Fix case after the updates in the GUI
[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
125* the *SCSI* controller, designed in 1985, is commonly found on server
189d3661 126grade hardware, and can connect up to 14 storage devices. {pve} emulates by
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127default a LSI 53C895A controller.
128
129* The *Virtio* controller is a generic paravirtualized controller, and is the
130recommended setting if you aim for performance. To use this controller, the OS
131need to have special drivers which may be included in your installation ISO or
132not. Linux distributions have support for the Virtio controller since 2010, and
133FreeBSD since 2014. For Windows OSes, you need to provide an extra iso
189d3661 134containing the Virtio drivers during the installation.
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135// see: https://pve.proxmox.com/wiki/Paravirtualized_Block_Drivers_for_Windows#During_windows_installation.
136You can connect up to 16 devices on this controller.
137
138On each controller you attach a number of emulated hard disks, which are backed
139by a file or a block device residing in the configured storage. The choice of
140a storage type will determine the format of the hard disk image. Storages which
141present block devices (LVM, ZFS, Ceph) will require the *raw disk image format*,
142whereas files based storages (Ext4, NFS, GlusterFS) will let you to choose
143either the *raw disk image format* or the *QEMU image format*.
144
145 * the *QEMU image format* is a copy on write format which allows snapshots, and
146 thin provisioning of the disk image.
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147 * the *raw disk image* is a bit-to-bit image of a hard disk, similar to what
148 you would get when executing the `dd` command on a block device in Linux. This
149 format do not support thin provisioning or snapshotting by itself, requiring
150 cooperation from the storage layer for these tasks. It is however 10% faster
151 than the *QEMU image format*. footnote:[See this benchmark for details
c4cba5d7 152 http://events.linuxfoundation.org/sites/events/files/slides/CloudOpen2013_Khoa_Huynh_v3.pdf]
189d3661 153 * the *VMware image format* only makes sense if you intend to import/export the
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154 disk image to other hypervisors.
155
156Setting the *Cache* mode of the hard drive will impact how the host system will
157notify the guest systems of block write completions. The *No cache* default
158means that the guest system will be notified that a write is complete when each
159block reaches the physical storage write queue, ignoring the host page cache.
160This provides a good balance between safety and speed.
161
162If you want the {pve} backup manager to skip a disk when doing a backup of a VM,
163you can set the *No backup* option on that disk.
164
165If your storage supports _thin provisioning_ (see the storage chapter in the
166{pve} guide), and your VM has a *SCSI* controller you can activate the *Discard*
167option on the hard disks connected to that controller. With *Discard* enabled,
168when the filesystem of a VM marks blocks as unused after removing files, the
169emulated SCSI controller will relay this information to the storage, which will
170then shrink the disk image accordingly.
171
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172The option *IO Thread* can only be enabled when using a disk with the *VirtIO* controller,
173or with the *SCSI* controller, when the emulated controller type is *VirtIO SCSI*.
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174With this enabled, Qemu uses one thread per disk, instead of one thread for all,
175so it should increase performance when using multiple disks.
176Note that backups do not currently work with *IO Thread* enabled.
177
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178CPU
179~~~
180A *CPU socket* is a physical slot on a PC motherboard where you can plug a CPU.
181This CPU can then contain one or many *cores*, which are independent
182processing units. Whether you have a single CPU socket with 4 cores, or two CPU
183sockets with two cores is mostly irrelevant from a performance point of view.
184However some software is licensed depending on the number of sockets you have in
185your machine, in that case it makes sense to set the number of of sockets to
186what the license allows you, and increase the number of cores. +
187Increasing the number of virtual cpus (cores and sockets) will usually provide a
188performance improvement though that is heavily dependent on the use of the VM.
189Multithreaded applications will of course benefit from a large number of
190virtual cpus, as for each virtual cpu you add, Qemu will create a new thread of
191execution on the host system. If you're not sure about the workload of your VM,
192it is usually a safe bet to set the number of *Total cores* to 2.
193
194NOTE: It is perfectly safe to set the _overall_ number of total cores in all
195your VMs to be greater than the number of of cores you have on your server (ie.
1964 VMs with each 4 Total cores running in a 8 core machine is OK) In that case
197the host system will balance the Qemu execution threads between your server
198cores just like if you were running a standard multithreaded application.
199However {pve} will prevent you to allocate on a _single_ machine more vcpus than
200physically available, as this will only bring the performance down due to the
201cost of context switches.
202
203Qemu can emulate a number different of *CPU types* from 486 to the latest Xeon
204processors. Each new processor generation adds new features, like hardware
205assisted 3d rendering, random number generation, memory protection, etc ...
206Usually you should select for your VM a processor type which closely matches the
207CPU of the host system, as it means that the host CPU features (also called _CPU
208flags_ ) will be available in your VMs. If you want an exact match, you can set
209the CPU type to *host* in which case the VM will have exactly the same CPU flags
210as your host system. +
211This has a downside though. If you want to do a live migration of VMs between
212different hosts, your VM might end up on a new system with a different CPU type.
213If the CPU flags passed to the guest are missing, the qemu process will stop. To
214remedy this Qemu has also its own CPU type *kvm64*, that {pve} uses by defaults.
215kvm64 is a Pentium 4 look a like CPU type, which has a reduced CPU flags set,
216but is guaranteed to work everywhere. +
217 In short, if you care about live migration and moving VMs between nodes, leave
218the kvm64 default. If you don’t care about live migration, set the CPU type to
219host, as in theory this will give your guests maximum performance.
220
221You can also optionally emulate a *NUMA* architecture in your VMs. The basics of
222the NUMA architecture mean that instead of having a global memory pool available
223to all your cores, the memory is spread into local banks close to each socket.
