Qemu/KVM Virtual Machines

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Qemu (short form for Quick Emulator) is an open source 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 emulate 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.

Note You may sometimes encounter the term KVM (Kernel-based Virtual Machine). It means that Qemu is running with the support of the virtualization processor extensions, via the Linux kvm module. In the context of Proxmox VE Qemu and KVM can be used interchangeably as Qemu in Proxmox VE will always try to load the kvm module.

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

gui-create-vm-general.png

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

gui-create-vm-os.png

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 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 of 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.

    A SCSI controller of type VirtIO SCSI is the recommended setting if you aim for performance and is automatically selected for newly created Linux VMs since Proxmox VE 4.3. Linux distributions have support for this controller since 2012, and FreeBSD since 2014. For Windows OSes, you need to provide an extra iso containing the drivers during the installation. If you aim at maximum performance, you can select a SCSI controller of type VirtIO SCSI single which will allow you to select the IO Thread option. When selecting VirtIO SCSI single Qemu will create a new controller for each disk, instead of adding all disks to the same controller.

  • The Virtio controller, also called virtio-blk to distinguish from the VirtIO SCSI controller, is an older type of paravirtualized controller which has been superseded in features by the Virtio SCSI Controller.

gui-create-vm-hard-disk.png

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 you want the Proxmox VE storage replication mechanism to skip a disk when starting a replication job, you can set the Skip replication option on that disk. As of Proxmox VE 5.0, replication requires the disk images to be on a storage of type zfspool, so adding a disk image to other storages when the VM has replication configured requires to skip replication for this disk image.

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.

IO Thread

The option IO Thread can only be used when using a disk with the VirtIO controller, or with the SCSI controller, when the emulated controller type is VirtIO SCSI single. With this enabled, Qemu creates one I/O thread per storage controller, instead of a single thread for all I/O, so it increases performance when multiple disks are used and each disk has its own storage controller. Note that backups do not currently work with IO Thread enabled.

CPU

gui-create-vm-cpu.png

A CPU socket is a physical slot on a PC motherboard where you can plug a CPU. This CPU can then contain one or many cores, which are independent processing units. Whether you have a single CPU socket with 4 cores, or two CPU sockets with two cores is mostly irrelevant from a performance point of view. However some software is licensed depending on the number of sockets you have in your machine, in that case it makes sense to set the number of of sockets to what the license allows you, and increase the number of cores.

Increasing the number of virtual cpus (cores and sockets) will usually provide a performance improvement though that is heavily dependent on the use of the VM. Multithreaded applications will of course benefit from a large number of virtual cpus, as for each virtual cpu you add, Qemu will create a new thread of execution on the host system. If you’re not sure about the workload of your VM, it is usually a safe bet to set the number of Total cores to 2.

Note It is perfectly safe to set the overall number of total cores in all your VMs to be greater than the number of of cores you have on your server (ie. 4 VMs with each 4 Total cores running in a 8 core machine is OK) In that case the host system will balance the Qemu execution threads between your server cores just like if you were running a standard multithreaded application. However Proxmox VE will prevent you to allocate on a single machine more vcpus than physically available, as this will only bring the performance down due to the cost of context switches.

Qemu can emulate a number different of CPU types from 486 to the latest Xeon processors. Each new processor generation adds new features, like hardware assisted 3d rendering, random number generation, memory protection, etc … Usually you should select for your VM a processor type which closely matches the CPU of the host system, as it means that the host CPU features (also called CPU flags ) will be available in your VMs. If you want an exact match, you can set the CPU type to host in which case the VM will have exactly the same CPU flags as your host system.

This has a downside though. If you want to do a live migration of VMs between different hosts, your VM might end up on a new system with a different CPU type. If the CPU flags passed to the guest are missing, the qemu process will stop. To remedy this Qemu has also its own CPU type kvm64, that Proxmox VE uses by defaults. kvm64 is a Pentium 4 look a like CPU type, which has a reduced CPU flags set, but is guaranteed to work everywhere.

In short, if you care about live migration and moving VMs between nodes, leave the kvm64 default. If you don’t care about live migration, set the CPU type to host, as in theory this will give your guests maximum performance.

You can also optionally emulate a NUMA architecture in your VMs. The basics of the NUMA architecture mean that instead of having a global memory pool available to all your cores, the memory is spread into local banks close to each socket. This can bring speed improvements as the memory bus is not a bottleneck anymore. If your system has a NUMA architecture
[if the command numactl --hardware | grep available returns more than one node, then your host system has a NUMA architecture]
we recommend to activate the option, as this will allow proper distribution of the VM resources on the host system. This option is also required in Proxmox VE to allow hotplugging of cores and RAM to a VM.

