QEMU

QEMU is an open source and very fast virtualization software that focuses on dynamic translation to achieve reasonable performance, while being easy to port to new host CPUs (processors).

A powerful machine emulator and virtualizer

It is also known as a machine emulator, engineered to emulate a full system, including a processor and its peripherals. The emulation part supports operating systems and programs created for a single hardware platform, but running on top of a different computer with a different architecture.

On the other hand, when the application is used as a virtualizer, it can achieve almost native performances by running the guest code straight on the host processor. It supports the Xen hypervisor and the KVM (Kernel Virtual Machine) kernel module.

Supports virtualization of numerous hardware platforms

If KVM is preferred, the application will be able to virtualize x86 (32-bit), s390, PowerPC, ARM, m68k, MIPS, CRIS, Microblaze, MIPSEL, or32, and SPARC machines. It can emulate the Windows XP, FreeDOS and SunOS systems, as well as Virtio, USB Root Hubs, networking, input, video and storage devices.

After VirtualBox and VMware, QEMU is the third biggest virtualization software for Linux platforms, but the first and most powerful one for the open source ecosystem. Its key feature is the ability to run as a native virtual machine on 64-bit or 32-bit architectures, or as a pure emulator.

Supported operating systems

It is a command-line software and runs on Linux-based operating systems, as well as Microsoft Windows and various UNIX flavors. A source archive is provided on the dedicated download section, allowing users to configure, compile and installed the program in any Linux distribution, as well as on OpenBSD, Solaris, AIX, MinGW, and Cygwin systems.

Bottom line

Whether you want to test software, try various operating systems, or just run applications that are not supported on your platform, QEMU provides users with one of the fastest virtualization and emulator machine.

What is new in this release:

