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>
Remove from salt
sudo salt-key -L | grep <VM NAME> sudo salt-key -d <FULL VM NAME>
Remove etc/hosts # just for newroco server
vi /etc/hosts # find the VM and delete the name and ip
Remove From zabbix
Search for <VM NAME> and them click on delete
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 $NEW_NAME
ssh to VM and follow the steps from here: changing the hostname
steps from salt minion need to be followed as well : salt
Additional steps delete it from zabbix , rename on the wiki if applicable , CAS changes
Resizing Memory With Script
VM_ID="my_vm_id" NEW_AMOUNT="4000" EDITOR='sed -i "s;[0-9]*</currentMemory>;$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
Edit a file in a virtual machine image.
# virt-edit -a /path/to/image.qcow2 /home/user/.bash_history
Display disk usage in a virtual machine.
# virt-df -h -d ubuntu
Display partition table in a virtual machine (helps a lot when growing a windows VM disk)
#virt-filesystems -a vm-image.qcow2 -l Name Type VFS Label Size Parent /dev/sda1 filesystem ntfs System Reserved 104857600 - /dev/sda2 filesystem ntfs - 53030682624 - /dev/sda3 filesystem ntfs - 548405248 -
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
With virsh
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
With qemu-img
This is helpful when the VM was migrated between hosts and snapshots definition was not copied/defined as well
List snapshots
qemu-img info vm-disk.qcow2
Delete snapshot
qemu-img snapshot -d snapshot-name vm-disk.qcow2
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
Enable Virsh Console Access For KVM Guests
In order to use VM console access (if it runs out of internet access, for example), the following commands must be run on each guest.
systemctl enable serial-getty@ttyS0.service systemctl start serial-getty@ttyS0.service
After running the two commands we can easily connect from the main host using the command:
sudo virsh console --domain <vm_name>
