How To Install and Use KVM on CentOS Stream 8
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In today’s guide we will be installing KVM on CentOS Stream 8 Linux operating system. KVM (Kernel-based Virtual Machine) is an open source virtualization technology built into Linux Kernel. KVM can be used on any x86 hardware with virtualization extensions (Intel VT or AMD-V). The role of KVM as hypervisor is specification of the host resources – Memory, CPUs, and virtual devices availed to the virtual machine instances being defined.
KVM consists of a loadable kernel module, kvm.ko, that provides the core virtualization infrastructure and a processor specific module, kvm-intel.ko or kvm-amd.ko. Below diagram illustrates how the KVM hypervisor virtualizes the compute resources for Linux on KVM.
Step 1: Confirm Virtualization extensions availability
Your hardware needs to have CPU virtualization extensions; Intel VT for Intel or AMD-V for AMD processor. In some systems, this is disabled on BIOS and you may need to enable it.
$ cat /proc/cpuinfo | egrep --color "vmx|svm"The lscpu command can also be used to check for virtualization CPU extensions:
$ lscpu | grep Virtualization
Virtualization: VT-xThis confirms I have Intel processor and VT-x extension
Step 2: Install KVM Virtualization Tools on CentOS Stream 8
Let’s start by performing system upgrades to use Kernel updates that could be available.
sudo dnf -y updateIf there are Kernel related updates consider performing system reboot then install KVM Virtualization Tools on CentOS Stream 8:
sudo dnf install @virtAccept installation by pressing the y key:
...
scrub x86_64 2.5.2-14.el8 appstream 44 k
seabios-bin noarch 1.13.0-2.module_el8.4.0+547+a85d02ba appstream 127 k
seavgabios-bin noarch 1.13.0-2.module_el8.4.0+547+a85d02ba appstream 42 k
sgabios-bin noarch 1:0.20170427git-3.module_el8.4.0+783+f8734d30 appstream 13 k
spice-server x86_64 0.14.3-4.el8 appstream 409 k
supermin x86_64 5.1.19-10.module_el8.4.0+547+a85d02ba appstream 709 k
syslinux x86_64 6.04-5.el8 baseos 578 k
syslinux-extlinux x86_64 6.04-5.el8 baseos 140 k
syslinux-extlinux-nonlinux noarch 6.04-5.el8 baseos 386 k
syslinux-nonlinux noarch 6.04-5.el8 baseos 554 k
systemd-container x86_64 239-45.el8 baseos 743 k
tar x86_64 2:1.30-5.el8 baseos 838 k
usbredir x86_64 0.8.0-1.el8 appstream 50 k
userspace-rcu x86_64 0.10.1-4.el8 baseos 101 k
xml-common noarch 0.6.3-50.el8 baseos 39 k
yajl x86_64 2.1.0-10.el8 appstream 41 k
Installing module profiles:
virt/common
Enabling module streams:
llvm-toolset rhel8
Transaction Summary
==================================================================================================================================================================
Install 166 Packages
Total download size: 99 M
Installed size: 352 M
Is this ok [y/N]: yCheck if Kernel modules are loaded:
$ lsmod | grep kvm
kvm_intel 315392 0
kvm 847872 1 kvm_intel
irqbypass 16384 1 kvmStep 3: Install other KVM Management Tools
Let’s perform installation of other tools that helps with the management of Virtual Machines on KVM:
sudo dnf -y install bridge-utils virt-top libvirt-devel libguestfs-toolsWe have an example guide showing how libguestfs-tools can be used: How to mount VM virtual disk on KVM hypervisor
Step 4: Start and enable KVM daemon
By default, KVM daemon libvirtd is not started, start the service using the command:
sudo systemctl start libvirtdAlso enable the service to be started at system boot:
sudo systemctl enable libvirtdCheck if service is started successfully:
$ systemctl status libvirtd
● libvirtd.service - Virtualization daemon
Loaded: loaded (/usr/lib/systemd/system/libvirtd.service; enabled; vendor preset: enabled)
