Qemu (short form for Quick Emulator) is an opensource hypervisor that emulates a physical computer. From the perspective of the host system where Qemu is running, Qemu is a user program which has access to a number of local resources like partitions, files, network cards which are then passed to an emulated computer which sees them as if they were real devices.

A guest operating system running in the emulated computer accesses these devices, and runs as it were running on real hardware. For instance you can pass an iso image as a parameter to Qemu, and the OS running in the emulated computer will see a real CDROM inserted in a CD drive.

Qemu can emulates a great variety of hardware from ARM to Sparc, but Proxmox VE is only concerned with 32 and 64 bits PC clone emulation, since it represents the overwhelming majority of server hardware. The emulation of PC clones is also one of the fastest due to the availability of processor extensions which greatly speed up Qemu when the emulated architecture is the same as the host architecture.
Qemu inside Proxmox VE runs as a root process, since this is required to access block and PCI devices.

Emulated devices and paravirtualized devices

The PC hardware emulated by Qemu includes a mainboard, network controllers, scsi, ide and sata controllers, serial ports (the complete list can be seen in the kvm(1) man page) all of them emulated in software. All these devices are the exact software equivalent of existing hardware devices, and if the OS running in the guest has the proper drivers it will use the devices as if it were running on real hardware. This allows Qemu to runs unmodified operating systems.

This however has a performance cost, as running in software what was meant to run in hardware involves a lot of extra work for the host CPU. To mitigate this, Qemu can present to the guest operating system paravirtualized devices, where the guest OS recognizes it is running inside Qemu and cooperates with the hypervisor.

Qemu relies on the virtio virtualization standard, and is thus able to presente paravirtualized virtio devices, which includes a paravirtualized generic disk controller, a paravirtualized network card, a paravirtualized serial port, a paravirtualized SCSI controller, etc …

It is highly recommended to use the virtio devices whenever you can, as they provide a big performance improvement. Using the virtio generic disk controller versus an emulated IDE controller will double the sequential write throughput, as measured with bonnie++(8). Using the virtio network interface can deliver up to three times the throughput of an emulated Intel E1000 network card, as measured with iperf(1).
[See this benchmark on the KVM wiki http://www.linux-kvm.org/page/Using_VirtIO_NIC]

Virtual Machines settings

Generally speaking Proxmox VE tries to choose sane defaults for virtual machines (VM). Make sure you understand the meaning of the settings you change, as it could incur a performance slowdown, or putting your data at risk.

General Settings

General settings of a VM include

  • the Node : the physical server on which the VM will run

  • the VM ID: a unique number in this Proxmox VE installation used to identify your VM

  • Name: a free form text string you can use to describe the VM

  • Resource Pool: a logical group of VMs

OS Settings

When creating a VM, setting the proper Operating System(OS) allows Proxmox VE to optimize some low level parameters. For instance Windows OS expect the BIOS clock to use the local time, while Unix based OS expect the BIOS clock to have the UTC time.

Hard Disk

Qemu can use a emulate a number of storage controllers:

  • the IDE controller, has a design which goes back to the 1984 PC/AT disk controller. Even if this controller has been superseded by more more designs, each and every OS you can think has support for it, making it a great choice if you want to run an OS released before 2003. You can connect up to 4 devices on this controller.

  • the SATA (Serial ATA) controller, dating from 2003, has a more modern design, allowing higher throughput and a greater number of devices to be connected. You can connect up to 6 devices on this controller.

  • the SCSI controller, designed in 1985, is commonly found on server grade hardware, and can connect up to 14 storage devices. Proxmox VE emulates by default a LSI 53C895A controller.

  • The Virtio controller is a generic paravirtualized controller, and is the recommended setting if you aim for performance. To use this controller, the OS need to have special drivers which may be included in your installation ISO or not. Linux distributions have support for the Virtio controller since 2010, and FreeBSD since 2014. For Windows OSes, you need to provide an extra iso containing the Virtio drivers during the installation. You can connect up to 16 devices on this controller.

