Driver (backend)

[townsend]

See also: How to set up the driver, local.driver

A driver is the technology that permits Multipass to emulate a running machine. It corresponds to a hypervisor or intermediary technology to run virtual machines. The driver is sometimes also referred to as ‘backend’.

Multipass relies on a driver to operate. It supports multiple drivers, but it runs with a single driver at a time. There is a Multipass setting to select the driver: local.driver.

On some platforms, the installer also allows choosing a driver. Until it is manually set, a platform-appropriate default driver is used.

Supported drivers

Different sets of drivers are available on different platforms:

• On Linux, Multipass can be configured to use QEMU, LXD, and libvirt.
• On macOS, the options are QEMU and VirtualBox. As of Multipass release 1.12, Hyperkit is available but deprecated and it will be removed in the next feature release.
• On Windows, Multipass uses either Hyper-V or VirtualBox.

Default drivers

When Multipass is installed, the following drivers are selected by default:

• On Linux, the default driver depends on the host’s architecture:
  • QEMU on amd64
  • LXD on other platforms.
• On macOS, QEMU is used.
• On Windows, Hyper-V is selected.

Instance scopes

In general, instances in Multipass are tied to a single driver (exceptions below). The set of instances that were launched with one driver are available only while that driver is in use.

When a new driver is selected, Multipass switches to a separate instance scope. There, the set of existing instances is empty to begin with. Users can launch instances with the same name in different drivers and changes to instances with one driver have no effect on the instances of another.

Nonetheless, instances are preserved across drivers. After switching back to a previously-used driver, Multipass restores the corresponding instance scope. It attempts to restore the state instances were in just before the switch and users can interact with them just as before.

Exceptions

There are two exceptions to the above:

• QEMU and libvirt share the same driver scope on Linux.
• Stopped Hyperkit instances are automatically migrated to QEMU by Multipass’s version 1.12(.*), on macOS.

Feature disparities

While we strive to offer a uniform interface across the board, not all features are available on all backends and there are some behavior differences:

• Native mounts are supported only on Hyper-V, QEMU, and LXD (the latter since version 1.13). This affects the --type option in the mount command)
• Extra networks are supported only on LXD, Hyper-V, VirtualBox, and QEMU on macOS. This affects the networks command, as well as --network and --bridged options in launch.
• VM suspension is supported on QEMU, libvirt, and VirtualBox. This affects the suspend command

Note that there are also feature disparities depending on the host platform as well.