If the NUMA option is used, it is recommended to set the number of sockets to the number of sockets of the host system.

Memory

For each VM you have the option to set a fixed size memory or asking Proxmox VE to dynamically allocate memory based on the current RAM usage of the host.

gui-create-vm-memory-fixed.png
Fixed Memory Allocation

When choosing a fixed size memory Proxmox VE will simply allocate what you specify to your VM.

Even when using a fixed memory size, the ballooning device gets added to the VM, because it delivers useful information such as how much memory the guest really uses. In general, you should leave ballooning enabled, but if you want to disable it (e.g. for debugging purposes), simply uncheck Ballooning or set

balloon: 0

in the configuration.

gui-create-vm-memory-dynamic.png
Automatic Memory Allocation

When choosing to automatically allocate memory, Proxmox VE will make sure that the minimum amount you specified is always available to the VM, and if RAM usage on the host is below 80%, will dynamically add memory to the guest up to the maximum memory specified.

When the host is becoming short on RAM, the VM will then release some memory back to the host, swapping running processes if needed and starting the oom killer in last resort. The passing around of memory between host and guest is done via a special balloon kernel driver running inside the guest, which will grab or release memory pages from the host.
[A good explanation of the inner workings of the balloon driver can be found here https://rwmj.wordpress.com/2010/07/17/virtio-balloon/]

When multiple VMs use the autoallocate facility, it is possible to set a Shares coefficient which indicates the relative amount of the free host memory that each VM shoud take. Suppose for instance you have four VMs, three of them running a HTTP server and the last one is a database server. To cache more database blocks in the database server RAM, you would like to prioritize the database VM when spare RAM is available. For this you assign a Shares property of 3000 to the database VM, leaving the other VMs to the Shares default setting of 1000. The host server has 32GB of RAM, and is curring using 16GB, leaving 32 * 80/100 - 16 = 9GB RAM to be allocated to the VMs. The database VM will get 9 * 3000 / (3000 + 1000 + 1000 + 1000) = 4.5 GB extra RAM and each HTTP server will get 1/5 GB.

All Linux distributions released after 2010 have the balloon kernel driver included. For Windows OSes, the balloon driver needs to be added manually and can incur a slowdown of the guest, so we don’t recommend using it on critical systems.

When allocating RAMs to your VMs, a good rule of thumb is always to leave 1GB of RAM available to the host.

Network Device

gui-create-vm-network.png

Each VM can have many Network interface controllers (NIC), of four different types:

  • Intel E1000 is the default, and emulates an Intel Gigabit network card.

  • the VirtIO paravirtualized NIC should be used if you aim for maximum performance. Like all VirtIO devices, the guest OS should have the proper driver installed.

  • the Realtek 8139 emulates an older 100 MB/s network card, and should only be used when emulating older operating systems ( released before 2002 )

  • the vmxnet3 is another paravirtualized device, which should only be used when importing a VM from another hypervisor.

Proxmox VE will generate for each NIC a random MAC address, so that your VM is addressable on Ethernet networks.

The NIC you added to the VM can follow one of two differents models:

  • in the default Bridged mode each virtual NIC is backed on the host by a tap device, ( a software loopback device simulating an Ethernet NIC ). This tap device is added to a bridge, by default vmbr0 in Proxmox VE. In this mode, VMs have direct access to the Ethernet LAN on which the host is located.

  • in the alternative NAT mode, each virtual NIC will only communicate with the Qemu user networking stack, where a builting router and DHCP server can provide network access. This built-in DHCP will serve adresses in the private 10.0.2.0/24 range. The NAT mode is much slower than the bridged mode, and should only be used for testing.

You can also skip adding a network device when creating a VM by selecting No network device.

Multiqueue

If you are using the VirtIO driver, you can optionally activate the Multiqueue option. This option allows the guest OS to process networking packets using multiple virtual CPUs, providing an increase in the total number of packets transfered.

When using the VirtIO driver with Proxmox VE, each NIC network queue is passed to the host kernel, where the queue will be processed by a kernel thread spawn by the vhost driver. With this option activated, it is possible to pass multiple network queues to the host kernel for each NIC.