On each controller you attach a number of emulated hard disks, which are backed by a file or a block device residing in the configured storage. The choice of a storage type will determine the format of the hard disk image. Storages which present block devices (LVM, ZFS, Ceph) will require the raw disk image format, whereas files based storages (Ext4, NFS, GlusterFS) will let you to choose either the raw disk image format or the QEMU image format.

  • the QEMU image format is a copy on write format which allows snapshots, and thin provisioning of the disk image.

  • the raw disk image is a bit-to-bit image of a hard disk, similar to what you would get when executing the dd command on a block device in Linux. This format do not support thin provisioning or snapshotting by itself, requiring cooperation from the storage layer for these tasks. It is however 10% faster than the QEMU image format.
    [See this benchmark for details http://events.linuxfoundation.org/sites/events/files/slides/CloudOpen2013_Khoa_Huynh_v3.pdf]

  • the VMware image format only makes sense if you intend to import/export the disk image to other hypervisors.

Setting the Cache mode of the hard drive will impact how the host system will notify the guest systems of block write completions. The No cache default means that the guest system will be notified that a write is complete when each block reaches the physical storage write queue, ignoring the host page cache. This provides a good balance between safety and speed.

If you want the Proxmox VE backup manager to skip a disk when doing a backup of a VM, you can set the No backup option on that disk.

If your storage supports thin provisioning (see the storage chapter in the Proxmox VE guide), and your VM has a SCSI controller you can activate the Discard option on the hard disks connected to that controller. With Discard enabled, when the filesystem of a VM marks blocks as unused after removing files, the emulated SCSI controller will relay this information to the storage, which will then shrink the disk image accordingly.

Managing Virtual Machines with qm

qm is the tool to manage Qemu/Kvm virtual machines on Proxmox VE. You can create and destroy virtual machines, and control execution (start/stop/suspend/resume). Besides that, you can use qm to set parameters in the associated config file. It is also possible to create and delete virtual disks.

CLI Usage Examples

Create a new VM with 4 GB IDE disk.

qm create 300 -ide0 4 -net0 e1000 -cdrom proxmox-mailgateway_2.1.iso

Start the new VM

qm start 300

Send a shutdown request, then wait until the VM is stopped.

qm shutdown 300 && qm wait 300

Same as above, but only wait for 40 seconds.

qm shutdown 300 && qm wait 300 -timeout 40

Configuration

All configuration files consists of lines in the form

PARAMETER: value

Configuration files are stored inside the Proxmox cluster file system, and can be accessed at /etc/pve/qemu-server/<VMID>.conf.

Options

acpi: boolean (default=1)

Enable/disable ACPI.

agent: boolean (default=0)

Enable/disable Qemu GuestAgent.

args: string

Arbitrary arguments passed to kvm, for example:

args: -no-reboot -no-hpet

Note this option is for experts only.
autostart: boolean (default=0)

Automatic restart after crash (currently ignored).

balloon: integer (0 - N)

Amount of target RAM for the VM in MB. Using zero disables the ballon driver.

bios: (ovmf | seabios) (default=seabios)

Select BIOS implementation.

boot: [acdn]{1,4} (default=cdn)

Boot on floppy (a), hard disk (c), CD-ROM (d), or network (n).

bootdisk: (ide|sata|scsi|virtio)\d+

Enable booting from specified disk.

cdrom: volume

This is an alias for option -ide2

cores: integer (1 - N) (default=1)

The number of cores per socket.

cpu: [cputype=]<cputype> [,hidden=<1|0>]

Emulated CPU type.

cputype=<cputype> (default=kvm64)

Emulated CPU type.

hidden=boolean (default=0)

Do not identify as a KVM virtual machine.

cpulimit: number (0 - 128) (default=0)

Limit of CPU usage.

Note If the computer has 2 CPUs, it has total of 2 CPU time. Value 0 indicates no CPU limit.
cpuunits: integer (0 - 500000) (default=1000)

CPU weight for a VM. Argument is used in the kernel fair scheduler. The larger the number is, the more CPU time this VM gets. Number is relative to weights of all the other running VMs.