• System emulation:
• Incompatible changes:
• The number of allow PCI host bridges for pSeries machine was reduced from 256 to 31 (more can be configured by setting up MMIO windows manually).
• Removed support for tftp:// in the block layer, since this has been broken forever for files bigger than 256KB.
• Future incompatible changes:
• Three options are using different names on the command line and in configuration file. In particular:
• The "acpi" configuration file section matches command-line option "acpitable";
• The "boot-opts" configuration file section matches command-line option "boot";
• The "smp-opts" configuration file section matches command-line option "smp".
• -readconfig will standardize on the name for the command line option.
• Behavior of automatic calculation of SMP topology when some SMP topology options for -smp are omitted (sockets, cores, threads) will change in the future. If guest ABI needs to be preserved on upgrades while using the SMP topology options, users should either set set all options explicitly (sockets, cores, threads), or omit all of them.
• Devices "allwinner-a10", "pc87312", "ssi-sd" will be configured with explicit properties instead of implicitly. This is unlikely to affect users.
• QMP command blockdev-add is still a work in progress. It doesn't support all block drivers, it lacks a matching blockdev-del, and more. It might change incompatibly.
• For x86, specifying a CPUID feature with both "+feature/-feature" and "feature=on/off" will cause a warning. The current behavior for this combination ("+feature/-feature" wins over "feature=on/off") will be changed so that "+feature" and "-feature" will be synonyms for "feature=on" and "feature=off" respectively).
• ARM:
• Improvements to the Aspeed board.
• Support for HLT semihosting traps in AArch32 mode (both ARM and Thumb).
• The ACPI tables for the "virt" machine type support ITS.
• The Cadence GEM device now supports multiple priority queues through the num-priority-queues property.
• The STM32F2xx board (Netduino 2) now includes ADC and SPI devices.
• MIPS:
• Support for 24KEc CPUs.
• PowerPC:
• Support for POWER9 CPUs.
• Improvements for the new "powernv" platform.
• pSeries:
• PCI host bridges can be associated to NUMA nodes.
• Support for more than 1 TiB of guest memory.
• Support for more than 64 GiB of MMIO window in a PCI host bridge.
• Support for the "-prom-env" parameter
• s390:
• Support for CPU models.
• Support for virtio-ccw revision 2.
• x86:
• Support for several new CPUID features related to AVX-512 instruction set extensions.
• The emulated IOAPIC (used by TCG and, with KVM, if the "-machine kernel_irqchip" option has the value "off" or "split") now defaults to version 0x20, which supports directed end-of-interrupt messages.
• Support for Extended Interrupt Mode (EIM) in the intel_iommu device. EIM requires KVM (Linux v4.7 or newer, for x2APIC support) and "-machine kernel-irqchip=split"; it is enabled automatically if interrupt remapping is enabled ("-machine kernel-irqchip=split -device intel_iommu,intremap=on").
• Support for up to 288 CPUs with the Q35 machine types. 256 or more CPUs are only supported if IOMMU and EIM are enabled.
• Xen:
• Support for unplugging SCSI disk.
• Support for SUSE xenlinux-compatible device unplug.
• Device emulation and assignment:
• QEMU now includes a generic loader pseudo-device that lets you load multiple images or values into memory at startup. This device is documented in docs/generic-loader.txt.
• ACPI:
• Support for hotplugging of NVDIMM devices (_FIT)
• Network devices:
• Support for fault tolerance based on coarse-grained lock stepping (COLO).
• PCI/PCIe:
• The sample EDU device now supports MSI.
• PCI Express Guidelines documentation has been added for advice on topology and PCI vs PCIe.
• virtio:
• New device vhost-vsock.
• Initial support for graceful handling of guest errors (i.e. QEMU should not exit on guest errors).
• Support for new virtio-crypto device.
• Xen:
• Support for grant copy.
• Crypto subsystem:
• Support for more hash algorithms for PBKDF.
• Support for CTR mode.
• GUI:
• SPICE can use pure OpenGL rendering if "gl=on" is specified.
• Monitor:
• Migration:
• Support for fault tolerance based on coarse-grained lock stepping (COLO).
• Network:
• Block devices and tools:
• More QMP commands support node-name (block-stream, block-commit, blockdev-backup, blockdev-mirror, blockdev-snapshot-delete-internal-sync, blockdev-snapshot-internal-sync, change-backing-file, drive-backup, drive-mirror, nbd-server-add).
• The BLOCK_IO_ERROR event now includes the node name.
• More QMP commands accept device model names (block_set_io_throttle, blockdev-change-medium, eject, x-blockdev-remove-medium, x-blockdev-insert-medium, blockdev-open-tray, blockdev-close-tray)
• The DEVICE_TRAY_MOVED event now includes the device id.
• Throttling now applies to the guest device only, and not to block jobs or the NBD server.
• drive-backup and blockdev-backup support writing out backups in compressed format.
• The LUKS format now can configure the PBKDF iteration count.
• block-stream supports streaming from a backing file to another backing file.
• Support for replication, for coarse-grained lock stepping (COLO) fault tolerance.
• New "dd" subcomamand of qemu-img.
• The DMG driver can be compiled to a separate driver, so as to make QEMU's dependency on libbz2 optional.
• Support for iSER in QEMU's iSCSI initiator through a iser:// URI.
• The NBD client and server support the NBD_CMD_WRITE_ZEROES extension.
• Raw images support "offset" and "size" options to access only a part of the file or device.
• Tracing:
• New tracing backend "syslog".
• Support for multiple "-d trace:PATTERN" command-line arguments.
• CLI options:
• User-mode emulation
• Removed target support
• The unicore32-linux-user target implemented a different system call ABI from mainline Linux for this architecture. Support for it has been dropped.
• New functionality:
• Added support for more syscalls including preadv, pwritev, syslog.
• Major scalability improvements for multi-threaded programs (ARM, SPARC, x86).
• QEMU can now understand and generate fence and cmpxchg operations.
• TCG:
• New TCG primitives have been added for safely modelling architectural synchronisation instructions (e.g. atomics, LL/SC, LOCK prefixes). arm, aarch64, alpha and x86 targets now use these primitives for multi-threaded linux-user programs. TCG target maintainers are encouraged to port their front-ends to use the new facilities.
• The TCG backends now emit appropriate barrier instructions for frontend barriers when running multi-threaded programs. However, emulating a strongly-ordered architecture (e.g., x86) on a weakly-ordered one (e.g., ARM or POWER) will not work yet.
• tb_flush() is finally thread-safe meaning multi-threaded programs are less likely to crash when the translation buffer is reset
• lock contention in the main cpu run-loop has been reduced improving performance for multi-threaded code
• a number of races were identified and fixed
• A lot of the TCG work merged in this cycle where prerequisites for supporting multi-threaded system emulation (MTTCG). While full MTTCG support is expected to be merged in the next development cycle, multi-threaded linux-user programs will already benefit from this work.