When using Multiqueue, it is recommended to set it to a value equal to the number of Total Cores of your guest. You also need to set in the VM the number of multi-purpose channels on each VirtIO NIC with the ethtool command:

ethtool -L ens1 combined X

where X is the number of the number of vcpus of the VM.

You should note that setting the Multiqueue parameter to a value greater than one will increase the CPU load on the host and guest systems as the traffic increases. We recommend to set this option only when the VM has to process a great number of incoming connections, such as when the VM is running as a router, reverse proxy or a busy HTTP server doing long polling.

USB Passthrough

There are two different types of USB passthrough devices:

  • Host USB passtrough

  • SPICE USB passthrough

Host USB passthrough works by giving a VM a USB device of the host. This can either be done via the vendor- and product-id, or via the host bus and port.

The vendor/product-id looks like this: 0123:abcd, where 0123 is the id of the vendor, and abcd is the id of the product, meaning two pieces of the same usb device have the same id.

The bus/port looks like this: 1-2.3.4, where 1 is the bus and 2.3.4 is the port path. This represents the physical ports of your host (depending of the internal order of the usb controllers).

If a device is present in a VM configuration when the VM starts up, but the device is not present in the host, the VM can boot without problems. As soon as the device/port ist available in the host, it gets passed through.

Warning Using this kind of USB passthrough means that you cannot move a VM online to another host, since the hardware is only available on the host the VM is currently residing.

The second type of passthrough is SPICE USB passthrough. This is useful if you use a SPICE client which supports it. If you add a SPICE USB port to your VM, you can passthrough a USB device from where your SPICE client is, directly to the VM (for example an input device or hardware dongle).

BIOS and UEFI

In order to properly emulate a computer, QEMU needs to use a firmware. By default QEMU uses SeaBIOS for this, which is an open-source, x86 BIOS implementation. SeaBIOS is a good choice for most standard setups.

There are, however, some scenarios in which a BIOS is not a good firmware to boot from, e.g. if you want to do VGA passthrough.
[Alex Williamson has a very good blog entry about this. http://vfio.blogspot.co.at/2014/08/primary-graphics-assignment-without-vga.html]
In such cases, you should rather use OVMF, which is an open-source UEFI implemenation.
[See the OVMF Project http://www.tianocore.org/ovmf/]

If you want to use OVMF, there are several things to consider:

In order to save things like the boot order, there needs to be an EFI Disk. This disk will be included in backups and snapshots, and there can only be one.

You can create such a disk with the following command:

qm set <vmid> -efidisk0 <storage>:1,format=<format>

Where <storage> is the storage where you want to have the disk, and <format> is a format which the storage supports. Alternatively, you can create such a disk through the web interface with AddEFI Disk in the hardware section of a VM.

When using OVMF with a virtual display (without VGA passthrough), you need to set the client resolution in the OVMF menu(which you can reach with a press of the ESC button during boot), or you have to choose SPICE as the display type.

Automatic Start and Shutdown of Virtual Machines

After creating your VMs, you probably want them to start automatically when the host system boots. For this you need to select the option Start at boot from the Options Tab of your VM in the web interface, or set it with the following command:

qm set <vmid> -onboot 1
gui-qemu-edit-start-order.png
Start and Shutdown Order

In some case you want to be able to fine tune the boot order of your VMs, for instance if one of your VM is providing firewalling or DHCP to other guest systems. For this you can use the following parameters:

  • Start/Shutdown order: Defines the start order priority. E.g. set it to 1 if you want the VM to be the first to be started. (We use the reverse startup order for shutdown, so a machine with a start order of 1 would be the last to be shut down)

  • Startup delay: Defines the interval between this VM start and subsequent VMs starts . E.g. set it to 240 if you want to wait 240 seconds before starting other VMs.

  • Shutdown timeout: Defines the duration in seconds Proxmox VE should wait for the VM to be offline after issuing a shutdown command. By default this value is set to 60, which means that Proxmox VE will issue a shutdown request, wait 60s for the machine to be offline, and if after 60s the machine is still online will notify that the shutdown action failed.

Note VMs managed by the HA stack do not follow the start on boot and boot order options currently. Those VMs will be skipped by the startup and shutdown algorithm as the HA manager itself ensures that VMs get started and stopped.

Please note that machines without a Start/Shutdown order parameter will always start after those where the parameter is set, and this parameter only makes sense between the machines running locally on a host, and not cluster-wide.

