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Manual Pages  — BHYVE


bhyve – run a guest operating system inside a virtual machine



bhyve [-AabCeHhPSuWwxY] [ -c [[cpus=]numcpus][,sockets= n][,cores= n][,threads= n]][-G port] [-g gdbport] [-l lpcdev [amp;, conf]] [-m memsize[K|k|M|m|G|g|T|t]] [-p vcpu amp;:hostcpu] [-s slotamp;, emulation [amp;, conf]] [-U uuid] vmname
bhyve -l help
bhyve -s help


bhyve is a hypervisor that runs guest operating systems inside a virtual machine.

Parameters such as the number of virtual CPUs, amount of guest memory, and I/O connectivity can be specified with command-line parameters.

If not using a boot ROM, the guest operating system must be loaded with bhyveload(8) or a similar boot loader before running bhyve, otherwise, it is enough to run bhyve with a boot ROM of choice.

bhyve runs until the guest operating system reboots or an unhandled hypervisor exit is detected.


  Generate ACPI tables. Required for FreeBSD Ns /amd64 guests.
  The guest's local APIC is configured in xAPIC mode. The xAPIC mode is the default setting so this option is redundant. It will be deprecated in a future version.
  Enable a low-level console device supported by FreeBSD kernels compiled with device bvmconsole . This option is deprecated and will be removed in FreeBSD 13.0 .
  Include guest memory in core file.
-c [setting ...]
  Number of guest virtual CPUs and/or the CPU topology. The default value for each of numcpus, sockets, cores, and threads is 1. The current maximum number of guest virtual CPUs is 16. If numcpus is not specified then it will be calculated from the other arguments. The topology must be consistent in that the numcpus must equal the product of sockets, cores, and threads. If a setting is specified more than once the last one has precedence.
  Destroy the VM on guest initiated power-off.
  Force bhyve to exit when a guest issues an access to an I/O port that is not emulated. This is intended for debug purposes.
-G port
  Start a debug server that uses the GDB protocol to export guest state to a debugger. An IPv4 TCP socket will be bound to the supplied port to listen for debugger connections. Only a single debugger may be attached to the debug server at a time. If port begins with 'w', bhyve will pause execution at the first instruction waiting for a debugger to attach.
-g gdbport
  For FreeBSD kernels compiled with device bvmdebug, allow a remote kernel kgdb to be relayed to the guest kernel gdb stub via a local IPv4 address and this port. This option is deprecated and will be removed in FreeBSD 13.0 .
  Yield the virtual CPU thread when a HLT instruction is detected. If this option is not specified, virtual CPUs will use 100% of a host CPU.
  Print help message and exit.
-k file
  Set configuration variables from a simple, key-value config file. Each line of the config file is expected to consist of a config variable name, an equals sign ('='), and a value. No spaces are permitted between the variable name, equals sign, or value. Blank lines and lines starting with '#' are ignored.
-l help
  Print a list of supported LPC devices.
-l lpcdev[ amp;,conf]
  Allow devices behind the LPC PCI-ISA bridge to be configured. The only supported devices are the TTY-class devices com1 and com2, the boot ROM device bootrom, and the debug/test device pc-testdev.

The possible values for the conf argument are listed in the -s flag description.

-m memsize[ K|k|M|m|G|g|T|t] Set the guest physical memory size This must be the same size that was given to bhyveload(8).

The size argument may be suffixed with one of K, M, G or T (either upper or lower case) to indicate a multiple of kilobytes, megabytes, gigabytes, or terabytes. If no suffix is given, the value is assumed to be in megabytes.

The default is 256M.

-o var =value
  Set the configuration variable var to value.
  Force the guest virtual CPU to exit when a PAUSE instruction is detected.
-p vcpu amp;:hostcpu
  Pin guest's virtual CPU vcpu to hostcpu.
  Force the guest virtual CPU to exit when a PAUSE instruction is detected.
  Wire guest memory.
-s help
  Print a list of supported PCI devices.
-s slot amp;,emulation[ amp;,conf]
  Configure a virtual PCI slot and function.

bhyve provides PCI bus emulation and virtual devices that can be attached to slots on the bus. There are 32 available slots, with the option of providing up to 8 functions per slot.

The slot can be specified in one of the following formats:

  • pcislot
  • pcislotamp;: function
  • busamp;: pcislotamp;: function

The pcislot value is 0 to 31. The optional function value is 0 to 7. The optional bus value is 0 to 255. If not specified, the function value defaults to 0. If not specified, the bus value defaults to 0.

