Introduction
Having the ability to run a Kernel Basd Virtual Machine (KVM) on a hosted solution is a luxury you won’t easily find on most cloud providers (Amazon, Google, Azure). On my hosting provider, I can get a quad core i7 32gb RAM server for less than 70 euros / month, a fraction of the cost that you would pay with a cloud provider.
I tought it might be interesting to see what kind of virtualization options I had on Centos and stumbled upon KVM, LibVRT and Qemu.
Installing some software
yum -y install qemu-kvm libvirt virt-install bridge-utils
yum -y install kvm virt-manager libvirt virt-install qemu-kvm xauth dejavu-lgc-sans-fonts
yum -y install /usr/bin/virt-sysprep
Verify install
[root@CentOS-72-64-minimal ~]# lsmod | grep kvm
kvm_intel 162153 12
kvm 525409 1 kvm_intel
Verify service
[root@CentOS-72-64-minimal ~]# systemctl status libvirtd
● libvirtd.service - Virtualization daemon
Loaded: loaded (/usr/lib/systemd/system/libvirtd.service; enabled; vendor preset: enabled)
Active: active (running) since Sat 2017-03-18 13:32:02 CET; 8h ago
Docs: man:libvirtd(8)
http://libvirt.org
Main PID: 11490 (libvirtd)
Memory: 6.1G
CGroup: /system.slice/libvirtd.service
├─11490 /usr/sbin/libvirtd
├─11563 /sbin/dnsmasq --conf-file=/var/lib/libvirt/dnsmasq/default.conf --leasefile-ro --dhcp-script=/usr/libexec/libvirt_leaseshelper
└─11564 /sbin/dnsmasq --conf-file=/var/lib/libvirt/dnsmasq/default.conf --leasefile-ro --dhcp-script=/usr/libexec/libvirt_leaseshelper
If the service isn’t started, start it using
systemctl status libvirtd
Creating a VM
You can create virtual machine with the following command
virt-install --name centos7 --ram 4096 \
--disk path=/var/kvm/images/centos7.img,size=30 \
--vcpus 2 --os-type linux --os-variant rhel7 \
--network bridge=virbr0 --graphics none --console pty,target_type=serial \
--location 'http://ftp.iij.ad.jp/pub/linux/centos/7/os/x86_64/'
--extra-args 'console=ttyS0,115200n8 serial'
The command above will start the installation process. You can then continue the text based installation and let it boot. Aftr the installation you can shutdown the machine.
you can always return to the host by pressing CTRL-].
Executing virsh console centos7 will get you back into the VM.
Commands
Starting VMs
virsh start centos7
virsh start centos7 --console
Stopping VMs
virsh shutdown centos7
virsh destroy centos7
Console VMs
virsh console centos7
Removing VMs
virsh undefine centos7
Cloning a VM
Now that you’ve done the entire installation of a VM, it might be interesting to make a clone of it.
Create a clone by issueing the following command
virt-clone --original centos7 --name template --file /var/kvm/images/template.img
This will generate a template.xml file and a tmplate image in the provided location.
Now that we have a template, it’s very easy to create some additional VMs basd on that template.
virt-clone --original template --name centos-a --file /var/kvm/images/centos-a.img
virt-clone --original template --name centos-b --file /var/kvm/images/centos-b.img
virt-clone --original template --name centos-manager --file /var/kvm/images/centos-manager.img
Importing an existing template
If you ever want to migrate VMs on another machine, its sufficient to copy the image file and the xml file, and execute the command below:
virsh define template.xml
File storage
Where does all of this get stored ?
- XML files are located in
/etc/libvirt/qemu/ - Image files are located in
/var/kvm/images/