Migration

gui-qemu-migrate.png

If you have a cluster, you can migrate your VM to another host with

qm migrate <vmid> <target>

There are generally two mechanisms for this

  • Online Migration (aka Live Migration)

  • Offline Migration

Online Migration

When your VM is running and it has no local resources defined (such as disks on local storage, passed through devices, etc.) you can initiate a live migration with the -online flag.

How it works

This starts a Qemu Process on the target host with the incoming flag, which means that the process starts and waits for the memory data and device states from the source Virtual Machine (since all other resources, e.g. disks, are shared, the memory content and device state are the only things left to transmit).

Once this connection is established, the source begins to send the memory content asynchronously to the target. If the memory on the source changes, those sections are marked dirty and there will be another pass of sending data. This happens until the amount of data to send is so small that it can pause the VM on the source, send the remaining data to the target and start the VM on the target in under a second.

Requirements

For Live Migration to work, there are some things required:

  • The VM has no local resources (e.g. passed through devices, local disks, etc.)

  • The hosts are in the same Proxmox VE cluster.

  • The hosts have a working (and reliable) network connection.

  • The target host must have the same or higher versions of the Proxmox VE packages. (It might work the other way, but this is never guaranteed)

Offline Migration

If you have local resources, you can still offline migrate your VMs, as long as all disk are on storages, which are defined on both hosts. Then the migration will copy the disk over the network to the target host.

Copies and Clones

gui-qemu-full-clone.png

VM installation is usually done using an installation media (CD-ROM) from the operation system vendor. Depending on the OS, this can be a time consuming task one might want to avoid.

An easy way to deploy many VMs of the same type is to copy an existing VM. We use the term clone for such copies, and distinguish between linked and full clones.

Full Clone

The result of such copy is an independent VM. The new VM does not share any storage resources with the original.

It is possible to select a Target Storage, so one can use this to migrate a VM to a totally different storage. You can also change the disk image Format if the storage driver supports several formats.

Note A full clone need to read and copy all VM image data. This is usually much slower than creating a linked clone.

Some storage types allows to copy a specific Snapshot, which defaults to the current VM data. This also means that the final copy never includes any additional snapshots from the original VM.

Linked Clone

Modern storage drivers supports a way to generate fast linked clones. Such a clone is a writable copy whose initial contents are the same as the original data. Creating a linked clone is nearly instantaneous, and initially consumes no additional space.

They are called linked because the new image still refers to the original. Unmodified data blocks are read from the original image, but modification are written (and afterwards read) from a new location. This technique is called Copy-on-write.

This requires that the original volume is read-only. With Proxmox VE one can convert any VM into a read-only Template). Such templates can later be used to create linked clones efficiently.

Note You cannot delete the original template while linked clones exists.

It is not possible to change the Target storage for linked clones, because this is a storage internal feature.

The Target node option allows you to create the new VM on a different node. The only restriction is that the VM is on shared storage, and that storage is also available on the target node.

To avoid resource conflicts, all network interface MAC addresses gets randomized, and we generate a new UUID for the VM BIOS (smbios1) setting.

Virtual Machine Templates

One can convert a VM into a Template. Such templates are read-only, and you can use them to create linked clones.

Note It is not possible to start templates, because this would modify the disk images. If you want to change the template, create a linked clone and modify that.

Importing Virtual Machines from foreign hypervisors

A VM export from a foreign hypervisor takes usually the form of one or more disk images, with a configuration file describing the settings of the VM (RAM, number of cores).
The disk images can be in the vmdk format, if the disks come from VMware or VirtualBox, or qcow2 if the disks come from a KVM hypervisor. The most popular configuration format for VM exports is the OVF standard, but in practice interoperation is limited because many settings are not implemented in the standard itself, and hypervisors export the supplementary information in non-standard extensions.

Besides the problem of format, importing disk images from other hypervisors may fail if the emulated hardware changes too much from one hypervisor to another. Windows VMs are particularly concerned by this, as the OS is very picky about any changes of hardware. This problem may be solved by installing the MergeIDE.zip utility available from the Internet before exporting and choosing a hard disk type of IDE before booting the imported Windows VM.

Finally there is the question of paravirtualized drivers, which improve the speed of the emulated system and are specific to the hypervisor. GNU/Linux and other free Unix OSes have all the necessary drivers installed by default and you can switch to the paravirtualized drivers right after importing the VM. For Windows VMs, you need to install the Windows paravirtualized drivers by yourself.

