[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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> CentOS at centos.org
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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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