Note You can disable fair-scheduler configuration by setting this to 0.
description: string

Description for the VM. Only used on the configuration web interface. This is saved as comment inside the configuration file.

freeze: boolean

Freeze CPU at startup (use c monitor command to start execution).

hostpci[n]: [host=]<HOSTPCIID[;HOSTPCIID2...]> [,pcie=<1|0>] [,rombar=<1|0>] [,x-vga=<1|0>]

Map host PCI devices into guest.

Note This option allows direct access to host hardware. So it is no longer possible to migrate such machines - use with special care.
Caution Experimental! User reported problems with this option.
host=<HOSTPCIID[;HOSTPCIID2...]>

Host PCI device pass through. The PCI ID of a host’s PCI device or a list of PCI virtual functions of the host. HOSTPCIID syntax is:

bus:dev.func (hexadecimal numbers)

You can us the lspci command to list existing PCI devices.

pcie=boolean (default=0)

Choose the PCI-express bus (needs the q35 machine model).

rombar=boolean (default=1)

Specify whether or not the device’s ROM will be visible in the guest’s memory map.

x-vga=boolean (default=0)

Enable vfio-vga device support.

hotplug: string (default=network,disk,usb)

Selectively enable hotplug features. This is a comma separated list of hotplug features: network, disk, cpu, memory and usb. Use 0 to disable hotplug completely. Value 1 is an alias for the default network,disk,usb.

ide[n]: [file=]<volume> [,aio=<native|threads>] [,backup=<1|0>] [,bps=<bps>] [,bps_rd=<bps>] [,bps_wr=<bps>] [,cache=<none|writethrough|writeback|unsafe|directsync>] [,cyls=<integer>] [,detect_zeroes=<1|0>] [,discard=<ignore|on>] [,format=<image format>] [,heads=<integer>] [,iops=<iops>] [,iops_max=<iops>] [,iops_rd=<iops>] [,iops_rd_max=<iops>] [,iops_wr=<iops>] [,iops_wr_max=<iops>] [,mbps=<mbps>] [,mbps_max=<mbps>] [,mbps_rd=<mbps>] [,mbps_rd_max=<mbps>] [,mbps_wr=<mbps>] [,mbps_wr_max=<mbps>] [,media=<cdrom|disk>] [,model=<model>] [,rerror=<ignore|report|stop>] [,secs=<integer>] [,serial=<serial>] [,size=<DiskSize>] [,snapshot=<1|0>] [,trans=<none|lba|auto>] [,werror=<enospc|ignore|report|stop>]

Use volume as IDE hard disk or CD-ROM (n is 0 to 3).

aio=(native | threads)

AIO type to use.

backup=boolean

Whether the drive should be included when making backups.

bps=<bps>

Maximum r/w speed speed in bytes per second.

bps_rd=<bps>

Maximum read speed speed in bytes per second.

bps_wr=<bps>

Maximum write speed speed in bytes per second.

cache=(directsync | none | unsafe | writeback | writethrough)

The drive’s cache mode

cyls=integer

Force the drive’s physical geometry to have a specific cylinder count.

detect_zeroes=boolean

Controls whether to detect and try to optimize writes of zeroes.

discard=(ignore | on)

Controls whether to pass discard/trim requests to the underlying storage.

file=<volume>

The drive’s backing volume.

format=<image format>

The drive’s backing file’s data format.

heads=integer

Force the drive’s physical geometry to have a specific head count.

iops=<iops>

Maximum r/w I/O speed in operations per second.

iops_max=<iops>

Maximum unthrottled r/w I/O pool speed in operations per second.

iops_rd=<iops>

Maximum read I/O speed in operations per second.

iops_rd_max=<iops>

Maximum unthrottled read I/O pool speed in operations per second.

iops_wr=<iops>

Maximum write I/O speed in operations per second.

iops_wr_max=<iops>

Maximum unthrottled write I/O pool speed in operations per second.

mbps=<mbps>

Maximum r/w speed speed in megabytes per second.

mbps_max=<mbps>

Maximum unthrottled r/w pool speed in megabytes per second.

mbps_rd=<mbps>

Maximum read speed speed in megabytes per second.

mbps_rd_max=<mbps>

Maximum unthrottled read pool speed in megabytes per second.

mbps_wr=<mbps>

Maximum write speed speed in megabytes per second.

