QEMU

General

Enable KVM full virtualization support:

  qemu-system-x86_64 -enable-kvm disk.img

or:

  qemu-system-x86_64 disk.img

Use KVM processor with all host features:
```
  qemu-system-x86_64 -cpu host disk.img
```

Emulate a standard PC machine:

  qemu-system-x86_64 -cpu host -machine type=pc disk.img

Set virtual RAM size to 2 GB:

  qemu-system-x86_64 -cpu host -machine type=pc -m 2G disk.img

Drives

Boot ISO file ‘boot.iso’ as CD-ROM drive:

  qemu-system-x86_64 -drive file=boot.iso,media=cdrom

Boot existing device ‘/dev/sdh’:

  qemu-system-x86_64 -drive file=/dev/sdh,media=disk

Boot a VMware Virtual Machine Disk (VMDK):

  qemu-system-x86_64 -drive file=disk.vmdk,media=disk

Boot image in read-only mode and without cache:

  qemu-system-x86_64 -drive file=disk.qcow2,readonly,cache=none,media=disk

Mount directory ‘/mnt/’ as a Virtual FAT filesystem (VVFAT):
```
  qemu-system-x86_64 -drive file=fat:rw:/mnt/,media=disk
```

Determine boot order to be ‘cd->disk->network’:

  qemu-system-x86_64 -boot order=dcn -cdrom boot.iso -hda disk.qcow2

Video

Select standard VGA card with resolutions up to 2560x1600:
```
  qemu-system-x86_64 -vga std disk.img
```

Start in full screen:

  qemu-system-x86_64 -vga std -full-screen disk.img

See supported screen resolutions (in guest machine):
```
  xrandr
```
Change screen resolution (in guest machine):
```
  xrandr --size 1
```
or:
```
  xrandr --size 1920x1080
```
Toggle full screen: Ctrl+Alt+f
Enlarge screen: Ctrl+Alt+`` + ``
Shrink screen: Ctrl+Alt+`` - ``
Restore the screen’s un-scaled dimensions: Ctrl+Alt+u

Audio

Enable audio and select Intel HD Audio hardware with PulseAudio (pa) as backend:
```
  qemu-system-x86_64 -audio pa,model=hda disk.img
```

Network

User Networking (SLIRP) default settings:

Setting IP

Network 10.0.2.0

Netmask 255.255.255.0

Gateway 10.0.2.2

Namerserver 10.0.2.3

SMB server 10.0.2.4

Setting	IP
Network	10.0.2.0
Netmask	255.255.255.0
Gateway	10.0.2.2
Namerserver	10.0.2.3
SMB server	10.0.2.4

Configure User Networking:

  qemu-system-x86_64 -netdev user,id=mynet0,net=192.168.76.0/24,dhcpstart=192.168.76.9

Dump Virtual Machine’s network traffic to PCAP file:

  qemu-system-x86_64 -netdev user,id=mynet0 -object filter-dump,id=dump0,netdev=mynet0,file=./vm0.pcap

Images

Create an image file of 4G of size:

  qemu-img create -f qcow2 disk.qcow2 4G

Convert from VMware Virtual Machine Disk (VMDK) to raw format:
```
  qemu-img convert -f vmdk disk.vmdk -O raw disk.img
```

Convert from raw format to qcow2 format:

  qemu-img convert -f raw disk.img -O qcow2 disk.qcow2

Convert from VirtualBox Disk Image (VDI) format to raw format:
```
  vboxmanage clonehd disk.vdi --format raw disk.img
```

Convert from raw format to VirtualBox Disk Image (VDI):

  vboxmanage convertfromraw disk.img --format VDI disk.vdi

Snapshots

Boot image with temporary snapshot so changes are discarded:
```
  qemu-system-x86_64 disk.qcow2 -snapshot
```

