.\" $OpenBSD: vm.conf.5,v 1.69 2025/07/06 15:45:02 schwarze Exp $
.\"
.\" Copyright (c) 2015 Mike Larkin <mlarkin@openbsd.org>
.\" Copyright (c) 2015 Reyk Floeter <reyk@openbsd.org>
.\"
.\" Permission to use, copy, modify, and distribute this software for any
.\" purpose with or without fee is hereby granted, provided that the above
.\" copyright notice and this permission notice appear in all copies.
.\"
.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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.Dd $Mdocdate: July 6 2025 $
.Dt VM.CONF 5
.Os
.Sh NAME
.Nm vm.conf
.Nd virtual machine configuration
.Sh DESCRIPTION
.Nm
is the configuration file for the virtual machine monitor,
.Xr vmm 4 ,
which is responsible for creating, destroying, and executing
virtual machines (VMs).
.Pp
.Nm
is divided into the following main sections:
.Bl -tag -width xxxx
.It Sx Macros
Definitions of variables that can be used later, simplifying the
configuration file.
.It Sx Global configuration
Global settings for
.Xr vmd 8 .
.It Sx VM configuration No and Sx VM instances
Configuration for each individual virtual machine.
.It Sx Switch configuration
Configuration for virtual switches.
.El
.Pp
The current line can be extended over multiple lines using a backslash
.Pq Sq \e .
Comments can be put anywhere in the file using a hash mark
.Pq Sq #
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.
.Pp
Arguments not beginning with a letter, digit, underscore, or slash
must be quoted.
.Pp
Additional configuration files can be included with the
.Ic include
keyword, for example:
.Bd -literal -offset indent
include "/etc/vm1.example.com.conf"
.Ed
.Ss Macros
A macro is defined with a command of the form
.Ar name Ns = Ns Ar value .
The macro
.Ar name
can contain letters, digits, and underscores and
cannot be a reserved word (for example,
.Ic vm ,
.Ic memory ,
or
.Ic disk ) .
Within unquoted arguments, the string
.Pf $ Ar name
is later expanded to
.Ar value .
.Pp
For example:
.Bd -literal -offset indent
ramdisk="/bsd.rd"
vm "vm1.example.com" {
	memory 512M
	boot $ramdisk
}
.Ed
.Ss Global configuration
The following settings can be configured globally:
.Bl -tag -width Ds
.It Ic agentx Oo Cm context Ar context Oc Op Cm path Ar socket
Export vm metrics via an AgentX compatible
.Xr snmpd 8
by connecting to the
.Ar socket .
Metrics can be found under the vmMIB subtree
.Pq mib-2.236 .
If
.Ar socket
is omitted it defaults to
.Pa /var/agentx/master .
.Ar context
is the SNMPv3 context and can usually be omitted.
.It Ic local Cm prefix Ar address Ns / Ns Ar prefix
Set the IPv4 network prefix that is used to allocate subnets for
local interfaces, see
.Ic local interface
in the
.Sx VM configuration
section below.
The default is 100.64.0.0/10.
.It Ic local Cm inet6 Op Cm prefix Ar address Ns / Ns Ar prefix
Enable IPv6 on local interfaces and allocate routable subnets.
If the prefix is not specified,
a random prefix from the
.Dq unique local
network range fd00::/8 is generated on startup.
The specified prefix length must be /64 or smaller.
.It Ic socket Cm owner Ar user : Ns Ar group
Set the
.Xr vmd 8
control socket owner to the specified
.Ar user
and
.Ar group .
Users with access to the control socket are allowed to use
.Xr vmctl 8
for restricted access to
.Xr vmd 8 .
If only
.Ar user
is given,
only the user is set.
If only
.Pf : Ar group
is given,
only the group is set.
The default is root:wheel.
.It Ic staggered start Cm parallel Ar parallelism Cm delay Ar delay
Start all configured VMs in a staggered fashion with
.Ar parallelism
instances in parallel every
.Ar delay
seconds.
Defaults to
.Ar parallelism
equal to number of online CPUs and a
.Ar delay
of 30 seconds.
.El
.Ss VM configuration
Each
.Ic vm
section starts with the declaration of a virtual machine
.Ar name :
.Bl -tag -width Ds
.It Ic vm Ar name Brq ...
The
.Ar name
starts with a letter and can contain alphanumeric characters, dots
.Pq Sq .\& ,
dashes
.Pq Sq \- ,
and underscores
.Pq Sq _ .
Typically this is a hostname.
.El
.Pp
The block enclosed in curly braces can contain the following parameters:
.Bl -tag -width Ds
.It Ic allow instance Brq ...
Set the permissions to create
.Sx VM instances .
.It Ic boot Ar path
Kernel or BIOS image to load when booting the VM.
