emulated computer which sees them as if they were real devices.
A guest operating system running in the emulated computer accesses these
-devices, and runs as it were running on real hardware. For instance you can pass
-an iso image as a parameter to Qemu, and the OS running in the emulated computer
-will see a real CDROM inserted in a CD drive.
+devices, and runs as if it were running on real hardware. For instance, you can pass
+an ISO image as a parameter to Qemu, and the OS running in the emulated computer
+will see a real CD-ROM inserted into a CD drive.
Qemu can emulate a great variety of hardware from ARM to Sparc, but {pve} is
only concerned with 32 and 64 bits PC clone emulation, since it represents the
NOTE: You may sometimes encounter the term _KVM_ (Kernel-based Virtual Machine).
It means that Qemu is running with the support of the virtualization processor
-extensions, via the Linux kvm module. In the context of {pve} _Qemu_ and
-_KVM_ can be used interchangeably as Qemu in {pve} will always try to load the kvm
+extensions, via the Linux KVM module. In the context of {pve} _Qemu_ and
+_KVM_ can be used interchangeably, as Qemu in {pve} will always try to load the KVM
module.
Qemu inside {pve} runs as a root process, since this is required to access block
--------------------------------------------
The PC hardware emulated by Qemu includes a mainboard, network controllers,
-scsi, ide and sata controllers, serial ports (the complete list can be seen in
+SCSI, IDE and SATA controllers, serial ports (the complete list can be seen in
the `kvm(1)` man page) all of them emulated in software. All these devices
are the exact software equivalent of existing hardware devices, and if the OS
running in the guest has the proper drivers it will use the devices as if it
as measured with `bonnie++(8)`. Using the virtio network interface can deliver
up to three times the throughput of an emulated Intel E1000 network card, as
measured with `iperf(1)`. footnote:[See this benchmark on the KVM wiki
-http://www.linux-kvm.org/page/Using_VirtIO_NIC]
+https://www.linux-kvm.org/page/Using_VirtIO_NIC]
[[qm_virtual_machines_settings]]
{pve} allows to boot VMs with different firmware and machine types, namely
xref:qm_bios_and_uefi[SeaBIOS and OVMF]. In most cases you want to switch from
-the default SeabBIOS to OVMF only if you plan to use
+the default SeaBIOS to OVMF only if you plan to use
xref:qm_pci_passthrough[PCIe pass through]. A VMs 'Machine Type' defines the
hardware layout of the VM's virtual motherboard. You can choose between the
default https://en.wikipedia.org/wiki/Intel_440FX[Intel 440FX] or the
format does not support thin provisioning or snapshots by itself, requiring
cooperation from the storage layer for these tasks. It may, however, be up to
10% faster than the *QEMU image format*. footnote:[See this benchmark for details
- http://events.linuxfoundation.org/sites/events/files/slides/CloudOpen2013_Khoa_Huynh_v3.pdf]
+ https://events.static.linuxfound.org/sites/events/files/slides/CloudOpen2013_Khoa_Huynh_v3.pdf]
* the *VMware image format* only makes sense if you intend to import/export the
disk image to other hypervisors.
in that case it makes sense to set the number of sockets to what the license
allows you.
-Increasing the number of virtual cpus (cores and sockets) will usually provide a
+Increasing the number of virtual CPUs (cores and sockets) will usually provide a
performance improvement though that is heavily dependent on the use of the VM.
-Multithreaded applications will of course benefit from a large number of
-virtual cpus, as for each virtual cpu you add, Qemu will create a new thread of
+Multi-threaded applications will of course benefit from a large number of
+virtual CPUs, as for each virtual cpu you add, Qemu will create a new thread of
execution on the host system. If you're not sure about the workload of your VM,
it is usually a safe bet to set the number of *Total cores* to 2.
is greater than the number of cores on the server (e.g., 4 VMs with each 4
cores on a machine with only 8 cores). In that case the host system will
balance the Qemu execution threads between your server cores, just like if you
-were running a standard multithreaded application. However, {pve} will prevent
+were running a standard multi-threaded application. However, {pve} will prevent
you from starting VMs with more virtual CPU cores than physically available, as
this will only bring the performance down due to the cost of context switches.
^^^^^^^^^^^^^
Modern operating systems introduced the capability to hot-plug and, to a
-certain extent, hot-unplug CPUs in a running systems. Virtualisation allows us
+certain extent, hot-unplug CPUs in a running system. Virtualization allows us
to avoid a lot of the (physical) problems real hardware can cause in such
scenarios.
Still, this is a rather new and complicated feature, so its use should be
There are, however, some scenarios in which a BIOS is not a good firmware
to boot from, e.g. if you want to do VGA passthrough. footnote:[Alex Williamson has a very good blog entry about this.
