1 [[chapter_virtual_machines]]
10 qm - Qemu/KVM Virtual Machine Manager
16 include::qm.1-synopsis.adoc[]
22 Qemu/KVM Virtual Machines
23 =========================
28 // http://pve.proxmox.com/wiki/Container_and_Full_Virtualization
29 // http://pve.proxmox.com/wiki/KVM
30 // http://pve.proxmox.com/wiki/Qemu_Server
32 Qemu (short form for Quick Emulator) is an open source hypervisor that emulates a
33 physical computer. From the perspective of the host system where Qemu is
34 running, Qemu is a user program which has access to a number of local resources
35 like partitions, files, network cards which are then passed to an
36 emulated computer which sees them as if they were real devices.
38 A guest operating system running in the emulated computer accesses these
39 devices, and runs as it were running on real hardware. For instance you can pass
40 an iso image as a parameter to Qemu, and the OS running in the emulated computer
41 will see a real CDROM inserted in a CD drive.
43 Qemu can emulate a great variety of hardware from ARM to Sparc, but {pve} is
44 only concerned with 32 and 64 bits PC clone emulation, since it represents the
45 overwhelming majority of server hardware. The emulation of PC clones is also one
46 of the fastest due to the availability of processor extensions which greatly
47 speed up Qemu when the emulated architecture is the same as the host
50 NOTE: You may sometimes encounter the term _KVM_ (Kernel-based Virtual Machine).
51 It means that Qemu is running with the support of the virtualization processor
52 extensions, via the Linux kvm module. In the context of {pve} _Qemu_ and
53 _KVM_ can be used interchangeably as Qemu in {pve} will always try to load the kvm
56 Qemu inside {pve} runs as a root process, since this is required to access block
60 Emulated devices and paravirtualized devices
61 --------------------------------------------
63 The PC hardware emulated by Qemu includes a mainboard, network controllers,
64 scsi, ide and sata controllers, serial ports (the complete list can be seen in
65 the `kvm(1)` man page) all of them emulated in software. All these devices
66 are the exact software equivalent of existing hardware devices, and if the OS
67 running in the guest has the proper drivers it will use the devices as if it
68 were running on real hardware. This allows Qemu to runs _unmodified_ operating
71 This however has a performance cost, as running in software what was meant to
72 run in hardware involves a lot of extra work for the host CPU. To mitigate this,
73 Qemu can present to the guest operating system _paravirtualized devices_, where
74 the guest OS recognizes it is running inside Qemu and cooperates with the
77 Qemu relies on the virtio virtualization standard, and is thus able to present
78 paravirtualized virtio devices, which includes a paravirtualized generic disk
79 controller, a paravirtualized network card, a paravirtualized serial port,
80 a paravirtualized SCSI controller, etc ...
82 It is highly recommended to use the virtio devices whenever you can, as they
83 provide a big performance improvement. Using the virtio generic disk controller
84 versus an emulated IDE controller will double the sequential write throughput,
85 as measured with `bonnie++(8)`. Using the virtio network interface can deliver
86 up to three times the throughput of an emulated Intel E1000 network card, as
87 measured with `iperf(1)`. footnote:[See this benchmark on the KVM wiki
88 http://www.linux-kvm.org/page/Using_VirtIO_NIC]
91 [[qm_virtual_machines_settings]]
92 Virtual Machines Settings
93 -------------------------
95 Generally speaking {pve} tries to choose sane defaults for virtual machines
96 (VM). Make sure you understand the meaning of the settings you change, as it
97 could incur a performance slowdown, or putting your data at risk.
100 [[qm_general_settings]]
104 [thumbnail="screenshot/gui-create-vm-general.png"]
106 General settings of a VM include
108 * the *Node* : the physical server on which the VM will run
109 * the *VM ID*: a unique number in this {pve} installation used to identify your VM
110 * *Name*: a free form text string you can use to describe the VM
111 * *Resource Pool*: a logical group of VMs
118 [thumbnail="screenshot/gui-create-vm-os.png"]
120 When creating a virtual machine (VM), setting the proper Operating System(OS)
121 allows {pve} to optimize some low level parameters. For instance Windows OS
122 expect the BIOS clock to use the local time, while Unix based OS expect the
123 BIOS clock to have the UTC time.
125 [[qm_system_settings]]
129 On VM creation you can change some basic system components of the new VM. You
130 can specify which xref:qm_display[display type] you want to use.
131 [thumbnail="screenshot/gui-create-vm-system.png"]
132 Additionally, the xref:qm_hard_disk[SCSI controller] can be changed.
133 If you plan to install the QEMU Guest Agent, or if your selected ISO image
134 already ships and installs it automatically, you may want to tick the 'Qemu
135 Agent' box, which lets {pve} know that it can use its features to show some
136 more information, and complete some actions (for example, shutdown or
137 snapshots) more intelligently.
139 {pve} allows to boot VMs with different firmware and machine types, namely
140 xref:qm_bios_and_uefi[SeaBIOS and OVMF]. In most cases you want to switch from
141 the default SeabBIOS to OVMF only if you plan to use
142 xref:qm_pci_passthrough[PCIe pass through]. A VMs 'Machine Type' defines the
143 hardware layout of the VM's virtual motherboard. You can choose between the
144 default https://en.wikipedia.org/wiki/Intel_440FX[Intel 440FX] or the
145 https://ark.intel.com/content/www/us/en/ark/products/31918/intel-82q35-graphics-and-memory-controller.html[Q35]
146 chipset, which also provides a virtual PCIe bus, and thus may be desired if
147 one want's to pass through PCIe hardware.
156 Qemu can emulate a number of storage controllers:
158 * the *IDE* controller, has a design which goes back to the 1984 PC/AT disk
159 controller. Even if this controller has been superseded by recent designs,
160 each and every OS you can think of has support for it, making it a great choice
161 if you want to run an OS released before 2003. You can connect up to 4 devices
164 * the *SATA* (Serial ATA) controller, dating from 2003, has a more modern
165 design, allowing higher throughput and a greater number of devices to be
166 connected. You can connect up to 6 devices on this controller.