GNU/Linux and other free Unix can usually be imported without hassle. Note that we cannot guarantee a successful import/export of Windows WM in all cases due to the problems above.

Step-by-step example of a Windows disk image import

Microsoft provides Virtual Machines exports in different formats for browser testing. We are going to use one of these to demonstrate a VMDK import.

Download the export zip

After getting informed about the user agreement, choose the Microsoft Edge on Windows 10 Virtual Machine for the VMware platform, and download the zip.

Extract the disk image from the zip

Using the unzip utility or any archiver of your choice, unpack the zip, and copy via ssh/scp the vmdk file to your Proxmox VE host.

Create a new virtual machine and import the disk

Create a virtual machine with 2 cores, 2GB RAM, and one NIC on the default vmbr0 bridge:

qm create 999 -net0 e1000,bridge=vmbr0 -name Win10 -memory 2048 -bootdisk sata0

Import the disk image to the local-lvm storage:

qm importdisk 999 MSEdge "MSEdge - Win10_preview.vmdk" local-lvm

The disk will be marked as Unused in the VM 999 configuration. After that you can go in the GUI, in the VM Hardware, Edit the unused disk and set the Bus/Device to SATA/0. The VM is ready to be started.

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

Using an iso file uploaded on the local storage, create a VM with a 4 GB IDE disk on the local-lvm storage

qm create 300 -ide0 local-lvm:4 -net0 e1000 -cdrom local:iso/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

VM configuration files are stored inside the Proxmox cluster file system, and can be accessed at /etc/pve/qemu-server/<VMID>.conf. Like other files stored inside /etc/pve/, they get automatically replicated to all other cluster nodes.

Note VMIDs < 100 are reserved for internal purposes, and VMIDs need to be unique cluster wide.
Example VM Configuration
cores: 1
sockets: 1
memory: 512
name: webmail
ostype: l26
bootdisk: virtio0
net0: e1000=EE:D2:28:5F:B6:3E,bridge=vmbr0
virtio0: local:vm-100-disk-1,size=32G

Those configuration files are simple text files, and you can edit them using a normal text editor (vi, nano, …). This is sometimes useful to do small corrections, but keep in mind that you need to restart the VM to apply such changes.

For that reason, it is usually better to use the qm command to generate and modify those files, or do the whole thing using the GUI. Our toolkit is smart enough to instantaneously apply most changes to running VM. This feature is called "hot plug", and there is no need to restart the VM in that case.

File Format

VM configuration files use a simple colon separated key/value format. Each line has the following format:

# this is a comment
OPTION: value

Blank lines in those files are ignored, and lines starting with a # character are treated as comments and are also ignored.

Snapshots

When you create a snapshot, qm stores the configuration at snapshot time into a separate snapshot section within the same configuration file. For example, after creating a snapshot called “testsnapshot”, your configuration file will look like this:

VM configuration with snapshot
memory: 512
swap: 512
parent: testsnaphot
...

[testsnaphot]
memory: 512
swap: 512
snaptime: 1457170803
...

There are a few snapshot related properties like parent and snaptime. The parent property is used to store the parent/child relationship between snapshots. snaptime is the snapshot creation time stamp (Unix epoch).

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=]<enum> [,hidden=<1|0>]

Emulated CPU type.

cputype=<486 | Broadwell | Broadwell-noTSX | Conroe | Haswell | Haswell-noTSX | IvyBridge | Nehalem | Opteron_G1 | Opteron_G2 | Opteron_G3 | Opteron_G4 | Opteron_G5 | Penryn | SandyBridge | Skylake-Client | Westmere | athlon | core2duo | coreduo | host | kvm32 | kvm64 | pentium | pentium2 | pentium3 | phenom | qemu32 | qemu64> (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 = 1024)

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.

efidisk0: [file=]<volume> [,format=<enum>] [,size=<DiskSize>]

Configure a Disk for storing EFI vars

file=<volume>

The drive’s backing volume.

format=<cloop | cow | qcow | qcow2 | qed | raw | vmdk>

The drive’s backing file’s data format.

size=<DiskSize>

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

freeze: <boolean>

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

hostpci[n]: [host=]<HOSTPCIID[;HOSTPCIID2...]> [,pcie=<1|0>] [,rombar=<1|0>] [,romfile=<string>] [,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.

romfile=<string>

Custom pci device rom filename (must be located in /usr/share/kvm/).

