snapshots of UEFI libvirt-based (KVM) virtual machines

Shut down VM and then

Listing
qemu-img snapshot -l <file>.qcow2

Create
qemu-img snapshot -c <snap-name> <file>.qcow2

Revert to 
qemu-img snapshot -a <snap-name> <file>.qcow2

Delete
qemu-img snapshot -d <snap-name> <file>.qcow2

KVM Snapshot with only one disk

virsh snapshot-create-as --domain ${VM}
--name "backup-${VM}" \
--atomic \
--disk-only \
--no-metadata \
--diskspec vda,file=${SNAP}/backup-snapshot-${VM} \
--diskspec vdb,snapshot=no

KVM add device

Add hostdev for VF in <devices>. In <source>/<address> use physical address for VF

<hostdev mode='subsystem' type='pci' managed='yes'>
     <source>        
         <address domain='0x0000' bus='0x5e' slot='0x0e' function='0x0'/>
    </source>      
    <address type='pci' domain='0x0000' bus='0x07' slot='0x01' function='0x0'/>  
</hostdev>

KVM install VM with vnc server

Install from img file (with disk size 15G and bridge name inner)

virt-install \
--name=bull \
--vcpus=8 \
--memory=24576 \
--disk path=/var/lib/libvirt/images/bull.qcow2,size=15 \
--cdrom /var/lib/libvirt/iso/debian-11.6.0-amd64-netinst.iso \
--network bridge=inner,mac=52:54:00:40:4a:5e \
--boot hd,uefi \
--machine q35 \
--osinfo detect=on,require=off \
--graphics vnc,listen=<IP_HOST_TO_LISTEN_TO>,password=<SECRET>

Install from PXE

virt-install \
--name=rhpxe \
--vcpus=4 \
--memory=2048 \
--network bridge=br0,mac=52:54:00:0e:27:FF \
--pxe \
--disk none \
--boot uefi \
--osinfo detect=on,require=off \
--graphics vnc,listen=<IP_HOST_TO_LISTEN_TO>,password=<SECRET> 

KVM – VNC Server from remote host

<graphics type=”vnc” port=”5900″ autoport=”yes” listen=”SERVER_IP” passwd=”SECRET_PASSWORD”>
<listen type=”address” address=”SERVER_IP”/>
</graphics>

KVM validate xml

Dump

virsh dumpxml debian11 > test.xml
virt-xml-validate test.xml

KVM Snapshots

Convert snapshot to standalone image

qemu-img convert -O qcow2 <snapshot.img> <new-image.img>

Create

virsh snapshot-create-as --domain debian11 --name debian11_snapshot01

List

virsh snapshot-create-as --domain debian11 --name debian11_snapshot01

Restore

virsh snapshot-revert debian11 debian11_snapshot01

Delete

virsh snapshot-delete --domain debian11 --snapshotname debian11_snapshot01

Info

virsh snapshot-info --domain debian11 --snapshotname debian11_snapshot01

KVM – detach disk

sudo virsh detach-disk --domain test --persistent --live --target vdb

KVM – Add / Attach Disk

Create disk:
qemu-img create \
-f qcow2 \
-o lazy_refcounts=on,preallocation=falloc \
$FILEPATH \
[size]G

qemu-img comes with various options for setting the allocation when creating new disk images.

preallocation=metadata – allocates the space required by the metadata but doesn’t allocate any space for the data. This is the quickest to provision but the slowest for guest writes.

preallocation=falloc – allocates space for the metadata and data but marks the blocks as unallocated. This will provision slower than metadata but quicker than full. Guest write performance will be much quicker than metadata and similar to full.

preallocation=full – allocates space for the metadata and data and will therefore consume all the physical space that you allocate (not sparse). All empty allocated space will be set as a zero. This is the slowest to provision and will give similar guest write performance to falloc.

Convert disk:
mv disk.qcow2 disk.qcow2.bak
qemu-img convert -O qcow2 -o lazy_refcounts=on,preallocation=falloc disk.qcow2.bak disk.qcow2


Attach disk:
virsh attach-disk [vm ID] \
--source /path/to/disk.qcow2 \
--target vd[x] \
--persistent \
--subdriver qcow2

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