mbps_wr_max=<mbps>

Maximum unthrottled write pool speed in megabytes per second.

media=(cdrom | disk) (default=disk)

The drive’s media type.

model=<model>

The drive’s reported model name, url-encoded, up to 40 bytes long.

rerror=(ignore | report | stop)

Read error action.

secs=integer

Force the drive’s physical geometry to have a specific sector count.

serial=<serial>

The drive’s reported serial number, url-encoded, up to 20 bytes long.

size=<DiskSize>

Disk size. This is purely informational and has no effect.

snapshot=boolean

Whether the drive should be included when making snapshots.

trans=(auto | lba | none)

Force disk geometry bios translation mode.

werror=(enospc | ignore | report | stop)

Write error action.

keyboard: (da | de | de-ch | en-gb | en-us | es | fi | fr | fr-be | fr-ca | fr-ch | hu | is | it | ja | lt | mk | nl | no | pl | pt | pt-br | sl | sv | tr) (default=en-us)

Keybord layout for vnc server. Default is read from the /etc/pve/datacenter.conf configuration file.

kvm: boolean (default=1)

Enable/disable KVM hardware virtualization.

localtime: boolean

Set the real time clock to local time. This is enabled by default if ostype indicates a Microsoft OS.

lock: (backup | migrate | rollback | snapshot)

Lock/unlock the VM.

machine: (pc|pc(-i440fx)?-\d+\.\d+(\.pxe)?|q35|pc-q35-\d+\.\d+(\.pxe)?)

Specific the Qemu machine type.

memory: integer (16 - N) (default=512)

Amount of RAM for the VM in MB. This is the maximum available memory when you use the balloon device.

migrate_downtime: number (0 - N) (default=0.1)

Set maximum tolerated downtime (in seconds) for migrations.

migrate_speed: integer (0 - N) (default=0)

Set maximum speed (in MB/s) for migrations. Value 0 is no limit.

name: string

Set a name for the VM. Only used on the configuration web interface.

net[n]: [model=]<model> [,bridge=<bridge>] [,firewall=<1|0>] [,link_down=<1|0>] [,macaddr=<XX:XX:XX:XX:XX:XX>] [,queues=<integer>] [,rate=<number>] [,tag=<integer>] [,trunks=<vlanid[;vlanid...]>] [,<model>=<macaddr>]

Specify network devices.

bridge=<bridge>

Bridge to attach the network device to. The Proxmox VE standard bridge is called vmbr0.

If you do not specify a bridge, we create a kvm user (NATed) network device, which provides DHCP and DNS services. The following addresses are used:

10.0.2.2   Gateway
10.0.2.3   DNS Server
10.0.2.4   SMB Server

The DHCP server assign addresses to the guest starting from 10.0.2.15.

firewall=boolean

Whether this interface should be protected by the firewall.

link_down=boolean

Whether this interface should be disconnected (like pulling the plug).

macaddr=<XX:XX:XX:XX:XX:XX>

MAC address. That address must be unique withing your network. This is automatically generated if not specified.

model=<model>

Network Card Model. The virtio model provides the best performance with very low CPU overhead. If your guest does not support this driver, it is usually best to use e1000.

queues=integer (0 - 16)

Number of packet queues to be used on the device.

rate=number (0 - N)

Rate limit in mbps (megabytes per second) as floating point number.

tag=integer (1 - 4094)

VLAN tag to apply to packets on this interface.

trunks=<vlanid[;vlanid...]>

VLAN trunks to pass through this interface.

numa: boolean (default=0)

Enable/disable NUMA.

numa[n]: cpus=<id[-id];...> [,hostnodes=<id[-id];...>] [,memory=<number>] [,policy=<preferred|bind|interleave>]

NUMA topology.

cpus=<id[-id];...>

CPUs accessing this NUMA node.

hostnodes=<id[-id];...>

Host NUMA nodes to use.

memory=number

Amount of memory this NUMA node provides.

policy=(bind | interleave | preferred)

NUMA allocation policy.

onboot: boolean (default=0)

Specifies whether a VM will be started during system bootup.