168 * the *SCSI* controller, designed in 1985, is commonly found on server grade
169 hardware, and can connect up to 14 storage devices. {pve} emulates by default a
170 LSI 53C895A controller.
172 A SCSI controller of type _VirtIO SCSI_ is the recommended setting if you aim for
173 performance and is automatically selected for newly created Linux VMs since
174 {pve} 4.3. Linux distributions have support for this controller since 2012, and
175 FreeBSD since 2014. For Windows OSes, you need to provide an extra iso
176 containing the drivers during the installation.
177 // https://pve.proxmox.com/wiki/Paravirtualized_Block_Drivers_for_Windows#During_windows_installation.
178 If you aim at maximum performance, you can select a SCSI controller of type
179 _VirtIO SCSI single_ which will allow you to select the *IO Thread* option.
180 When selecting _VirtIO SCSI single_ Qemu will create a new controller for
181 each disk, instead of adding all disks to the same controller.
183 * The *VirtIO Block* controller, often just called VirtIO or virtio-blk,
184 is an older type of paravirtualized controller. It has been superseded by the
185 VirtIO SCSI Controller, in terms of features.
187 [thumbnail="screenshot/gui-create-vm-hard-disk.png"]
189 [[qm_hard_disk_formats]]
192 On each controller you attach a number of emulated hard disks, which are backed
193 by a file or a block device residing in the configured storage. The choice of
194 a storage type will determine the format of the hard disk image. Storages which
195 present block devices (LVM, ZFS, Ceph) will require the *raw disk image format*,
196 whereas files based storages (Ext4, NFS, CIFS, GlusterFS) will let you to choose
197 either the *raw disk image format* or the *QEMU image format*.
199 * the *QEMU image format* is a copy on write format which allows snapshots, and
200 thin provisioning of the disk image.
201 * the *raw disk image* is a bit-to-bit image of a hard disk, similar to what
202 you would get when executing the `dd` command on a block device in Linux. This
203 format does not support thin provisioning or snapshots by itself, requiring
204 cooperation from the storage layer for these tasks. It may, however, be up to
205 10% faster than the *QEMU image format*. footnote:[See this benchmark for details
206 http://events.linuxfoundation.org/sites/events/files/slides/CloudOpen2013_Khoa_Huynh_v3.pdf]
207 * the *VMware image format* only makes sense if you intend to import/export the
208 disk image to other hypervisors.
210 [[qm_hard_disk_cache]]
213 Setting the *Cache* mode of the hard drive will impact how the host system will
214 notify the guest systems of block write completions. The *No cache* default
215 means that the guest system will be notified that a write is complete when each
216 block reaches the physical storage write queue, ignoring the host page cache.
217 This provides a good balance between safety and speed.
219 If you want the {pve} backup manager to skip a disk when doing a backup of a VM,
220 you can set the *No backup* option on that disk.
222 If you want the {pve} storage replication mechanism to skip a disk when starting
223 a replication job, you can set the *Skip replication* option on that disk.
224 As of {pve} 5.0, replication requires the disk images to be on a storage of type
225 `zfspool`, so adding a disk image to other storages when the VM has replication
226 configured requires to skip replication for this disk image.
228 [[qm_hard_disk_discard]]
231 If your storage supports _thin provisioning_ (see the storage chapter in the
232 {pve} guide), you can activate the *Discard* option on a drive. With *Discard*
233 set and a _TRIM_-enabled guest OS footnote:[TRIM, UNMAP, and discard
234 https://en.wikipedia.org/wiki/Trim_%28computing%29], when the VM's filesystem
235 marks blocks as unused after deleting files, the controller will relay this
236 information to the storage, which will then shrink the disk image accordingly.
237 For the guest to be able to issue _TRIM_ commands, you must enable the *Discard*
238 option on the drive. Some guest operating systems may also require the
239 *SSD Emulation* flag to be set. Note that *Discard* on *VirtIO Block* drives is
240 only supported on guests using Linux Kernel 5.0 or higher.
242 If you would like a drive to be presented to the guest as a solid-state drive
243 rather than a rotational hard disk, you can set the *SSD emulation* option on
244 that drive. There is no requirement that the underlying storage actually be
245 backed by SSDs; this feature can be used with physical media of any type.
246 Note that *SSD emulation* is not supported on *VirtIO Block* drives.
249 [[qm_hard_disk_iothread]]
252 The option *IO Thread* can only be used when using a disk with the
253 *VirtIO* controller, or with the *SCSI* controller, when the emulated controller
254 type is *VirtIO SCSI single*.
255 With this enabled, Qemu creates one I/O thread per storage controller,
256 instead of a single thread for all I/O, so it can increase performance when
257 multiple isks are used and each disk has its own storage controller.
264 [thumbnail="screenshot/gui-create-vm-cpu.png"]
266 A *CPU socket* is a physical slot on a PC motherboard where you can plug a CPU.
267 This CPU can then contain one or many *cores*, which are independent
268 processing units. Whether you have a single CPU socket with 4 cores, or two CPU
269 sockets with two cores is mostly irrelevant from a performance point of view.
270 However some software licenses depend on the number of sockets a machine has,
271 in that case it makes sense to set the number of sockets to what the license
274 Increasing the number of virtual cpus (cores and sockets) will usually provide a
275 performance improvement though that is heavily dependent on the use of the VM.
276 Multithreaded applications will of course benefit from a large number of
277 virtual cpus, as for each virtual cpu you add, Qemu will create a new thread of
278 execution on the host system. If you're not sure about the workload of your VM,
279 it is usually a safe bet to set the number of *Total cores* to 2.
281 NOTE: It is perfectly safe if the _overall_ number of cores of all your VMs
282 is greater than the number of cores on the server (e.g., 4 VMs with each 4
283 cores on a machine with only 8 cores). In that case the host system will
284 balance the Qemu execution threads between your server cores, just like if you
285 were running a standard multithreaded application. However, {pve} will prevent
286 you from assigning more virtual CPU cores than physically available, as this will
287 only bring the performance down due to the cost of context switches.
289 [[qm_cpu_resource_limits]]
293 In addition to the number of virtual cores, you can configure how much resources
294 a VM can get in relation to the host CPU time and also in relation to other
296 With the *cpulimit* (``Host CPU Time'') option you can limit how much CPU time
297 the whole VM can use on the host. It is a floating point value representing CPU
298 time in percent, so `1.0` is equal to `100%`, `2.5` to `250%` and so on. If a
299 single process would fully use one single core it would have `100%` CPU Time
300 usage. If a VM with four cores utilizes all its cores fully it would
301 theoretically use `400%`. In reality the usage may be even a bit higher as Qemu
302 can have additional threads for VM peripherals besides the vCPU core ones.
