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[pve-docs.git] / qm.adoc
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1ifdef::manvolnum[]
2PVE({manvolnum})
3================
38fd0958 4include::attributes.txt[]
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5
6NAME
7----
8
9qm - Qemu/KVM Virtual Machine Manager
10
11
12SYNOPSYS
13--------
14
15include::qm.1-synopsis.adoc[]
16
17DESCRIPTION
18-----------
19endif::manvolnum[]
20
21ifndef::manvolnum[]
22Qemu/KVM Virtual Machines
23=========================
38fd0958 24include::attributes.txt[]
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25endif::manvolnum[]
26
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27// deprecates
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
31
32Qemu (short form for Quick Emulator) is an opensource hypervisor that emulates a
33physical computer. From the perspective of the host system where Qemu is
34running, Qemu is a user program which has access to a number of local resources
35like partitions, files, network cards which are then passed to an
189d3661 36emulated computer which sees them as if they were real devices.
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37
38A guest operating system running in the emulated computer accesses these
39devices, and runs as it were running on real hardware. For instance you can pass
40an iso image as a parameter to Qemu, and the OS running in the emulated computer
189d3661 41will see a real CDROM inserted in a CD drive.
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189d3661 43Qemu can emulates a great variety of hardware from ARM to Sparc, but {pve} is
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44only concerned with 32 and 64 bits PC clone emulation, since it represents the
45overwhelming majority of server hardware. The emulation of PC clones is also one
46of the fastest due to the availability of processor extensions which greatly
47speed up Qemu when the emulated architecture is the same as the host
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48architecture.
49
50NOTE: You may sometimes encounter the term _KVM_ (Kernel-based Virtual Machine).
51It means that Qemu is running with the support of the virtualization processor
52extensions, via the Linux kvm module. In the context of {pve} _Qemu_ and
53_KVM_ can be use interchangeably as Qemu in {pve} will always try to load the kvm
54module.
55
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56Qemu inside {pve} runs as a root process, since this is required to access block
57and PCI devices.
58
59Emulated devices and paravirtualized devices
60--------------------------------------------
61
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62The PC hardware emulated by Qemu includes a mainboard, network controllers,
63scsi, ide and sata controllers, serial ports (the complete list can be seen in
64the `kvm(1)` man page) all of them emulated in software. All these devices
65are the exact software equivalent of existing hardware devices, and if the OS
66running in the guest has the proper drivers it will use the devices as if it
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67were running on real hardware. This allows Qemu to runs _unmodified_ operating
68systems.
69
70This however has a performance cost, as running in software what was meant to
71run in hardware involves a lot of extra work for the host CPU. To mitigate this,
72Qemu can present to the guest operating system _paravirtualized devices_, where
73the guest OS recognizes it is running inside Qemu and cooperates with the
74hypervisor.
75
76Qemu relies on the virtio virtualization standard, and is thus able to presente
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77paravirtualized virtio devices, which includes a paravirtualized generic disk
78controller, a paravirtualized network card, a paravirtualized serial port,
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79a paravirtualized SCSI controller, etc ...
80
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81It is highly recommended to use the virtio devices whenever you can, as they
82provide a big performance improvement. Using the virtio generic disk controller
83versus an emulated IDE controller will double the sequential write throughput,
84as measured with `bonnie++(8)`. Using the virtio network interface can deliver
c4cba5d7 85up to three times the throughput of an emulated Intel E1000 network card, as
189d3661 86measured with `iperf(1)`. footnote:[See this benchmark on the KVM wiki
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87http://www.linux-kvm.org/page/Using_VirtIO_NIC]
88
89Virtual Machines settings
90-------------------------
91Generally speaking {pve} tries to choose sane defaults for virtual machines
92(VM). Make sure you understand the meaning of the settings you change, as it
93could incur a performance slowdown, or putting your data at risk.
94
95General Settings
96~~~~~~~~~~~~~~~~
97General settings of a VM include
98
99* the *Node* : the physical server on which the VM will run
100* the *VM ID*: a unique number in this {pve} installation used to identify your VM
101* *Name*: a free form text string you can use to describe the VM
102* *Resource Pool*: a logical group of VMs
103
104OS Settings
105~~~~~~~~~~~
106When creating a VM, setting the proper Operating System(OS) allows {pve} to
107optimize some low level parameters. For instance Windows OS expect the BIOS
108clock to use the local time, while Unix based OS expect the BIOS clock to have
109the UTC time.
