qm.adoc

   1 ifdef::manvolnum[]
   2 PVE({manvolnum})
   3 ================
   4 include::attributes.txt[]
   5
   6 NAME
   7 ----
   8
   9 qm - Qemu/KVM Virtual Machine Manager
  10
  11
  12 SYNOPSYS
  13 --------
  14
  15 include::qm.1-synopsis.adoc[]
  16
  17 DESCRIPTION
  18 -----------
  19 endif::manvolnum[]
  20
  21 ifndef::manvolnum[]
  22 Qemu/KVM Virtual Machines
  23 =========================
  24 include::attributes.txt[]
  25 endif::manvolnum[]
  26
  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
  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.
  37
  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.
  42
  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
  50 NOTE: You may sometimes encounter the term _KVM_ (Kernel-based Virtual Machine).
  51 It means that Qemu is running with the support of the virtualization processor
  52 extensions, 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
  54 module.
  55
  56 Qemu inside {pve} runs as a root process, since this is required to access block
  57 and PCI devices.
  58
  59 Emulated devices and paravirtualized devices
  60 --------------------------------------------
  61
  62 The PC hardware emulated by Qemu includes a mainboard, network controllers,
  63 scsi, ide and sata controllers, serial ports (the complete list can be seen in
  64 the `kvm(1)` man page) all of them emulated in software. All these devices
  65 are the exact software equivalent of existing hardware devices, and if the OS
  66 running in the guest has the proper drivers it will use the devices as if it
  67 were running on real hardware. This allows Qemu to runs _unmodified_ operating
  68 systems.
  69
  70 This however has a performance cost, as running in software what was meant to
  71 run in hardware involves a lot of extra work for the host CPU. To mitigate this,
  72 Qemu can present to the guest operating system _paravirtualized devices_, where
  73 the guest OS recognizes it is running inside Qemu and cooperates with the
  74 hypervisor.
  75
  76 Qemu relies on the virtio virtualization standard, and is thus able to presente
  77 paravirtualized virtio devices, which includes a paravirtualized generic disk
  78 controller, a paravirtualized network card, a paravirtualized serial port,
  79 a paravirtualized SCSI controller, etc ...
  80
  81 It is highly recommended to use the virtio devices whenever you can, as they
  82 provide a big performance improvement. Using  the virtio generic disk controller
  83 versus an emulated IDE controller will double the sequential write throughput,
  84 as measured with `bonnie++(8)`. Using the virtio network interface can deliver
  85 up to three times the throughput of an emulated Intel E1000 network card, as
  86 measured with `iperf(1)`. footnote:[See this benchmark on the KVM wiki
  87 http://www.linux-kvm.org/page/Using_VirtIO_NIC]
  88
  89 Virtual Machines settings
  90 -------------------------
  91 Generally 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
  93 could incur a performance slowdown, or putting your data at risk.
  94
  95 General Settings
  96 ~~~~~~~~~~~~~~~~
  97 General 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
 104 OS Settings
 105 ~~~~~~~~~~~
 106 When creating a VM, setting the proper Operating System(OS) allows {pve} to
 107 optimize some low level parameters. For instance Windows OS expect the BIOS
 108 clock to use the local time, while Unix based OS expect the BIOS clock to have
 109 the UTC time.
 110
 111 Hard Disk
 112 ~~~~~~~~~
 113 Qemu can emulate a number of storage controllers:
 114
 115 * the *IDE* controller, has a design which goes back to the 1984 PC/AT disk
 116 controller. Even if this controller has been superseded by more more designs,
 117 each and every OS you can think has support for it, making it a great choice
 118 if you want to run an OS released before 2003. You can connect up to 4 devices
 119 on this controller.
 120
 121 * the *SATA* (Serial ATA) controller, dating from 2003, has a more modern
 122 design, allowing higher throughput and a greater number of devices to be
 123 connected. You can connect up to 6 devices on this controller.
 124
 125 * the *SCSI* controller, designed in 1985, is commonly found on server
 126 grade hardware, and can connect up to 14 storage devices. {pve} emulates by
 127 default a LSI 53C895A controller.