If not specified, the default is to boot using the BIOS image in
.Pa /etc/firmware/vmm-bios .
.It Ic boot Cm device Ar device
Force VM to boot from
.Ar device .
Valid values are:
.Bl -tag -width "cdrom"
.It Cm cdrom
Boot the ISO image file specified using the
.Ic cdrom
parameter.
.It Cm disk
Boot from the disk image file specified using the
.Ic disk
parameter.
.It Cm net
Boot the kernel specified using the
.Ic boot
parameter as if the VM was network booted.
In addition, the DHCP lease advertises
.Dq auto_install
in the bootfile option making it suitable for use with
.Xr autoinstall 8 .
Note, this is not to be confused with
.Xr pxeboot 8
but rather a simulated network boot.
.El
.Pp
Currently
.Cm disk
and
.Cm cdrom
only work with VMs booted using BIOS.
.It Ic cdrom Ar path
ISO image file.
.It Ic enable
Automatically start the VM.
This is the default if neither
.Ic enable
nor
.Ic disable
is specified.
.It Ic disable
Do not automatically start this VM.
.It Ic disk Ar path Op Cm format Ar fmt
Disk image file (may be specified multiple times to add multiple disk images).
The format may be specified as either
.Cm qcow2
(a sparse file format which reduces storage) or
.Cm raw .
If left unspecified, the format defaults to
.Cm raw
if it cannot be derived automatically.
.It Oo Ic local Oc Ic interface Oo Ar name Oc Op Brq ...
Network interface to add to the VM.
The optional
.Ar name
can be either
.Cm tap
to select the next available
.Xr tap 4
interface on the VM host side (the default) or
.Cm tap Ns Ar N
to select a specific one.
.Pp
Valid options are:
.Bl -tag -width Ds
.It Ic group Ar group-name
Assign the interface to a specific interface
.Dq group .
For example, this can be used to write
.Xr pf.conf 5
rules for several VM interfaces in the same group.
The
.Ar group-name
must not be longer than 15 characters or end with a digit,
as described in
.Xr ifconfig 8 .
.It Oo Ic locked Oc Ic lladdr Op Ar 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
.Xr vmd 8 .
If the
.Ic locked
keyword is specified,
.Xr vmd 8
drops packets from the VM with altered source addresses.
.It Cm rdomain Ar rdomainid
Attach the interface to the routing domain with the specified
.Ar rdomainid .
If attaching to a switch that also has an
.Ar rdomainid
set, the
.Ar rdomainid
configured for the interface takes precedence.
.It Ic switch Ar name
Set the virtual switch by
.Ar name .
See the
.Sx Switch configuration
section about virtual switches.
This option is ignored if a switch with a matching name cannot be found.
.It Ic up
Start the interface forwarding packets.
This is the default.
.It Ic down
Stop the interface from forwarding packets.
.El
.Pp
A
.Ic 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.
.Pp
If the global
.Ic local Cm inet6
option is enabled, a routable IPv6 gateway address is generated
on the host side.
Unlike the IPv4 option,
.Xr vmd 8
does not respond to DHCPv6 or router solicitation messages itself.
Use
.Xr rad 8
listening on the interface group, e.g.\&
.Ic interface Cm tap
for auto-configuring the VMs accordingly.
.It Ic interfaces Ar count
Optional minimum number of network interfaces to add to the VM.
If the
.Ar count
is greater than the number of
.Ic interface
statements, additional default interfaces are added.
.It Ic memory Ar bytes
Memory size of the VM in bytes, rounded to megabytes.
A scale multiplier can be used as described in
.Xr scan_scaled 3 .
The default is 512M.
.It Ic owner Ar user : Ns Ar group
Set the owner of the VM to the specified
.Ar user
and
.Ar group .
The owner is allowed to start or stop the VM, pause or unpause the VM,
and open the VM's console.
If only
.Ar user
is given,
only the user is set.
If only
.Pf : Ar group
is given,
only the group is set.
.It Ic sev
Enables AMD Secure Encrypted Virtualization (SEV) for the guest.
.Xr vmd 8
uses
.Xr psp 4
to configure the guest for SEV.
.It Ic seves
Enables AMD Encrypted State (SEV-ES) for the guest.
This implicitly enables SEV, too.
.El
.Ss 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
.Ic vm
and is configured with the following declaration of the virtual machine
.Ar name :
.Bl -tag -width Ds
.It Ic vm Ar parent Ic instance Ar name Brq ...
A virtual machine can be created as an instance of any other configured VM.
.El
.Pp
The new instance inherits settings from the VM
.Ar parent ,
except for exclusive options such as
.Ic disk ,
.Ic interface lladdr ,
or
.Ic interface Ar name .
The configuration options are identical to the
.Sx VM configuration ,
but restricted to the allowed instance options.
