»QEMU Builder

Type: qemu

The Qemu Packer builder is able to create KVM and Xen virtual machine images.

The builder builds a virtual machine by creating a new virtual machine from scratch, booting it, installing an OS, rebooting the machine with the boot media as the virtual hard drive, provisioning software within the OS, then shutting it down. The result of the Qemu builder is a directory containing the image file necessary to run the virtual machine on KVM or Xen.

»Basic Example

Here is a basic example. This example is functional so long as you fixup paths to files, URLS for ISOs and checksums.

  "builders": [
      "type": "qemu",
      "iso_url": "http://mirror.raystedman.net/centos/6/isos/x86_64/CentOS-6.9-x86_64-minimal.iso",
      "iso_checksum": "af4a1640c0c6f348c6c41f1ea9e192a2",
      "iso_checksum_type": "md5",
      "output_directory": "output_centos_tdhtest",
      "shutdown_command": "echo 'packer' | sudo -S shutdown -P now",
      "disk_size": "5000M",
      "format": "qcow2",
      "accelerator": "kvm",
      "http_directory": "path/to/httpdir",
      "ssh_username": "root",
      "ssh_password": "s0m3password",
      "ssh_timeout": "20m",
      "vm_name": "tdhtest",
      "net_device": "virtio-net",
      "disk_interface": "virtio",
      "boot_wait": "10s",
      "boot_command": [
        "<tab> text ks=http://{{ .HTTPIP }}:{{ .HTTPPort }}/centos6-ks.cfg<enter><wait>"

This is an example only, and will time out waiting for SSH because we have not provided a kickstart file. You must add a valid kickstart file to the "http_directory" and then provide the file in the "boot_command" in order for this build to run. We recommend you check out the Community Templates for a practical usage example.

Note that you will need to set "headless": true if you are running Packer on a Linux server without X11; or if you are connected via ssh to a remote Linux server and have not enabled X11 forwarding (ssh -X).

»Qemu Specific Configuration Reference

There are many configuration options available for the builder. In addition to the items listed here, you will want to look at the general configuration references for ISO, HTTP, Floppy, Boot, Shutdown, Communicator configuration references, which are necessary for this build to succeed and can be found further down the page.


  • iso_skip_cache (bool) - Use iso from provided url. Qemu must support curl block device. This defaults to false.

  • accelerator (string) - The accelerator type to use when running the VM. This may be none, kvm, tcg, hax, hvf, whpx, or xen. The appropriate software must have already been installed on your build machine to use the accelerator you specified. When no accelerator is specified, Packer will try to use kvm if it is available but will default to tcg otherwise.

    -> The hax accelerator has issues attaching CDROM ISOs. This is an upstream issue which can be tracked here.

    -> The hvf and whpx accelerator are new and experimental as of QEMU 2.12.0. You may encounter issues unrelated to Packer when using these. You may need to add [ "-global", "virtio-pci.disable-modern=on" ] to qemuargs depending on the guest operating system.

    -> For whpx, note that Stefan Weil's QEMU for Windows distribution does not include WHPX support and users may need to compile or source a build of QEMU for Windows themselves with WHPX support.

  • disk_additional_size ([]string) - Additional disks to create. Uses vm_name as the disk name template and appends -# where # is the position in the array. # starts at 1 since 0 is the default disk. Each string represents the disk image size in bytes. Optional suffixes 'k' or 'K' (kilobyte, 1024), 'M' (megabyte, 1024k), 'G' (gigabyte, 1024M), 'T' (terabyte, 1024G), 'P' (petabyte, 1024T) and 'E' (exabyte, 1024P) are supported. 'b' is ignored. Per qemu-img documentation. Each additional disk uses the same disk parameters as the default disk. Unset by default.

  • cpus (int) - The number of cpus to use when building the VM. The default is 1 CPU.