Active: active (running) since Mon 2021-06-21 20:29:16 CEST; 59s ago
Docs: man:libvirtd(8)
https://libvirt.org
Main PID: 23126 (libvirtd)
Tasks: 19 (limit: 32768)
Memory: 15.3M
CGroup: /system.slice/libvirtd.service
├─23126 /usr/sbin/libvirtd --timeout 120
├─23251 /usr/sbin/dnsmasq --conf-file=/var/lib/libvirt/dnsmasq/default.conf --leasefile-ro --dhcp-script=/usr/libexec/libvirt_leaseshelper
└─23252 /usr/sbin/dnsmasq --conf-file=/var/lib/libvirt/dnsmasq/default.conf --leasefile-ro --dhcp-script=/usr/libexec/libvirt_leaseshelper
Jun 21 20:29:17 kvm-desktop dnsmasq[23251]: reading /etc/resolv.conf
Jun 21 20:29:17 kvm-desktop dnsmasq[23251]: using nameserver 213.133.100.100#53
Jun 21 20:29:17 kvm-desktop dnsmasq[23251]: using nameserver 213.133.99.99#53
Jun 21 20:29:17 kvm-desktop dnsmasq[23251]: using nameserver 213.133.98.98#53
Jun 21 20:29:17 kvm-desktop dnsmasq[23251]: using nameserver 2a01:4f8:0:1::add:9898#53
Jun 21 20:29:17 kvm-desktop dnsmasq[23251]: using nameserver 2a01:4f8:0:1::add:1010#53
Jun 21 20:29:17 kvm-desktop dnsmasq[23251]: using nameserver 2a01:4f8:0:1::add:9999#53
Jun 21 20:29:17 kvm-desktop dnsmasq[23251]: read /etc/hosts - 9 addresses
Jun 21 20:29:17 kvm-desktop dnsmasq[23251]: read /var/lib/libvirt/dnsmasq/default.addnhosts - 0 addresses
Jun 21 20:29:17 kvm-desktop dnsmasq-dhcp[23251]: read /var/lib/libvirt/dnsmasq/default.hostsfileStep 5: Install Virtual machine Manager GUI – Optional
If running a Desktop Environment on your CentOS Stream 8, you can install the virt-manager package which provides Desktop Management application for your KVM Virtual Machines.
sudo dnf install virt-managerBegin installation of Virt-manager on CentOS Stream 8:
Installing weak dependencies:
abattis-cantarell-fonts noarch 0.0.25-6.el8 appstream 156 k
dejavu-sans-mono-fonts noarch 2.35-7.el8 baseos 447 k
Transaction Summary
==================================================================================================================================================================
Install 62 Packages
Total download size: 27 M
Installed size: 83 M
Is this ok [y/N]: yStep 6: Network Bridge Creation for KVM instances (Optional)
The Linux bridge virbr0 is created at the time of installation and can be used to create Virtual Machines that doesn’t need external IP connectivity. It uses NAT to give VMs internet access.
$ brctl show
bridge name bridge id STP enabled interfaces
virbr0 8000.525400876bb5 yes virbr0-nicIf you need a bridge with external connections support, refer to the guide below on creation:
How to Create a Linux Network Bridge on RHEL / CentOS 8
Step 7: Create Virtual Machines on KVM
You can use virt-install command to create a Linux Virtual Machine on KVM.
I’ll download CentOS Stream 8 DVD installation ISO file
cd ~/
wget http://centos.mirror.liquidtelecom.com/8-stream/isos/x86_64/CentOS-Stream-8-x86_64-20210617-dvd1.isoVM installation using virt-install:
virt-install \
--name centos-stream-8 \
--ram 2048 \
--vcpus 2 \
--disk path=/var/lib/libvirt/images/centos-stream-8.img,size=20 \
--os-variant centos-stream8 \
--os-type linux \
--network bridge=virbr0 \
--graphics none \
--console pty,target_type=serial \
--location ~/CentOS-Stream-8-x86_64-20210617-dvd1.iso \
--extra-args 'console=ttyS0,115200n8 serial'The installation is on text mode but the procedure of installation is similar to GUI. After finishing the installation, reboot the instance and login
CentOS Stream 8
Kernel 4.18.0-240.el8.x86_64 on an x86_64
Activate the web console with: systemctl enable --now cockpit.socket
localhost login:You can also login through console:
$ virsh console centos-stream-8Press <ENTER> key on getting:
Escape character is ^]More guides on KVM:
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