What is new in version :

• System emulation:
• Incompatible changes:
• The number of allow PCI host bridges for pSeries machine was reduced from 256 to 31 (more can be configured by setting up MMIO windows manually).
• Removed support for tftp:// in the block layer, since this has been broken forever for files bigger than 256KB.
• Future incompatible changes:
• Three options are using different names on the command line and in configuration file. In particular:
• The "acpi" configuration file section matches command-line option "acpitable";
• The "boot-opts" configuration file section matches command-line option "boot";
• The "smp-opts" configuration file section matches command-line option "smp".
• -readconfig will standardize on the name for the command line option.
• Behavior of automatic calculation of SMP topology when some SMP topology options for -smp are omitted (sockets, cores, threads) will change in the future. If guest ABI needs to be preserved on upgrades while using the SMP topology options, users should either set set all options explicitly (sockets, cores, threads), or omit all of them.
• Devices "allwinner-a10", "pc87312", "ssi-sd" will be configured with explicit properties instead of implicitly. This is unlikely to affect users.
• QMP command blockdev-add is still a work in progress. It doesn't support all block drivers, it lacks a matching blockdev-del, and more. It might change incompatibly.
• For x86, specifying a CPUID feature with both "+feature/-feature" and "feature=on/off" will cause a warning. The current behavior for this combination ("+feature/-feature" wins over "feature=on/off") will be changed so that "+feature" and "-feature" will be synonyms for "feature=on" and "feature=off" respectively).
• ARM:
• Improvements to the Aspeed board.
• Support for HLT semihosting traps in AArch32 mode (both ARM and Thumb).
• The ACPI tables for the "virt" machine type support ITS.
• The Cadence GEM device now supports multiple priority queues through the num-priority-queues property.
• The STM32F2xx board (Netduino 2) now includes ADC and SPI devices.
• MIPS:
• Support for 24KEc CPUs.
• PowerPC:
• Support for POWER9 CPUs.
• Improvements for the new "powernv" platform.
• pSeries:
• PCI host bridges can be associated to NUMA nodes.
• Support for more than 1 TiB of guest memory.
• Support for more than 64 GiB of MMIO window in a PCI host bridge.
• Support for the "-prom-env" parameter
• s390:
• Support for CPU models.
• Support for virtio-ccw revision 2.
• x86:
• Support for several new CPUID features related to AVX-512 instruction set extensions.
• The emulated IOAPIC (used by TCG and, with KVM, if the "-machine kernel_irqchip" option has the value "off" or "split") now defaults to version 0x20, which supports directed end-of-interrupt messages.
• Support for Extended Interrupt Mode (EIM) in the intel_iommu device. EIM requires KVM (Linux v4.7 or newer, for x2APIC support) and "-machine kernel-irqchip=split"; it is enabled automatically if interrupt remapping is enabled ("-machine kernel-irqchip=split -device intel_iommu,intremap=on").
• Support for up to 288 CPUs with the Q35 machine types. 256 or more CPUs are only supported if IOMMU and EIM are enabled.
• Xen:
• Support for unplugging SCSI disk.
• Support for SUSE xenlinux-compatible device unplug.
• Device emulation and assignment:
• QEMU now includes a generic loader pseudo-device that lets you load multiple images or values into memory at startup. This device is documented in docs/generic-loader.txt.
• ACPI:
• Support for hotplugging of NVDIMM devices (_FIT)
• Network devices:
• Support for fault tolerance based on coarse-grained lock stepping (COLO).
• PCI/PCIe:
• The sample EDU device now supports MSI.
• PCI Express Guidelines documentation has been added for advice on topology and PCI vs PCIe.
• virtio:
• New device vhost-vsock.
• Initial support for graceful handling of guest errors (i.e. QEMU should not exit on guest errors).
• Support for new virtio-crypto device.
• Xen:
• Support for grant copy.
• Crypto subsystem:
• Support for more hash algorithms for PBKDF.
• Support for CTR mode.
• GUI:
• SPICE can use pure OpenGL rendering if "gl=on" is specified.
• Monitor:
• Migration:
• Support for fault tolerance based on coarse-grained lock stepping (COLO).
• Network:
• Block devices and tools:
• More QMP commands support node-name (block-stream, block-commit, blockdev-backup, blockdev-mirror, blockdev-snapshot-delete-internal-sync, blockdev-snapshot-internal-sync, change-backing-file, drive-backup, drive-mirror, nbd-server-add).
• The BLOCK_IO_ERROR event now includes the node name.
• More QMP commands accept device model names (block_set_io_throttle, blockdev-change-medium, eject, x-blockdev-remove-medium, x-blockdev-insert-medium, blockdev-open-tray, blockdev-close-tray)
• The DEVICE_TRAY_MOVED event now includes the device id.
• Throttling now applies to the guest device only, and not to block jobs or the NBD server.
• drive-backup and blockdev-backup support writing out backups in compressed format.
• The LUKS format now can configure the PBKDF iteration count.
• block-stream supports streaming from a backing file to another backing file.
• Support for replication, for coarse-grained lock stepping (COLO) fault tolerance.
• New "dd" subcomamand of qemu-img.
• The DMG driver can be compiled to a separate driver, so as to make QEMU's dependency on libbz2 optional.
• Support for iSER in QEMU's iSCSI initiator through a iser:// URI.
• The NBD client and server support the NBD_CMD_WRITE_ZEROES extension.
• Raw images support "offset" and "size" options to access only a part of the file or device.
• Tracing:
• New tracing backend "syslog".
• Support for multiple "-d trace:PATTERN" command-line arguments.
• CLI options:
• User-mode emulation
• Removed target support
• The unicore32-linux-user target implemented a different system call ABI from mainline Linux for this architecture. Support for it has been dropped.
• New functionality:
• Added support for more syscalls including preadv, pwritev, syslog.
• Major scalability improvements for multi-threaded programs (ARM, SPARC, x86).
• QEMU can now understand and generate fence and cmpxchg operations.
• TCG:
• New TCG primitives have been added for safely modelling architectural synchronisation instructions (e.g. atomics, LL/SC, LOCK prefixes). arm, aarch64, alpha and x86 targets now use these primitives for multi-threaded linux-user programs. TCG target maintainers are encouraged to port their front-ends to use the new facilities.
• The TCG backends now emit appropriate barrier instructions for frontend barriers when running multi-threaded programs. However, emulating a strongly-ordered architecture (e.g., x86) on a weakly-ordered one (e.g., ARM or POWER) will not work yet.
• tb_flush() is finally thread-safe meaning multi-threaded programs are less likely to crash when the translation buffer is reset
• lock contention in the main cpu run-loop has been reduced improving performance for multi-threaded code
• a number of races were identified and fixed
• A lot of the TCG work merged in this cycle where prerequisites for supporting multi-threaded system emulation (MTTCG). While full MTTCG support is expected to be merged in the next development cycle, multi-threaded linux-user programs will already benefit from this work.