ostype: (l24 | l26 | other | solaris | w2k | w2k3 | w2k8 | win7 | win8 | wvista | wxp)

Specify guest operating system. This is used to enable special optimization/features for specific operating systems:

other

unspecified OS

wxp

Microsoft Windows XP

w2k

Microsoft Windows 2000

w2k3

Microsoft Windows 2003

w2k8

Microsoft Windows 2008

wvista

Microsoft Windows Vista

win7

Microsoft Windows 7

win8

Microsoft Windows 8/2012

l24

Linux 2.4 Kernel

l26

Linux 2.6/3.X Kernel

solaris

Solaris/OpenSolaris/OpenIndiania kernel

parallel[n]: /dev/parport\d+|/dev/usb/lp\d+

Map host parallel devices (n is 0 to 2).

Note This option allows direct access to host hardware. So it is no longer possible to migrate such machines - use with special care.
Caution Experimental! User reported problems with this option.
protection: boolean (default=0)

Sets the protection flag of the VM. This will disable the remove VM and remove disk operations.

reboot: boolean (default=1)

Allow reboot. If set to 0 the VM exit on reboot.

sata[n]: [file=]<volume> [,aio=<native|threads>] [,backup=<1|0>] [,bps=<bps>] [,bps_rd=<bps>] [,bps_wr=<bps>] [,cache=<none|writethrough|writeback|unsafe|directsync>] [,cyls=<integer>] [,detect_zeroes=<1|0>] [,discard=<ignore|on>] [,format=<image format>] [,heads=<integer>] [,iops=<iops>] [,iops_max=<iops>] [,iops_rd=<iops>] [,iops_rd_max=<iops>] [,iops_wr=<iops>] [,iops_wr_max=<iops>] [,mbps=<mbps>] [,mbps_max=<mbps>] [,mbps_rd=<mbps>] [,mbps_rd_max=<mbps>] [,mbps_wr=<mbps>] [,mbps_wr_max=<mbps>] [,media=<cdrom|disk>] [,rerror=<ignore|report|stop>] [,secs=<integer>] [,serial=<serial>] [,size=<DiskSize>] [,snapshot=<1|0>] [,trans=<none|lba|auto>] [,werror=<enospc|ignore|report|stop>]

Use volume as SATA hard disk or CD-ROM (n is 0 to 5).

aio=(native | threads)

AIO type to use.

backup=boolean

Whether the drive should be included when making backups.

bps=<bps>

Maximum r/w speed speed in bytes per second.

bps_rd=<bps>

Maximum read speed speed in bytes per second.

bps_wr=<bps>

Maximum write speed speed in bytes per second.

cache=(directsync | none | unsafe | writeback | writethrough)

The drive’s cache mode

cyls=integer

Force the drive’s physical geometry to have a specific cylinder count.

detect_zeroes=boolean

Controls whether to detect and try to optimize writes of zeroes.

discard=(ignore | on)

Controls whether to pass discard/trim requests to the underlying storage.

file=<volume>

The drive’s backing volume.

format=<image format>

The drive’s backing file’s data format.

heads=integer

Force the drive’s physical geometry to have a specific head count.

iops=<iops>

Maximum r/w I/O speed in operations per second.

iops_max=<iops>

Maximum unthrottled r/w I/O pool speed in operations per second.

iops_rd=<iops>

Maximum read I/O speed in operations per second.

iops_rd_max=<iops>

Maximum unthrottled read I/O pool speed in operations per second.

iops_wr=<iops>

Maximum write I/O speed in operations per second.

iops_wr_max=<iops>

Maximum unthrottled write I/O pool speed in operations per second.

mbps=<mbps>

Maximum r/w speed speed in megabytes per second.

mbps_max=<mbps>

Maximum unthrottled r/w pool speed in megabytes per second.

mbps_rd=<mbps>

Maximum read speed speed in megabytes per second.

mbps_rd_max=<mbps>

Maximum unthrottled read pool speed in megabytes per second.

mbps_wr=<mbps>

Maximum write speed speed in megabytes per second.

mbps_wr_max=<mbps>

Maximum unthrottled write pool speed in megabytes per second.

media=(cdrom | disk) (default=disk)