303 This setting can be useful if a VM should have multiple vCPUs, as it runs a few
304 processes in parallel, but the VM as a whole should not be able to run all
305 vCPUs at 100% at the same time. Using a specific example: lets say we have a VM
306 which would profit from having 8 vCPUs, but at no time all of those 8 cores
307 should run at full load - as this would make the server so overloaded that
308 other VMs and CTs would get to less CPU. So, we set the *cpulimit* limit to
309 `4.0` (=400%). If all cores do the same heavy work they would all get 50% of a
310 real host cores CPU time. But, if only 4 would do work they could still get
311 almost 100% of a real core each.
313 NOTE: VMs can, depending on their configuration, use additional threads e.g.,
314 for networking or IO operations but also live migration. Thus a VM can show up
315 to use more CPU time than just its virtual CPUs could use. To ensure that a VM
316 never uses more CPU time than virtual CPUs assigned set the *cpulimit* setting
317 to the same value as the total core count.
319 The second CPU resource limiting setting, *cpuunits* (nowadays often called CPU
320 shares or CPU weight), controls how much CPU time a VM gets in regards to other
321 VMs running. It is a relative weight which defaults to `1024`, if you increase
322 this for a VM it will be prioritized by the scheduler in comparison to other
323 VMs with lower weight. E.g., if VM 100 has set the default 1024 and VM 200 was
324 changed to `2048`, the latter VM 200 would receive twice the CPU bandwidth than
327 For more information see `man systemd.resource-control`, here `CPUQuota`
328 corresponds to `cpulimit` and `CPUShares` corresponds to our `cpuunits`
329 setting, visit its Notes section for references and implementation details.
334 Qemu can emulate a number different of *CPU types* from 486 to the latest Xeon
335 processors. Each new processor generation adds new features, like hardware
336 assisted 3d rendering, random number generation, memory protection, etc ...
337 Usually you should select for your VM a processor type which closely matches the
338 CPU of the host system, as it means that the host CPU features (also called _CPU
339 flags_ ) will be available in your VMs. If you want an exact match, you can set
340 the CPU type to *host* in which case the VM will have exactly the same CPU flags
343 This has a downside though. If you want to do a live migration of VMs between
344 different hosts, your VM might end up on a new system with a different CPU type.
345 If the CPU flags passed to the guest are missing, the qemu process will stop. To
346 remedy this Qemu has also its own CPU type *kvm64*, that {pve} uses by defaults.
347 kvm64 is a Pentium 4 look a like CPU type, which has a reduced CPU flags set,
348 but is guaranteed to work everywhere.
350 In short, if you care about live migration and moving VMs between nodes, leave
351 the kvm64 default. If you don’t care about live migration or have a homogeneous
352 cluster where all nodes have the same CPU, set the CPU type to host, as in
353 theory this will give your guests maximum performance.
355 Meltdown / Spectre related CPU flags
356 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
358 There are several CPU flags related to the Meltdown and Spectre vulnerabilities
359 footnote:[Meltdown Attack https://meltdownattack.com/] which need to be set
360 manually unless the selected CPU type of your VM already enables them by default.
362 There are two requirements that need to be fulfilled in order to use these
365 * The host CPU(s) must support the feature and propagate it to the guest's virtual CPU(s)
366 * The guest operating system must be updated to a version which mitigates the
367 attacks and is able to utilize the CPU feature
369 Otherwise you need to set the desired CPU flag of the virtual CPU, either by
370 editing the CPU options in the WebUI, or by setting the 'flags' property of the
371 'cpu' option in the VM configuration file.
373 For Spectre v1,v2,v4 fixes, your CPU or system vendor also needs to provide a
374 so-called ``microcode update'' footnote:[You can use `intel-microcode' /
375 `amd-microcode' from Debian non-free if your vendor does not provide such an
376 update. Note that not all affected CPUs can be updated to support spec-ctrl.]
380 To check if the {pve} host is vulnerable, execute the following command as root:
383 for f in /sys/devices/system/cpu/vulnerabilities/*; do echo "${f##*/} -" $(cat "$f"); done
386 A community script is also available to detect is the host is still vulnerable.
387 footnote:[spectre-meltdown-checker https://meltdown.ovh/]
394 This reduces the performance impact of the Meltdown (CVE-2017-5754) mitigation
395 called 'Kernel Page-Table Isolation (KPTI)', which effectively hides
396 the Kernel memory from the user space. Without PCID, KPTI is quite an expensive
397 mechanism footnote:[PCID is now a critical performance/security feature on x86
398 https://groups.google.com/forum/m/#!topic/mechanical-sympathy/L9mHTbeQLNU].
400 To check if the {pve} host supports PCID, execute the following command as root:
403 # grep ' pcid ' /proc/cpuinfo
406 If this does not return empty your host's CPU has support for 'pcid'.
410 Required to enable the Spectre v1 (CVE-2017-5753) and Spectre v2 (CVE-2017-5715) fix,
411 in cases where retpolines are not sufficient.
412 Included by default in Intel CPU models with -IBRS suffix.
413 Must be explicitly turned on for Intel CPU models without -IBRS suffix.
414 Requires an updated host CPU microcode (intel-microcode >= 20180425).
418 Required to enable the Spectre V4 (CVE-2018-3639) fix. Not included by default in any Intel CPU model.
419 Must be explicitly turned on for all Intel CPU models.
420 Requires an updated host CPU microcode(intel-microcode >= 20180703).
428 Required to enable the Spectre v1 (CVE-2017-5753) and Spectre v2 (CVE-2017-5715) fix,
429 in cases where retpolines are not sufficient.
430 Included by default in AMD CPU models with -IBPB suffix.
431 Must be explicitly turned on for AMD CPU models without -IBPB suffix.
432 Requires the host CPU microcode to support this feature before it can be used for guest CPUs.
438 Required to enable the Spectre v4 (CVE-2018-3639) fix.
439 Not included by default in any AMD CPU model.
440 Must be explicitly turned on for all AMD CPU models.
441 This should be provided to guests, even if amd-ssbd is also provided, for maximum guest compatibility.
442 Note that this must be explicitly enabled when when using the "host" cpu model,
443 because this is a virtual feature which does not exist in the physical CPUs.