224This can bring speed improvements as the memory bus is not a bottleneck
225anymore. If your system has a NUMA architecture footnote:[if the command
226`numactl --hardware | grep available` returns more than one node, then your host
227system has a NUMA architecture] we recommend to activate the option, as this
228will allow proper distribution of the VM resources on the host system. This
229option is also required in {pve} to allow hotplugging of cores and RAM to a VM.
230
231If the NUMA option is used, it is recommended to set the number of sockets to
232the number of sockets of the host system.
233
234Memory
235~~~~~~
236For each VM you have the option to set a fixed size memory or asking
237{pve} to dynamically allocate memory based on the current RAM usage of the
238host.
239
240When choosing a *fixed size memory* {pve} will simply allocate what you
241specify to your VM.
242
243// see autoballoon() in pvestatd.pm
244When choosing to *automatically allocate memory*, {pve} will make sure that the
245minimum amount you specified is always available to the VM, and if RAM usage on
246the host is below 80%, will dynamically add memory to the guest up to the
247maximum memory specified. +
248When the host is becoming short on RAM, the VM will then release some memory
249back to the host, swapping running processes if needed and starting the oom
250killer in last resort. The passing around of memory between host and guest is
251done via a special `balloon` kernel driver running inside the guest, which will
252grab or release memory pages from the host.
253footnote:[A good explanation of the inner workings of the balloon driver can be found here https://rwmj.wordpress.com/2010/07/17/virtio-balloon/]
254
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255When multiple VMs use the autoallocate facility, it is possible to set a
256*Shares* coefficient which indicates the relative amount of the free host memory
257that each VM shoud take. Suppose for instance you have four VMs, three of them
258running a HTTP server and the last one is a database server. To cache more
259database blocks in the database server RAM, you would like to prioritize the
260database VM when spare RAM is available. For this you assign a Shares property
261of 3000 to the database VM, leaving the other VMs to the Shares default setting
262of 1000. The host server has 32GB of RAM, and is curring using 16GB, leaving 32
263* 80/100 - 16 = 9GB RAM to be allocated to the VMs. The database VM will get 9 *
2643000 / (3000 + 1000 + 1000 + 1000) = 4.5 GB extra RAM and each HTTP server will
265get 1/5 GB.
266
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267All Linux distributions released after 2010 have the balloon kernel driver
268included. For Windows OSes, the balloon driver needs to be added manually and can
269incur a slowdown of the guest, so we don't recommend using it on critical
270systems.
271// see https://forum.proxmox.com/threads/solved-hyper-threading-vs-no-hyper-threading-fixed-vs-variable-memory.20265/
272
273When allocating RAMs to your VMs, a good rule of thumb is always to leave 1GB
274of RAM available to the host.
275
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276USB Passthrough
277~~~~~~~~~~~~~~~
278There are two different types of USB passthrough devices:
279
280* Host USB passtrough
281* SPICE USB passthrough
282
283Host USB passthrough works by giving a VM a USB device of the host.
284This can either be done via the vendor- and product-id, or
285via the host bus and port.
286
287The vendor/product-id looks like this: *0123:abcd*,
288where *0123* is the id of the vendor, and *abcd* is the id
289of the product, meaning two pieces of the same usb device
290have the same id.
291
292The bus/port looks like this: *1-2.3.4*, where *1* is the bus
293and *2.3.4* is the port path. This represents the physical
294ports of your host (depending of the internal order of the
295usb controllers).
296
297If a device is present in a VM configuration when the VM starts up,
298but the device is not present in the host, the VM can boot without problems.
299As soon as the device/port ist available in the host, it gets passed through.
300
301WARNING: Using this kind of USB passthrough, means that you cannot move
302a VM online to another host, since the hardware is only available
303on the host the VM is currently residing.
304
305The second type of passthrough is SPICE USB passthrough. This is useful
306if you use a SPICE client which supports it. If you add a SPICE USB port
307to your VM, you can passthrough a USB device from where your SPICE client is,
308directly to the VM (for example an input device or hardware dongle).
309
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310Managing Virtual Machines with 'qm'
311------------------------------------
f69cfd23 312
dd042288 313qm is the tool to manage Qemu/Kvm virtual machines on {pve}. You can
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314create and destroy virtual machines, and control execution
315(start/stop/suspend/resume). Besides that, you can use qm to set
316parameters in the associated config file. It is also possible to
317create and delete virtual disks.
318
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319CLI Usage Examples
320~~~~~~~~~~~~~~~~~~
321
322Create a new VM with 4 GB IDE disk.
323
324 qm create 300 -ide0 4 -net0 e1000 -cdrom proxmox-mailgateway_2.1.iso
325
326Start the new VM
327
328 qm start 300
329
330Send a shutdown request, then wait until the VM is stopped.
331
332 qm shutdown 300 && qm wait 300
333
334Same as above, but only wait for 40 seconds.
335
336 qm shutdown 300 && qm wait 300 -timeout 40
337
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338Configuration
339-------------
340
341All configuration files consists of lines in the form
342
343 PARAMETER: value
344
871e1fd6 345Configuration files are stored inside the Proxmox cluster file
c4cba5d7 346system, and can be accessed at '/etc/pve/qemu-server/<VMID>.conf'.
f69cfd23 347
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348Options
349~~~~~~~
350
351include::qm.conf.5-opts.adoc[]
352
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353
354Locks
355-----
356
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357Online migrations and backups ('vzdump') set a lock to prevent incompatible
358concurrent actions on the affected VMs. Sometimes you need to remove such a
359lock manually (e.g., after a power failure).
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360
361 qm unlock <vmid>
362
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363
364ifdef::manvolnum[]
365include::pve-copyright.adoc[]
366endif::manvolnum[]