Tag: kvm

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Running KVM and docker on the same host with a bridge

I have been running kvm with a bridge on my fedora machine for a while, when trying to run docker on the same host access to the kvm hosts would die as soon as docker came up. I read up online and most places mention that the two technologies should be able to co-exist with each other without any problems, after some further searching I was able to find an article that mentioned that if you have already setup a bridge for KVM you can tell docker to use this bridge. I was able to test this on my setup and it worked allowing docker to run without interfering with the existing bridge. Looking at the interfaces I can still see docker created an interface docker0 but it doesn’t seem to be active.

The docker configuration involved adding this file /etc/docker/daemon.jsonwith the following entry.
{ "bridge": "br0" }
Make sure the bridge number matches your existing bridge number in use by kvm.

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KVM usage tips

I have been playing around with KVM lately, just to see how it stacks up against VirtualBox and am loving it. I have found the following commands interesting while working with VMs.

List all VMs
virsh list --all

Start stop a VM
virsh start/stop vmName

Clone VM
virt-clone --original vmName --name newVmName --file /some/path/newVmName.qcow2

Clone VM and assign Random Mac address to new image
virt-clone --original vmName --name newVmName --file /some/path/newVmName.qcow2 --mac=RANDOM
Copy over the xml for the new clone which you can use to define your clone if moving the image to another host
cp /etc/libvirt/qemu/newVmName.xml /some/path/newVmName.xml

Shrink/Sparcify VM image
virt-sparsify --format qcow2 --compress vmName.bkp.qcow2 vmName.qcow2 --tmp /some/path
This command assumes you renamed the original VM image file to “vmName.bkp.qcow2” incase the new image has problems you can revert to original image. You can skip the –tmp argument if you have more than double the size of the VM image available in your /tmp directory. You will need to make sure you have package “libguestfs-tools” installed which supplies the sparsify command.

Delete VM
virsh undefine vmName
This removes the XMl configuration for qemu you might have to delete the VM image yourself.

List storage pools
virsh pool-list

Refresh pool data
virsh pool-refresh poolName
You will need to run this command if you delete a VM and you need to reuse the VM name you had used, so make sure you refresh the pool where your deleted image was located.

Disable autostarting of a VM

virsh autostart vmName --disable

Move VM to another system Offline
Step 1 from original host shutdown your VM, copy xml and image to backup location.

virsh dumpxml vmName > /bkpLocation/vmName.xml
cp /locationofVMs/vmname.qcow2 /bkpLocation/vmName.qcow2

Bye default if you didn’t change image storage location it will be “/var/lib/libvirt/images”. I prefer to store them in a separate partition from the OS.

Step 2 on new host get VM xml and image and enjoy.

virsh define /bkpLocation/vmName.xml
Domain vmName defined from /bkpLocation/vmName.xml
virsh start vmName

This all works if you are moving from host1 and host2 with similar cpus, for my purpose host2 had a different cpu type so I had to first create a new vm in host2 and compare the xml with my backed up copy then changed a few lines specific to CPU on host2.