Personal Cheatsheet on Virtualization on CentOS

First off, qemu.org is used by Linux virtualization software, including KVM. QEMU is a generic, open source machine emulator and virtualizer.

It is installed using dnf. It confirm you have it, run: sudo dnf list | grep -i qemu sudo dnf info qemu-img.x86_64

zintis@c8host ~$ sudo dnf list | grep -i qemu
ipxe-roms-qemu.noarch                                20181214-1.git133f4c47.el8                              @AppStream         
libvirt-daemon-driver-qemu.x86_64                    4.5.0-24.3.module_el8.0.0+189+f9babebb                  @AppStream         
qemu-guest-agent.x86_64                              15:2.12.0-65.module_el8.0.0+189+f9babebb.5              @AppStream         
qemu-img.x86_64                                      15:2.12.0-65.module_el8.0.0+189+f9babebb.5              @AppStream         
qemu-kvm.x86_64                                      15:2.12.0-65.module_el8.0.0+189+f9babebb.5              @AppStream         
qemu-kvm-block-curl.x86_64                           15:2.12.0-65.module_el8.0.0+189+f9babebb.5              @AppStream         
qemu-kvm-block-gluster.x86_64                        15:2.12.0-65.module_el8.0.0+189+f9babebb.5              @AppStream         
qemu-kvm-block-iscsi.x86_64                          15:2.12.0-65.module_el8.0.0+189+f9babebb.5              @AppStream         
qemu-kvm-block-rbd.x86_64                            15:2.12.0-65.module_el8.0.0+189+f9babebb.5              @AppStream         
qemu-kvm-block-ssh.x86_64                            15:2.12.0-65.module_el8.0.0+189+f9babebb.5              @AppStream         
qemu-kvm-common.x86_64                               15:2.12.0-65.module_el8.0.0+189+f9babebb.5              @AppStream         
qemu-kvm-core.x86_64                                 15:2.12.0-65.module_el8.0.0+189+f9babebb.5              @AppStream         

zintis@c8host ~$ sudo dnf info qemu-img.x86_64 
Installed Packages
Name         : qemu-img
Epoch        : 15
Version      : 2.12.0
Release      : 65.module_el8.0.0+189+f9babebb.5
Arch         : x86_64
Size         : 4.7 M
Source       : qemu-kvm-2.12.0-65.module_el8.0.0+189+f9babebb.5.src.rpm
Repo         : @System
From repo    : AppStream
Summary      : QEMU command line tool for manipulating disk images
URL          : http://www.qemu.org/
License      : GPLv2 and GPLv2+ and CC-BY
Description  : This package provides a command line tool for manipulating disk images.

zintis@c8host ~$ grep -E '(vmx|svm)' /proc/cpuinfo flags : fpu vme de pse tsc msr pae mce cx8 apic sep m …. blah blah… Import thing is that this output proves the host supports hardware virtualization.

zintis@c8host ~$ modprobe -a kvm_intel zintis@c8host ~$ cat sys/module/kvm kvm kvm_intel/ zintis@c8host ~$ cat /sys/module/kvm_intel/parameters/nested Y zintis@c8host ~$ pwd /home/zintis zintis@c8host ~$ sudo dnf install qemu-kvm qemu-img libvirt virt-install libvirt-client [sudo] password for zintis: CentOS-8 - AppStream 1.8 kB/s | 4.3 kB 00:02 CentOS-8 - Base 1.8 kB/s | 3.9 kB 00:02 CentOS-8 - Extras 667 B/s | 1.5 kB 00:02 Adobe Systems Incorporated 2.6 kB/s | 2.9 kB 00:01 Package qemu-kvm-15:2.12.0-65.module_el8.0.0+189+f9babebb.5.x86₆₄ is already installed. Package qemu-img-15:2.12.0-65.module_el8.0.0+189+f9babebb.5.x86₆₄ is already installed. Package libvirt-4.5.0-24.3.module_el8.0.0+189+f9babebb.x86₆₄ is already installed. Package virt-install-2.0.0-5.1.el8.noarch is already installed. Package libvirt-client-4.5.0-24.3.module_el8.0.0+189+f9babebb.x86₆₄ is already installed. Dependencies resolved. Nothing to do. Complete!

zintis@c8host ~$ lsmod | grep kvm kvm_intel 245760 0 kvm 745472 1 kvm_intel irqbypass 16384 1 kvm zintis@c8host ~$ systemctl start libvirtd zintis@c8host ~$ systemctl enable libvirtd

While my host had virsh and other virualization components, … it did not have VMM, so I used the GUI as follows: Activities : Software : <search> Virtual Machine Manager : install .

From the Seneca Lab2 notes, I deviated slightly, by installing CentOS8 minimum rather than CentOS7

As such the CentOS Full Network Install URL I used was: mirror.netflash.net for CentOS8 And NOT the lab suggested: mirror.netflash.net for CentOS7

There is a good redhat article on networking for Linux Virtualization, that creates this

Virtualized Linux Interfaces

As you can see, the host has a physical inteface, usually eth0. Then there is the virtual bridge created by the hypervisor, QEMU, called br0

That 'bridge' or virtual ethernet switch has several ports that each VM can connect to.

Use ip link help to get a list of interfaces, or more exactly: ip link show

The above diagram has four interfaces connecting into the bridge 0. All of these interfaces can be created using just these commands:

#BEGIN_EXAMPLE

ip link add br0 typ bridge ip link set eth0 master br0 ip link set tap1 master br0 ip link set tap2 master br0 ip link set veth1 master br0

From archlinux.org description on Nework bridge, you can see that any real interface, e.g. eth0 and anuy virtual devices e.g. tap0 can be connected to it.

This is read by the boot system. But, keep the devices that you are bridging OUT OF THIS CONFIG, as a boot will mess up your bridging. All sorts of crazy can happen to your bridge configurations in QEMU.

So, create your briges do it manually, and NOT in the /etc/network/interfaces file.

See man 8 brctl (i.e. brctl(8))

brctl addbr bridge_name brctl addif bridge_name eth0