
# Running OpenVMM

This page offers a high-level overview of different ways to launch and interact
with OpenVMM.

These examples are by no means "exhaustive", and should be treated as a useful
jumping-off point for subsequent self-guided experimentation with OpenVMM.

## Obtaining a copy of OpenVMM

To get started, ensure you have a copy of the OpenVMM executable and its runtime
dependencies, via one of the following options:

### Building OpenVMM Locally

Follow the instructions on: [Building OpenVMM](../../dev_guide/getting_started/build_openvmm.md).

### Pre-Built Binaries

If you would prefer to try OpenVMM without building it from scratch, you can
download pre-built copies of the binary from
[OpenVMM CI](https://github.com/microsoft/openvmm/actions/workflows/openvmm-ci.yaml).

Simply select a successful pipeline run (should have a Green checkbox), and
scroll down to select an appropriate `*-openvmm` artifact for your particular
architecture and operating system.  **You must be signed into GitHub in order
to download artifacts**.

## Examples

```admonish tip
These examples all use `cargo run --`, with the assumption that you are a
developer building your own copy of OpenVMM locally!

To run these examples using a pre-compiled copy of OpenVMM, swap `cargo run
--` with `/path/to/openvmm`.
```

~~~admonish tip title="UEFI firmware required when running outside cargo"
When running via `cargo run`, environment variables in `.cargo/config.toml`
automatically point OpenVMM to the `mu_msvm` UEFI firmware (`MSVM.fd`)
downloaded by `cargo xflowey restore-packages`.

When running the `openvmm` binary directly, these environment variables are
**not set**, and you will get:

> fatal error: must provide uefi firmware when booting with uefi

To fix this, **explicitly pass the firmware** using `--uefi-firmware`:

```shell
openvmm --uefi --uefi-firmware path/to/MSVM.fd --disk memdiff:path/to/disk.vhdx
```

If you ran `cargo xflowey restore-packages`, the firmware is at:

```text
.packages/hyperv.uefi.mscoreuefi.x64.RELEASE/MsvmX64/RELEASE_VS2022/FV/MSVM.fd        # x64
.packages/hyperv.uefi.mscoreuefi.AARCH64.RELEASE/MsvmAARCH64/RELEASE_VS2022/FV/MSVM.fd # aarch64
```

If you used `cargo xflowey vmm-tests --build-only --dir <out>`, the firmware
is copied into that output directory under the same relative path.

Alternatively, set the environment variable so you don't need the flag each time:

```shell
# x64
export X86_64_OPENVMM_UEFI_FIRMWARE=path/to/MSVM.fd

# aarch64
export AARCH64_OPENVMM_UEFI_FIRMWARE=path/to/MSVM.fd
```
~~~

If you run into any issues, please refer to [Troubleshooting](./troubleshooting.md).

### _Preface:_ Quitting OpenVMM

By default, OpenVMM will connect the guests's COM1 serial port to the current
terminal session, forwarding all keystrokes directly to the VM.

As such, a simple `ctrl-c` does not suffice to quit OpenVMM!

Instead, you can type `crtl-q` to enter OpenVMM's [interactive console](../../reference/openvmm/management/interactive_console.md), and enter `q` to quit.

### Sample Linux Kernel, via direct-boot

This example will launch Linux via direct boot (i.e: without going through UEFI
or BIOS), and appends `single` to the kernel command line.

The Linux guest's console will be hooked up to COM1, and is relayed to the host
terminal by default.

To launch Linux with an interactive console into the shell within initrd, simply
run:

```shell
cargo run
```

This works by setting the default `[env]` vars in `.cargo/config.toml` to
configure OpenVMM to use a set of pre-compiled test kernel + initrd images,
which are downloaded as part of the `cargo xflowey restore-packages` command.
Note that this behavior only happens when run via `cargo run` (as `cargo` is the
tool which ensures the required env-vars are set).

The source for the sample kernel + initrd can be found on the
[microsoft/openvmm-deps](https://github.com/microsoft/openvmm-deps) repo.

The kernel and initrd can be controlled via options:

* `--kernel <PATH>`: The kernel image. Must be an uncompressed kernel (vmlinux, not bzImage).
* `--initrd <PATH>`: The initial ramdisk image.
* `-c <STRING>` or `--cmdline <STRING>`: Extra kernel command line options, such as `root=/dev/sda`.