  • disk_interface (string) - The interface to use for the disk. Allowed values include any of ide, scsi, virtio or virtio-scsi^*. Note also that any boot commands or kickstart type scripts must have proper adjustments for resulting device names. The Qemu builder uses virtio by default.

    ^* Please be aware that use of the scsi disk interface has been disabled by Red Hat due to a bug described here. If you are running Qemu on RHEL or a RHEL variant such as CentOS, you must choose one of the other listed interfaces. Using the scsi interface under these circumstances will cause the build to fail.

  • disk_size (string) - The size in bytes of the hard disk of the VM. Suffix with the first letter of common byte types. Use "k" or "K" for kilobytes, "M" for megabytes, G for gigabytes, and T for terabytes. If no value is provided for disk_size, Packer uses a default of 40960M (40 GB). If a disk_size number is provided with no units, Packer will default to Megabytes.

  • disk_cache (string) - The cache mode to use for disk. Allowed values include any of writethrough, writeback, none, unsafe or directsync. By default, this is set to writeback.

  • disk_discard (string) - The discard mode to use for disk. Allowed values include any of unmap or ignore. By default, this is set to ignore.

  • disk_detect_zeroes (string) - The detect-zeroes mode to use for disk. Allowed values include any of unmap, on or off. Defaults to off. When the value is "off" we don't set the flag in the qemu command, so that Packer still works with old versions of QEMU that don't have this option.

  • skip_compaction (bool) - Packer compacts the QCOW2 image using qemu-img convert. Set this option to true to disable compacting. Defaults to false.

  • disk_compression (bool) - Apply compression to the QCOW2 disk file using qemu-img convert. Defaults to false.

  • format (string) - Either qcow2 or raw, this specifies the output format of the virtual machine image. This defaults to qcow2.

  • headless (bool) - Packer defaults to building QEMU virtual machines by launching a GUI that shows the console of the machine being built. When this value is set to true, the machine will start without a console.

    You can still see the console if you make a note of the VNC display number chosen, and then connect using vncviewer -Shared <host>:<display>

  • disk_image (bool) - Packer defaults to building from an ISO file, this parameter controls whether the ISO URL supplied is actually a bootable QEMU image. When this value is set to true, the machine will either clone the source or use it as a backing file (if use_backing_file is true); then, it will resize the image according to disk_size and boot it.

  • use_backing_file (bool) - Only applicable when disk_image is true and format is qcow2, set this option to true to create a new QCOW2 file that uses the file located at iso_url as a backing file. The new file will only contain blocks that have changed compared to the backing file, so enabling this option can significantly reduce disk usage.

  • machine_type (string) - The type of machine emulation to use. Run your qemu binary with the flags -machine help to list available types for your system. This defaults to pc.

  • memory (int) - The amount of memory to use when building the VM in megabytes. This defaults to 512 megabytes.

  • net_device (string) - The driver to use for the network interface. Allowed values ne2k_pci, i82551, i82557b, i82559er, rtl8139, e1000, pcnet, virtio, virtio-net, virtio-net-pci, usb-net, i82559a, i82559b, i82559c, i82550, i82562, i82557a, i82557c, i82801, vmxnet3, i82558a or i82558b. The Qemu builder uses virtio-net by default.

  • output_directory (string) - This is the path to the directory where the resulting virtual machine will be created. This may be relative or absolute. If relative, the path is relative to the working directory when packer is executed. This directory must not exist or be empty prior to running the builder. By default this is output-BUILDNAME where "BUILDNAME" is the name of the build.

  • qemuargs ([][]string) - Allows complete control over the qemu command line (though not, at this time, qemu-img). Each array of strings makes up a command line switch that overrides matching default switch/value pairs. Any value specified as an empty string is ignored. All values after the switch are concatenated with no separator.

    ~> Warning: The qemu command line allows extreme flexibility, so beware of conflicting arguments causing failures of your run. For instance, using --no-acpi could break the ability to send power signal type commands (e.g., shutdown -P now) to the virtual machine, thus preventing proper shutdown. To see the defaults, look in the packer.log file and search for the qemu-system-x86 command. The arguments are all printed for review.