What is new in version 2.9.0:

• System emulation:
• Incompatible changes:
• The number of allow PCI host bridges for pSeries machine was reduced from 256 to 31 (more can be configured by setting up MMIO windows manually).
• Removed support for tftp:// in the block layer, since this has been broken forever for files bigger than 256KB.
• Future incompatible changes:
• Three options are using different names on the command line and in configuration file. In particular:
• The "acpi" configuration file section matches command-line option "acpitable";
• The "boot-opts" configuration file section matches command-line option "boot";
• The "smp-opts" configuration file section matches command-line option "smp".
• -readconfig will standardize on the name for the command line option.
• Behavior of automatic calculation of SMP topology when some SMP topology options for -smp are omitted (sockets, cores, threads) will change in the future. If guest ABI needs to be preserved on upgrades while using the SMP topology options, users should either set set all options explicitly (sockets, cores, threads), or omit all of them.
• Devices "allwinner-a10", "pc87312", "ssi-sd" will be configured with explicit properties instead of implicitly. This is unlikely to affect users.
• QMP command blockdev-add is still a work in progress. It doesn't support all block drivers, it lacks a matching blockdev-del, and more. It might change incompatibly.
• For x86, specifying a CPUID feature with both "+feature/-feature" and "feature=on/off" will cause a warning. The current behavior for this combination ("+feature/-feature" wins over "feature=on/off") will be changed so that "+feature" and "-feature" will be synonyms for "feature=on" and "feature=off" respectively).
• ARM:
• Improvements to the Aspeed board.
• Support for HLT semihosting traps in AArch32 mode (both ARM and Thumb).
• The ACPI tables for the "virt" machine type support ITS.
• The Cadence GEM device now supports multiple priority queues through the num-priority-queues property.
• The STM32F2xx board (Netduino 2) now includes ADC and SPI devices.
• MIPS:
• Support for 24KEc CPUs.
• PowerPC:
• Support for POWER9 CPUs.
• Improvements for the new "powernv" platform.
• pSeries:
• PCI host bridges can be associated to NUMA nodes.
• Support for more than 1 TiB of guest memory.
• Support for more than 64 GiB of MMIO window in a PCI host bridge.
• Support for the "-prom-env" parameter
• s390:
• Support for CPU models.
• Support for virtio-ccw revision 2.
• x86:
• Support for several new CPUID features related to AVX-512 instruction set extensions.
• The emulated IOAPIC (used by TCG and, with KVM, if the "-machine kernel_irqchip" option has the value "off" or "split") now defaults to version 0x20, which supports directed end-of-interrupt messages.
• Support for Extended Interrupt Mode (EIM) in the intel_iommu device. EIM requires KVM (Linux v4.7 or newer, for x2APIC support) and "-machine kernel-irqchip=split"; it is enabled automatically if interrupt remapping is enabled ("-machine kernel-irqchip=split -device intel_iommu,intremap=on").
• Support for up to 288 CPUs with the Q35 machine types. 256 or more CPUs are only supported if IOMMU and EIM are enabled.
• Xen:
• Support for unplugging SCSI disk.
• Support for SUSE xenlinux-compatible device unplug.
• Device emulation and assignment:
• QEMU now includes a generic loader pseudo-device that lets you load multiple images or values into memory at startup. This device is documented in docs/generic-loader.txt.
• ACPI:
• Support for hotplugging of NVDIMM devices (_FIT)
• Network devices:
• Support for fault tolerance based on coarse-grained lock stepping (COLO).
