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BHYVE_CONFIG(5) FreeBSD File Formats Manual BHYVE_CONFIG(5)

bhyve_config —
bhyve configuration variables

bhyve(8) uses a hierarchical tree of configuration variables to describe global and per-device settings. Internal nodes in this tree do not have a value, only leaf nodes have values. This manual describes the configuration variables understood by bhyve(8). If additional variables are defined, bhyve(8) will ignore them and will not emit errors for unknown variables. However, these additional variables can be referenced by other variables as described below.

Configuration variable values are stored as strings. A configuration variable value may refer to one or more other configuration values by name. Instances of the pattern ‘%(var)’ are replaced by the value of the configuration variable var. To avoid unwanted expansion, ‘%’ characters can be escaped by a leading ‘%’. For example, if a configuration variable disk uses the value /dev/zvol/bhyve/%(name), then the final value of the disk variable will be set to the path of a ZFS volume whose name matches the name of the virtual machine on the pool bhyve.

Some configuration variables may be interpreted as a boolean value. For those variables the following case-insensitive values may be used to indicate true:

  • true
  • on
  • yes
  • 1

The following values may be used to indicate false:

  • false
  • off
  • no
  • 0

Some configuration variables may be interperted as an integer. For those variables, any syntax supported by strtol(3) may be used.

Name Format Default Description
name string The name of the VM.
cpus integer 1 The total number of virtual CPUs.
cores integer 1 The number of virtual cores in each virtual socket.
threads integer 1 The number of virtual CPUs in each virtual core.
sockets integer 1 The number of virtual sockets.
memory.guest_in_core bool false Include guest memory in core file.
memory.size string 256M Guest physical memory size in bytes. The value must be formatted as described in expand_number(3).
memory.wired bool false Wire guest memory.
acpi_tables bool false Generate ACPI tables.
destroy_on_poweroff bool false Destroy the VM on guest-initiated power-off.
gdb.port integer 0 TCP port number for the debug server. If this is set to a non-zero value, a debug server will listen for connections on this port.
gdb.wait bool false If the debug server is enabled, wait for a debugger to connect before starting the guest.
rtc.use_localtime bool true The real time clock uses the local time of the host. If this is set to false, the real time clock uses UTC.
uuid string The universally unique identifier (UUID) to use in the guest's System Management BIOS System Information structure. If an explicit value is not set, a valid UUID is generated from the host's hostname and the VM name.
virtio_msix bool true Use MSI-X interrupts for PCI VirtIO devices. If set to false, MSI interrupts are used instead.
config.dump bool false If this value is set to true after bhyve(8) has finished parsing command line options, then bhyve(8) will write all of its configuration variables to stdout and exit. No VM will be started.

Name Format Default Description
x86.mptable bool true Generate an MPTable.
x86.x2apic bool false Configure guest's local APICs in x2APIC mode.
x86.strictio bool false Exit if a guest accesses an I/O port that is not emulated. By default, writes are ignored and reads return all bits set.
x86.strictmsr bool true Inject a general protection fault if a guest accesses a Model Specific Register (MSR) that is not emulated. If this is false, writes are ignored and reads return zero.
x86.vmexit_on_hlt bool false Force a VM exit when a guest CPU executes the HLT instruction. This allows idle guest CPUs to yield the host CPU.
x86.vmexit_on_pause bool false Force a VM exit when a guest CPU executes the PAUSE instruction.

Device settings are stored under a device node. The device node's name is set by the parent bus of the device.

PCI devices are described by a device node named “pcibus.slot.function” where each of bus, slot, and function are formatted as decimal values with no padding. All PCI device nodes must contain a configuration variable named “device” which specifies the device model to use. The following PCI device models are supported:
Provide a simple PCI-Host bridge device. This is usually configured at pci0:0:0 and is required by most guest operating systems.
AHCI storage controller.
Intel e82545 network interface.
VGA framebuffer device attached to VNC server.
LPC PCI-ISA bridge with COM1-COM4 16550 serial ports, a boot ROM, and an optional debug/test device. This device must be configured on bus 0.
High Definition audio controller.
NVM Express (NVMe) controller.
PCI pass-through device.
PCI 16550 serial device.
VirtIO 9p (VirtFS) interface.
VirtIO block storage interface.
VirtIO console interface.
VirtIO network interface.
VirtIO RNG interface.
VirtIO SCSI interface.
Extensible Host Controller Interface (XHCI) USB controller.

USB controller devices contain zero or more child USB devices attached to slots. Each USB device stores its settings in a node named “slot.N” under the controller's device node. N is the number of the slot to which the USB device is attached. Note that USB slot numbers begin at 1. All USB device nodes must contain a configuration variable named “device” which specifies the device model to use. The following USB device models are supported:
A USB tablet device which provides precise cursor synchronization when using VNC.

Block devices use the following settings to configure their backing store. These settings are stored in the configuration node of the respective device.
Name Format Default Description
path string The path of the file or disk device to use as the backing store.
nocache bool false Disable caching on the backing file by opening the backing file with O_DIRECT.
nodelete bool false Disable emulation of guest trim requests via DIOCGDELETE requests.
sync bool false Write changes to the backing file with synchronous writes.
direct bool false An alias for sync.
ro bool false Disable writes to the backing file.
sectorsize logical[/physical] Specify the logical and physical sector size of the emulated disk. If the physical size is not specified, it is equal to the logical size.