The drive’s media type.

rerror=(ignore | report | stop)

Read error action.

secs=integer

Force the drive’s physical geometry to have a specific sector count.

serial=<serial>

The drive’s reported serial number, url-encoded, up to 20 bytes long.

size=<DiskSize>

Disk size. This is purely informational and has no effect.

snapshot=boolean

Whether the drive should be included when making snapshots.

trans=(auto | lba | none)

Force disk geometry bios translation mode.

werror=(enospc | ignore | report | stop)

Write error action.

scsi[n]: [file=]<volume> [,aio=<native|threads>] [,backup=<1|0>] [,bps=<bps>] [,bps_rd=<bps>] [,bps_wr=<bps>] [,cache=<none|writethrough|writeback|unsafe|directsync>] [,cyls=<integer>] [,detect_zeroes=<1|0>] [,discard=<ignore|on>] [,format=<image format>] [,heads=<integer>] [,iops=<iops>] [,iops_max=<iops>] [,iops_rd=<iops>] [,iops_rd_max=<iops>] [,iops_wr=<iops>] [,iops_wr_max=<iops>] [,iothread=<1|0>] [,mbps=<mbps>] [,mbps_max=<mbps>] [,mbps_rd=<mbps>] [,mbps_rd_max=<mbps>] [,mbps_wr=<mbps>] [,mbps_wr_max=<mbps>] [,media=<cdrom|disk>] [,queues=<integer>] [,secs=<integer>] [,serial=<serial>] [,size=<DiskSize>] [,snapshot=<1|0>] [,trans=<none|lba|auto>] [,werror=<enospc|ignore|report|stop>]

Use volume as SCSI hard disk or CD-ROM (n is 0 to 13).

aio=(native | threads)

AIO type to use.

backup=boolean

Whether the drive should be included when making backups.

bps=<bps>

Maximum r/w speed speed in bytes per second.

bps_rd=<bps>

Maximum read speed speed in bytes per second.

bps_wr=<bps>

Maximum write speed speed in bytes per second.

cache=(directsync | none | unsafe | writeback | writethrough)

The drive’s cache mode

cyls=integer

Force the drive’s physical geometry to have a specific cylinder count.

detect_zeroes=boolean

Controls whether to detect and try to optimize writes of zeroes.

discard=(ignore | on)

Controls whether to pass discard/trim requests to the underlying storage.

file=<volume>

The drive’s backing volume.

format=<image format>

The drive’s backing file’s data format.

heads=integer

Force the drive’s physical geometry to have a specific head count.

iops=<iops>

Maximum r/w I/O speed in operations per second.

iops_max=<iops>

Maximum unthrottled r/w I/O pool speed in operations per second.

iops_rd=<iops>

Maximum read I/O speed in operations per second.

iops_rd_max=<iops>

Maximum unthrottled read I/O pool speed in operations per second.

iops_wr=<iops>

Maximum write I/O speed in operations per second.

iops_wr_max=<iops>

Maximum unthrottled write I/O pool speed in operations per second.

iothread=boolean

Whether to use iothreads for this drive

mbps=<mbps>

Maximum r/w speed speed in megabytes per second.

mbps_max=<mbps>

Maximum unthrottled r/w pool speed in megabytes per second.

mbps_rd=<mbps>

Maximum read speed speed in megabytes per second.

mbps_rd_max=<mbps>

Maximum unthrottled read pool speed in megabytes per second.

mbps_wr=<mbps>

Maximum write speed speed in megabytes per second.

mbps_wr_max=<mbps>

Maximum unthrottled write pool speed in megabytes per second.

media=(cdrom | disk) (default=disk)

The drive’s media type.

queues=integer (2 - N)

Number of queues.

secs=integer

Force the drive’s physical geometry to have a specific sector count.

serial=<serial>

The drive’s reported serial number, url-encoded, up to 20 bytes long.

size=<DiskSize>

Disk size. This is purely informational and has no effect.

snapshot=boolean

Whether the drive should be included when making snapshots.

trans=(auto | lba | none)

Force disk geometry bios translation mode.

werror=(enospc | ignore | report | stop)

Write error action.

scsihw: (lsi | lsi53c810 | megasas | pvscsi | virtio-scsi-pci | virtio-scsi-single) (default=lsi)

SCSI controller model

serial[n]: (/dev/.+|socket)

Create a serial device inside the VM (n is 0 to 3), and pass through a host serial device (i.e. /dev/ttyS0), or create a unix socket on the host side (use qm terminal to open a terminal connection).

