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BHYVE(8) System Manager's Manual BHYVE(8)

bhyve — run a guest operating system inside a virtual machine

bhyve [-aCDeHhPSuWwxY] [-c [[cpus=]numcpus][,sockets=n][,cores=n][,threads=n]] [-f name,[string|file]=data] [-G [w][bind_address:]port] [-k config_file] [-K layout] [-l lpcdev[,conf]] [-m memsize[K|k|M|m|G|g|T|t]] [-o var=value] [-p vcpu:hostcpu] [-r file] [-s slot,emulation[,conf]] [-U uuid] vmname

bhyve -l help

bhyve -s help

bhyve is a hypervisor that runs guest operating systems inside a virtual machine. It can run guests on amd64 and arm64 platforms with suitable hardware support.

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

bhyve is typically used with a boot ROM that can load the guest operating system. On arm64 platforms, this is currently required. 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. On amd64, the edk2-bhyve package provides a UEFI firmware that can be used to boot the guest; on arm64 the u-boot-bhyve-arm64 package provides a U-Boot image that can be used to boot the guest.

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

The guest's local APIC is configured in xAPIC mode. This option only applies to the amd64 platform. xAPIC mode is the default setting so this option is redundant. It will be deprecated in a future version.
Include guest memory in core files.
[setting ...]
Number of guest virtual CPUs and/or the CPU topology. The default value for each of numcpus, sockets, cores, and threads is 1. 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.

The maximum number of virtual CPUs defaults to the number of active physical CPUs in the system available via the hw.vmm.maxcpu sysctl(8) variable. The limit can be adjusted via the hw.vmm.maxcpu loader tunable.

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 and only applies to the amd64 platform.
name,[string|file]=data
Add a fw_cfg file name to the fw_cfg interface. If a string is specified, the fw_cfg file contains the string as data. If a file is specified, bhyve reads the file and adds the file content as fw_cfg data.
[w][bind_address:]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 bind_address and port to listen for debugger connections. Only a single debugger may be attached to the debug server at a time. If the option begins with ‘w’, bhyve will pause execution at the first instruction waiting for a debugger to attach.
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. This option applies only to the amd64 platform.
Print help message and exit.
config_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. See bhyve_config(5) for more details.
layout
Specify the keyboard layout. The value that can be specified sets the file name in /usr/share/bhyve/kbdlayout. This specification only works when loaded with UEFI mode for VNC. When using a VNC client that supports QEMU Extended Key Event Message (e.g. TigerVNC), this option isn't needed. When using a VNC client that doesn't support QEMU Extended Key Event Message (e.g. tightVNC), the layout defaults to the US keyboard unless specified otherwise.
help
Print a list of supported LPC devices.
lpcdev[,conf]
Allow devices behind the LPC PCI-ISA bridge to be configured. The only supported devices are the TTY-class devices com1, com2, com3, and com4, the TPM module tpm, the boot ROM device bootrom, the fwcfg type and the debug/test device pc-testdev.

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

This option applies only to the amd64 platform. On arm64, the console and boot ROM devices are configured using the more generic -o option.

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.

var=value
Set the configuration variable var to value. See bhyve_config(5) for configuration options.
Force the guest virtual CPU to exit when a PAUSE instruction is detected. This option applies only to the amd64 platform.
vcpu:hostcpu
Pin guest's virtual CPU to . Host CPUs and guest virtual CPUs are numbered starting from 0. A -p option is required for every guest vCPU to be pinned. To map a 4 vCPU guest to host CPUs 12-15: 
-p 0:12 -p 1:13 -p 2:14 -p 3:15
file
Resume a guest from a snapshot. The guest memory contents are restored from file, and the guest device and vCPU state are restored from the file “file.kern”.

Note that the current snapshot file format requires that the configuration of devices in the new VM match the VM from which the snapshot was taken by specifying the same -s and -l options. The count of vCPUs and memory configuration are read from the snapshot.

Wire guest memory.
help
Print a list of supported PCI devices.
slot,emulation[,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
  • pcislot:function
  • bus:pcislot: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.

See PCI EMULATION for available options for the emulation argument.

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. This option applies only to the amd64 platform.
Disable MPtable generation. This option applies only to the amd64 platform.
vmname
Alphanumeric name of the guest. This should be the same as that created by bhyveload(8).

bhyve provides emulation for various PCI devices. They are specified by the -s slot,emulation,conf configuration's emulation argument, which can be one of the following:

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.
PCI pass-through device.
Virtio network interface.
Virtio block storage interface.
Virtio SCSI interface.
Virtio 9p (VirtFS) interface.
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.
Virtio input interface.
AHCI controller attached to arbitrary devices.
AHCI controller attached to an ATAPI CD/DVD.
AHCI controller attached to a SATA hard drive.
Intel e82545 network interface.
PCI 16550 serial device.
LPC PCI-ISA bridge with COM1, COM2, COM3, and COM4 16550 serial ports, a boot ROM, and, optionally, a TPM module, a fwcfg type, and the debug/test device. The LPC bridge emulation can only be configured on bus 0.
Raw framebuffer device attached to VNC server.
eXtensible Host Controller Interface (xHCI) USB controller.
NVM Express (NVMe) controller.
High Definition Audio 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.