448 Required to enable the Spectre v4 (CVE-2018-3639) fix.
449 Not included by default in any AMD CPU model. Must be explicitly turned on for all AMD CPU models.
450 This provides higher performance than virt-ssbd, therefore a host supporting this should always expose this to guests if possible.
451 virt-ssbd should none the less also be exposed for maximum guest compatibility as some kernels only know about virt-ssbd.
456 Recommended to indicate the host is not vulnerable to Spectre V4 (CVE-2018-3639).
457 Not included by default in any AMD CPU model.
458 Future hardware generations of CPU will not be vulnerable to CVE-2018-3639,
459 and thus the guest should be told not to enable its mitigations, by exposing amd-no-ssb.
460 This is mutually exclusive with virt-ssbd and amd-ssbd.
465 You can also optionally emulate a *NUMA*
466 footnote:[https://en.wikipedia.org/wiki/Non-uniform_memory_access] architecture
467 in your VMs. The basics of the NUMA architecture mean that instead of having a
468 global memory pool available to all your cores, the memory is spread into local
469 banks close to each socket.
470 This can bring speed improvements as the memory bus is not a bottleneck
471 anymore. If your system has a NUMA architecture footnote:[if the command
472 `numactl --hardware | grep available` returns more than one node, then your host
473 system has a NUMA architecture] we recommend to activate the option, as this
474 will allow proper distribution of the VM resources on the host system.
475 This option is also required to hot-plug cores or RAM in a VM.
477 If the NUMA option is used, it is recommended to set the number of sockets to
478 the number of nodes of the host system.
483 Modern operating systems introduced the capability to hot-plug and, to a
484 certain extent, hot-unplug CPUs in a running systems. Virtualisation allows us
485 to avoid a lot of the (physical) problems real hardware can cause in such
487 Still, this is a rather new and complicated feature, so its use should be
488 restricted to cases where its absolutely needed. Most of the functionality can
489 be replicated with other, well tested and less complicated, features, see
490 xref:qm_cpu_resource_limits[Resource Limits].
492 In {pve} the maximal number of plugged CPUs is always `cores * sockets`.
493 To start a VM with less than this total core count of CPUs you may use the
494 *vpus* setting, it denotes how many vCPUs should be plugged in at VM start.
496 Currently only this feature is only supported on Linux, a kernel newer than 3.10
497 is needed, a kernel newer than 4.7 is recommended.
499 You can use a udev rule as follow to automatically set new CPUs as online in
503 SUBSYSTEM=="cpu", ACTION=="add", TEST=="online", ATTR{online}=="0", ATTR{online}="1"
506 Save this under /etc/udev/rules.d/ as a file ending in `.rules`.
508 Note: CPU hot-remove is machine dependent and requires guest cooperation.
509 The deletion command does not guarantee CPU removal to actually happen,
510 typically it's a request forwarded to guest using target dependent mechanism,
511 e.g., ACPI on x86/amd64.
518 For each VM you have the option to set a fixed size memory or asking
519 {pve} to dynamically allocate memory based on the current RAM usage of the
522 .Fixed Memory Allocation
523 [thumbnail="screenshot/gui-create-vm-memory.png"]
525 When setting memory and minimum memory to the same amount
526 {pve} will simply allocate what you specify to your VM.
528 Even when using a fixed memory size, the ballooning device gets added to the
529 VM, because it delivers useful information such as how much memory the guest
531 In general, you should leave *ballooning* enabled, but if you want to disable
532 it (e.g. for debugging purposes), simply uncheck
533 *Ballooning Device* or set
537 in the configuration.
539 .Automatic Memory Allocation
541 // see autoballoon() in pvestatd.pm
542 When setting the minimum memory lower than memory, {pve} will make sure that the
543 minimum amount you specified is always available to the VM, and if RAM usage on
544 the host is below 80%, will dynamically add memory to the guest up to the
545 maximum memory specified.
547 When the host is running low on RAM, the VM will then release some memory
548 back to the host, swapping running processes if needed and starting the oom
549 killer in last resort. The passing around of memory between host and guest is
550 done via a special `balloon` kernel driver running inside the guest, which will
551 grab or release memory pages from the host.
552 footnote:[A good explanation of the inner workings of the balloon driver can be found here https://rwmj.wordpress.com/2010/07/17/virtio-balloon/]
554 When multiple VMs use the autoallocate facility, it is possible to set a
555 *Shares* coefficient which indicates the relative amount of the free host memory
556 that each VM should take. Suppose for instance you have four VMs, three of them
557 running an HTTP server and the last one is a database server. To cache more
558 database blocks in the database server RAM, you would like to prioritize the
559 database VM when spare RAM is available. For this you assign a Shares property
560 of 3000 to the database VM, leaving the other VMs to the Shares default setting
561 of 1000. The host server has 32GB of RAM, and is currently using 16GB, leaving 32
562 * 80/100 - 16 = 9GB RAM to be allocated to the VMs. The database VM will get 9 *
563 3000 / (3000 + 1000 + 1000 + 1000) = 4.5 GB extra RAM and each HTTP server will
566 All Linux distributions released after 2010 have the balloon kernel driver
567 included. For Windows OSes, the balloon driver needs to be added manually and can
568 incur a slowdown of the guest, so we don't recommend using it on critical
570 // see https://forum.proxmox.com/threads/solved-hyper-threading-vs-no-hyper-threading-fixed-vs-variable-memory.20265/
572 When allocating RAM to your VMs, a good rule of thumb is always to leave 1GB
573 of RAM available to the host.
576 [[qm_network_device]]
580 [thumbnail="screenshot/gui-create-vm-network.png"]
582 Each VM can have many _Network interface controllers_ (NIC), of four different
585 * *Intel E1000* is the default, and emulates an Intel Gigabit network card.
586 * the *VirtIO* paravirtualized NIC should be used if you aim for maximum
587 performance. Like all VirtIO devices, the guest OS should have the proper driver
589 * the *Realtek 8139* emulates an older 100 MB/s network card, and should
590 only be used when emulating older operating systems ( released before 2002 )
591 * the *vmxnet3* is another paravirtualized device, which should only be used
592 when importing a VM from another hypervisor.