Create snapshot of image:

  qemu-img snapshot -c name-of-snapshot disk.qcow2

List snapshots for image file:
```
  qemu-img snapshot -l disk.qcow2
```

Revert to specific snapshot:

  qemu-img snapshot -a name-of-snapshot disk.qcow2

Delete specific snapshot:

  qemu-img snapshot -d name-of-snapshot disk.qcow2

Create a new disk image based on an existing image:
```
  qemu-img create -b disk.qcow2 new-disk.qcow2
```
Copy an image based on a backing image so both are merged into one:
```
  qemu-img convert new-disk.qcow2 new-disk-merged.qcow2
```

Vagrant

Install plugin for libvirt:

  vagrant plugin install vagrant-libvirt

Install plugin to convert vagrant boxes:
```
  vagrant plugin install vagrant-mutate
```

Migrate official Vagrant boxes to libvirt format:

  vagrant box add debian/jessie64
  vagrant mutate debian/jessie64 libvirt

Start Vagrant environment using libvirt as provider:
```
  vagrant up --provider libvirt
```

virsh

Edit virtual machine’s XML configuration:
```
  virsh edit "<vmname>"
```

Configure port redirection in XML configuration:

  <domain type='kvm' xmlns:qemu='http://libvirt.org/schemas/domain/qemu/1.0'>
    ...
    <qemu:commandline>
      <qemu:arg value='-netdev'/>
      <qemu:arg value='user,id=net0,net=10.0.10.0/24,hostfwd=tcp:127.0.0.1:2222-:22'/>
      <qemu:arg value='-device'/>
      <qemu:arg value='e1000,netdev=net0'/>
    </qemu:commandline>
  </domain>

Setup

Prepare an image file:

  qemu-img create -f qcow2 ./disk.img 4G
  sudo modprobe nbd max_part=16
  sudo qemu-nbd -c /dev/nbd0 ./disk.img
  printf 'o\nn\np\n1\n\n\nw\n' | sudo fdisk /dev/nbd0
  sudo partprobe /dev/nbd0
  sudo mkfs.ext4 /dev/nbd0p1
  sudo qemu-nbd -d /dev/nbd0
  sudo modprobe -r nbd

Alternative way to prepare a RAW image file:

  qemu-img create -f raw ./disk.img 4G
  printf 'o\nn\np\n1\n\n\nw\n' | fdisk ./disk.img
  sudo losetup /dev/loop0 ./disk.img
  sudo partprobe /dev/loop0
  sudo mkfs.ext4 /dev/loop0p1
  sudo losetup -d /dev/loop0

Yet another way to prepare a RAW image file:

  qemu-img create -f raw ./disk.img 4G
  printf 'o\nn\np\n1\n\n\nw\n' | fdisk ./disk.img
  sudo kpartx -av ./disk.img
  sudo mkfs.ext4 /dev/mapper/loop0p1
  sudo kpartx -dv ./disk.img

Mount and unmount partition inside image file:

  guestmount -a ./disk.img -m /dev/sda1 --rw /mnt/loop
  ls -l /mnt/loop
  guestunmount /mnt/loop

Use debootstrap to install a system into a partition inside an image file and chroot into it:

  sudo modprobe nbd max_part=16
  sudo qemu-nbd -c /dev/nbd0 ./disk.img
  sudo partprobe /dev/nbd0
  sudo mount /dev/nbd0p1 /mnt/loop
  sudo debootstrap --arch amd64 stretch /mnt/loop http://deb.debian.org/debian
  sudo mount -t proc /proc /mnt/loop/proc
  sudo mount --rbind --make-rslave /dev /mnt/loop/dev
  sudo mount --rbind --make-rslave /sys /mnt/loop/sys
  sudo mount --rbind --make-rslave /run /mnt/loop/run
  sudo chroot /mnt/loop /bin/bash
  # # commands inside chroot
  sudo umount -R /mnt/loop
  sudo qemu-nbd -d /dev/nbd0
  sudo modprobe -r nbd