Add note explaining what is KVM
[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.
c4cba5d7 42
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*.
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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178Managing Virtual Machines with 'qm'
179------------------------------------
f69cfd23 180
dd042288 181qm is the tool to manage Qemu/Kvm virtual machines on {pve}. You can
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182create and destroy virtual machines, and control execution
183(start/stop/suspend/resume). Besides that, you can use qm to set
184parameters in the associated config file. It is also possible to
185create and delete virtual disks.
186
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187CLI Usage Examples
188~~~~~~~~~~~~~~~~~~
189
190Create a new VM with 4 GB IDE disk.
191
192 qm create 300 -ide0 4 -net0 e1000 -cdrom proxmox-mailgateway_2.1.iso
193
194Start the new VM
195
196 qm start 300
197
198Send a shutdown request, then wait until the VM is stopped.
199
200 qm shutdown 300 && qm wait 300
201
202Same as above, but only wait for 40 seconds.
203
204 qm shutdown 300 && qm wait 300 -timeout 40
205
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206Configuration
207-------------
208
209All configuration files consists of lines in the form
210
211 PARAMETER: value
212
871e1fd6 213Configuration files are stored inside the Proxmox cluster file
c4cba5d7 214system, and can be accessed at '/etc/pve/qemu-server/<VMID>.conf'.
f69cfd23 215
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216Options
217~~~~~~~
218
219include::qm.conf.5-opts.adoc[]
220
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221
222Locks
223-----
224
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225Online migrations and backups ('vzdump') set a lock to prevent incompatible
226concurrent actions on the affected VMs. Sometimes you need to remove such a
227lock manually (e.g., after a power failure).
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228
229 qm unlock <vmid>
230
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231
232ifdef::manvolnum[]
233include::pve-copyright.adoc[]
234endif::manvolnum[]