110
111Hard Disk
112~~~~~~~~~
2ec49380 113Qemu can emulate a number of storage controllers:
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114
115* the *IDE* controller, has a design which goes back to the 1984 PC/AT disk
116controller. Even if this controller has been superseded by more more designs,
117each and every OS you can think has support for it, making it a great choice
118if you want to run an OS released before 2003. You can connect up to 4 devices
119on this controller.
120
121* the *SATA* (Serial ATA) controller, dating from 2003, has a more modern
122design, allowing higher throughput and a greater number of devices to be
123connected. You can connect up to 6 devices on this controller.
124
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125* the *SCSI* controller, designed in 1985, is commonly found on server grade
126hardware, and can connect up to 14 storage devices. {pve} emulates by default a
127LSI 53C895A controller. +
128A SCSI controller of type _Virtio_ is the recommended setting if you aim for
129performance and is automatically selected for newly created Linux VMs since
130{pve} 4.3. Linux distributions have support for this controller since 2012, and
c4cba5d7 131FreeBSD since 2014. For Windows OSes, you need to provide an extra iso
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132containing the drivers during the installation.
133// https://pve.proxmox.com/wiki/Paravirtualized_Block_Drivers_for_Windows#During_windows_installation.
134
135* The *Virtio* controller, also called virtio-blk to distinguish from
136the Virtio SCSI controller, is an older type of paravirtualized controller
137which has been superseded in features by the Virtio SCSI Controller.
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138
139On each controller you attach a number of emulated hard disks, which are backed
140by a file or a block device residing in the configured storage. The choice of
141a storage type will determine the format of the hard disk image. Storages which
142present block devices (LVM, ZFS, Ceph) will require the *raw disk image format*,
143whereas files based storages (Ext4, NFS, GlusterFS) will let you to choose
144either the *raw disk image format* or the *QEMU image format*.
145
146 * the *QEMU image format* is a copy on write format which allows snapshots, and
147 thin provisioning of the disk image.
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148 * the *raw disk image* is a bit-to-bit image of a hard disk, similar to what
149 you would get when executing the `dd` command on a block device in Linux. This
150 format do not support thin provisioning or snapshotting by itself, requiring
151 cooperation from the storage layer for these tasks. It is however 10% faster
152 than the *QEMU image format*. footnote:[See this benchmark for details
c4cba5d7 153 http://events.linuxfoundation.org/sites/events/files/slides/CloudOpen2013_Khoa_Huynh_v3.pdf]
189d3661 154 * the *VMware image format* only makes sense if you intend to import/export the
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155 disk image to other hypervisors.
156
157Setting the *Cache* mode of the hard drive will impact how the host system will
158notify the guest systems of block write completions. The *No cache* default
159means that the guest system will be notified that a write is complete when each
160block reaches the physical storage write queue, ignoring the host page cache.
161This provides a good balance between safety and speed.
162
163If you want the {pve} backup manager to skip a disk when doing a backup of a VM,
164you can set the *No backup* option on that disk.
165
166If your storage supports _thin provisioning_ (see the storage chapter in the
167{pve} guide), and your VM has a *SCSI* controller you can activate the *Discard*
168option on the hard disks connected to that controller. With *Discard* enabled,
169when the filesystem of a VM marks blocks as unused after removing files, the
170emulated SCSI controller will relay this information to the storage, which will
171then shrink the disk image accordingly.
172
af9c6de1 173.IO Thread
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174The option *IO Thread* can only be enabled when using a disk with the *VirtIO* controller,
175or with the *SCSI* controller, when the emulated controller type is *VirtIO SCSI*.
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176With this enabled, Qemu uses one thread per disk, instead of one thread for all,
177so it should increase performance when using multiple disks.
178Note that backups do not currently work with *IO Thread* enabled.
179
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180CPU
181~~~
182A *CPU socket* is a physical slot on a PC motherboard where you can plug a CPU.
