Enable Virsh Console Access For KVM Guests

To do so, log in to your guest machine via SSH or Virt-manager or Cockpit and run the following commands to enable and start a serial console:

systemctl enable serial-getty@ttyS0.service
systemctl start serial-getty@ttyS0.service

connect to console from Host
virsh console

KVM – set CPU resources

virsh vcpucount <vm_name>
virsh setvcpus <vm_name> <max-number-of-CPUs> –maximum –config
virsh setvcpus <vm_name> <number-of-CPUs> –config
virsh setvcpus <vm_name> <number-of-CPUs> –live

KVM add interface live and permanent

virsh net-list --all

 Name State Autostart Persistent
----------------------------------------------------
default inactive yes yes
inner-network active yes yes
outer-network active yes yes


virsh attach-interface --domain debian11 --type bridge --source inner --mac 52:54:00:29:5c:2e --model virtio --config --live

KVM – create new virtual network

Create new bridge

sudo ip link add <bridge-name> type bridge

Add interface to bridge

sudo ip link set <ethX> up
sudo ip link set <ethX> master <bridge-name>

Add IP address to bridge and bring it up

sudo ip address add dev <bridge-name> 192.168.0.90/24

sudo ip link set dev <bridge-name> up

Create file bridged-network.xml

<network>
    <name>bridged-network</name>
    <forward mode="bridge" />
    <bridge name="<bridge-name>" />
</network>

Add bridged-network to our KVM

sudo virsh net-define bridged-network.xml

Activate network and set autostart

sudo virsh net-start bridged-network 
sudo virsh net-autostart bridged-network

Verify

virsh net-list --all

KVM – Migrate VM to another host

1. copy the VM’s disks from /var/lib/libvirt/images on src host to the same dir on destination host
2. on the source host run virsh dumpxml VMNAME > domxml.xml and copy this xml to the destination host
3. on the destination host run virsh define domxml.xml
4. start the VM.

• If the disk location differs, you need to edit the xml’s devices/disk node to point to the image on the destination host
• If the VM is attached to custom defined networks, you’ll need to either edit them out of the xml on the destination host or redefine them as well
  1. On source machine virsh net-dumpxml NETNAME > netxml.xml
  2. copy netxml.xml to target machine
  3. On target machine virsh net-define netxml.xml && virsh net-start NETNAME & virsh net-autostart NETNAME

resize img size for QEMU / KVM

STOP VM !

Add +5G do disk

qemu-img resize chr-7.2.img +5G

Change disk size to 20G

qemu-img resize chr-7.2.img 20G

This example will convert a raw image file named image.img to a qcow2 image file.

qemu-img convert -f raw -O qcow2 image.img image.qcow2

Rescan resized partition

partprobe /dev/vdb

or

growpart /dev/vdb 1

Resize partition

resize2fs /dev/vdb1

Useful commands

virsh destroy vm_name
virsh list
virsh edit vm_name

Set CPU resources

virsh vcpucount <vm_name>
virsh setvcpus <vm_name> <max-number-of-CPUs> --maximum --config
virsh setvcpus <vm_name> <number-of-CPUs> --config
virsh setvcpus <vm_name> <number-of-CPUs> --live