying to find a way to do that. A search on Google showed that GParted
>>> is tool to do that. I had to install all Desktop and X as Gparted is a
>>> GUI tool. Installed vncserver. Then, I found out that GParted can not
>>> resize the live guest. So, I downloaded GParted Live CD.
>>>
>>> Now, the questions:
>>>
>>> 1. If it was a physical machine I would boot from the CD. If I can boot
>>> it from host CDROM but then how should I operate on a specific guest?
>>> What is the easiest way to access GUI of the guest if I boot from Live CD.
>>> 2. I am wondering if a simple LVM route at the beginning would be
>>> preferred. Changing size of the iscsi volume on my NAS is easy. I
>>> thought there was no need for more complication, so went with basic
>>> /boot / and swap partitions. Is resizing partitions for LVM easier than
>>> basic partitioning (without LVM)?
>>> 3. Is there a specific tool in KVM suit which performs resizing
>>> partition within the image? Or as I prefer command line tools, is there
>>> a way to achieve resizing without any graphical tool like GParted? With
>>> GParted I had to install all the X and Gnome files, vncserver which
>>> otherwise I don't need.
>>>
>>> I would appreciate any information/hint/experience.
>>>
>>> All the best.
>> Hi.
>>
>> My view is:
>>
>> a) Use LVM so you can manipulate size of partition(s). Resizing etx4
>> partitions is horrible job, long and dangerous.
>>
>> b) You can mount ISO image file of any CD via Guests VirtualCD, no need
>> to mess with physical CD/DVD drives. There is System Rescue CD, CentOS
>> LiveCD (I have one 5.3 with mdadm raid support and bunch of tools,I will
>> soon be making 6.1 version) or Hiren's Boot CD - Parted. Root partition
>> needs offline resize since extX partitions can not be mounted at the
>> time of the resizing.
>>
>> c) All text-based resize tools require higher knowledge and/or
>> experience, like alignment to sectors and similar mambo-jumbo. When you
>> need to make it happen on production server without experimentation and
>> you have done it only once 3 years ago it IS mambo-jumbo.
>>
>> d) As far as I know, KVM can not mount virtual hard drives, so meesing
>> with them is not an option, unless you use "raw" partition on the Host
>> (still haven't tried it).
>>
>
> It is good to know at the very beginning that LVM is the way to go. So,
> I am reinstalling the server with LVM. It is good to know about it so early.
>
> Just for learning, could you please provide some more info about booting
> up the LiveCD ISO image (uploaded to the host) to work on a guest? How
> is the command line?
>
> Thank you for your kind help.
>
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>

Sorry, I do not use command line for KVM. I use my Desktop to connect to 
Servers KVM Domain:

Virtual Machine Manager -> File -> Add New Connection -> Fill: 
Hipervisor: QEMU/KVM; Connect to remote host; Metod: SSHl username + 
password; Hostname: xxx

And you should have full access to your servers KVM domain.

But even if you need to use command line, I am sure you will be able to 
find it by googling for "kvm linux boot from cd command line".

Also check out CentOS-virt mailing list Archive (on this same mailing 
list server).

http://www.linux-kvm.org is official site for KVM.

-- 

Ljubomir Ljubojevic
(Love is in the Air)
PL Computers
Serbia, Europe

Google is the Mother, Google is the Father, and traceroute is your
trusty Spiderman...
StarOS, Mikrotik and CentOS/RHEL/Linux consultant


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