    The following shows a sample usage:

      "qemuargs": [
        [ "-m", "1024M" ],
        [ "--no-acpi", "" ],
        [ "-device", "virtio-net,netdev=mynet0" ]

    would produce the following (not including other defaults supplied by the builder and not otherwise conflicting with the qemuargs):

    qemu-system-x86 -m 1024m --no-acpi -netdev
    user,id=mynet0,hostfwd=hostip:hostport-guestip:guestport -device

    ~> Windows Users: QEMU for Windows builds are available though an environmental variable does need to be set for QEMU for Windows to redirect stdout to the console instead of stdout.txt.

    The following shows the environment variable that needs to be set for Windows QEMU support:


    You can also use the SSHHostPort template variable to produce a packer template that can be invoked by make in parallel:

      "qemuargs": [
        [ "-netdev", "user,hostfwd=tcp::{{ .SSHHostPort }}-:22,id=forward"],
        [ "-device", "virtio-net,netdev=forward,id=net0"]

    make -j 3 my-awesome-packer-templates spawns 3 packer processes, each of which will bind to their own SSH port as determined by each process. This will also work with WinRM, just change the port forward in qemuargs to map to WinRM's default port of 5985 or whatever value you have the service set to listen on.

    This is a template engine and allows access to the following variables: {{ .HTTPIP }}, {{ .HTTPPort }}, {{ .HTTPDir }}, {{ .OutputDir }}, {{ .Name }}, and {{ .SSHHostPort }}

  • qemu_binary (string) - The name of the Qemu binary to look for. This defaults to qemu-system-x86_64, but may need to be changed for some platforms. For example qemu-kvm, or qemu-system-i386 may be a better choice for some systems.

  • qmp_enable (bool) - Enable QMP socket. Location is specified by qmp_socket_path. Defaults to false.

  • qmp_socket_path (string) - QMP Socket Path when qmp_enable is true. Defaults to output_directory/vm_name.monitor.

  • ssh_host_port_min (int) - The minimum and maximum port to use for the SSH port on the host machine which is forwarded to the SSH port on the guest machine. Because Packer often runs in parallel, Packer will choose a randomly available port in this range to use as the host port. By default this is 2222 to 4444.

  • ssh_host_port_max (int) - SSH Host Port Max

  • use_default_display (bool) - If true, do not pass a -display option to qemu, allowing it to choose the default. This may be needed when running under macOS, and getting errors about sdl not being available.

  • display (string) - What QEMU -display option to use. Defaults to gtk, use none to not pass the -display option allowing QEMU to choose the default. This may be needed when running under macOS, and getting errors about sdl not being available.

  • vnc_bind_address (string) - The IP address that should be binded to for VNC. By default packer will use for this. If you wish to bind to all interfaces use

  • vnc_use_password (bool) - Whether or not to set a password on the VNC server. This option automatically enables the QMP socket. See qmp_socket_path. Defaults to false.

  • vnc_port_min (int) - The minimum and maximum port to use for VNC access to the virtual machine. The builder uses VNC to type the initial boot_command. Because Packer generally runs in parallel, Packer uses a randomly chosen port in this range that appears available. By default this is 5900 to 6000. The minimum and maximum ports are inclusive.

  • vnc_port_max (int) - VNC Port Max

  • vm_name (string) - This is the name of the image (QCOW2 or IMG) file for the new virtual machine. By default this is packer-BUILDNAME, where "BUILDNAME" is the name of the build. Currently, no file extension will be used unless it is specified in this option.

»ISO Configuration

By default, Packer will symlink, download or copy image files to the Packer cache into a "hash($iso_url+$iso_checksum).$iso_target_extension" file. Packer uses hashicorp/go-getter in file mode in order to perform a download.

go-getter supports the following protocols:

  • Local files
  • Git
  • Mercurial
  • HTTP
  • Amazon S3

Examples: go-getter can guess the checksum type based on iso_checksum len.