  • N[,mac=xx:xx:xx:xx:xx:xx][,mtu=N]
  • N[,mac=xx:xx:xx:xx:xx:xx][,mtu=N]
  • ADDRESS,peerhook=HOOK[,socket=NAME][,hook=HOOK][,mac=xx:xx:xx:xx:xx:xx][,mtu=N]
  • proto:hostaddr:hostport-guestaddr:guestport

If mac is not specified, the MAC address is derived from a fixed OUI, and the remaining bytes from an MD5 hash of the slot and function numbers and the device name.

The MAC address is an ASCII string in ethers(5) format.

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.

With netgraph backend, the path and peerhook parameters must be specified to set the destination node and corresponding hook. The optional parameters socket and hook may be used to set the ng_socket(4) node name and source hook. The ADDRESS, HOOK, and NAME must comply with netgraph(4) addressing rules.

The slirp backend can be used to provide a NATed network to the guest. This backend has poor performance but does not require any network configuration on the host system. It depends on the net/libslirp port. The hostfwd option takes a 5-tuple describing how connections from the host are to be forwarded to the guest. Multiple rules can be specified, separated by semicolons. Note that semicolons must be escaped or quoted to prevent the shell from interpreting them.

  • /filename[,block-device-options]
  • /dev/xxx[,block-device-options]

The block-device-options are:

Open the file with O_DIRECT.
Open the file using O_SYNC.
Force the file to be opened read-only.
logical[/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.
Disable emulation of guest trim requests via DIOCGDELETE requests.
index
Add the device to the bootorder at index. A fwcfg file is used to specify the bootorder. The guest firmware may ignore or doesn't support this fwcfg file. In that case, this feature doesn't work as expected.

  • /dev/cam/ctl[pp.vp][,scsi-device-options]

The scsi-device-options are:

IID
Initiator ID to use when sending requests to specified CTL port. The default value is 0.
index
Add the device to the bootorder at index. A fwcfg file is used to specify the bootorder. The guest firmware may ignore or doesn't support this fwcfg file. In that case, this feature doesn't work as expected.

  • sharename=/path/to/share[,9p-device-options]

The 9p-device-options are:

Expose the share in read-only mode.

Connect the serial port to the standard input and output of the bhyve process.
/dev/xxx
Use the host TTY device for serial port I/O.
tcp=ip:port
Use the TCP server for serial port I/O. Configuring this option will start a TCP server that waits for connections. Only one connection is allowed at any time. Other connection try to connect to TCP server will be disconnected immediately. Note that this feature allows unprivileged users to access the guest console, so ensure that access is appropriately restricted.

  • type,path[,tpm-device-options]

Emulate a TPM device. Supported options for type:

Use a physical TPM device. The argument path needs to point to a valid TPM device path, i.e. /dev/tpm0.
Connect to a running swtpm instance. The argument path needs to point to a UNIX domain socket that a swtpm process is listening on.

The tpm-device-options are:

version
Version of the TPM device according to the TCG specification. Defaults to 2.0, which is the only version currently supported.

  • romfile[,varfile]

Map romfile in the guest address space reserved for boot firmware.

If varfile is provided, that file is also mapped in the boot firmware guest address space, and any modifications the guest makes will be saved to that file.

Fwcfg types:

fwcfg
The fwcfg interface is used to pass information such as the CPU count or ACPI tables to the guest firmware. Supported values are ‘bhyve’ and ‘qemu’. Due to backward compatibility reasons, ‘bhyve’ is the default option. When ‘bhyve’ is used, bhyve's fwctl interface is used. It currently reports only the CPU count to the guest firmware. The ‘qemu’ option uses QEMU's fwcfg interface. This interface is widely used and allows user-defined information to be passed to the guest. It is used for passing the CPU count, ACPI tables, a boot order and many other things to the guest. Some operating systems such as Fedora CoreOS can be configured by qemu's fwcfg interface as well.

  • N[,passthru-device-options]
  • bus/slot/function[,passthru-device-options]
  • bus:slot:function[,passthru-device-options]

Connect to a PCI device on the host either named ppt N or at the selector described by slot, bus, and function numbers.

The passthru-device-options are:

romfile
Add romfile as option ROM to the PCI device. The ROM will be loaded by firmware and should be capable of initializing the device.
index
Add the device to the bootorder at index. A fwcfg file is used to specify the bootorder. The guest firmware may ignore or doesn't support this fwcfg file. In that case, this feature doesn't work as expected.

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).

  • /path/to/port1.sock[,portN=/path/to/port2.sock ...]

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.

Limitations:

  • Due to the lack of destructors in bhyve, sockets on the filesystem must be cleaned up manually after bhyve exits.
  • There is no way to use the “console port” feature, nor the console port resize at present.
  • Emergency write is advertised, but no-op at present.

  • /dev/input/eventX

Send input events of /dev/input/eventX to guest by VirtIO Input Interface.

