---
name: "vm.conf"
section: "5"
platform: "openbsd"
package: "man"
version: "8.0-current-20261101"
release: "OpenBSD 8.0-current (2026-11-01)"
platforms: ["openbsd"]
url: "https://new.carta.tech/vm.conf"
---

# vm.conf(5)

virtual machine configuration

## NAME

**vm.conf** – virtual machine configuration

## DESCRIPTION

**vm.conf** is the configuration file for the virtual machine monitor, [vmm(4)](/vmm/4.md), which is responsible for creating, destroying, and executing virtual machines (VMs).

**vm.conf** is divided into the following main sections:

- Macros

  Definitions of variables that can be used later, simplifying the configuration file.

- Global configuration

  Global settings for [vmd(8)](/vmd/8.md).

- VM configuration and VM instances

  Configuration for each individual virtual machine.

- Switch configuration

  Configuration for virtual switches.

The current line can be extended over multiple lines using a backslash (‘\\’). Comments can be put anywhere in the file using a hash mark (‘#’) and extend to the end of the current line. Care should be taken when commenting out multi-line text: the comment is effective until the end of the entire block.

Arguments not beginning with a letter, digit, underscore, or slash must be quoted.

Additional configuration files can be included with the **include** keyword, for example:

```
include "/etc/vm1.example.com.conf"
```

### Macros

A macro is defined with a command of the form *name*=*value*. The macro *name* can contain letters, digits, and underscores and cannot be a reserved word (for example, **vm**, **memory**, or **disk**). Within unquoted arguments, the string $*name* is later expanded to *value*.

For example:

```
ramdisk="/bsd.rd"
vm "vm1.example.com" {
	memory 512M
	boot $ramdisk
}
```

### Global configuration

The following settings can be configured globally:

- **agentx** \[**context** *context*\] \[**path** *socket*\]

  Export vm metrics via an AgentX compatible [snmpd(8)](/snmpd/8.md) by connecting to the *socket*. Metrics can be found under the vmMIB subtree (mib-2.236). If *socket* is omitted it defaults to */var/agentx/master*. *context* is the SNMPv3 context and can usually be omitted.

- **local** **prefix** *address*/*prefix*

  Set the IPv4 network prefix that is used to allocate subnets for local interfaces, see **local** **interface** in the VM configuration section below. The default is 100.64.0.0/10.

- **local** **inet6** \[**prefix** *address*/*prefix*\]

  Enable IPv6 on local interfaces and allocate routable subnets. If the prefix is not specified, a random prefix from the “unique local” network range fd00::/8 is generated on startup. The specified prefix length must be /64 or smaller.

- **socket** **owner** *user*:*group*

  Set the [vmd(8)](/vmd/8.md) control socket owner to the specified *user* and *group*. Users with access to the control socket are allowed to use [vmctl(8)](/vmctl/8.md) for restricted access to [vmd(8)](/vmd/8.md). If only *user* is given, only the user is set. If only :*group* is given, only the group is set. The default is root:wheel.

- **staggered** **start** **parallel** *parallelism* **delay** *delay*

  Start all configured VMs in a staggered fashion with *parallelism* instances in parallel every *delay* seconds. Defaults to *parallelism* equal to number of online CPUs and a *delay* of 30 seconds.

### VM configuration

Each **vm** section starts with the declaration of a virtual machine *name*:

- **vm** *name* {...}

  The *name* starts with a letter and can contain alphanumeric characters, dots (‘.’), dashes (‘-’), and underscores (‘\_’). Typically this is a hostname.

The block enclosed in curly braces can contain the following parameters:

- **allow** **instance** {...}

  Set the permissions to create VM instances.

- **cpus** *count*

  Number of virtual CPUs to provide to the VM. The default is 1 and the maximum is 64.

- **boot** *path*

  Kernel or BIOS image to load when booting the VM. If not specified, the default is to boot using the BIOS image in */etc/firmware/vmm-bios*.

- **boot** **device** *device*

  Force VM to boot from *device*. Valid values are:

  - **cdrom**

    Boot the ISO image file specified using the **cdrom** parameter.

  - **disk**

    Boot from the disk image file specified using the **disk** parameter.

  - **net**

    Boot the kernel specified using the **boot** parameter as if the VM was network booted. In addition, the DHCP lease advertises “auto\_install” in the bootfile option making it suitable for use with [autoinstall(8)](/autoinstall/8.md). Note, this is not to be confused with [pxeboot(8)](/pxeboot/8.md) but rather a simulated network boot.

    Currently **disk** and **cdrom** only work with VMs booted using BIOS.