594 {pve} will generate for each NIC a random *MAC address*, so that your VM is
595 addressable on Ethernet networks.
597 The NIC you added to the VM can follow one of two different models:
599 * in the default *Bridged mode* each virtual NIC is backed on the host by a
600 _tap device_, ( a software loopback device simulating an Ethernet NIC ). This
601 tap device is added to a bridge, by default vmbr0 in {pve}. In this mode, VMs
602 have direct access to the Ethernet LAN on which the host is located.
603 * in the alternative *NAT mode*, each virtual NIC will only communicate with
604 the Qemu user networking stack, where a built-in router and DHCP server can
605 provide network access. This built-in DHCP will serve addresses in the private
606 10.0.2.0/24 range. The NAT mode is much slower than the bridged mode, and
607 should only be used for testing. This mode is only available via CLI or the API,
608 but not via the WebUI.
610 You can also skip adding a network device when creating a VM by selecting *No
614 If you are using the VirtIO driver, you can optionally activate the
615 *Multiqueue* option. This option allows the guest OS to process networking
616 packets using multiple virtual CPUs, providing an increase in the total number
617 of packets transferred.
619 //http://blog.vmsplice.net/2011/09/qemu-internals-vhost-architecture.html
620 When using the VirtIO driver with {pve}, each NIC network queue is passed to the
621 host kernel, where the queue will be processed by a kernel thread spawned by the
622 vhost driver. With this option activated, it is possible to pass _multiple_
623 network queues to the host kernel for each NIC.
625 //https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/7/html/Virtualization_Tuning_and_Optimization_Guide/sect-Virtualization_Tuning_Optimization_Guide-Networking-Techniques.html#sect-Virtualization_Tuning_Optimization_Guide-Networking-Multi-queue_virtio-net
626 When using Multiqueue, it is recommended to set it to a value equal
627 to the number of Total Cores of your guest. You also need to set in
628 the VM the number of multi-purpose channels on each VirtIO NIC with the ethtool
631 `ethtool -L ens1 combined X`
633 where X is the number of the number of vcpus of the VM.
635 You should note that setting the Multiqueue parameter to a value greater
636 than one will increase the CPU load on the host and guest systems as the
637 traffic increases. We recommend to set this option only when the VM has to
638 process a great number of incoming connections, such as when the VM is running
639 as a router, reverse proxy or a busy HTTP server doing long polling.
645 QEMU can virtualize a few types of VGA hardware. Some examples are:
647 * *std*, the default, emulates a card with Bochs VBE extensions.
648 * *cirrus*, this was once the default, it emulates a very old hardware module
649 with all its problems. This display type should only be used if really
650 necessary footnote:[https://www.kraxel.org/blog/2014/10/qemu-using-cirrus-considered-harmful/
651 qemu: using cirrus considered harmful], e.g., if using Windows XP or earlier
652 * *vmware*, is a VMWare SVGA-II compatible adapter.
653 * *qxl*, is the QXL paravirtualized graphics card. Selecting this also
654 enables https://www.spice-space.org/[SPICE] (a remote viewer protocol) for the
657 You can edit the amount of memory given to the virtual GPU, by setting
658 the 'memory' option. This can enable higher resolutions inside the VM,
659 especially with SPICE/QXL.
661 As the memory is reserved by display device, selecting Multi-Monitor mode
662 for SPICE (e.g., `qxl2` for dual monitors) has some implications:
664 * Windows needs a device for each monitor, so if your 'ostype' is some
665 version of Windows, {pve} gives the VM an extra device per monitor.
666 Each device gets the specified amount of memory.
668 * Linux VMs, can always enable more virtual monitors, but selecting
669 a Multi-Monitor mode multiplies the memory given to the device with
670 the number of monitors.
672 Selecting `serialX` as display 'type' disables the VGA output, and redirects
673 the Web Console to the selected serial port. A configured display 'memory'
674 setting will be ignored in that case.
676 [[qm_usb_passthrough]]
680 There are two different types of USB passthrough devices:
682 * Host USB passthrough
683 * SPICE USB passthrough
685 Host USB passthrough works by giving a VM a USB device of the host.
686 This can either be done via the vendor- and product-id, or
687 via the host bus and port.
689 The vendor/product-id looks like this: *0123:abcd*,
690 where *0123* is the id of the vendor, and *abcd* is the id
691 of the product, meaning two pieces of the same usb device
694 The bus/port looks like this: *1-2.3.4*, where *1* is the bus
695 and *2.3.4* is the port path. This represents the physical
696 ports of your host (depending of the internal order of the
699 If a device is present in a VM configuration when the VM starts up,
700 but the device is not present in the host, the VM can boot without problems.
701 As soon as the device/port is available in the host, it gets passed through.
703 WARNING: Using this kind of USB passthrough means that you cannot move
704 a VM online to another host, since the hardware is only available
705 on the host the VM is currently residing.
707 The second type of passthrough is SPICE USB passthrough. This is useful
708 if you use a SPICE client which supports it. If you add a SPICE USB port
709 to your VM, you can passthrough a USB device from where your SPICE client is,
710 directly to the VM (for example an input device or hardware dongle).
717 In order to properly emulate a computer, QEMU needs to use a firmware.
718 Which, on common PCs often known as BIOS or (U)EFI, is executed as one of the
719 first steps when booting a VM. It is responsible for doing basic hardware
720 initialization and for providing an interface to the firmware and hardware for
721 the operating system. By default QEMU uses *SeaBIOS* for this, which is an
722 open-source, x86 BIOS implementation. SeaBIOS is a good choice for most
725 There are, however, some scenarios in which a BIOS is not a good firmware
726 to boot from, e.g. if you want to do VGA passthrough. footnote:[Alex Williamson has a very good blog entry about this.
727 http://vfio.blogspot.co.at/2014/08/primary-graphics-assignment-without-vga.html]
728 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/]
730 If you want to use OVMF, there are several things to consider:
732 In order to save things like the *boot order*, there needs to be an EFI Disk.
733 This disk will be included in backups and snapshots, and there can only be one.
735 You can create such a disk with the following command:
737 qm set <vmid> -efidisk0 <storage>:1,format=<format>
739 Where *<storage>* is the storage where you want to have the disk, and
740 *<format>* is a format which the storage supports. Alternatively, you can
741 create such a disk through the web interface with 'Add' -> 'EFI Disk' in the
742 hardware section of a VM.
