install qemu with linux

purpose

• start QEMU virtual machine with KVM(Kernel-based Virtual Machine) accelerator

pre-requirements

• linux operating system with x86_64 chip(take Ubuntu 20.04.2 LTS as an example)
• cpu support virtualization(to use KVM accelerator)

do it

install qemu binary

• Ubuntu 20.04.2 LTS

  • apt-get -y install qemu-kvm
    

• CentOS 8

  • dnf install qemu-kvm \
        && mkdir -p /root/bin \
        && ln -s /usr/libexec/qemu-kvm /root/bin/qemu-kvm \
        && ln -s /root/bin/qemu-kvm /root/bin/qemu-system-x86_64
    

check your cpu

• 'vmx' or 'svm' is expected

  • cat /proc/cpuinfo | egrep "vmx|svm" | uniq
    

• 'kvm' is expected

  • qemu-system-x86_64 -accel help
    

start qemu

1. create virtual disk

   • qemu-img create -f qcow2 centos.8.qcow2 40G
     

2. download boot image of centos 8

   • curl -LO http://mirrors.aliyun.com/centos/8-stream/isos/x86_64/CentOS-Stream-8-x86_64-latest-boot.iso
     ln -s CentOS-Stream-8-x86_64-latest-boot.iso CentOS-Stream-8-x86_64-boot.iso
     

3. start qemu machine with boot image and the virtual disk created

   • qemu-system-x86_64 \
         -accel kvm \
         -cpu kvm64 -smp cpus=1 \
         -m 1G \
         -drive file=$(pwd)/CentOS-Stream-8-x86_64-boot.iso,index=1,media=cdrom \
         -drive file=$(pwd)/centos.8.qcow2,if=virtio,index=0,media=disk,format=qcow2 \
         -rtc base=localtime \
         -pidfile $(pwd)/centos.8.qcow2.pid \
         -display none \
         -vnc 0.0.0.0:1 \
         -daemonize
     

   • -accel kvm will use kvm as accelerator
   • -cpu kvm64 specifies the cpu, use qemu-system-x86_64 -cpu help to see more options
   • -drive ... defines drives
     • adding CentOS-8.4.2105-x86_64-boot.iso as a cdrom
     • adding centos.8.qcow2(the virtual disk created) as a hard disk
   • -rtc base=localtime let the RTC start at local time
   • -pidfile specifies the pid file for the QEMU process
   • -display none will not display the video output but the guest will still see an emulated graphics card
   • -vnc 0.0.0.0:1 will open a vnc port and redirect the VGA display over the VNC session
   • -daemonize will daemonize the QEMU process after initialization
4. use novnc to connect

   • docker run --name novnc --rm -p 6080:6080 \
             -e VNC_SERVER=host.docker.internal:5901 \
             --add-host host.docker.internal:host-gateway \
             -d wangz2019/docker-novnc:1.2.0
     

   • open http://localhost:6080/vnc.html with chrome, you will see the vnc client interface
5. install centos 8 system
   • after installation, login the machine with root and shutdown it

     • shutdown -h now
       

6. stop novnc docker container because we won't need it from now on

   • docker kill novnc
     

7. start qemu machine with the virtual disk

   • qemu-system-x86_64 \
         -accel kvm \
         -cpu kvm64 -smp cpus=1 \
         -m 1G \
         -drive file=$(pwd)/centos.8.qcow2,if=virtio,index=0,media=disk,format=qcow2 \
         -rtc base=localtime \
         -pidfile $(pwd)/centos.8.qcow2.pid \
         -display none \
         -nic user,hostfwd=tcp::1022-:22 \
         -daemonize
     

   • -nic user,hostfwd=tcp::1022-:22 will bind port 1022 in host with port 22 in guest
8. login and play with ssh

   • ssh -o "UserKnownHostsFile /dev/null" -p 1022 root@localhost
     

9. clean
   • stop virtual machine

     • ssh -o "UserKnownHostsFile /dev/null" -p 1022 root@localhost 'shutdown -h now'
       

   • you can also kill the process to force stop it