- **cdrom** *path*

  ISO image file.

- **enable**

  Automatically start the VM. This is the default if neither **enable** nor **disable** is specified.

- **disable**

  Do not automatically start this VM.

- **disk** *path* \[**format** *fmt*\]

  Disk image file (may be specified multiple times to add multiple disk images). The format may be specified as either **qcow2** (a sparse file format which reduces storage) or **raw**. If left unspecified, the format defaults to **raw** if it cannot be derived automatically.

- \[**local**\] **interface** \[*name*\] \[{...}\]

  Network interface to add to the VM. The optional *name* can be either **tap** to select the next available [tap(4)](/tap/4.md) interface on the VM host side (the default) or **tap***N* to select a specific one.

  Valid options are:

  - **group** *group-name*

    Assign the interface to a specific interface “group”. For example, this can be used to write [pf.conf(5)](/pf.conf/5.md) rules for several VM interfaces in the same group. The *group-name* must not be longer than 15 characters or end with a digit, as described in [ifconfig(8)](/ifconfig/8.md).

  - \[**locked**\] **lladdr** \[*etheraddr*\]

    Change the link layer address (MAC address) of the interface on the VM guest side. If not specified, a randomized address is assigned by [vmd(8)](/vmd/8.md). If the **locked** keyword is specified, [vmd(8)](/vmd/8.md) drops packets from the VM with altered source addresses.

  - **rdomain** *rdomainid*

    Attach the interface to the routing domain with the specified *rdomainid*. If attaching to a switch that also has an *rdomainid* set, the *rdomainid* configured for the interface takes precedence.

  - **switch** *name*

    Set the virtual switch by *name*. See the Switch configuration section about virtual switches. This option is ignored if a switch with a matching name cannot be found.

  - **up**

    Start the interface forwarding packets. This is the default.

  - **down**

    Stop the interface from forwarding packets.

    A **local** interface auto-generates an IPv4 subnet for the interface, configures a gateway address on the VM host side, and runs a simple DHCP/BOOTP server for the VM. This option can be used for layer 3 mode without configuring a switch.

    If the global **local** **inet6** option is enabled, a routable IPv6 gateway address is generated on the host side. Unlike the IPv4 option, [vmd(8)](/vmd/8.md) does not respond to DHCPv6 or router solicitation messages itself. Use [rad(8)](/rad/8.md) listening on the interface group, e.g. **interface** **tap** for auto-configuring the VMs accordingly.

- **interfaces** *count*

  Optional minimum number of network interfaces to add to the VM. If the *count* is greater than the number of **interface** statements, additional default interfaces are added.

- **memory** *bytes*

  Memory size of the VM in bytes, rounded to megabytes. A scale multiplier can be used as described in scan\_scaled(3). The default is 512M.

- **owner** *user*:*group*

  Set the owner of the VM to the specified *user* and *group*. The owner is allowed to start or stop the VM, pause or unpause the VM, and open the VM's console. If only *user* is given, only the user is set. If only :*group* is given, only the group is set.

- **sev**

  Enables AMD Secure Encrypted Virtualization (SEV) for the guest. [vmd(8)](/vmd/8.md) uses [psp(4)](/psp/4.md) to configure the guest for SEV.

- **seves**

  Enables AMD Encrypted State (SEV-ES) for the guest. This implicitly enables SEV, too.

### VM instances

It is possible to use configured or running VMs as a template for additional instances of the VM. An instance is just like a normal **vm** and is configured with the following declaration of the virtual machine *name*:

- **vm** *parent* **instance** *name* {...}

  A virtual machine can be created as an instance of any other configured VM.

The new instance inherits settings from the VM *parent*, except for exclusive options such as **disk**, **interface** **lladdr**, or **interface** *name*. The configuration options are identical to the VM configuration, but restricted to the allowed instance options.

The allowed instance options are configured in the *parent* VM:

- **allow** **instance** {...}

  Allow users to use this VM as a template for VM instances. By default, the root user can always create instances without restrictions and users or non-root owners cannot create instances. An instance inherits the configuration from the VM and the user, if permitted, is allowed to configure individual VM options.

Valid options are:

- **boot**

  Allow user to configure the kernel or BIOS image. The user needs read access to the image.

- **cpus**

  Allow user to configure the number of virtual CPUs.

- **cdrom**

  Allow user to configure the ISO file. The user needs read access to the file.

- **disk**

  Allow user to configure the disk images. The user needs read and write access to image and instances are not allowed to reuse disks from the parent VM.

- **instance**

  Allow user to create additional instances from the instances.