  "iso_checksum": "946a6077af6f5f95a51f82fdc44051c7aa19f9cfc5f737954845a6050543d7c2",
  "iso_url": "ubuntu.org/.../ubuntu-14.04.1-server-amd64.iso"
  "iso_checksum_type": "file",
  "iso_checksum": "ubuntu.org/..../ubuntu-14.04.1-server-amd64.iso.sum",
  "iso_url": "ubuntu.org/.../ubuntu-14.04.1-server-amd64.iso"
  "iso_checksum_url": "./shasums.txt",
  "iso_url": "ubuntu.org/.../ubuntu-14.04.1-server-amd64.iso"
  "iso_checksum_type": "sha256",
  "iso_checksum_url": "./shasums.txt",
  "iso_url": "ubuntu.org/.../ubuntu-14.04.1-server-amd64.iso"


  • iso_checksum (string) - The checksum for the ISO file or virtual hard drive file. The algorithm to use when computing the checksum can be optionally specified with iso_checksum_type. When iso_checksum_type is not set packer will guess the checksumming type based on iso_checksum length. iso_checksum can be also be a file or an URL, in which case iso_checksum_type must be set to file; the go-getter will download it and use the first hash found.
  • iso_url (string) - A URL to the ISO containing the installation image or virtual hard drive (VHD or VHDX) file to clone.


  • iso_checksum_url (string) - An URL to a checksum file containing a checksum for the ISO file. At least one of iso_checksum and iso_checksum_url must be defined. iso_checksum_url will be ignored if iso_checksum is non empty.
  • iso_checksum_type (string) - The algorithm to be used when computing the checksum of the file specified in iso_checksum. Currently, valid values are "", "none", "md5", "sha1", "sha256", "sha512" or "file". Since the validity of ISO and virtual disk files are typically crucial to a successful build, Packer performs a check of any supplied media by default. While setting "none" will cause Packer to skip this check, corruption of large files such as ISOs and virtual hard drives can occur from time to time. As such, skipping this check is not recommended. iso_checksum_type must be set to file when iso_checksum is an url.
  • iso_urls ([]string) - Multiple URLs for the ISO to download. Packer will try these in order. If anything goes wrong attempting to download or while downloading a single URL, it will move on to the next. All URLs must point to the same file (same checksum). By default this is empty and iso_url is used. Only one of iso_url or iso_urls can be specified.
  • iso_target_path (string) - The path where the iso should be saved after download. By default will go in the packer cache, with a hash of the original filename and checksum as its name.
  • iso_target_extension (string) - The extension of the iso file after download. This defaults to iso.

»Http directory configuration

Packer will create an http server serving http_directory when it is set, a random free port will be selected and the architecture of the directory referenced will be available in your builder.

Example usage from a builder:

wget http://{{ .HTTPIP }}:{{ .HTTPPort }}/foo/bar/preseed.cfg


  • http_directory (string) - Path to a directory to serve using an HTTP server. The files in this directory will be available over HTTP that will be requestable from the virtual machine. This is useful for hosting kickstart files and so on. By default this is an empty string, which means no HTTP server will be started. The address and port of the HTTP server will be available as variables in boot_command. This is covered in more detail below.
  • http_port_min (int) - These are the minimum and maximum port to use for the HTTP server started to serve the http_directory. Because Packer often runs in parallel, Packer will choose a randomly available port in this range to run the HTTP server. If you want to force the HTTP server to be on one port, make this minimum and maximum port the same. By default the values are 8000 and 9000, respectively.
  • http_port_max (int) - HTTP Port Max

»Floppy configuration

A floppy can be made available for your build. This is most useful for unattended Windows installs, which look for an Autounattend.xml file on removable media. By default, no floppy will be attached. All files listed in this setting get placed into the root directory of the floppy and the floppy is attached as the first floppy device. The summary size of the listed files must not exceed 1.44 MB. The supported ways to move large files into the OS are using http_directory or the file provisioner.