 128
 129 * The *Virtio* controller is a generic paravirtualized controller, and is the
 130 recommended setting if you aim for performance. To use this controller, the OS
 131 need to have special drivers which may be included in your installation ISO or
 132 not. Linux distributions have support for the Virtio controller since 2010, and
 133 FreeBSD since 2014. For Windows OSes, you need to provide an extra iso
 134 containing the Virtio drivers during the installation.
 135 // see: https://pve.proxmox.com/wiki/Paravirtualized_Block_Drivers_for_Windows#During_windows_installation.
 136 You can connect up to 16 devices on this controller.
 137
 138 On each controller you attach a number of emulated hard disks, which are backed
 139 by a file or a block device residing in the configured storage. The choice of
 140 a storage type will determine the format of the hard disk image. Storages which
 141 present block devices (LVM, ZFS, Ceph) will require the *raw disk image format*,
 142 whereas files based storages (Ext4, NFS, GlusterFS) will let you to choose
 143 either 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.
 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
 152  http://events.linuxfoundation.org/sites/events/files/slides/CloudOpen2013_Khoa_Huynh_v3.pdf]
 153  * the *VMware image format* only makes sense if you intend to import/export the
 154  disk image to other hypervisors.
 155
 156 Setting the *Cache* mode of the hard drive will impact how the host system will
 157 notify the guest systems of block write completions. The *No cache* default
 158 means that the guest system will be notified that a write is complete when each
 159 block reaches the physical storage write queue, ignoring the host page cache.
 160 This provides a good balance between safety and speed.
 161
 162 If you want the {pve} backup manager to skip a disk when doing a backup of a VM,
 163 you can set the *No backup* option on that disk.
 164
 165 If 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*
 167 option on the hard disks connected to that controller. With *Discard* enabled,
 168 when the filesystem of a VM marks blocks as unused after removing files, the
 169 emulated SCSI controller will relay this information to the storage, which will
 170 then shrink the disk image accordingly.
 171
 172 The option *IO Thread* can only be enabled when using a disk with the *Virtio* controller,
 173 or with the *SCSI* controller, when the emulated controller type is *VIRTIO*.
 174 With this enabled, Qemu uses one thread per disk, instead of one thread for all,
 175 so it should increase performance when using multiple disks.
 176 Note that backups do not currently work with *IO Thread* enabled.
 177
 178 Managing Virtual Machines with 'qm'
 179 ------------------------------------
 180
 181 qm is the tool to manage Qemu/Kvm virtual machines on {pve}. You can
 182 create and destroy virtual machines, and control execution
 183 (start/stop/suspend/resume). Besides that, you can use qm to set
 184 parameters in the associated config file. It is also possible to
 185 create and delete virtual disks.
 186
 187 CLI Usage Examples
 188 ~~~~~~~~~~~~~~~~~~
 189
 190 Create a new VM with 4 GB IDE disk.
 191
 192  qm create 300 -ide0 4 -net0 e1000 -cdrom proxmox-mailgateway_2.1.iso
 193
 194 Start the new VM
 195
 196  qm start 300
 197
 198 Send a shutdown request, then wait until the VM is stopped.
 199
 200  qm shutdown 300 && qm wait 300
 201
 202 Same as above, but only wait for 40 seconds.
 203
 204  qm shutdown 300 && qm wait 300 -timeout 40
 205
 206 Configuration
 207 -------------
 208
 209 All configuration files consists of lines in the form
 210
 211  PARAMETER: value
 212
 213 Configuration files are stored inside the Proxmox cluster file
 214 system, and can be accessed at '/etc/pve/qemu-server/<VMID>.conf'.
 215
 216 Options
 217 ~~~~~~~
 218
 219 include::qm.conf.5-opts.adoc[]
 220
 221
 222 Locks
 223 -----
 224
 225 Online migrations and backups ('vzdump') set a lock to prevent incompatible
 226 concurrent actions on the affected VMs. Sometimes you need to remove such a
 227 lock manually (e.g., after a power failure).
 228
 229  qm unlock <vmid>
 230
 231
 232 ifdef::manvolnum[]
 233 include::pve-copyright.adoc[]
 234 endif::manvolnum[]