183This CPU can then contain one or many *cores*, which are independent
184processing units. Whether you have a single CPU socket with 4 cores, or two CPU
185sockets with two cores is mostly irrelevant from a performance point of view.
186However some software is licensed depending on the number of sockets you have in
187your machine, in that case it makes sense to set the number of of sockets to
188what the license allows you, and increase the number of cores. +
189Increasing the number of virtual cpus (cores and sockets) will usually provide a
190performance improvement though that is heavily dependent on the use of the VM.
191Multithreaded applications will of course benefit from a large number of
192virtual cpus, as for each virtual cpu you add, Qemu will create a new thread of
193execution on the host system. If you're not sure about the workload of your VM,
194it is usually a safe bet to set the number of *Total cores* to 2.
195
196NOTE: It is perfectly safe to set the _overall_ number of total cores in all
197your VMs to be greater than the number of of cores you have on your server (ie.
1984 VMs with each 4 Total cores running in a 8 core machine is OK) In that case
199the host system will balance the Qemu execution threads between your server
200cores just like if you were running a standard multithreaded application.
201However {pve} will prevent you to allocate on a _single_ machine more vcpus than
202physically available, as this will only bring the performance down due to the
203cost of context switches.
204
205Qemu can emulate a number different of *CPU types* from 486 to the latest Xeon
206processors. Each new processor generation adds new features, like hardware
207assisted 3d rendering, random number generation, memory protection, etc ...
208Usually you should select for your VM a processor type which closely matches the
209CPU of the host system, as it means that the host CPU features (also called _CPU
210flags_ ) will be available in your VMs. If you want an exact match, you can set
211the CPU type to *host* in which case the VM will have exactly the same CPU flags
212as your host system. +
213This has a downside though. If you want to do a live migration of VMs between
214different hosts, your VM might end up on a new system with a different CPU type.
215If the CPU flags passed to the guest are missing, the qemu process will stop. To
216remedy this Qemu has also its own CPU type *kvm64*, that {pve} uses by defaults.
217kvm64 is a Pentium 4 look a like CPU type, which has a reduced CPU flags set,
218but is guaranteed to work everywhere. +
219 In short, if you care about live migration and moving VMs between nodes, leave
220the kvm64 default. If you don’t care about live migration, set the CPU type to
221host, as in theory this will give your guests maximum performance.
222
223You can also optionally emulate a *NUMA* architecture in your VMs. The basics of
224the NUMA architecture mean that instead of having a global memory pool available
225to all your cores, the memory is spread into local banks close to each socket.
226This can bring speed improvements as the memory bus is not a bottleneck
227anymore. If your system has a NUMA architecture footnote:[if the command
228`numactl --hardware | grep available` returns more than one node, then your host
229system has a NUMA architecture] we recommend to activate the option, as this
230will allow proper distribution of the VM resources on the host system. This
231option is also required in {pve} to allow hotplugging of cores and RAM to a VM.
232
233If the NUMA option is used, it is recommended to set the number of sockets to
234the number of sockets of the host system.
235
236Memory
237~~~~~~
238For each VM you have the option to set a fixed size memory or asking
239{pve} to dynamically allocate memory based on the current RAM usage of the
240host.
241
242When choosing a *fixed size memory* {pve} will simply allocate what you
243specify to your VM.
244
245// see autoballoon() in pvestatd.pm
246When choosing to *automatically allocate memory*, {pve} will make sure that the
247minimum amount you specified is always available to the VM, and if RAM usage on
248the host is below 80%, will dynamically add memory to the guest up to the
249maximum memory specified. +
250When the host is becoming short on RAM, the VM will then release some memory
251back to the host, swapping running processes if needed and starting the oom
252killer in last resort. The passing around of memory between host and guest is
253done via a special `balloon` kernel driver running inside the guest, which will
254grab or release memory pages from the host.