744 When using OVMF with a virtual display (without VGA passthrough),
745 you need to set the client resolution in the OVMF menu(which you can reach
746 with a press of the ESC button during boot), or you have to choose
747 SPICE as the display type.
750 Inter-VM shared memory
751 ~~~~~~~~~~~~~~~~~~~~~~
753 You can add an Inter-VM shared memory device (`ivshmem`), which allows one to
754 share memory between the host and a guest, or also between multiple guests.
756 To add such a device, you can use `qm`:
758 qm set <vmid> -ivshmem size=32,name=foo
760 Where the size is in MiB. The file will be located under
761 `/dev/shm/pve-shm-$name` (the default name is the vmid).
763 NOTE: Currently the device will get deleted as soon as any VM using it got
764 shutdown or stopped. Open connections will still persist, but new connections
765 to the exact same device cannot be made anymore.
767 A use case for such a device is the Looking Glass
768 footnote:[Looking Glass: https://looking-glass.hostfission.com/] project,
769 which enables high performance, low-latency display mirroring between
776 To add an audio device run the following command:
779 qm set <vmid> -audio0 device=<device>
782 Supported audio devices are:
784 * `ich9-intel-hda`: Intel HD Audio Controller, emulates ICH9
785 * `intel-hda`: Intel HD Audio Controller, emulates ICH6
786 * `AC97`: Audio Codec '97, useful for older operating systems like Windows XP
788 NOTE: The audio device works only in combination with SPICE. Remote protocols
789 like Microsoft's RDP have options to play sound. To use the physical audio
790 device of the host use device passthrough (see
791 xref:qm_pci_passthrough[PCI Passthrough] and
792 xref:qm_usb_passthrough[USB Passthrough]).
794 [[qm_startup_and_shutdown]]
795 Automatic Start and Shutdown of Virtual Machines
796 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
798 After creating your VMs, you probably want them to start automatically
799 when the host system boots. For this you need to select the option 'Start at
800 boot' from the 'Options' Tab of your VM in the web interface, or set it with
801 the following command:
803 qm set <vmid> -onboot 1
805 .Start and Shutdown Order
807 [thumbnail="screenshot/gui-qemu-edit-start-order.png"]
809 In some case you want to be able to fine tune the boot order of your
810 VMs, for instance if one of your VM is providing firewalling or DHCP
811 to other guest systems. For this you can use the following
814 * *Start/Shutdown order*: Defines the start order priority. E.g. set it to 1 if
815 you want the VM to be the first to be started. (We use the reverse startup
816 order for shutdown, so a machine with a start order of 1 would be the last to
817 be shut down). If multiple VMs have the same order defined on a host, they will
818 additionally be ordered by 'VMID' in ascending order.
819 * *Startup delay*: Defines the interval between this VM start and subsequent
820 VMs starts . E.g. set it to 240 if you want to wait 240 seconds before starting
822 * *Shutdown timeout*: Defines the duration in seconds {pve} should wait
823 for the VM to be offline after issuing a shutdown command.
824 By default this value is set to 180, which means that {pve} will issue a
825 shutdown request and wait 180 seconds for the machine to be offline. If
826 the machine is still online after the timeout it will be stopped forcefully.
828 NOTE: VMs managed by the HA stack do not follow the 'start on boot' and
829 'boot order' options currently. Those VMs will be skipped by the startup and
830 shutdown algorithm as the HA manager itself ensures that VMs get started and
833 Please note that machines without a Start/Shutdown order parameter will always
834 start after those where the parameter is set. Further, this parameter can only
835 be enforced between virtual machines running on the same host, not
838 [[qm_spice_enhancements]]
842 SPICE Enhancements are optional features that can improve the remote viewer
845 To enable them via the GUI go to the *Options* panel of the virtual machine. Run
846 the following command to enable them via the CLI:
849 qm set <vmid> -spice_enhancements foldersharing=1,videostreaming=all
852 NOTE: To use these features the <<qm_display,*Display*>> of the virtual machine
853 must be set to SPICE (qxl).
858 Share a local folder with the guest. The `spice-webdavd` daemon needs to be
859 installed in the guest. It makes the shared folder available through a local
860 WebDAV server located at http://localhost:9843.
862 For Windows guests the installer for the 'Spice WebDAV daemon' can be downloaded
864 https://www.spice-space.org/download.html#windows-binaries[official SPICE website].
866 Most Linux distributions have a package called `spice-webdavd` that can be
869 To share a folder in Virt-Viewer (Remote Viewer) go to 'File -> Preferences'.
870 Select the folder to share and then enable the checkbox.
872 NOTE: Folder sharing currently only works in the Linux version of Virt-Viewer.
877 Fast refreshing areas are encoded into a video stream. Two options exist:
879 * *all*: Any fast refreshing area will be encoded into a video stream.
880 * *filter*: Additional filters are used to decide if video streaming should be
881 used (currently only small window surfaces are skipped).
883 A general recommendation if video streaming should be enabled and which option
884 to choose from cannot be given. Your mileage may vary depending on the specific
890 .Shared folder does not show up
892 Make sure the WebDAV service is enabled and running in the guest. On Windows it
893 is called 'Spice webdav proxy'. In Linux the name is 'spice-webdavd' but can be
894 different depending on the distribution.
896 If the service is running, check the WebDAV server by opening
897 http://localhost:9843 in a browser in the guest.
899 It can help to restart the SPICE session.
905 [thumbnail="screenshot/gui-qemu-migrate.png"]
907 If you have a cluster, you can migrate your VM to another host with
909 qm migrate <vmid> <target>
911 There are generally two mechanisms for this
913 * Online Migration (aka Live Migration)
919 When your VM is running and it has no local resources defined (such as disks
920 on local storage, passed through devices, etc.) you can initiate a live
921 migration with the -online flag.
