A quick reference to KVM.
Created on: 2019-01-22
Tag: cheat_sheet
Check that our CPU supports hardware virtualization 1:
egrep -c '(vmx|svm)' /proc/cpuinfo
if it is more 0 then your hardware doesn't support virtualization. If it is more then 0 then we are good to go. Alternatively we can use:
egrep -c ' lm ' /proc/cpuinfo
which will give similar result.
to install KVM in Ubuntu 2:
sudo apt-get install qemu-kvm libvirt-daemon-system libvirt-clients bridge-utils virt-manager -y
on post-installation we need to configure the network. Here I will only give the example of bridged networking in DHCP.[3]_. First make backup of your netowrk configuration:
sudo cp /etc/network/interfaces /etc/network/interfaces.bak
Warning
Unfortunately, the draw back of this method is that, on next boot it disables the network manager. If we use this we need to run sudo /etc/init.d/networking restart everytime to bring the bridge interface up.
Now open /etc/network/interfaces file with your choice of editor and paste the following:
iface eth0 inet manual # change eth0 to your ethernet adapter name
auto lo
iface lo inet loopback
auto br0
iface br0 inet dhcp
bridge_ports eth0 # change eth0 to your ethernet adapter name
bridge_stp off
bridge_fd 0
bridge_maxwait 0
Also, edit /etc/sysctl.conf to uncomment:
net.ipv4.ip_forward=1
Got it from this source: https://askubuntu.com/a/1134422
Now restart the network adapter:
sudo systemctl restart networking.service
sudo apt-get remove --purge qemu-kvm libvirt-daemon-system libvirt-clients bridge-utils virt-manager -y
also check and remove this:
sudo rm -rf /etc/kvm sudo rm -rf /etc/udev/rules.d/45-kvm.rules sudo rm -rf /etc/init.d/kvm
source: https://askubuntu.com/a/385358
I normally do this:
sudo rm -rf /etc/apparmor.d/libvirt sudo rm -rf /etc/libvirt sudo rm -rf /usr/lib/libvirt sudo rm -rf /usr/lib/qemu sudo rm -rf /usr/lib/x86_64-linux-gnu/qemu/ sudo rm -rf /usr/share/libvirt sudo rm -rf /var/lib/libvirt
To create a new guest instance from ISO, run the following:
sudo virt-install --virt-type=kvm --name $name --ram $ram_size_in_mb --vcpus=2 --hvm --network=bridge:$bridge_name --cdrom=$iso_location --disk $img_file_location,size=$disk_size_in_gb
To make a guest from an existing .img file, run the following:
sudo virt-install --virt-type=kvm --name $name --ram 512 --vcpus=1 --hvm --network=bridge:$bridge_name --import --disk $new_img_file_location
This makes possible to make one base image and then copy the image and spun a new guest. For example, let's consider we have a base image name ubuntu_1604_server.img to make a new $name guest, we do:
sudo cp ubuntu_1604_server.img $name.img sudo virt-install --virt-type=kvm --name $name --ram 1024 --vcpus=1 --hvm --import --disk $name.img
To make a Windows guest from ISO, run this:
virt-install --name=windows10 --ram=4048 --vcpus=4 --os-type=windows --os-variant=win8.1 --network=bridge:br0 --cdrom=Windows_10.iso --disk windows10,size=40
We will use qemu-img to create a new .img file of 2 GB:
qemu-img create -f qcow2 $name.img 2g
We can see the information of an existing .img file using qemu-img:
qemu-img info $name
to clone guest:
virt-clone --original $DOMAIN_NAME --auto-clone
also we can give the new guest a name with --name flag:
virt-clone --original $DOMAIN_NAME --name $NEW_DOMAIN_NAME --auto-clone
The virsh program is the main interface for managing virsh guest domains.
More resource:
To start KVM guest on host boot:
virsh autostart $DOMAIN_NAME
source: https://serverfault.com/a/144477
to delete guest:
virsh undefine $DOMAIN_NAME
We can also specify --managed-save to delete any managed save images and --snapshots-metadata to remove snapshots for the specified guest
source: https://serverfault.com/a/402650
to shutdown guest:
virsh shutdown $DOMAIN_NAME
to see ip of a guest, first see the networks:
virsh net-list
Now find out what is the name of the network of the guest. Now we can find all the guest with this command:
virsh net-dhcp-leases $NETWORK-NAME
If we know the MAC of the guest, then:
virsh net-dhcp-leases $NETWORK-NAME --mac $MAC-ADDRESS
source: https://unix.stackexchange.com/a/283059
OR using this small great script:
HOSTNAME=[your vm name]
MAC=$(virsh domiflist $HOSTNAME | awk '{ print $5 }' | tail -2 | head -1)
arp -a | grep $MAC | awk '{ print $2 }' | sed 's/[()]//g'
source: https://superuser.com/a/1383158
to see the guest in full screen mode we need to change the display setting which can be done:
From the virt-manager main window:
Edit -> Preferences -> Console -> Resize guest with window
Or from a guest VM console view:
View -> Scale Display -> Auto resize VM with window
source: https://centosfaq.org/centos/virt-manager-and-full-screen-display/
to fix this error, try reloading apparmor:
sudo systemctl reload apparmor
source: https://askubuntu.com/a/888220
to change the DHCP network of KVM:
virsh net-list virsh net-edit $NETWORK_NAME
Now find the <dhcp> section and make changes. This can also be done by editing the /etc/libvirt/qemu/networks/$NETWORK_NAME.xml file.
source: https://serverfault.com/a/627245
to migrating with virt-manager:
right click on a guest
select migrate
select the new host
click migrate
Note
check the /etc/libvirt/ directory