• PCI/PCIe:
• The sample EDU device now supports MSI.
• PCI Express Guidelines documentation has been added for advice on topology and PCI vs PCIe.
• virtio:
• New device vhost-vsock.
• Initial support for graceful handling of guest errors (i.e. QEMU should not exit on guest errors).
• Support for new virtio-crypto device.
• Xen:
• Support for grant copy.
• Crypto subsystem:
• Support for more hash algorithms for PBKDF.
• Support for CTR mode.
• GUI:
• SPICE can use pure OpenGL rendering if "gl=on" is specified.
• Monitor:
• Migration:
• Support for fault tolerance based on coarse-grained lock stepping (COLO).
• Network:
• Block devices and tools:
• More QMP commands support node-name (block-stream, block-commit, blockdev-backup, blockdev-mirror, blockdev-snapshot-delete-internal-sync, blockdev-snapshot-internal-sync, change-backing-file, drive-backup, drive-mirror, nbd-server-add).
• The BLOCK_IO_ERROR event now includes the node name.
• More QMP commands accept device model names (block_set_io_throttle, blockdev-change-medium, eject, x-blockdev-remove-medium, x-blockdev-insert-medium, blockdev-open-tray, blockdev-close-tray)
• The DEVICE_TRAY_MOVED event now includes the device id.
• Throttling now applies to the guest device only, and not to block jobs or the NBD server.
• drive-backup and blockdev-backup support writing out backups in compressed format.
• The LUKS format now can configure the PBKDF iteration count.
• block-stream supports streaming from a backing file to another backing file.
• Support for replication, for coarse-grained lock stepping (COLO) fault tolerance.
• New "dd" subcomamand of qemu-img.
• The DMG driver can be compiled to a separate driver, so as to make QEMU's dependency on libbz2 optional.
• Support for iSER in QEMU's iSCSI initiator through a iser:// URI.
• The NBD client and server support the NBD_CMD_WRITE_ZEROES extension.
• Raw images support "offset" and "size" options to access only a part of the file or device.
• Tracing:
• New tracing backend "syslog".
• Support for multiple "-d trace:PATTERN" command-line arguments.
• CLI options:
• User-mode emulation
• Removed target support
• The unicore32-linux-user target implemented a different system call ABI from mainline Linux for this architecture. Support for it has been dropped.
• New functionality:
• Added support for more syscalls including preadv, pwritev, syslog.
• Major scalability improvements for multi-threaded programs (ARM, SPARC, x86).
• QEMU can now understand and generate fence and cmpxchg operations.
• TCG:
• New TCG primitives have been added for safely modelling architectural synchronisation instructions (e.g. atomics, LL/SC, LOCK prefixes). arm, aarch64, alpha and x86 targets now use these primitives for multi-threaded linux-user programs. TCG target maintainers are encouraged to port their front-ends to use the new facilities.
• The TCG backends now emit appropriate barrier instructions for frontend barriers when running multi-threaded programs. However, emulating a strongly-ordered architecture (e.g., x86) on a weakly-ordered one (e.g., ARM or POWER) will not work yet.
• tb_flush() is finally thread-safe meaning multi-threaded programs are less likely to crash when the translation buffer is reset
• lock contention in the main cpu run-loop has been reduced improving performance for multi-threaded code
• a number of races were identified and fixed
• A lot of the TCG work merged in this cycle where prerequisites for supporting multi-threaded system emulation (MTTCG). While full MTTCG support is expected to be merged in the next development cycle, multi-threaded linux-user programs will already benefit from this work.