.Pp
The allowed instance options are configured in the
.Ar parent
VM:
.Bl -tag -width Ds
.It Ic allow instance Brq ...
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.
.El
.Pp
Valid options are:
.Bl -tag -width Ds
.It Ic boot
Allow user to configure the kernel or BIOS image.
The user needs read access to the image.
.It Ic cdrom
Allow user to configure the ISO file.
The user needs read access to the file.
.It Ic 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.
.It Ic instance
Allow user to create additional instances from the instances.
.It Ic interface
Allow user to change network interface settings.
.It Ic memory
Allow user to configure the memory size.
.It Ic owner Ar user Ns Op : Ns Ar 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.
.It Ic owner Pf : Ar group
Set the owner to the specified group.
.El
.Ss Switch configuration
A virtual switch allows VMs to communicate with other network interfaces on the
host system via either
.Xr bridge 4
or
.Xr veb 4 .
The network interface for each virtual switch defined in
.Nm
is pre-configured using
.Xr hostname.if 5
or
.Xr ifconfig 8
(see the BRIDGE and VEB sections in
.Xr ifconfig 8
accordingly).
When a VM is started, virtual network interfaces which are assigned to a
virtual switch have their
.Xr tap 4
interface automatically added into the corresponding
.Xr bridge 4
or
.Xr veb 4
interface underlying the virtual switch.
.Pp
Virtual switches can be configured at any point in the configuration file.
Each
.Ic switch
section starts with a declaration of the virtual switch:
.Bl -tag -width Ds
.It Ic switch Ar name Brq ...
This name can be any string, and is typically a network name.
.El
.Pp
The block enclosed in curly braces can contain the following parameters:
.Bl -tag -width Ds
.It Ic enable
Automatically configure the switch.
This is the default if neither
.Ic enable
nor
.Ic disable
is specified.
.It Ic locked lladdr
If this option is specified,
.Xr vmd 8
drops packets with altered source addresses that do not match the
link layer addresses (MAC addresses) of the VM interfaces in this switch.
.It Ic disable
Do not automatically configure this switch.
.It Ic group Ar group-name
Assign each interface to a specific interface
.Dq group .
For example, this can be used to write
.Xr pf.conf 5
rules for several VM interfaces in the same group.
The
.Ar group-name
must not be longer than 15 characters or end with a digit,
as described in
.Xr ifconfig 8 .
.It Ic interface Ar name
Set the
.Xr bridge 4
or
.Xr veb 4
network interface of this switch.
.It Ic rdomain Ar rdomainid
Set the routing domain of the switch and all of its VM interfaces to
.Ar rdomainid .
.It Ic up
Start the switch forwarding packets.
This is the default.
.It Ic down
Stop the switch from forwarding packets.
.El
.Sh FILES
.Bl -tag -width /etc/firmware/vmm-bios -compact
.It Pa /etc/vm.conf
default
.Xr vmd 8
and
.Xr vmctl 8
configuration file
.It Pa /etc/examples/vm.conf
example configuration file
.It Pa /var/run/vmd.sock
Unix domain
.Xr socket 2
where
.Xr vmd 8
listens
.It Pa /etc/firmware/vmm-bios
default BIOS image for booting
.It Pa /var/agentx/master
default Unix domain
.Xr socket 2
where
.Xr snmpd 8
listens
.El
.Sh EXAMPLES
Create a new VM with 1GB memory, 1 network interface connected to
.Dq uplink ,
with one disk image
.Pa /home/joe/vm2-disk.img ,
owned by user
.Sq joe :
.Bd -literal -offset indent
vm "vm2.example.com" {
	memory 1G
	disk "/home/joe/vm2-disk.img"
	interface { switch "uplink" }
	owner joe
}
.Ed
.Pp
Create a new VM as an instance from
.Sq vm2.example.com :
.Bd -literal -offset indent
vm "vm2.example.com" instance "vm3.example.com" {
	disk "/home/joe/vm3-disk.img"
}
.Ed
.Pp
Create the switch "uplink" with an additional physical network interface:
.Bd -literal -offset indent
switch "uplink" {
	interface bridge0
}
.Ed
.Sh SEE ALSO
.Xr vmm 4 ,
.Xr MAKEDEV 8 ,
.Xr vmctl 8 ,
.Xr vmd 8
.Sh HISTORY
The
.Nm
file format first appeared in
.Ox 5.9 .
.Sh AUTHORS
.An -nosplit
.An Mike Larkin Aq Mt mlarkin@openbsd.org
and
.An Reyk Floeter Aq Mt reyk@openbsd.org .
.Sh CAVEATS
Each guest requires one
.Xr tap 4
device per assigned interface and one
.Xr pty 4
device.
Administrators may need to create additional devices using
.Xr MAKEDEV 8 .