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 Qemu inside {pve} runs as a root process, since this is required to access block
  50 and PCI devices.
  51
  52 Emulated devices and paravirtualized devices
  53 --------------------------------------------
  54
  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.
  62
  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.
  68
  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 ...
  73
  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
  80 http://www.linux-kvm.org/page/Using_VirtIO_NIC]
  81
  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.
  87
  88 General Settings
  89 ~~~~~~~~~~~~~~~~
  90 General 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
  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.
 103
 104 Hard Disk
 105 ~~~~~~~~~
 106 Qemu can emulate a number of storage controllers:
 107
 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.
 113
 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.
 117
 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.
 121
 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: https://pve.proxmox.com/wiki/Paravirtualized_Block_Drivers_for_Windows#During_windows_installation.
 129 You can connect up to 16 devices on this controller.
 130
 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*.
 137
 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
 145  http://events.linuxfoundation.org/sites/events/files/slides/CloudOpen2013_Khoa_Huynh_v3.pdf]
 146  * the *VMware image format* only makes sense if you intend to import/export the
 147  disk image to other hypervisors.
 148
 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.
 154
 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.
 157
 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.
 164
 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.
 170
 171 Managing Virtual Machines with 'qm'
 172 ------------------------------------
 173
 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.
 179
 180 CLI Usage Examples
 181 ~~~~~~~~~~~~~~~~~~
 182
 183 Create a new VM with 4 GB IDE disk.
 184
 185  qm create 300 -ide0 4 -net0 e1000 -cdrom proxmox-mailgateway_2.1.iso
 186
 187 Start the new VM
 188
 189  qm start 300
 190
 191 Send a shutdown request, then wait until the VM is stopped.
 192
 193  qm shutdown 300 && qm wait 300
 194
 195 Same as above, but only wait for 40 seconds.
 196
 197  qm shutdown 300 && qm wait 300 -timeout 40
 198
 199 Configuration
 200 -------------
 201
 202 All configuration files consists of lines in the form
 203
 204  PARAMETER: value
 205
 206 Configuration files are stored inside the Proxmox cluster file
 207 system, and can be accessed at '/etc/pve/qemu-server/<VMID>.conf'.
 208
 209 Options
 210 ~~~~~~~
 211
 212 include::qm.conf.5-opts.adoc[]
 213
 214
 215 Locks
 216 -----
 217
 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).
 221
 222  qm unlock <vmid>
 223
 224
 225 ifdef::manvolnum[]
 226 include::pve-copyright.adoc[]
 227 endif::manvolnum[]