How to install KVM on CentOS 7

Check CPU support for virtualization using egrep -c '(vmx|svm)' /proc/cpuinfo, where a result of 1 or higher indicates support; 2. Install KVM packages including qemu-kvm, libvirt, and virt-install using sudo yum install -y; 3. Start and enable libvirtd service with systemctl start and enable, then verify its status; 4. Confirm KVM modules are loaded via lsmod | grep kvm and ensure /dev/kvm exists, loading the module manually if needed and adding it to /etc/modules-load.d/kvm.conf for persistence; 5. Use default NAT networking by starting and enabling the default network with virsh net-start and net-autostart, or set up bridged networking optionally; 6. Create a VM using virt-install with specified parameters such as name, RAM, vCPUs, disk path, OS type, network, and ISO location, then follow terminal prompts to complete installation; 7. Manage VMs via virsh commands to list, start, shutdown, connect, or delete virtual machines; 8. Optionally enable nested virtualization by configuring kvm-intel.conf and reloading the module, verifying with cat /sys/module/kvm_intel/parameters/nested, which should return Y, completing a fully functional KVM setup on CentOS 7.

Installing KVM (Kernel-based Virtual Machine) on CentOS 7 allows you to run virtual machines efficiently using hardware virtualization. Here’s a step-by-step guide to set up KVM and create a basic virtualization environment.

1. Check Hardware Virtualization Support

Before installing KVM, ensure your CPU supports hardware virtualization (Intel VT-x or AMD-V) and that it’s enabled in BIOS.

Run this command:

egrep -c '(vmx|svm)' /proc/cpuinfo

• If the output is 0, virtualization is not supported or disabled.
• If the output is 1 or higher, your system supports KVM.

You can also check if /dev/kvm exists after loading the module (next step).

2. Install KVM and Related Packages

Install the necessary packages for KVM and virtual machine management:

sudo yum install -y qemu-kvm libvirt libvirt-python libguestfs-tools virt-install

• qemu-kvm: Main KVM module for emulation.
• libvirt: Provides the libvirtd daemon for managing VMs.
• virt-install: Command-line tool to create VMs.
• libguestfs-tools: Tools for manipulating guest disk images.

Now start and enable the libvirtd service:

sudo systemctl start libvirtd
sudo systemctl enable libvirtd

Verify the service is running:

sudo systemctl status libvirtd

3. Verify KVM Installation

Check that KVM modules are loaded:

lsmod | grep kvm

You should see kvm_intel (or kvm_amd) and kvm.

Also confirm that /dev/kvm exists:

ls -l /dev/kvm

If it's missing, load the module manually:

sudo modprobe kvm-intel    # For Intel CPUs
# OR
sudo modprobe kvm-amd      # For AMD CPUs

Add the module to be loaded at boot:

echo "kvm-intel" | sudo tee /etc/modules-load.d/kvm.conf

Note: On CentOS 7, the module is usually loaded automatically when libvirtd starts.

4. Set Up Network Bridging (Optional but Recommended)

By default, libvirt uses NAT networking via virbr0. For better performance and direct network access, consider setting up a bridge.

But for basic use, the default network is sufficient. Start and enable it:

sudo virsh net-start default
sudo virsh net-autostart default

Check with:

sudo virsh net-list --all

5. Create a Virtual Machine

Use virt-install to create a VM. Example: Install a CentOS 7 VM from an ISO.

First, download an ISO and place it in /var/lib/libvirt/images/.

Then run:

sudo virt-install \
  --name centos7-vm \
  --ram 2048 \
  --vcpus 2 \
  --disk path=/var/lib/libvirt/images/centos7-vm.qcow2,size=20 \
  --os-type linux \
  --os-variant rhel7 \
  --network network=default \
  --graphics none \
  --console pty,target_type=serial \
  --location '/var/lib/libvirt/images/CentOS-7-x86_64-Minimal-2009.iso' \
  --extra-args "console=ttyS0"

Replace the ISO path with your actual ISO file. This example uses text-mode installation via console.

After running the command, the installation will begin in the terminal. Follow the prompts to complete the OS setup.

6. Manage Virtual Machines

Use virsh to manage VMs:

• List running VMs:

  sudo virsh list

• List all VMs (including shut off):

  sudo virsh list --all

• Start, shutdown, or reboot:

  sudo virsh start centos7-vm
  sudo virsh shutdown centos7-vm

• Connect to VM console:

  sudo virsh console centos7-vm

• Delete a VM:

  sudo virsh destroy centos7-vm
  sudo virsh undefine centos7-vm

7. Enable Nested Virtualization (Optional)

If you want to run VMs inside a KVM guest (e.g., for lab environments), enable nested virtualization:

For Intel:

echo "options kvm-intel nested=Y" | sudo tee /etc/modprobe.d/kvm-intel.conf

Then reload the module:

sudo rmmod kvm-intel
sudo modprobe kvm-intel

Verify:

cat /sys/module/kvm_intel/parameters/nested

Should output Y.

That’s it. You now have a working KVM setup on CentOS 7. You can create and manage virtual machines using command-line tools or optionally install virt-manager on a desktop system for GUI access.

Basically just follow the steps, make sure virtualization is enabled, and use virt-install or virsh to manage your VMs.

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