926 This starts a Qemu Process on the target host with the 'incoming' flag, which
927 means that the process starts and waits for the memory data and device states
928 from the source Virtual Machine (since all other resources, e.g. disks,
929 are shared, the memory content and device state are the only things left
932 Once this connection is established, the source begins to send the memory
933 content asynchronously to the target. If the memory on the source changes,
934 those sections are marked dirty and there will be another pass of sending data.
935 This happens until the amount of data to send is so small that it can
936 pause the VM on the source, send the remaining data to the target and start
937 the VM on the target in under a second.
942 For Live Migration to work, there are some things required:
944 * The VM has no local resources (e.g. passed through devices, local disks, etc.)
945 * The hosts are in the same {pve} cluster.
946 * The hosts have a working (and reliable) network connection.
947 * The target host must have the same or higher versions of the
948 {pve} packages. (It *might* work the other way, but this is never guaranteed)
953 If you have local resources, you can still offline migrate your VMs,
954 as long as all disk are on storages, which are defined on both hosts.
955 Then the migration will copy the disk over the network to the target host.
957 [[qm_copy_and_clone]]
961 [thumbnail="screenshot/gui-qemu-full-clone.png"]
963 VM installation is usually done using an installation media (CD-ROM)
964 from the operation system vendor. Depending on the OS, this can be a
965 time consuming task one might want to avoid.
967 An easy way to deploy many VMs of the same type is to copy an existing
968 VM. We use the term 'clone' for such copies, and distinguish between
969 'linked' and 'full' clones.
973 The result of such copy is an independent VM. The
974 new VM does not share any storage resources with the original.
977 It is possible to select a *Target Storage*, so one can use this to
978 migrate a VM to a totally different storage. You can also change the
979 disk image *Format* if the storage driver supports several formats.
982 NOTE: A full clone needs to read and copy all VM image data. This is
983 usually much slower than creating a linked clone.
986 Some storage types allows to copy a specific *Snapshot*, which
987 defaults to the 'current' VM data. This also means that the final copy
988 never includes any additional snapshots from the original VM.
993 Modern storage drivers support a way to generate fast linked
994 clones. Such a clone is a writable copy whose initial contents are the
995 same as the original data. Creating a linked clone is nearly
996 instantaneous, and initially consumes no additional space.
999 They are called 'linked' because the new image still refers to the
1000 original. Unmodified data blocks are read from the original image, but
1001 modification are written (and afterwards read) from a new
1002 location. This technique is called 'Copy-on-write'.
1005 This requires that the original volume is read-only. With {pve} one
1006 can convert any VM into a read-only <<qm_templates, Template>>). Such
1007 templates can later be used to create linked clones efficiently.
1010 NOTE: You cannot delete an original template while linked clones
1014 It is not possible to change the *Target storage* for linked clones,
1015 because this is a storage internal feature.
1018 The *Target node* option allows you to create the new VM on a
1019 different node. The only restriction is that the VM is on shared
1020 storage, and that storage is also available on the target node.
1022 To avoid resource conflicts, all network interface MAC addresses get
1023 randomized, and we generate a new 'UUID' for the VM BIOS (smbios1)
1028 Virtual Machine Templates
1029 -------------------------
1031 One can convert a VM into a Template. Such templates are read-only,
1032 and you can use them to create linked clones.
1034 NOTE: It is not possible to start templates, because this would modify
1035 the disk images. If you want to change the template, create a linked
1036 clone and modify that.
1041 {pve} supports Virtual Machine Generation ID ('vmgenid') footnote:[Official
1042 'vmgenid' Specification
1043 https://docs.microsoft.com/en-us/windows/desktop/hyperv_v2/virtual-machine-generation-identifier]
1044 for virtual machines.
1045 This can be used by the guest operating system to detect any event resulting
1046 in a time shift event, for example, restoring a backup or a snapshot rollback.
1048 When creating new VMs, a 'vmgenid' will be automatically generated and saved
1049 in its configuration file.
1051 To create and add a 'vmgenid' to an already existing VM one can pass the
1052 special value `1' to let {pve} autogenerate one or manually set the 'UUID'
1053 footnote:[Online GUID generator http://guid.one/] by using it as value,
1057 qm set VMID -vmgenid 1
1058 qm set VMID -vmgenid 00000000-0000-0000-0000-000000000000
1061 NOTE: The initial addition of a 'vmgenid' device to an existing VM, may result
1062 in the same effects as a change on snapshot rollback, backup restore, etc., has
1063 as the VM can interpret this as generation change.
1065 In the rare case the 'vmgenid' mechanism is not wanted one can pass `0' for
1066 its value on VM creation, or retroactively delete the property in the
1070 qm set VMID -delete vmgenid
1073 The most prominent use case for 'vmgenid' are newer Microsoft Windows
1074 operating systems, which use it to avoid problems in time sensitive or
1075 replicate services (e.g., databases, domain controller
1076 footnote:[https://docs.microsoft.com/en-us/windows-server/identity/ad-ds/get-started/virtual-dc/virtualized-domain-controller-architecture])
1077 on snapshot rollback, backup restore or a whole VM clone operation.
1079 Importing Virtual Machines and disk images
1080 ------------------------------------------
1082 A VM export from a foreign hypervisor takes usually the form of one or more disk
1083 images, with a configuration file describing the settings of the VM (RAM,
1085 The disk images can be in the vmdk format, if the disks come from
1086 VMware or VirtualBox, or qcow2 if the disks come from a KVM hypervisor.
1087 The most popular configuration format for VM exports is the OVF standard, but in
1088 practice interoperation is limited because many settings are not implemented in
1089 the standard itself, and hypervisors export the supplementary information
1090 in non-standard extensions.
1092 Besides the problem of format, importing disk images from other hypervisors
1093 may fail if the emulated hardware changes too much from one hypervisor to
1094 another. Windows VMs are particularly concerned by this, as the OS is very
1095 picky about any changes of hardware. This problem may be solved by
1096 installing the MergeIDE.zip utility available from the Internet before exporting
1097 and choosing a hard disk type of *IDE* before booting the imported Windows VM.
1099 Finally there is the question of paravirtualized drivers, which improve the
1100 speed of the emulated system and are specific to the hypervisor.
1101 GNU/Linux and other free Unix OSes have all the necessary drivers installed by
1102 default and you can switch to the paravirtualized drivers right after importing
1103 the VM. For Windows VMs, you need to install the Windows paravirtualized
1104 drivers by yourself.
