packer-cn/website/source/docs/builders/qemu.html.md.erb

---
modeline: |
  vim: set ft=pandoc:
description: |
    The Qemu Packer builder is able to create KVM and Xen virtual machine images.
layout: docs
page_title: 'QEMU - Builders'
sidebar_current: 'docs-builders-qemu'
---

# QEMU Builder

Type: `qemu`

The Qemu Packer builder is able to create [KVM](http://www.linux-kvm.org) and
[Xen](http://www.xenproject.org) 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.

``` json
{
  "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": 5000,
      "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](https://www.packer.io/community-tools.html#templates)
for a practical usage example.

## Configuration Reference

There are many configuration options available for the Qemu builder. They are
organized below into two categories: required and optional. Within each
category, the available options are alphabetized and described.

In addition to the options listed here, a
[communicator](/docs/templates/communicator.html) can be configured for this
builder.

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`).

### Required:

-   `iso_checksum` (string) - The checksum for the OS ISO file. Because ISO
    files are so large, this is required and Packer will verify it prior to
    booting a virtual machine with the ISO attached. The type of the checksum is
    specified with `iso_checksum_type`, documented below. At least one of
    `iso_checksum` and `iso_checksum_url` must be defined. This has precedence
    over `iso_checksum_url` type.

-   `iso_checksum_type` (string) - The type of the checksum specified in
    `iso_checksum`. Valid values are `none`, `md5`, `sha1`, `sha256`, or
    `sha512` currently. While `none` will skip checksumming, this is not
    recommended since ISO files are generally large and corruption does happen
    from time to time.

-   `iso_checksum_url` (string) - A URL to a GNU or BSD style checksum file
    containing a checksum for the OS ISO file. At least one of `iso_checksum`
    and `iso_checksum_url` must be defined. This will be ignored if
    `iso_checksum` is non empty.

-   `iso_url` (string) - A URL to the ISO containing the installation image.
    This URL can be either an HTTP URL or a file URL (or path to a file). If
    this is an HTTP URL, Packer will download it and cache it between runs.
    This can also be a URL to an IMG or QCOW2 file, in which case QEMU will
    boot directly from it. When passing a path to an IMG or QCOW2 file, you
    should set `disk_image` to `true`.

### Optional:

-   `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.

    -&gt; The `hax` accelerator has issues attaching CDROM ISOs. This is an
    upstream issue which can be tracked
    [here](https://github.com/intel/haxm/issues/20).

    -&gt; The `hvf` and `whpx` accelerator are new and experimental as of
    [QEMU 2.12.0](https://wiki.qemu.org/ChangeLog/2.12#Host_support).
    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.

    -&gt; For `whpx`, note that [Stefan Weil's QEMU for Windows distribution](https://qemu.weilnetz.de/w64/)
    does not include WHPX support and users may need to compile or source a
    build of QEMU for Windows themselves with WHPX support.

-   `boot_command` (array of strings) - 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.

-   `boot_wait` (string) - 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.

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

-   `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_compression` (boolean) - Apply compression to the QCOW2 disk file
    using `qemu-img convert`. Defaults to `false`.

-   `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.

-   `disk_image` (boolean) - 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.

-   `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](https://bugzilla.redhat.com/show_bug.cgi?id=1019220).
    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` (number) - The size, in megabytes, of the hard disk to create
    for the VM. By default, this is `40960` (40 GB).

-   `floppy_dirs` (array of strings) - 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_files` (array of strings) - A list of files to place onto a floppy
    disk that is attached when the VM is booted. 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. 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. 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](https://www.packer.io/docs/provisioners/file.html).

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

-   `headless` (boolean) - 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>`

-   `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` and `http_port_max` (number) - 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.

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

-   `iso_target_extension` (string) - The extension of the iso file after
    download. This defaults to `iso`.

-   `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 as its name.

-   `iso_urls` (array of strings) - 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.

-   `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` (number) - 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.

-   `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.

-   `qemuargs` (array of array of strings) - 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.

    ~&gt; **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:

    ``` json
    {
      "qemuargs": [
        [ "-m", "1024M" ],
        [ "--no-acpi", "" ],
        [
          "-netdev",
          "user,id=mynet0,",
          "hostfwd=hostip:hostport-guestip:guestport",
          ""
        ],
        [ "-device", "virtio-net,netdev=mynet0" ]
      ]
    }
    ```

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

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

    ~&gt; **Windows Users:** [QEMU for Windows](https://qemu.weilnetz.de/) 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:

    ``` text
    setx SDL_STDIO_REDIRECT=0
    ```

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

    ``` json
    {
      "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.

-   `use_backing_file` (boolean) - 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.

-   `use_default_display` (boolean) - 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.

-   `shutdown_command` (string) - The command to use to gracefully shut down the
    machine once all the provisioning is done. By default this is an empty
    string, which tells Packer to just forcefully shut down the machine unless a
    shutdown command takes place inside script so this may safely be omitted. It
    is important to add a `shutdown_command`. By default Packer halts the virtual
    machine and the file system may not be sync'd. Thus, changes made in a
    provisioner might not be saved. If one or more scripts require a reboot it is
    suggested to leave this blank since reboots may fail and specify the final
    shutdown command in your last script.

-   `shutdown_timeout` (string) - The amount of time to wait after executing the
    `shutdown_command` for the virtual machine to actually shut down. If it
    doesn't shut down in this time, it is an error. By default, the timeout is
    `5m` or five minutes.

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

-   `ssh_host_port_min` and `ssh_host_port_max` (number) - 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`.

-   `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.

-   `vnc_bind_address` (string / IP address) - The IP address that should be
    binded to for VNC. By default packer will use `127.0.0.1` for this. If you
    wish to bind to all interfaces use `0.0.0.0`.

-   `vnc_port_min` and `vnc_port_max` (number) - 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.

## Boot Command

The `boot_command` configuration is very important: it 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 ISO.

As documented above, 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.

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

-&gt; 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, for example:

```
{
  "builders": [
    {
      "type": "qemu",
      "boot_key_interval": "10ms"
      ...
    }
  ]
}
```

<%= partial "partials/builders/boot-command" %>

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

``` json
{
"boot_command": [
    "<tab><wait>",
    " ks=http://{{ .HTTPIP }}:{{ .HTTPPort }}/centos6-ks.cfg<enter>"
  ]
}
```

For more examples of various boot commands, see the sample projects from our
[community templates page](/community-tools.html#templates).

### Troubleshooting

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.