remove trailing whitespaces
[pve-docs.git] / qm.adoc
1 ifdef::manvolnum[]
2 PVE({manvolnum})
3 ================
4 include::attributes.txt[]
7 ----
9 qm - Qemu/KVM Virtual Machine Manager
13 --------
15 include::qm.1-synopsis.adoc[]
18 -----------
19 endif::manvolnum[]
21 ifndef::manvolnum[]
22 Qemu/KVM Virtual Machines
23 =========================
24 include::attributes.txt[]
25 endif::manvolnum[]
27 // deprecates
28 //
29 //
30 //
32 Qemu (short form for Quick Emulator) is an opensource 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 emulates 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
48 architecture. +
49 Qemu inside {pve} runs as a root process, since this is required to access block
50 and PCI devices.
52 Emulated devices and paravirtualized devices
53 --------------------------------------------
55 The PC hardware emulated by Qemu includes a mainboard, network controllers,
56 scsi, ide and sata controllers, serial ports (the complete list can be seen in
57 the `kvm(1)` man page) all of them emulated in software. All these devices
58 are the exact software equivalent of existing hardware devices, and if the OS
59 running in the guest has the proper drivers it will use the devices as if it
60 were running on real hardware. This allows Qemu to runs _unmodified_ operating
61 systems.
63 This however has a performance cost, as running in software what was meant to
64 run in hardware involves a lot of extra work for the host CPU. To mitigate this,
65 Qemu can present to the guest operating system _paravirtualized devices_, where
66 the guest OS recognizes it is running inside Qemu and cooperates with the
67 hypervisor.
69 Qemu relies on the virtio virtualization standard, and is thus able to presente
70 paravirtualized virtio devices, which includes a paravirtualized generic disk
71 controller, a paravirtualized network card, a paravirtualized serial port,
72 a paravirtualized SCSI controller, etc ...
74 It is highly recommended to use the virtio devices whenever you can, as they
75 provide a big performance improvement. Using the virtio generic disk controller
76 versus an emulated IDE controller will double the sequential write throughput,
77 as measured with `bonnie++(8)`. Using the virtio network interface can deliver
78 up to three times the throughput of an emulated Intel E1000 network card, as
79 measured with `iperf(1)`. footnote:[See this benchmark on the KVM wiki
82 Virtual Machines settings
83 -------------------------
84 Generally 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
86 could incur a performance slowdown, or putting your data at risk.
88 General Settings
89 ~~~~~~~~~~~~~~~~
90 General settings of a VM include
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
97 OS Settings
98 ~~~~~~~~~~~
99 When creating a VM, setting the proper Operating System(OS) allows {pve} to
100 optimize some low level parameters. For instance Windows OS expect the BIOS
101 clock to use the local time, while Unix based OS expect the BIOS clock to have
102 the UTC time.
104 Hard Disk
105 ~~~~~~~~~
106 Qemu can emulate a number of storage controllers:
108 * the *IDE* controller, has a design which goes back to the 1984 PC/AT disk
109 controller. Even if this controller has been superseded by more more designs,
110 each and every OS you can think has support for it, making it a great choice
111 if you want to run an OS released before 2003. You can connect up to 4 devices
112 on this controller.
114 * the *SATA* (Serial ATA) controller, dating from 2003, has a more modern
115 design, allowing higher throughput and a greater number of devices to be
116 connected. You can connect up to 6 devices on this controller.
118 * the *SCSI* controller, designed in 1985, is commonly found on server
119 grade hardware, and can connect up to 14 storage devices. {pve} emulates by
120 default a LSI 53C895A controller.
122 * The *Virtio* controller is a generic paravirtualized controller, and is the
123 recommended setting if you aim for performance. To use this controller, the OS
124 need to have special drivers which may be included in your installation ISO or
125 not. Linux distributions have support for the Virtio controller since 2010, and
126 FreeBSD since 2014. For Windows OSes, you need to provide an extra iso
127 containing the Virtio drivers during the installation.
128 // see:
129 You can connect up to 16 devices on this controller.
131 On each controller you attach a number of emulated hard disks, which are backed
132 by a file or a block device residing in the configured storage. The choice of
133 a storage type will determine the format of the hard disk image. Storages which
134 present block devices (LVM, ZFS, Ceph) will require the *raw disk image format*,
135 whereas files based storages (Ext4, NFS, GlusterFS) will let you to choose
136 either the *raw disk image format* or the *QEMU image format*.
138 * the *QEMU image format* is a copy on write format which allows snapshots, and
139 thin provisioning of the disk image.
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
146 * the *VMware image format* only makes sense if you intend to import/export the
147 disk image to other hypervisors.
149 Setting the *Cache* mode of the hard drive will impact how the host system will
150 notify the guest systems of block write completions. The *No cache* default
151 means that the guest system will be notified that a write is complete when each
152 block reaches the physical storage write queue, ignoring the host page cache.
153 This provides a good balance between safety and speed.
155 If you want the {pve} backup manager to skip a disk when doing a backup of a VM,
156 you can set the *No backup* option on that disk.
158 If 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*
160 option on the hard disks connected to that controller. With *Discard* enabled,
161 when the filesystem of a VM marks blocks as unused after removing files, the
162 emulated SCSI controller will relay this information to the storage, which will
163 then shrink the disk image accordingly.
165 The option *IO Thread* can only be enabled when using a disk with the *Virtio* controller,
166 or with the *SCSI* controller, when the emulated controller type is *VIRTIO*.
167 With this enabled, Qemu uses one thread per disk, instead of one thread for all,
168 so it should increase performance when using multiple disks.
169 Note that backups do not currently work with *IO Thread* enabled.
171 Managing Virtual Machines with 'qm'
172 ------------------------------------
174 qm is the tool to manage Qemu/Kvm virtual machines on {pve}. You can
175 create and destroy virtual machines, and control execution
176 (start/stop/suspend/resume). Besides that, you can use qm to set
177 parameters in the associated config file. It is also possible to
178 create and delete virtual disks.
180 CLI Usage Examples
181 ~~~~~~~~~~~~~~~~~~
183 Create a new VM with 4 GB IDE disk.
185 qm create 300 -ide0 4 -net0 e1000 -cdrom proxmox-mailgateway_2.1.iso
187 Start the new VM
189 qm start 300
191 Send a shutdown request, then wait until the VM is stopped.
193 qm shutdown 300 && qm wait 300
195 Same as above, but only wait for 40 seconds.
197 qm shutdown 300 && qm wait 300 -timeout 40
199 Configuration
200 -------------
202 All configuration files consists of lines in the form
204 PARAMETER: value
206 Configuration files are stored inside the Proxmox cluster file
207 system, and can be accessed at '/etc/pve/qemu-server/<VMID>.conf'.
209 Options
210 ~~~~~~~
212 include::qm.conf.5-opts.adoc[]
215 Locks
216 -----
218 Online migrations and backups ('vzdump') set a lock to prevent incompatible
219 concurrent actions on the affected VMs. Sometimes you need to remove such a
220 lock manually (e.g., after a power failure).
222 qm unlock <vmid>
225 ifdef::manvolnum[]
226 include::pve-copyright.adoc[]
227 endif::manvolnum[]