Basic KVM operations
SEE ALSO!
List all the VMs, and see which ones are running
# sudo virsh list --all
Start, stop, reboot a VM
Start
You can list the VMs first, then:
# sudo virsh start <name of your vm>
Shutdown
Note: this require the VM to have support for ACPI - at the moment it doesn't seem to work with windows VMs (seems OK to me- Jo).
# sudo virsh shutdown <name of the vm>
Reboot
# virsh reboot <name of the vm>
Destroy
Same thing as taking the plug off. Use with care.
# sudo virsh destroy <name of the vm>
Guest start on boot ( Autostart )
sudo virsh autostart $VM_ID or sudo virsh autostart --disable $VM_ID
Delete a VM
THIS REMOVES A VM. NO RESTORE POSSIBLE. PLEASE USE WITH SPECIAL CARE.
# sudo virsh shutdown <name of the vm> # sudo virsh undefine <name of the vm> # sudo rm -rf /var/lib/kvm/<name of the vm>
Back up a VM
After shutting down:
# cd /var/lib/kvm # cp -R <name of the vm> /to/safe/place
Copy or move a VM to another host
Copy the VM image to remote server in /tmp dir (make sure the VM is shutdown):
rsync /var/lib/kvm/<vm-name>/<vm-image> <remote-server-ip>:/tmp/
On the remote server create a dir for the VM and copy it from /tmp to that dir:
mkdir /var/lib/kvm/<vm-name> mv /tmp/<vm-image> /var/lib/kvm/<vm-name>/
Now you also need the xml file for that VM. Since it is just text you can copy it, create a file on remote server and paste it there. The xml file is found in this dir:
/etc/libvirt/qemu
After you copied the VM image and xml file you can define and start it:
virsh define /etc/libvirt/qemu/<vm-name>.xml virsh start <vm-name> virsh autostart <vm-name>
Rename a VM
Shutdown the VM, dump the xml file and edit it.
virsh shutdown oldname virsh dumpxml oldname > /etc/libvirt/qemu/newname.xml vi /etc/libvirt/qemu/newname.xml
In newname.xml change "<name>oldname</name>" to "<name>newname</name>" and "
" to "
". Undefine the VM and define the new one.
virsh undefine oldname mv /var/lib/kvm/oldname /var/lib/kvm/newname virsh define /etc/libvirt/qemu/newname.xml virsh start newname
or use
# virsh domrename $OLD_NAME $NEW_NAME
ssh to VM and follow the steps from here: changing the hostname
Resizing Memory With Script
VM_ID="my_vm_id" NEW_AMOUNT="4000" EDITOR='sed -i "s;[0-9]*</currentMemory>;$NEW_AMOUNT</currentMemory>;"' virsh edit $VM_ID EDITOR='sed -i "s;[0-9]*</memory>;$NEW_AMOUNT</memory>;"' virsh edit $VM_ID sudo virsh shutdown $VM_ID sudo virsh start $VM_ID
Useful Tools
Install tools
apt-get -y install libguestfs-tools virt-top
"ls" List a directory in a virtual machine.
# virt-ls -l -d ubuntu /root
"cat" Display content of a file in a virtual machine.
# virt-cat -d ubuntu /etc/network/interfaces
Edit a file in a virtual machine.
# virt-edit -d ubuntu /etc/netplan/01-netcfg.yaml
Display disk usage in a virtual machine.
# virt-df -h -d ubuntu
Mount a disk of a virtual machine
# guestmount -d ubuntu -i /mnt # ll /mnt
Display the status of virtual machines
# virt-top
VM-disk deleted - resolution
Solution 1
# lsof | grep 101 ... kvm 3649 root 18u REG 253,2 2147483648 524290 (deleted)/var/lib/vz/images/101/vm-101-disk-1.raw ...
