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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
48architecture. +
49Qemu inside {pve} runs as a root process, since this is required to access block
50and PCI devices.
51
52Emulated devices and paravirtualized devices
53--------------------------------------------
54
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55The PC hardware emulated by Qemu includes a mainboard, network controllers,
56scsi, ide and sata controllers, serial ports (the complete list can be seen in
57the `kvm(1)` man page) all of them emulated in software. All these devices
58are the exact software equivalent of existing hardware devices, and if the OS
59running in the guest has the proper drivers it will use the devices as if it
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60were running on real hardware. This allows Qemu to runs _unmodified_ operating
61systems.
62
63This however has a performance cost, as running in software what was meant to
64run in hardware involves a lot of extra work for the host CPU. To mitigate this,
65Qemu can present to the guest operating system _paravirtualized devices_, where
66the guest OS recognizes it is running inside Qemu and cooperates with the
67hypervisor.
68
69Qemu relies on the virtio virtualization standard, and is thus able to presente
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70paravirtualized virtio devices, which includes a paravirtualized generic disk
71controller, a paravirtualized network card, a paravirtualized serial port,
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72a paravirtualized SCSI controller, etc ...
73
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74It is highly recommended to use the virtio devices whenever you can, as they
75provide a big performance improvement. Using the virtio generic disk controller
76versus an emulated IDE controller will double the sequential write throughput,
77as measured with `bonnie++(8)`. Using the virtio network interface can deliver
c4cba5d7 78up to three times the throughput of an emulated Intel E1000 network card, as
189d3661 79measured with `iperf(1)`. footnote:[See this benchmark on the KVM wiki
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80http://www.linux-kvm.org/page/Using_VirtIO_NIC]
81
82Virtual Machines settings
83-------------------------
84Generally speaking {pve} tries to choose sane defaults for virtual machines
85(VM). Make sure you understand the meaning of the settings you change, as it
86could incur a performance slowdown, or putting your data at risk.
87
88General Settings
89~~~~~~~~~~~~~~~~
90General settings of a VM include
91
92* the *Node* : the physical server on which the VM will run
93* the *VM ID*: a unique number in this {pve} installation used to identify your VM
94* *Name*: a free form text string you can use to describe the VM
95* *Resource Pool*: a logical group of VMs
96
97OS Settings
98~~~~~~~~~~~
99When creating a VM, setting the proper Operating System(OS) allows {pve} to
100optimize some low level parameters. For instance Windows OS expect the BIOS
101clock to use the local time, while Unix based OS expect the BIOS clock to have
102the UTC time.
103
104Hard Disk
105~~~~~~~~~
2ec49380 106Qemu can emulate a number of storage controllers:
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107
108* the *IDE* controller, has a design which goes back to the 1984 PC/AT disk
109controller. Even if this controller has been superseded by more more designs,
110each and every OS you can think has support for it, making it a great choice
111if you want to run an OS released before 2003. You can connect up to 4 devices
112on this controller.
113
114* the *SATA* (Serial ATA) controller, dating from 2003, has a more modern
115design, allowing higher throughput and a greater number of devices to be
116connected. You can connect up to 6 devices on this controller.
117
118* the *SCSI* controller, designed in 1985, is commonly found on server
189d3661 119grade hardware, and can connect up to 14 storage devices. {pve} emulates by
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120default a LSI 53C895A controller.
121
122* The *Virtio* controller is a generic paravirtualized controller, and is the
123recommended setting if you aim for performance. To use this controller, the OS
124need to have special drivers which may be included in your installation ISO or
125not. Linux distributions have support for the Virtio controller since 2010, and
126FreeBSD since 2014. For Windows OSes, you need to provide an extra iso
189d3661 127containing the Virtio drivers during the installation.
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128// see: https://pve.proxmox.com/wiki/Paravirtualized_Block_Drivers_for_Windows#During_windows_installation.
129You can connect up to 16 devices on this controller.