-http://vfio.blogspot.co.at/2014/08/primary-graphics-assignment-without-vga.html]
-In such cases, you should rather use *OVMF*, which is an open-source UEFI implementation. footnote:[See the OVMF Project http://www.tianocore.org/ovmf/]
+https://vfio.blogspot.co.at/2014/08/primary-graphics-assignment-without-vga.html]
+In such cases, you should rather use *OVMF*, which is an open-source UEFI implementation. footnote:[See the OVMF Project https://github.com/tianocore/tianocore.github.io/wiki/OVMF]
If you want to use OVMF, there are several things to consider:
to the exact same device cannot be made anymore.
A use case for such a device is the Looking Glass
-footnote:[Looking Glass: https://looking-glass.hostfission.com/] project,
-which enables high performance, low-latency display mirroring between
-host and guest.
+footnote:[Looking Glass: https://looking-glass.io/] project, which enables high
+performance, low-latency display mirroring between host and guest.
[[qm_audio_device]]
Audio Device
* `intel-hda`: Intel HD Audio Controller, emulates ICH6
* `AC97`: Audio Codec '97, useful for older operating systems like Windows XP
-NOTE: The audio device works only in combination with SPICE. Remote protocols
-like Microsoft's RDP have options to play sound. To use the physical audio
-device of the host use device passthrough (see
-xref:qm_pci_passthrough[PCI Passthrough] and
-xref:qm_usb_passthrough[USB Passthrough]).
+There are two backends available:
+
+* 'spice'
+* 'none'
+
+The 'spice' backend can be used in combination with xref:qm_display[SPICE] while
+the 'none' backend can be useful if an audio device is needed in the VM for some
+software to work. To use the physical audio device of the host use device
+passthrough (see xref:qm_pci_passthrough[PCI Passthrough] and
+xref:qm_usb_passthrough[USB Passthrough]). Remote protocols like Microsoft’s RDP
+have options to play sound.
+
[[qm_virtio_rng]]
VirtIO RNG
be enforced between virtual machines running on the same host, not
cluster-wide.
+
+[[qm_qemu_agent]]
+Qemu Guest Agent
+~~~~~~~~~~~~~~~~
+
+The Qemu Guest Agent is a service which runs inside the VM, providing a
+communication channel between the host and the guest. It is used to exchange
+information and allows the host to issue commands to the guest.
+
+For example, the IP addresses in the VM summary panel are fetched via the guest
+agent.
+
+Or when starting a backup, the guest is told via the guest agent to sync
+outstanding writes via the 'fs-freeze' and 'fs-thaw' commands.
+
+For the guest agent to work properly the following steps must be taken:
+
+* install the agent in the guest and make sure it is running
+* enable the communication via the agent in {pve}
+
+Install Guest Agent
+^^^^^^^^^^^^^^^^^^^
+
+For most Linux distributions, the guest agent is available. The package is
+usually named `qemu-guest-agent`.
+
+For Windows, it can be installed from the
+https://fedorapeople.org/groups/virt/virtio-win/direct-downloads/stable-virtio/virtio-win.iso[Fedora
+VirtIO driver ISO].
+
+Enable Guest Agent Communication
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Communication from {pve} with the guest agent can be enabled in the VM's
+*Options* panel. A fresh start of the VM is necessary for the changes to take
+effect.
+
+It is possible to enable the 'Run guest-trim' option. With this enabled,
+{pve} will issue a trim command to the guest after the following
+operations that have the potential to write out zeros to the storage:
+
+* moving a disk to another storage
+* live migrating a VM to another node with local storage
+
+On a thin provisioned storage, this can help to free up unused space.
+
+Troubleshooting
+^^^^^^^^^^^^^^^
+
+.VM does not shut down
+
+Make sure the guest agent is installed and running.
+
+Once the guest agent is enabled, {pve} will send power commands like
+'shutdown' via the guest agent. If the guest agent is not running, commands
+cannot get executed properly and the shutdown command will run into a timeout.
+
[[qm_spice_enhancements]]
SPICE Enhancements
~~~~~~~~~~~~~~~~~~
You can add a hook script to VMs with the config property `hookscript`.
- qm set 100 -hookscript local:snippets/hookscript.pl
+ qm set 100 --hookscript local:snippets/hookscript.pl
It will be called during various phases of the guests lifetime.
For an example and documentation see the example script under
qm shutdown 300 && qm wait 300 -timeout 40
+Destroying a VM always removes it from Access Control Lists and it always
+removes the firewall configuration of the VM. You have to activate
+'--purge', if you want to additionally remove the VM from replication jobs,
+backup jobs and HA resource configurations.
+
+ qm destroy 300 --purge
+
+
[[qm_configuration]]
Configuration
projects / pve-docs.git / blobdiff