  • floppy_files ([]string) - A list of files to place onto a floppy disk that is attached when the VM is booted. Currently, no support exists for creating sub-directories on the floppy. Wildcard characters (\*, ?, and []) are allowed. Directory names are also allowed, which will add all the files found in the directory to the floppy.
  • floppy_dirs ([]string) - A list of directories to place onto the floppy disk recursively. This is similar to the floppy_files option except that the directory structure is preserved. This is useful for when your floppy disk includes drivers or if you just want to organize it's contents as a hierarchy. Wildcard characters (\*, ?, and []) are allowed. The maximum summary size of all files in the listed directories are the same as in floppy_files.
  • floppy_label (string) - Floppy Label

»Shutdown configuration


  • shutdown_command (string) - The command to use to gracefully shut down the machine once all provisioning is complete. By default this is an empty string, which tells Packer to just forcefully shut down the machine. This setting can be safely omitted if for example, a shutdown command to gracefully halt the machine is configured inside a provisioning script. If one or more scripts require a reboot it is suggested to leave this blank (since reboots may fail) and instead specify the final shutdown command in your last script.
  • shutdown_timeout (duration string | ex: "1h5m2s") - The amount of time to wait after executing the shutdown_command for the virtual machine to actually shut down. If the machine doesn't shut down in this time it is considered an error. By default, the time out is "5m" (five minutes).

»Boot Configuration

The boot command "typed" character for character over a VNC connection to the machine, simulating a human actually typing the keyboard.

Keystrokes are typed as separate key up/down events over VNC with a default 100ms delay. The delay alleviates issues with latency and CPU contention. You can tune this delay on a per-builder basis by specifying "boot_key_interval" in your Packer template.

The boot configuration is very important: boot_command specifies the keys to type when the virtual machine is first booted in order to start the OS installer. This command is typed after boot_wait, which gives the virtual machine some time to actually load.

The boot_command is an array of strings. The strings are all typed in sequence. It is an array only to improve readability within the template.

There are a set of special keys available. If these are in your boot command, they will be replaced by the proper key:

  • <bs> - Backspace

  • <del> - Delete

  • <enter> <return> - Simulates an actual "enter" or "return" keypress.

  • <esc> - Simulates pressing the escape key.

  • <tab> - Simulates pressing the tab key.

  • <f1> - <f12> - Simulates pressing a function key.

  • <up> <down> <left> <right> - Simulates pressing an arrow key.

  • <spacebar> - Simulates pressing the spacebar.

  • <insert> - Simulates pressing the insert key.

  • <home> <end> - Simulates pressing the home and end keys.

  • <pageUp> <pageDown> - Simulates pressing the page up and page down keys.

  • <menu> - Simulates pressing the Menu key.

  • <leftAlt> <rightAlt> - Simulates pressing the alt key.

  • <leftCtrl> <rightCtrl> - Simulates pressing the ctrl key.

  • <leftShift> <rightShift> - Simulates pressing the shift key.

  • <leftSuper> <rightSuper> - Simulates pressing the ⌘ or Windows key.

  • <wait> <wait5> <wait10> - Adds a 1, 5 or 10 second pause before sending any additional keys. This is useful if you have to generally wait for the UI to update before typing more.

  • <waitXX> - Add an arbitrary pause before sending any additional keys. The format of XX is a sequence of positive decimal numbers, each with optional fraction and a unit suffix, such as 300ms, 1.5h or 2h45m. Valid time units are ns, us (or µs), ms, s, m, h. For example <wait10m> or <wait1m20s>.

  • <XXXOn> <XXXOff> - Any printable keyboard character, and of these "special" expressions, with the exception of the <wait> types, can also be toggled on or off. For example, to simulate ctrl+c, use <leftCtrlOn>c<leftCtrlOff>. Be sure to release them, otherwise they will be held down until the machine reboots. To hold the c key down, you would use <cOn>. Likewise, <cOff> to release.