130
131On each controller you attach a number of emulated hard disks, which are backed
132by a file or a block device residing in the configured storage. The choice of
133a storage type will determine the format of the hard disk image. Storages which
134present block devices (LVM, ZFS, Ceph) will require the *raw disk image format*,
135whereas files based storages (Ext4, NFS, GlusterFS) will let you to choose
136either the *raw disk image format* or the *QEMU image format*.
137
138 * the *QEMU image format* is a copy on write format which allows snapshots, and
139 thin provisioning of the disk image.
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140 * the *raw disk image* is a bit-to-bit image of a hard disk, similar to what
141 you would get when executing the `dd` command on a block device in Linux. This
142 format do not support thin provisioning or snapshotting by itself, requiring
143 cooperation from the storage layer for these tasks. It is however 10% faster
144 than the *QEMU image format*. footnote:[See this benchmark for details
c4cba5d7 145 http://events.linuxfoundation.org/sites/events/files/slides/CloudOpen2013_Khoa_Huynh_v3.pdf]
189d3661 146 * the *VMware image format* only makes sense if you intend to import/export the
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147 disk image to other hypervisors.
148
149Setting the *Cache* mode of the hard drive will impact how the host system will
150notify the guest systems of block write completions. The *No cache* default
151means that the guest system will be notified that a write is complete when each
152block reaches the physical storage write queue, ignoring the host page cache.
153This provides a good balance between safety and speed.
154
155If you want the {pve} backup manager to skip a disk when doing a backup of a VM,
156you can set the *No backup* option on that disk.
157
158If your storage supports _thin provisioning_ (see the storage chapter in the
159{pve} guide), and your VM has a *SCSI* controller you can activate the *Discard*
160option on the hard disks connected to that controller. With *Discard* enabled,
161when the filesystem of a VM marks blocks as unused after removing files, the
162emulated SCSI controller will relay this information to the storage, which will
163then shrink the disk image accordingly.
164
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165The option *IO Thread* can only be enabled when using a disk with the *Virtio* controller,
166or with the *SCSI* controller, when the emulated controller type is *VIRTIO*.
167With this enabled, Qemu uses one thread per disk, instead of one thread for all,
168so it should increase performance when using multiple disks.
169Note that backups do not currently work with *IO Thread* enabled.
170
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171Managing Virtual Machines with 'qm'
172------------------------------------
f69cfd23 173
dd042288 174qm is the tool to manage Qemu/Kvm virtual machines on {pve}. You can
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175create and destroy virtual machines, and control execution
176(start/stop/suspend/resume). Besides that, you can use qm to set
177parameters in the associated config file. It is also possible to
178create and delete virtual disks.
179
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180CLI Usage Examples
181~~~~~~~~~~~~~~~~~~
182
183Create a new VM with 4 GB IDE disk.
184
185 qm create 300 -ide0 4 -net0 e1000 -cdrom proxmox-mailgateway_2.1.iso
186
187Start the new VM
188
189 qm start 300
190
191Send a shutdown request, then wait until the VM is stopped.
192
193 qm shutdown 300 && qm wait 300
194
195Same as above, but only wait for 40 seconds.
196
197 qm shutdown 300 && qm wait 300 -timeout 40
198
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199Configuration
200-------------
201
202All configuration files consists of lines in the form
203
204 PARAMETER: value
205
871e1fd6 206Configuration files are stored inside the Proxmox cluster file
c4cba5d7 207system, and can be accessed at '/etc/pve/qemu-server/<VMID>.conf'.
f69cfd23 208
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209Options
210~~~~~~~
211
212include::qm.conf.5-opts.adoc[]
213
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214
215Locks
216-----
217
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218Online migrations and backups ('vzdump') set a lock to prevent incompatible
219concurrent actions on the affected VMs. Sometimes you need to remove such a
220lock manually (e.g., after a power failure).
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221
222 qm unlock <vmid>
223
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224
225ifdef::manvolnum[]
226include::pve-copyright.adoc[]
227endif::manvolnum[]