1106 GNU/Linux and other free Unix can usually be imported without hassle. Note
1107 that we cannot guarantee a successful import/export of Windows VMs in all
1108 cases due to the problems above.
1110 Step-by-step example of a Windows OVF import
1111 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1114 https://developer.microsoft.com/en-us/windows/downloads/virtual-machines/[Virtual Machines downloads]
1115 to get started with Windows development.We are going to use one of these
1116 to demonstrate the OVF import feature.
1118 Download the Virtual Machine zip
1119 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
1121 After getting informed about the user agreement, choose the _Windows 10
1122 Enterprise (Evaluation - Build)_ for the VMware platform, and download the zip.
1124 Extract the disk image from the zip
1125 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
1127 Using the `unzip` utility or any archiver of your choice, unpack the zip,
1128 and copy via ssh/scp the ovf and vmdk files to your {pve} host.
1130 Import the Virtual Machine
1131 ^^^^^^^^^^^^^^^^^^^^^^^^^^
1133 This will create a new virtual machine, using cores, memory and
1134 VM name as read from the OVF manifest, and import the disks to the +local-lvm+
1135 storage. You have to configure the network manually.
1137 qm importovf 999 WinDev1709Eval.ovf local-lvm
1139 The VM is ready to be started.
1141 Adding an external disk image to a Virtual Machine
1142 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1144 You can also add an existing disk image to a VM, either coming from a
1145 foreign hypervisor, or one that you created yourself.
1147 Suppose you created a Debian/Ubuntu disk image with the 'vmdebootstrap' tool:
1149 vmdebootstrap --verbose \
1150 --size 10GiB --serial-console \
1151 --grub --no-extlinux \
1152 --package openssh-server \
1153 --package avahi-daemon \
1154 --package qemu-guest-agent \
1155 --hostname vm600 --enable-dhcp \
1156 --customize=./copy_pub_ssh.sh \
1157 --sparse --image vm600.raw
1159 You can now create a new target VM for this image.
1161 qm create 600 --net0 virtio,bridge=vmbr0 --name vm600 --serial0 socket \
1162 --bootdisk scsi0 --scsihw virtio-scsi-pci --ostype l26
1164 Add the disk image as +unused0+ to the VM, using the storage +pvedir+:
1166 qm importdisk 600 vm600.raw pvedir
1168 Finally attach the unused disk to the SCSI controller of the VM:
1170 qm set 600 --scsi0 pvedir:600/vm-600-disk-1.raw
1172 The VM is ready to be started.
1176 include::qm-cloud-init.adoc[]
1180 include::qm-pci-passthrough.adoc[]
1186 You can add a hook script to VMs with the config property `hookscript`.
1188 qm set 100 -hookscript local:snippets/hookscript.pl
1190 It will be called during various phases of the guests lifetime.
1191 For an example and documentation see the example script under
1192 `/usr/share/pve-docs/examples/guest-example-hookscript.pl`.
1194 Managing Virtual Machines with `qm`
1195 ------------------------------------
1197 qm is the tool to manage Qemu/Kvm virtual machines on {pve}. You can
1198 create and destroy virtual machines, and control execution
1199 (start/stop/suspend/resume). Besides that, you can use qm to set
1200 parameters in the associated config file. It is also possible to
1201 create and delete virtual disks.
1206 Using an iso file uploaded on the 'local' storage, create a VM
1207 with a 4 GB IDE disk on the 'local-lvm' storage
1209 qm create 300 -ide0 local-lvm:4 -net0 e1000 -cdrom local:iso/proxmox-mailgateway_2.1.iso
1215 Send a shutdown request, then wait until the VM is stopped.
1217 qm shutdown 300 && qm wait 300
1219 Same as above, but only wait for 40 seconds.
1221 qm shutdown 300 && qm wait 300 -timeout 40
1224 [[qm_configuration]]
1228 VM configuration files are stored inside the Proxmox cluster file
1229 system, and can be accessed at `/etc/pve/qemu-server/<VMID>.conf`.
1230 Like other files stored inside `/etc/pve/`, they get automatically
1231 replicated to all other cluster nodes.
1233 NOTE: VMIDs < 100 are reserved for internal purposes, and VMIDs need to be
1234 unique cluster wide.
1236 .Example VM Configuration
1244 net0: e1000=EE:D2:28:5F:B6:3E,bridge=vmbr0
1245 virtio0: local:vm-100-disk-1,size=32G
1248 Those configuration files are simple text files, and you can edit them
1249 using a normal text editor (`vi`, `nano`, ...). This is sometimes
1250 useful to do small corrections, but keep in mind that you need to
1251 restart the VM to apply such changes.
1253 For that reason, it is usually better to use the `qm` command to
1254 generate and modify those files, or do the whole thing using the GUI.
1255 Our toolkit is smart enough to instantaneously apply most changes to
1256 running VM. This feature is called "hot plug", and there is no
1257 need to restart the VM in that case.
1263 VM configuration files use a simple colon separated key/value
1264 format. Each line has the following format:
1271 Blank lines in those files are ignored, and lines starting with a `#`
1272 character are treated as comments and are also ignored.
1279 When you create a snapshot, `qm` stores the configuration at snapshot
1280 time into a separate snapshot section within the same configuration
1281 file. For example, after creating a snapshot called ``testsnapshot'',
1282 your configuration file will look like this:
1284 .VM configuration with snapshot
1294 snaptime: 1457170803
1298 There are a few snapshot related properties like `parent` and
1299 `snaptime`. The `parent` property is used to store the parent/child
1300 relationship between snapshots. `snaptime` is the snapshot creation
1301 time stamp (Unix epoch).
1308 include::qm.conf.5-opts.adoc[]
1314 Online migrations, snapshots and backups (`vzdump`) set a lock to
1315 prevent incompatible concurrent actions on the affected VMs. Sometimes
1316 you need to remove such a lock manually (e.g., after a power failure).
1320 CAUTION: Only do that if you are sure the action which set the lock is
1329 * link:/wiki/Cloud-Init_Support[Cloud-Init Support]
1339 `/etc/pve/qemu-server/<VMID>.conf`::
1341 Configuration file for the VM '<VMID>'.
1344 include::pve-copyright.adoc[]