  • {{ .HTTPIP }} {{ .HTTPPort }} - The IP and port, respectively of an HTTP server that is started serving the directory specified by the http_directory configuration parameter. If http_directory isn't specified, these will be blank!

  • {{ .Name }} - The name of the VM.

Example boot command. This is actually a working boot command used to start an CentOS 6.4 installer:

"boot_command": [
    " ks=http://{{ .HTTPIP }}:{{ .HTTPPort }}/centos6-ks.cfg<enter>"

The example shown below is a working boot command used to start an Ubuntu 12.04 installer:

  "/install/vmlinuz noapic ",
  "preseed/url=http://{{ .HTTPIP }}:{{ .HTTPPort }}/preseed.cfg ",
  "debian-installer=en_US auto locale=en_US kbd-chooser/method=us ",
  "hostname={{ .Name }} ",
  "fb=false debconf/frontend=noninteractive ",
  "keyboard-configuration/modelcode=SKIP keyboard-configuration/layout=USA ",
  "keyboard-configuration/variant=USA console-setup/ask_detect=false ",
  "initrd=/install/initrd.gz -- <enter>"

For more examples of various boot commands, see the sample projects from our community templates page.


  • disable_vnc (bool) - Whether to create a VNC connection or not. A boot_command cannot be used when this is true. Defaults to false.
  • boot_key_interval (duration string | ex: "1h5m2s") - Time in ms to wait between each key press
  • boot_keygroup_interval (duration string | ex: "1h5m2s") - Time to wait after sending a group of key pressses. The value of this should be a duration. Examples are 5s and 1m30s which will cause Packer to wait five seconds and one minute 30 seconds, respectively. If this isn't specified, a sensible default value is picked depending on the builder type.
  • boot_wait (duration string | ex: "1h5m2s") - The time to wait after booting the initial virtual machine before typing the boot_command. The value of this should be a duration. Examples are 5s and 1m30s which will cause Packer to wait five seconds and one minute 30 seconds, respectively. If this isn't specified, the default is 10s or 10 seconds. To set boot_wait to 0s, use a negative number, such as "-1s"
  • boot_command ([]string) - This is an array of commands to type when the virtual machine is first booted. The goal of these commands should be to type just enough to initialize the operating system installer. Special keys can be typed as well, and are covered in the section below on the boot command. If this is not specified, it is assumed the installer will start itself.

»Communicator Configuration


  • communicator (string) - Packer currently supports three kinds of communicators:

    • none - No communicator will be used. If this is set, most provisioners also can't be used.

    • ssh - An SSH connection will be established to the machine. This is usually the default.

    • winrm - A WinRM connection will be established.

    In addition to the above, some builders have custom communicators they can use. For example, the Docker builder has a "docker" communicator that uses docker exec and docker cp to execute scripts and copy files.

  • pause_before_connecting (duration string | ex: "1h5m2s") - We recommend that you enable SSH or WinRM as the very last step in your guest's bootstrap script, but sometimes you may have a race condition where you need Packer to wait before attempting to connect to your guest.

    If you end up in this situation, you can use the template option pause_before_connecting. By default, there is no pause. For example:

      "communicator": "ssh",
      "ssh_username": "myuser",
      "pause_before_connecting": "10m"

    In this example, Packer will check whether it can connect, as normal. But once a connection attempt is successful, it will disconnect and then wait 10 minutes before connecting to the guest and beginning provisioning.


Some users have experienced errors complaining about invalid keymaps. This seems to be related to having a common directory or file in the directory they've run Packer in, like the packer source directory. This appears to be an upstream bug with qemu, and the best solution for now is to remove the file/directory or run in another directory.

Some users have reported issues with incorrect keymaps using qemu version 2.11. This is a bug with qemu, and the solution is to upgrade, or downgrade to 2.10.1 or earlier.