### Windows, via UEFI

This example will launch a modern copy of Windows via UEFI, using the `mu_msvm`
firmware package.

A copy of the `mu_msvm` UEFI firmware is automatically downloaded via `cargo
xflowey restore-packages`.

```shell
cargo run -- --uefi --disk memdiff:path/to/windows.vhdx --gfx
```

For more info on `--gfx`, and how to actually interact with the VM using a
mouse/keyboard/video, see the [Graphical Console](../../reference/openvmm/graphical_console.md)
docs.

The file `windows.vhdx` can be any format of VHD(X).

Note that OpenVMM does not currently support using dynamic VHD/VHDX files on
Linux hosts. Unless you have a fixed VHD1 image, you will need to convert the
image to raw format, using the following command:

```shell
qemu-img convert -f vhdx -O raw windows.vhdx windows.img
```

Also, note the use of `memdiff`, which creates a memory-backed "differencing
disk" shim between the VMM and the backing disk image, which ensures that any
writes the VM makes to the VHD are not persisted between runs. This is very
useful when iterating on OpenVMM code, since booting the VM becomes repeatable
and you don't have to worry about shutting down properly. Use `file` instead for
normal persistent storage.

### OpenHCL, via Linux Direct Boot

This example will boot OpenHCL in Linux direct mode, running a minimal shell
inside VTL2. This is the same configuration used by the `openhcl_linux_direct_x64`
integration tests.

First, build the test artifacts from Linux or WSL using `vmm-tests --build-only`.
The IGVM must be built on Linux:

```shell
cargo xflowey vmm-tests --build-only --dir <out> --target windows-x64
```

```admonish tip
If you only need the IGVM binary (and already have `openvmm.exe`), you can
use `cargo xflowey build-igvm` instead — it's faster than building the full
test suite.
```

This places `openvmm.exe` and `openhcl-x64-test-linux-direct.bin` in the
`<out>` directory. Then, on Windows, from the `<out>` directory:

```powershell
.\openvmm.exe `
    --hv `
    --vtl2 `
    --igvm openhcl-x64-test-linux-direct.bin `
    -c "panic=-1 reboot=triple UNDERHILL_SERIAL_WAIT_FOR_RTS=1 UNDERHILL_CMDLINE_APPEND=rdinit=/bin/sh" `
    -m 2GB `
    --vmbus-com1-serial "term,name=VTL0 Linux" `
    --com3 "term,name=VTL2 OpenHCL" `
    --vtl2-vsock-path $env:temp\ohcldiag-dev
```

```admonish warning
The `--vmbus-com1-serial` flag is **required** when using `rdinit=/bin/sh`.
The shell running as PID 1 needs a controlling terminal (tty) — without one
it exits immediately, causing a kernel panic and infinite reboot loop.

The `--com3` flag is optional but recommended — it gives you VTL2 (OpenHCL)
kernel console output for debugging.
```

For more details on running OpenHCL on OpenVMM, including
[VMBus relay](../../reference/architecture/openhcl/vmbus.md) and device
assignment, see [Running OpenHCL: OpenVMM](../openhcl/run/openvmm.md).

### Alpine Linux, via Direct Boot

See the dedicated [Alpine Linux](./alpine.md) guide for a full walkthrough of
booting Alpine from a cloud disk image using direct boot with PCIe and
virtio-blk.

### DOS, via PCAT BIOS

While DOS in particular is not a scenario that the OpenVMM has heavily invested
in, the fact DOS is able to boot in OpenVMM serves as a testament to OpenVMM's
solid support of legacy x86 devices and infrastructure.

The following command will boot a copy of DOS from a virtual floppy disk, using
the [Hyper-V PCAT BIOS](../../reference/devices/firmware/pcat_bios.md).

Booting via PCAT is not just for DOS though! Many older operating systems,
including older copies of Windows / Linux, require booting via BIOS.

```bash
cargo run -- --pcat --gfx --floppy memdiff:/path/to/msdos.vfd --pcat-boot-order=floppy,optical,hdd
```