Important is the pid (3649) and the filediscriptor (18) do an copy (before that, it's a good idea to stop important services with open files inside the VM, like databases)
cp /proc/3649/fd/18 /var/lib/vz/images/101/vm-101-disk-1.raw
Voila, the disk-file (of an open-VM!) is copied back.
Solution 2
To conver the image from raw to qcow2
qemu-img convert -p -f qcow2 -O raw /proc/2850/fd/19 vm-100-disk-1.raw
Test the copied file with an dummy-VM before shutdown the original VM!
List all the VMs with the autostart option activated
# sudo virsh list --autostart
Snapshoot operations
Create snapshoot
virsh shutdown vm_name virsh snapshot-create-as --domain vm_name --name "snapshot_name" --description "Snapshot"
Restore snapshoot
virsh snapshot-list --domain vm_name virsh snapshot-revert --domain vm_name --snapshotname snapshot_name
Delete snapshoot
virsh snapshot-delete --domain vm_name --snapshotname snapshot_name_to_be_deleted
Adding a disk to VM
On the host, create an image
qemu-img create -f qcow2 /path/to/image.qcow2 10G
Attach the disk to the VM (check before if vda is used; if yes use vdb, vdc, etc.). Make sure to provide the full path to the image.
virsh shutdown vm-name virsh attach-disk vm-name --source /path/to/image.qcow2 vdb --driver qemu --subdriver qcow2 --targetbus virtio --persistent
Before starting the VM check that the disk attached as qcow2 and not another type like raw.
#virsh edit vm-name <disk type='file' device='disk'> <driver name='qemu' type='qcow2'/> <source file='/var/lib/kvm/ourbus-nc/ourbus-ncstorage1.qcow2'/> <target dev='vda' bus='virtio'/> <address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x0'/> </disk>
If type is not qcow2 change it and start the VM.
virsh start vm-name
On the VM, check disk vda has been attached
# ls -l /dev/disk/by-path/ lrwxrwxrwx 1 root root 9 Oct 23 13:44 virtio-pci-0000:00:05.0 -> ../../vda
Create a partition with parted or other tool
parted /dev/vda
If parted throws a warning that the disk size is only a few KB, there is a problem with the disk. In this case go back and investigate, otherwise go ahead and create the partition.
Format it
mkfs.ext4 /dev/vda1
If the disk will be used for data storage then reduce the space reserved for root operations
tune2fs -m 1 /dev/vda1
Find the UUID of the partition (the groups of numbers/letters before the arrow -> )
#ls -l /dev/disk/by-uuid/ lrwxrwxrwx 1 root root 10 Oct 23 13:45 936de7fd-084f-4456-898f-483341df1cf1 -> ../../vda1
Mount the partition using the UUID
mount /dev/disk/by-uuid/youruuid /path/to/mymountpoint
Append a line to /etc/fstab so your mount can survive a reboot
UUID=youruuid /path/to/mymountpoint ext4 defaults 0 0
Detach disk from a VM
virsh detach-disk vm-name vda --config
Converting
Info about image
qemu-img info image.vmdk
From .vdi to .qcow2
qemu-img convert -f vdi -O qcow2 from.vdi to.qcow2
From qcow2 to .vdi
qemu-img convert -O vdi from.qcow2 to.vdi
From .img to .qcow2
qemu-img convert -f raw from.img -O qcow2 to.qcow2
From .qcow2 to .raw
qemu-img convert -O raw from.qcow2 to.raw
List OS suported variants bt virt-install
When creating a guest with virt-install you need to specify the --os-variant. To get a list of acceptable values (on Ubuntu 16.04), install the libosinfo-bin package before running the command below:
# osinfo-query os
Reset and set the root password of a certain VM
First shutdown the VM:
virsh shutdown <vm_name>
Secondly get the path of the image:
virsh dumpxml <vm_name> | grep 'source file'
Afterwards set the root password:
virt-customize -a <path_of_image> --root-password password:NewRootUserPasswordHere --uninstall cloud-init