Note If you pass through a host serial device, it is no longer possible to migrate such machines - use with special care.
Caution Experimental! User reported problems with this option.
shares: integer (0 - 50000) (default=1000)

Amount of memory shares for auto-ballooning. The larger the number is, the more memory this VM gets. Number is relative to weights of all other running VMs. Using zero disables auto-ballooning

smbios1: [family=<string>] [,manufacturer=<string>] [,product=<string>] [,serial=<string>] [,sku=<string>] [,uuid=<UUID>] [,version=<string>]

Specify SMBIOS type 1 fields.

family=<string>

Set SMBIOS1 family string.

manufacturer=<string>

Set SMBIOS1 manufacturer.

product=<string>

Set SMBIOS1 product ID.

serial=<string>

Set SMBIOS1 serial number.

sku=<string>

Set SMBIOS1 SKU string.

uuid=<UUID>

Set SMBIOS1 UUID.

version=<string>

Set SMBIOS1 version.

smp: integer (1 - N) (default=1)

The number of CPUs. Please use option -sockets instead.

sockets: integer (1 - N) (default=1)

The number of CPU sockets.

startdate: (now | YYYY-MM-DD | YYYY-MM-DDTHH:MM:SS) (default=now)

Set the initial date of the real time clock. Valid format for date are: now or 2006-06-17T16:01:21 or 2006-06-17.

startup: `[[order=]\d+] [,up=\d+] [,down=\d+] `

Startup and shutdown behavior. Order is a non-negative number defining the general startup order. Shutdown in done with reverse ordering. Additionally you can set the up or down delay in seconds, which specifies a delay to wait before the next VM is started or stopped.

tablet: boolean (default=1)

Enable/disable the USB tablet device. This device is usually needed to allow absolute mouse positioning with VNC. Else the mouse runs out of sync with normal VNC clients. If you’re running lots of console-only guests on one host, you may consider disabling this to save some context switches. This is turned off by default if you use spice (-vga=qxl).

tdf: boolean (default=0)

Enable/disable time drift fix.

template: boolean (default=0)

Enable/disable Template.

unused[n]: string

Reference to unused volumes. This is used internally, and should not be modified manually.

usb[n]: [host=]<HOSTUSBDEVICE|spice> [,usb3=<1|0>]

Configure an USB device (n is 0 to 4).

host=<HOSTUSBDEVICE|spice>

The Host USB device or port or the value spice. HOSTUSBDEVICE syntax is: 

'bus-port(.port)*' (decimal numbers) or
'vendor_id:product_id' (hexadeciaml numbers) or
'spice'

You can use the lsusb -t command to list existing usb devices.

Note This option allows direct access to host hardware. So it is no longer possible to migrate such machines - use with special care.

The value spice can be used to add a usb redirection devices for spice.

usb3=boolean (default=0)

Specifies whether if given host option is a USB3 device or port (this does currently not work reliably with spice redirection and is then ignored).

vcpus: integer (1 - N) (default=0)

Number of hotplugged vcpus.

vga: (cirrus | qxl | qxl2 | qxl3 | qxl4 | serial0 | serial1 | serial2 | serial3 | std | vmware)

Select the VGA type. If you want to use high resolution modes (>= 1280x1024x16) then you should use the options std or vmware. Default is std for win8/win7/w2k8, and cirrus for other OS types. The qxl option enables the SPICE display sever. For win* OS you can select how many independent displays you want, Linux guests can add displays them self. You can also run without any graphic card, using a serial device as terminal.