  • [rfb=ip-and-port][,w=width][,h=height][,vga=vgaconf][,wait][,password=password]

Configuration options are defined as follows:

ip-and-port (or tcp=ip-and-port)
An IP address and a port VNC should listen on. There are two formats:

  • [IPv4:]port
  • [IPv6%zone]: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.

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 3840x2160 pixels.
vgaconf
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 (https://wiki.freebsd.org/bhyve) for configuration notes of particular guests.

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.
password
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.

  • tablet

A USB tablet device that provides precise cursor synchronization when using VNC.

  • devpath[,maxq=#][,qsz=#][,ioslots=#][,sectsz=#][,ser=#][,eui64=#][,dsm=opt]

Configuration options are defined as follows:

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

  • [[hd:|cd:]path][,nmrr=nmrr][,ser=#][,rev=#][,model=#]

Configuration options are defined as follows:

Nominal Media Rotation Rate, known as RPM. Value 1 will indicate device as Solid State Disk. Default value is 0, not report.
Serial Number with maximum 20 characters.
Revision Number with maximum 8 characters.
Model Number with maximum 40 characters.

  • [play=playback][,rec=recording]

Configuration options are defined as follows:

Playback device, typically /dev/dsp0.
Recording device, typically /dev/dsp0.

bhyve uses an internal tree of configuration variables to describe global and per-device settings. When bhyve starts, it parses command line options (including config files) in the order given on the command line. Each command line option sets one or more configuration variables. For example, the -s option creates a new tree node for a PCI device and sets one or more variables under that node including the device model and device model-specific variables. Variables may be set multiple times during this parsing stage with the final value overriding previous values.

Once all of the command line options have been processed, the configuration values are frozen. bhyve then uses the value of configuration values to initialize device models and global settings.

More details on configuration variables can be found in bhyve_config(5).

The -k flag allows one to provide a path to a configuration file holding all settings, which otherwise would need to be defined by providing a long list of program arguments to bhyve.

There is a very simple way to translate a complex set of program arguments to an equivalent configuration file in bhyve_config(5) format.

Use -o config.dump=1 to make bhyve dump a configuration file representing the used flags and arguments to stdout. You can pipe the output into a file to persist the generated settings.

Make sure to remove the config.dump line from the resulting configuration file before using it to start bhyve.

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 and written by the debugger. 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:

SIGTERM
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 -H -P -m 1G vm1

To do the same on arm64:

bhyve -c 2 -s 0,hostbridge -s 1,virtio-blk,/my/image -o console=stdio \
-o bootrom=/usr/local/share/u-boot/u-boot-bhyve-arm64/u-boot.bin -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 \
  -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,\
hd:/images/disk.3,hd:/images/disk.4,\
hd:/images/disk.5,hd:/images/disk.6,\
hd:/images/disk.7,hd:/images/disk.8,\
cd:/images/install.iso \
  -s 3,virtio-net,tap0 \
  -l com1,/dev/nmdm0A \
  -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: 0.0.0.0:5900 or via serial console over TCP at: 127.0.0.1:1234 (unsafe if you expose serial console without protection).

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=0.0.0.0:5900,w=800,h=600,wait \
  -s 30,xhci,tablet \
  -s 31,lpc -l com1,tcp=127.0.0.1:1234 \
  -l bootrom,/usr/local/share/uefi-firmware/BHYVE_UEFI.fd \
   uefivm

Run a UEFI virtual machine with a VNC display that is bound to all IPv6 addresses on port 5900 and a serial I/O port bound to TCP port 1234 of loopback address (unsafe if you expose serial console without protection).

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,tcp=[::1]:1234 \
  -l bootrom,/usr/local/share/uefi-firmware/BHYVE_UEFI.fd \
   uefivm

Run a UEFI virtual machine with a VARS file to save EFI variables. Note that bhyve will write guest modifications to the given VARS file. Be sure to create a per-guest copy of the template VARS file from /usr.

bhyve -c 2 -m 4g -w -H \
  -s 0,hostbridge \
  -s 31,lpc -l com1,stdio \
  -l bootrom,/usr/local/share/uefi-firmware/BHYVE_UEFI_CODE.fd,BHYVE_UEFI_VARS.fd
   uefivm

To create a configuration file configfile for a virtual machine, use -o config.dump=1:

/usr/sbin/bhyve -c 2 -m 256 -H -P \
  -s 0:0,hostbridge -s 1:0,virtio-net,tap0 \
  -s 2:0,ahci-hd,./vm0.img \
  -s 31,lpc -l com1,stdio \
  -o config.dump=1 vm0 > configfile

Then use an editor of your choice to remove the line "config.dump=1" from the newly generated configfile.

To start bhyve using this configuration file, use flag -k:

/usr/sbin/bhyve -k configfile vm0

bhyve(4), netgraph(4), ng_socket(4), nmdm(4), vmm(4), bhyve_config(5), 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 <neel@freebsd.org>
Peter Grehan <grehan@freebsd.org>

August 21, 2024 dev