255footnote:[A good explanation of the inner workings of the balloon driver can be found here https://rwmj.wordpress.com/2010/07/17/virtio-balloon/]
256
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257When multiple VMs use the autoallocate facility, it is possible to set a
258*Shares* coefficient which indicates the relative amount of the free host memory
259that each VM shoud take. Suppose for instance you have four VMs, three of them
260running a HTTP server and the last one is a database server. To cache more
261database blocks in the database server RAM, you would like to prioritize the
262database VM when spare RAM is available. For this you assign a Shares property
263of 3000 to the database VM, leaving the other VMs to the Shares default setting
264of 1000. The host server has 32GB of RAM, and is curring using 16GB, leaving 32
265* 80/100 - 16 = 9GB RAM to be allocated to the VMs. The database VM will get 9 *
2663000 / (3000 + 1000 + 1000 + 1000) = 4.5 GB extra RAM and each HTTP server will
267get 1/5 GB.
268
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269All Linux distributions released after 2010 have the balloon kernel driver
270included. For Windows OSes, the balloon driver needs to be added manually and can
271incur a slowdown of the guest, so we don't recommend using it on critical
272systems.
273// see https://forum.proxmox.com/threads/solved-hyper-threading-vs-no-hyper-threading-fixed-vs-variable-memory.20265/
274
275When allocating RAMs to your VMs, a good rule of thumb is always to leave 1GB
276of RAM available to the host.
277
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278Network Device
279~~~~~~~~~~~~~~
280Each VM can have many _Network interface controllers_ (NIC), of four different
281types:
282
283 * *Intel E1000* is the default, and emulates an Intel Gigabit network card.
284 * the *VirtIO* paravirtualized NIC should be used if you aim for maximum
285performance. Like all VirtIO devices, the guest OS should have the proper driver
286installed.
287 * the *Realtek 8139* emulates an older 100 MB/s network card, and should
288only be used when emulating older operating systems ( released before 2002 )
289 * the *vmxnet3* is another paravirtualized device, which should only be used
290when importing a VM from another hypervisor.
291
292{pve} will generate for each NIC a random *MAC address*, so that your VM is
293addressable on Ethernet networks.
294
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295The NIC you added to the VM can follow one of two differents models:
296
297 * in the default *Bridged mode* each virtual NIC is backed on the host by a
298_tap device_, ( a software loopback device simulating an Ethernet NIC ). This
299tap device is added to a bridge, by default vmbr0 in {pve}. In this mode, VMs
300have direct access to the Ethernet LAN on which the host is located.
301 * in the alternative *NAT mode*, each virtual NIC will only communicate with
302the Qemu user networking stack, where a builting router and DHCP server can
303provide network access. This built-in DHCP will serve adresses in the private
30410.0.2.0/24 range. The NAT mode is much slower than the bridged mode, and
305should only be used for testing.
306
307You can also skip adding a network device when creating a VM by selecting *No
308network device*.
309
310.Multiqueue
1ff7835b 311If you are using the VirtIO driver, you can optionally activate the
af9c6de1 312*Multiqueue* option. This option allows the guest OS to process networking
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313packets using multiple virtual CPUs, providing an increase in the total number
314of packets transfered.
315
316//http://blog.vmsplice.net/2011/09/qemu-internals-vhost-architecture.html
317When using the VirtIO driver with {pve}, each NIC network queue is passed to the
318host kernel, where the queue will be processed by a kernel thread spawn by the
319vhost driver. With this option activated, it is possible to pass _multiple_
320network queues to the host kernel for each NIC.
321
322//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
af9c6de1 323When using Multiqueue, it is recommended to set it to a value equal
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324to the number of Total Cores of your guest. You also need to set in
325the VM the number of multi-purpose channels on each VirtIO NIC with the ethtool
326command:
327
328`ethtool -L eth0 combined X`
329
330where X is the number of the number of vcpus of the VM.
331
af9c6de1 332You should note that setting the Multiqueue parameter to a value greater
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333than one will increase the CPU load on the host and guest systems as the
334traffic increases. We recommend to set this option only when the VM has to
335process a great number of incoming connections, such as when the VM is running
336as a router, reverse proxy or a busy HTTP server doing long polling.
337
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338USB Passthrough
339~~~~~~~~~~~~~~~
340There are two different types of USB passthrough devices:
341
342* Host USB passtrough
343* SPICE USB passthrough
344
345Host USB passthrough works by giving a VM a USB device of the host.
346This can either be done via the vendor- and product-id, or
347via the host bus and port.