The emulation argument can be one of the following:

hostbridge A simple host bridge. This is usually configured at slot 0, and is required by most guest operating systems.
  Emulation identical to hostbridge using a PCI vendor ID of AMD.
passthru PCI pass-through device.
virtio-net Virtio network interface.
virtio-blk Virtio block storage interface.
virtio-scsi Virtio SCSI interface.
virtio-rnd Virtio RNG interface.
  Virtio console interface, which exposes multiple ports to the guest in the form of simple char devices for simple IO between the guest and host userspaces.
ahci AHCI controller attached to arbitrary devices.
ahci-cd AHCI controller attached to an ATAPI CD/DVD.
ahci-hd AHCI controller attached to a SATA hard drive.
e1000 Intel e82545 network interface.
uart PCI 16550 serial device.
lpc LPC PCI-ISA bridge with COM1, COM2, and 16550 serial ports, a boot ROM, and, optionally, the debug/test device. The LPC bridge emulation can only be configured on bus 0.
fbuf Raw framebuffer device attached to VNC server.
xhci eXtensible Host Controller Interface (xHCI) USB controller.
nvme NVM Express (NVMe) controller.

The optional parameter conf describes the backend for device emulations. If conf is not specified, the device emulation has no backend and can be considered unconnected.

Network device backends:

With virtio-net devices, the mtu parameter can be specified to inform the guest about the largest MTU that should be allowed, expressed in bytes.

Block storage device backends:

The block-device-options are:
  Open the file with O_DIRECT.
  Open the file using O_SYNC.
ro Force the file to be opened read-only.
sectorsize=logical[ amp;/physical ]
  Specify the logical and physical sector sizes of the emulated disk. The physical sector size is optional and is equal to the logical sector size if not explicitly specified.

SCSI device backends:

The scsi-device-options are:
  Initiator ID to use when sending requests to specified CTL port. The default value is 0.

TTY device backends:
stdio Connect the serial port to the standard input and output of the bhyve process.
  Use the host TTY device for serial port I/O.

Boot ROM device backends:
  Map romfile in the guest address space reserved for boot firmware.

Pass-through device backends:
slot amp;/bus amp;/function
  Connect to a PCI device on the host at the selector described by slot, bus, and function numbers.

Guest memory must be wired using the -S option when a pass-through device is configured.

The host device must have been reserved at boot-time using the pptdevs loader variable as described in vmm(4).

Virtio console device backends:

A maximum of 16 ports per device can be created. Every port is named and corresponds to a Unix domain socket created by bhyve. bhyve accepts at most one connection per port at a time.


Framebuffer devices backends:

Configuration options are defined as follows:
rfb=ip-and-port (or tcp=ip-and-port)
  An IP address and a port VNC should listen on. There are two formats:

  • [IPv4amp;:]port
  • amp;[ IPv6%zoneamp;]amp;: port

The default is to listen on localhost IPv4 address and default VNC port 5900. An IPv6 address must be enclosed in square brackets and may contain an optional zone identifier.

w=width and h=height
  A display resolution, width and height, respectively. If not specified, a default resolution of 1024x768 pixels will be used. Minimal supported resolution is 640x480 pixels, and maximum is 1920x1200 pixels.
  Possible values for this option are io (default), on , and off. PCI graphics cards have a dual personality in that they are standard PCI devices with BAR addressing, but may also implicitly decode legacy VGA I/O space ( 0x3c0-3df) and memory space (64KB at 0xA0000). The default io option should be used for guests that attempt to issue BIOS calls which result in I/O port queries, and fail to boot if I/O decode is disabled.

The on option should be used along with the CSM BIOS capability in UEFI to boot traditional BIOS guests that require the legacy VGA I/O and memory regions to be available.

The off option should be used for the UEFI guests that assume that VGA adapter is present if they detect the I/O ports. An example of such a guest is OpenBSD in UEFI mode.

Please refer to the bhyve FreeBSD wiki page (Lk https://wiki.freebsd.org/bhyve) for configuration notes of particular guests.

wait Instruct bhyve to only boot upon the initiation of a VNC connection, simplifying the installation of operating systems that require immediate keyboard input. This can be removed for post-installation use.
  This type of authentication is known to be cryptographically weak and is not intended for use on untrusted networks. Many implementations will want to use stronger security, such as running the session over an encrypted channel provided by IPsec or SSH.

xHCI USB device backends:
  A USB tablet device which provides precise cursor synchronization when using VNC.

NVMe device backends:

Configuration options are defined as follows:
  Accepted device paths are: /dev/blockdev or /path/to/image or ram=size_in_MiB.
maxq Max number of queues.
qsz Max elements in each queue.
  Max number of concurrent I/O requests.
  Sector size (defaults to blockif sector size).
ser Serial number with maximum 20 characters.
eui64 IEEE Extended Unique Identifier (8 byte value).
dsm DataSet Management support. Supported values are: auto, enable, and disable.

AHCI device backends:

Configuration options are defined as follows:
nmrr Nominal Media Rotation Rate, known as RPM. Value 1 will indicate device as Solid State Disk. Default value is 0, not report.
ser Serial Number with maximum 20 characters.
rev Revision Number with maximum 8 characters.
model Model Number with maximum 40 characters.