Network devices use the following settings to configure their backend. The backend is responsible for passing packets between the device model and a desired destination. Configuring a backend requires setting the backend variable to one of the following values:
tapN
Use the named tap(4) interface as the backend.
vmnetN
Use the named vmnet(4) interface as the backend.
netgraph
Use a netgraph(4) socket hook as the backend. This backend uses the following additional variables:
Name Format Default Description
path string The name of the netgraph(4) destination node.
peerhook string The name of the destination hook.
socket string The name of the created ng_socket(4) node.
hook string vmlink The name of the source hook on the created ng_socket(4) node.
netmap:interface
Use netmap(4) on a network interface as the backend.
valebridge:port
Use a port on a vale(4) bridge as the backend.

Name Format Default Description
path path Backend device for the serial port. Either the pathname of a character device or “stdio” to use standard input and output of the bhyve(8) process.

Name Format Default Description
vendor integer 0x1275 PCI vendor ID.
devid integer 0x1275 PCI device ID.

AHCI controller devices contain zero or more ports each of which provides a storage device. Each port stores its settings in a node named “port.N” under the controller's device node. The N values are formatted as successive decimal values starting with 0. In addition to the block device settings described above, each port supports the following settings:
Name Format Default Description
type string The type of storage device to emulate. Must be set to either “cd” or “hd”.
nmrr integer 0 Nominal Media Rotation Rate, also known as RPM. A value 1 of indicates a device with no rate such as a Solid State Disk.
ser string generated Serial number of up to twenty characters. A default serial number is generated using a hash of the backing store's pathname.
rev string 001 Revision number of up to eight characters.
model string Model number of up to forty characters. Separate default model strings are used for “cd” and “hd” device types.

In addition to the network backend settings, Intel e82545 network interfaces support the following variables:
Name Format Default Description
mac MAC address generated MAC address. If an explicit address is not provided, a MAC address is generated from a hash of the device's PCI address.

Name Format Default Description
wait bool false Wait for a remote connection before starting the VM.
rfb [IP:]port 127.0.0.1:5900 TCP address to listen on for remote connections. The IP address must be given as a numeric address. IPv6 addresses must be enclosed in square brackets and support scoped identifiers as described in getaddrinfo(3). A bare port number may be given in which case the IPv4 localhost address is used.
vga string io VGA configuration. More details are provided in bhyve(8).
w integer 1024 Frame buffer width in pixels.
h integer 768 Frame buffer height in pixels.
password string Password to use for VNC authentication. This type of authentication is known to be cryptographically weak and is not intended for use on untrusted networks.

Name Format Default Description
play path Host playback device, typically /dev/dsp0.
rec path Host recording device, typically /dev/dsp0.

The LPC bridge stores its configuration under a top-level lpc node rather than under the PCI LPC device's node. The following nodes are available under lpc:
Name Format Default Description
bootrom path Path to a boot ROM. The contents of this file are copied into the guest's memory ending just before the 4GB physical address. If a boot ROM is present, a firmware interface device is also enabled for use by the boot ROM.
com1 node Settings for the COM1 serial port device.
com2 node Settings for the COM2 serial port device.
com3 node Settings for the COM3 serial port device.
com4 node Settings for the COM4 serial port device.
pc-testdev bool false Enable the PC debug/test device.

Each NVMe controller supports a single storage device. The device can be backed either by a memory disk described by the ram variable, or a block device using the the block device settings described above. In addition, each controller supports the following settings:
Name Format Default Description
maxq integer 16 Maximum number of I/O submission and completion queue pairs.
qsz integer 2058 Number of elements in each I/O queue.
ioslots integer 8 Maximum number of concurrent I/O requests.
sectsz integer Sector size. Can be one of 512, 4096, or 8192. Devices backed by a memory disk use 4096 as the default. Devices backed by a block device use the block device's sector size as the default.
ser string Serial number of up to twenty characters. A default serial number is generated using a hash of the device's PCI address.
eui64 integer IEEE Extended Unique Identifier. If an EUI is not provided, a default is generated using a checksum of the device's PCI address.
dsm string auto Whether or not to advertise DataSet Management support. One of “auto”, “enable”, or “disable”. The “auto” setting only advertises support if the backing store supports resource freeing, for example via TRIM.
ram integer If set, allocate a memory disk as the backing store. The value of this variable is the size of the memory disk in megabytes.

Name Format Default Description
bus integer Host PCI bus address of device to pass through.
slot integer Host PCI slot address of device to pass through.
func integer Host PCI function address of device to pass through.

Each VirtIO 9p device exposes a single filesystem from a host path.
Name Format Default Description
sharename string The share name exposed to the guest.
path path The path of a directory on the host to export to the guest.
ro bool false If true, the guest filesystem is read-only.

In addition to the block device settings described above, each VirtIO block device supports the following settings:
Name Format Default Description
ser string generated Serial number of up to twenty characters. A default serial number is generated using a hash of the backing store's pathname.

Each VirtIO Console device contains one or more console ports. Each port stores its settings in a node named “port.N” under the controller's device node. The N values are formatted as successive decimal values starting with 0. Each port supports the following settings:
Name Format Default Description
name string The name of the port exposed to the guest.
path path The path of a UNIX domain socket providing the host connection for the port.

In addition to the network backend settings, VirtIO network interfaces support the following variables:
Name Format Default Description
mac MAC address generated MAC address. If an explicit address is not provided, a MAC address is generated from a hash of the device's PCI address.
mtu integer 1500 The largest supported MTU advertised to the guest.

Name Format Default Description
dev path The path of a CAM target layer (CTL) device to export: /dev/cam/ctl[pp.vp].
iid integer 0 Initiator ID to use when sending requests to the CTL port.

expand_number(3), getaddrinfo(3), strtol(3), netgraph(4), netmap(4), ng_socket(4), tap(4), vale(4), vmnet(4), bhyve(8)
September 17, 2021 FreeBSD 13.1-RELEASE
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