348
349The vendor/product-id looks like this: *0123:abcd*,
350where *0123* is the id of the vendor, and *abcd* is the id
351of the product, meaning two pieces of the same usb device
352have the same id.
353
354The bus/port looks like this: *1-2.3.4*, where *1* is the bus
355and *2.3.4* is the port path. This represents the physical
356ports of your host (depending of the internal order of the
357usb controllers).
358
359If a device is present in a VM configuration when the VM starts up,
360but the device is not present in the host, the VM can boot without problems.
361As soon as the device/port ist available in the host, it gets passed through.
362
363WARNING: Using this kind of USB passthrough, means that you cannot move
364a VM online to another host, since the hardware is only available
365on the host the VM is currently residing.
366
367The second type of passthrough is SPICE USB passthrough. This is useful
368if you use a SPICE client which supports it. If you add a SPICE USB port
369to your VM, you can passthrough a USB device from where your SPICE client is,
370directly to the VM (for example an input device or hardware dongle).
371
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372BIOS and UEFI
373~~~~~~~~~~~~~
374
375In order to properly emulate a computer, QEMU needs to use a firmware.
376By default QEMU uses *SeaBIOS* for this, which is an open-source, x86 BIOS
377implementation. SeaBIOS is a good choice for most standard setups.
378
379There are, however, some scenarios in which a BIOS is not a good firmware
380to boot from, e.g. if you want to do VGA passthrough. footnote:[Alex Williamson has a very good blog entry about this.
381http://vfio.blogspot.co.at/2014/08/primary-graphics-assignment-without-vga.html]
382In such cases, you should rather use *OVMF*, which is an open-source UEFI implemenation. footnote:[See the OVMF Project http://www.tianocore.org/ovmf/]
383
384If you want to use OVMF, there are several things to consider:
385
386In order to save things like the *boot order*, there needs to be an EFI Disk.
387This disk will be included in backups and snapshots, and there can only be one.
388
389You can create such a disk with the following command:
390
391 qm set <vmid> -efidisk0 <storage>:1,format=<format>
392
393Where *<storage>* is the storage where you want to have the disk, and
394*<format>* is a format which the storage supports. Alternatively, you can
395create such a disk through the web interface with 'Add' -> 'EFI Disk' in the
396hardware section of a VM.
397
398When using OVMF with a virtual display (without VGA passthrough),
399you need to set the client resolution in the OVMF menu(which you can reach
400with a press of the ESC button during boot), or you have to choose
401SPICE as the display type.
402
403
8c1189b6 404Managing Virtual Machines with `qm`
dd042288 405------------------------------------
f69cfd23 406
dd042288 407qm is the tool to manage Qemu/Kvm virtual machines on {pve}. You can
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408create and destroy virtual machines, and control execution
409(start/stop/suspend/resume). Besides that, you can use qm to set
410parameters in the associated config file. It is also possible to
411create and delete virtual disks.
412
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413CLI Usage Examples
414~~~~~~~~~~~~~~~~~~
415
416Create a new VM with 4 GB IDE disk.
417
418 qm create 300 -ide0 4 -net0 e1000 -cdrom proxmox-mailgateway_2.1.iso
419
420Start the new VM
421
422 qm start 300
423
424Send a shutdown request, then wait until the VM is stopped.
425
426 qm shutdown 300 && qm wait 300
427
428Same as above, but only wait for 40 seconds.
429
430 qm shutdown 300 && qm wait 300 -timeout 40
431
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432Configuration
433-------------
434
435All configuration files consists of lines in the form
436
437 PARAMETER: value
438
871e1fd6 439Configuration files are stored inside the Proxmox cluster file
8c1189b6 440system, and can be accessed at `/etc/pve/qemu-server/<VMID>.conf`.
f69cfd23 441
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442Options
443~~~~~~~
444
445include::qm.conf.5-opts.adoc[]
446
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447
448Locks
449-----
450
8c1189b6 451Online migrations and backups (`vzdump`) set a lock to prevent incompatible
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452concurrent actions on the affected VMs. Sometimes you need to remove such a
453lock manually (e.g., after a power failure).
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454
455 qm unlock <vmid>
456
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457
458ifdef::manvolnum[]
459include::pve-copyright.adoc[]
460endif::manvolnum[]