virtio[n]: [file=]<volume> [,aio=<native|threads>] [,backup=<1|0>] [,bps=<bps>] [,bps_rd=<bps>] [,bps_wr=<bps>] [,cache=<none|writethrough|writeback|unsafe|directsync>] [,cyls=<integer>] [,detect_zeroes=<1|0>] [,discard=<ignore|on>] [,format=<image format>] [,heads=<integer>] [,iops=<iops>] [,iops_max=<iops>] [,iops_rd=<iops>] [,iops_rd_max=<iops>] [,iops_wr=<iops>] [,iops_wr_max=<iops>] [,iothread=<1|0>] [,mbps=<mbps>] [,mbps_max=<mbps>] [,mbps_rd=<mbps>] [,mbps_rd_max=<mbps>] [,mbps_wr=<mbps>] [,mbps_wr_max=<mbps>] [,media=<cdrom|disk>] [,rerror=<ignore|report|stop>] [,secs=<integer>] [,serial=<serial>] [,size=<DiskSize>] [,snapshot=<1|0>] [,trans=<none|lba|auto>] [,werror=<enospc|ignore|report|stop>]

Use volume as VIRTIO hard disk (n is 0 to 15).

aio=(native | threads)

AIO type to use.

backup=boolean

Whether the drive should be included when making backups.

bps=<bps>

Maximum r/w speed speed in bytes per second.

bps_rd=<bps>

Maximum read speed speed in bytes per second.

bps_wr=<bps>

Maximum write speed speed in bytes per second.

cache=(directsync | none | unsafe | writeback | writethrough)

The drive’s cache mode

cyls=integer

Force the drive’s physical geometry to have a specific cylinder count.

detect_zeroes=boolean

Controls whether to detect and try to optimize writes of zeroes.

discard=(ignore | on)

Controls whether to pass discard/trim requests to the underlying storage.

file=<volume>

The drive’s backing volume.

format=<image format>

The drive’s backing file’s data format.

heads=integer

Force the drive’s physical geometry to have a specific head count.

iops=<iops>

Maximum r/w I/O speed in operations per second.

iops_max=<iops>

Maximum unthrottled r/w I/O pool speed in operations per second.

iops_rd=<iops>

Maximum read I/O speed in operations per second.

iops_rd_max=<iops>

Maximum unthrottled read I/O pool speed in operations per second.

iops_wr=<iops>

Maximum write I/O speed in operations per second.

iops_wr_max=<iops>

Maximum unthrottled write I/O pool speed in operations per second.

iothread=boolean

Whether to use iothreads for this drive

mbps=<mbps>

Maximum r/w speed speed in megabytes per second.

mbps_max=<mbps>

Maximum unthrottled r/w pool speed in megabytes per second.

mbps_rd=<mbps>

Maximum read speed speed in megabytes per second.

mbps_rd_max=<mbps>

Maximum unthrottled read pool speed in megabytes per second.

mbps_wr=<mbps>

Maximum write speed speed in megabytes per second.

mbps_wr_max=<mbps>

Maximum unthrottled write pool speed in megabytes per second.

media=(cdrom | disk) (default=disk)

The drive’s media type.

rerror=(ignore | report | stop)

Read error action.

secs=integer

Force the drive’s physical geometry to have a specific sector count.

serial=<serial>

The drive’s reported serial number, url-encoded, up to 20 bytes long.

size=<DiskSize>

Disk size. This is purely informational and has no effect.

snapshot=boolean

Whether the drive should be included when making snapshots.

trans=(auto | lba | none)

Force disk geometry bios translation mode.

werror=(enospc | ignore | report | stop)

Write error action.

watchdog: [[model=]<i6300esb|ib700>] [,action=<reset|shutdown|poweroff|pause|debug|none>]

Create a virtual hardware watchdog device. Once enabled (by a guest action), the watchdog must be periodically polled by an agent inside the guest or else the watchdog will reset the guest (or execute the respective action specified)

action=(debug | none | pause | poweroff | reset | shutdown)

The action to perform if after activation the guest fails to poll the watchdog in time.

model=(i6300esb | ib700) (default=i6300esb)

Watchdog type to emulate.

Locks

Online migrations and backups (vzdump) set a lock to prevent incompatible concurrent actions on the affected VMs. Sometimes you need to remove such a lock manually (e.g., after a power failure).

qm unlock <vmid>