- **interface**

  Allow user to change network interface settings.

- **memory**

  Allow user to configure the memory size.

- **owner** *user*\[:*group*\]

  Allow the specified user or group to create the instances. The owner is allowed to create VM instances, start or stop the instances, pause or unpause the instances, and open the instances' consoles.

- **owner** :*group*

  Set the owner to the specified group.

### Switch configuration

A virtual switch allows VMs to communicate with other network interfaces on the host system via either [bridge(4)](/bridge/4.md) or [veb(4)](/veb/4.md). The network interface for each virtual switch defined in **vm.conf** is pre-configured using [hostname.if(5)](/hostname.if/5.md) or [ifconfig(8)](/ifconfig/8.md) (see the BRIDGE and VEB sections in [ifconfig(8)](/ifconfig/8.md) accordingly). When a VM is started, virtual network interfaces which are assigned to a virtual switch have their [tap(4)](/tap/4.md) interface automatically added into the corresponding [bridge(4)](/bridge/4.md) or [veb(4)](/veb/4.md) interface underlying the virtual switch.

Virtual switches can be configured at any point in the configuration file. Each **switch** section starts with a declaration of the virtual switch:

- **switch** *name* {...}

  This name can be any string, and is typically a network name.

The block enclosed in curly braces can contain the following parameters:

- **enable**

  Automatically configure the switch. This is the default if neither **enable** nor **disable** is specified.

- **locked** **lladdr**

  If this option is specified, [vmd(8)](/vmd/8.md) drops packets with altered source addresses that do not match the link layer addresses (MAC addresses) of the VM interfaces in this switch.

- **disable**

  Do not automatically configure this switch.

- **description** \[*string*\]

  Set the description of the underlying [bridge(4)](/bridge/4.md) or [veb(4)](/veb/4.md) interface. If *string* is omitted, [vmd(8)](/vmd/8.md) generates a description containing the switch identifier and name. If the **description** option is omitted, the existing interface description is left unchanged. An empty *string* clears the interface description.

- **group** *group-name*

  Assign each interface to a specific interface “group”. For example, this can be used to write [pf.conf(5)](/pf.conf/5.md) rules for several VM interfaces in the same group. The *group-name* must not be longer than 15 characters or end with a digit, as described in [ifconfig(8)](/ifconfig/8.md).

- **interface** *name*

  Set the [bridge(4)](/bridge/4.md) or [veb(4)](/veb/4.md) network interface of this switch.

- **rdomain** *rdomainid*

  Set the routing domain of the switch and all of its VM interfaces to *rdomainid*.

- **up**

  Start the switch forwarding packets. This is the default.

- **down**

  Stop the switch from forwarding packets.

## FILES

- */etc/vm.conf*

  default [vmd(8)](/vmd/8.md) and [vmctl(8)](/vmctl/8.md) configuration file

- */etc/examples/vm.conf*

  example configuration file

- */var/run/vmd.sock*

  Unix domain [socket(2)](/socket/2.md) where [vmd(8)](/vmd/8.md) listens

- */etc/firmware/vmm-bios*

  default BIOS image for booting

- */var/agentx/master*

  default Unix domain [socket(2)](/socket/2.md) where [snmpd(8)](/snmpd/8.md) listens

## EXAMPLES

Create a new VM with 1GB memory, 1 network interface connected to “uplink”, with one disk image */home/joe/vm2-disk.img*, owned by user ‘joe’:

```
vm "vm2.example.com" {
	memory 1G
	disk "/home/joe/vm2-disk.img"
	interface { switch "uplink" }
	owner joe
}
```

Create a new VM as an instance from ‘vm2.example.com’:

```
vm "vm2.example.com" instance "vm3.example.com" {
	disk "/home/joe/vm3-disk.img"
}
```

Create the switch "uplink" with an additional physical network interface:

```
switch "uplink" {
	interface bridge0
}
```

## SEE ALSO

[vmm(4)](/vmm/4.md), [MAKEDEV(8)](/MAKEDEV/8.md), [vmctl(8)](/vmctl/8.md), [vmd(8)](/vmd/8.md)

## HISTORY

The **vm.conf** file format first appeared in OpenBSD 5.9.

## AUTHORS

Mike Larkin ⟨*mlarkin@openbsd.org*⟩ and Reyk Floeter ⟨*reyk@openbsd.org*⟩.

## CAVEATS

Each guest requires one [tap(4)](/tap/4.md) device per assigned interface and one [pty(4)](/pty/4.md) device. Administrators may need to create additional devices using [MAKEDEV(8)](/MAKEDEV/8.md).