HD Audio device backends:

Configuration options are defined as follows:
play Playback device, typically /dev/dsp0.
rec Recording device, typically /dev/dsp0.
-U uuid
  Set the universally unique identifier (UUID) in the guest's System Management BIOS System Information structure. By default a UUID is generated from the host's hostname and vmname.
  RTC keeps UTC time.
  Force virtio PCI device emulations to use MSI interrupts instead of MSI-X interrupts.
  Ignore accesses to unimplemented Model Specific Registers (MSRs). This is intended for debug purposes.
  The guest's local APIC is configured in x2APIC mode.
  Disable MPtable generation.
  Alphanumeric name of the guest. This should be the same as that created by bhyveload(8).


The current debug server provides limited support for debuggers.


Each virtual CPU is exposed to the debugger as a thread.

General purpose registers can be queried for each virtual CPU, but other registers such as floating-point and system registers cannot be queried.


Memory (including memory mapped I/O regions) can be read by the debugger, but not written. Memory operations use virtual addresses that are resolved to physical addresses via the current virtual CPU's active address translation.


The running guest can be interrupted by the debugger at any time (for example, by pressing Ctrl-C in the debugger).

Single stepping is only supported on Intel CPUs supporting the MTRAP VM exit.

Breakpoints are supported on Intel CPUs that support single stepping. Note that continuing from a breakpoint while interrupts are enabled in the guest may not work as expected due to timer interrupts firing while single stepping over the breakpoint.


bhyve deals with the following signals:

  Trigger ACPI poweroff for a VM


Exit status indicates how the VM was terminated:

0 rebooted
1 powered off
2 halted
3 triple fault
4 exited due to an error


If not using a boot ROM, the guest operating system must have been loaded with bhyveload(8) or a similar boot loader before bhyve(4) can be run. Otherwise, the boot loader is not needed.

To run a virtual machine with 1GB of memory, two virtual CPUs, a virtio block device backed by the /my/image filesystem image, and a serial port for the console:

bhyve -c 2 -s 0,hostbridge -s 1,lpc -s 2,virtio-blk,/my/image \
  -l com1,stdio -A -H -P -m 1G vm1

Run a 24GB single-CPU virtual machine with three network ports, one of which has a MAC address specified:

bhyve -s 0,hostbridge -s 1,lpc -s 2:0,virtio-net,tap0 \
  -s 2:1,virtio-net,tap1 \
  -s 2:2,virtio-net,tap2,mac=00:be:fa:76:45:00 \
  -s 3,virtio-blk,/my/image -l com1,stdio \
  -A -H -P -m 24G bigvm

Run an 8GB quad-CPU virtual machine with 8 AHCI SATA disks, an AHCI ATAPI CD-ROM, a single virtio network port, an AMD hostbridge, and the console port connected to an nmdm(4) null-modem device.

bhyve -c 4 \
  -s 0,amd_hostbridge -s 1,lpc \
  -s 1:0,ahci,hd:/images/disk.1,hd:/images/disk.2,\
cd:/images/install.iso \
  -s 3,virtio-net,tap0 \
  -l com1,/dev/nmdm0A \
  -A -H -P -m 8G

Run a UEFI virtual machine with a display resolution of 800 by 600 pixels that can be accessed via VNC at:

bhyve -c 2 -m 4G -w -H \
  -s 0,hostbridge \
  -s 3,ahci-cd,/path/to/uefi-OS-install.iso \
  -s 4,ahci-hd,disk.img \
  -s 5,virtio-net,tap0 \
  -s 29,fbuf,tcp=,w=800,h=600,wait \
  -s 30,xhci,tablet \
  -s 31,lpc -l com1,stdio \
  -l bootrom,/usr/local/share/uefi-firmware/BHYVE_UEFI.fd \

Run a UEFI virtual machine with a VNC display that is bound to all IPv6 addresses on port 5900.

bhyve -c 2 -m 4G -w -H \
  -s 0,hostbridge \
  -s 4,ahci-hd,disk.img \
  -s 5,virtio-net,tap0 \
  -s 29,fbuf,tcp=[::]:5900,w=800,h=600 \
  -s 30,xhci,tablet \
  -s 31,lpc -l com1,stdio \
  -l bootrom,/usr/local/share/uefi-firmware/BHYVE_UEFI.fd \


bhyve(4), nmdm(4), vmm(4), ethers(5), bhyvectl(8), bhyveload(8)

Intel, 64 and IA-32 Architectures Software Developer’s Manual, Volume 3,


bhyve first appeared in FreeBSD 10.0 .


Neel Natu <Mt neel@freebsd.org> Peter Grehan <Mt grehan@freebsd.org>

BHYVE (8) April 18, 2021

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