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.

hugepages: <1024 | 2 | any>

Enable/disable hugepages memory.

ide[n]: [file=]<volume> [,aio=<native|threads>] [,backup=<1|0>] [,bps=<bps>] [,bps_max_length=<seconds>] [,bps_rd=<bps>] [,bps_rd_max_length=<seconds>] [,bps_wr=<bps>] [,bps_wr_max_length=<seconds>] [,cache=<enum>] [,cyls=<integer>] [,detect_zeroes=<1|0>] [,discard=<ignore|on>] [,format=<enum>] [,heads=<integer>] [,iops=<iops>] [,iops_max=<iops>] [,iops_max_length=<seconds>] [,iops_rd=<iops>] [,iops_rd_max=<iops>] [,iops_rd_max_length=<seconds>] [,iops_wr=<iops>] [,iops_wr_max=<iops>] [,iops_wr_max_length=<seconds>] [,mbps=<mbps>] [,mbps_max=<mbps>] [,mbps_rd=<mbps>] [,mbps_rd_max=<mbps>] [,mbps_wr=<mbps>] [,mbps_wr_max=<mbps>] [,media=<cdrom|disk>] [,model=<model>] [,replicate=<1|0>] [,rerror=<ignore|report|stop>] [,secs=<integer>] [,serial=<serial>] [,size=<DiskSize>] [,snapshot=<1|0>] [,trans=<none|lba|auto>] [,werror=<enum>]

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 in bytes per second.

bps_max_length=<seconds>

Maximum length of I/O bursts in seconds.

bps_rd=<bps>

Maximum read speed in bytes per second.

bps_rd_max_length=<seconds>

Maximum length of read I/O bursts in seconds.

bps_wr=<bps>

Maximum write speed in bytes per second.

bps_wr_max_length=<seconds>

Maximum length of write I/O bursts in seconds.

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=<cloop | cow | qcow | qcow2 | qed | raw | vmdk>

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 in operations per second.

iops_max=<iops>

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

iops_max_length=<seconds>

Maximum length of I/O bursts in seconds.

iops_rd=<iops>

Maximum read I/O in operations per second.

iops_rd_max=<iops>

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

iops_rd_max_length=<seconds>

Maximum length of read I/O bursts in seconds.

iops_wr=<iops>

Maximum write I/O in operations per second.

iops_wr_max=<iops>

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

iops_wr_max_length=<seconds>

Maximum length of write I/O bursts in seconds.

mbps=<mbps>

Maximum r/w speed in megabytes per second.

mbps_max=<mbps>

Maximum unthrottled r/w pool in megabytes per second.

mbps_rd=<mbps>

Maximum read speed in megabytes per second.

mbps_rd_max=<mbps>

Maximum unthrottled read pool in megabytes per second.

mbps_wr=<mbps>

Maximum write speed in megabytes per second.

mbps_wr_max=<mbps>

Maximum unthrottled write pool 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.

replicate=<boolean> (default = 1)

Whether the drive should considered for replication jobs.

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=]<enum> [,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=<e1000 | e1000-82540em | e1000-82544gc | e1000-82545em | i82551 | i82557b | i82559er | ne2k_isa | ne2k_pci | pcnet | rtl8139 | virtio | vmxnet3>

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 | win10 | 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_max_length=<seconds>] [,bps_rd=<bps>] [,bps_rd_max_length=<seconds>] [,bps_wr=<bps>] [,bps_wr_max_length=<seconds>] [,cache=<enum>] [,cyls=<integer>] [,detect_zeroes=<1|0>] [,discard=<ignore|on>] [,format=<enum>] [,heads=<integer>] [,iops=<iops>] [,iops_max=<iops>] [,iops_max_length=<seconds>] [,iops_rd=<iops>] [,iops_rd_max=<iops>] [,iops_rd_max_length=<seconds>] [,iops_wr=<iops>] [,iops_wr_max=<iops>] [,iops_wr_max_length=<seconds>] [,mbps=<mbps>] [,mbps_max=<mbps>] [,mbps_rd=<mbps>] [,mbps_rd_max=<mbps>] [,mbps_wr=<mbps>] [,mbps_wr_max=<mbps>] [,media=<cdrom|disk>] [,replicate=<1|0>] [,rerror=<ignore|report|stop>] [,secs=<integer>] [,serial=<serial>] [,size=<DiskSize>] [,snapshot=<1|0>] [,trans=<none|lba|auto>] [,werror=<enum>]

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 in bytes per second.

bps_max_length=<seconds>

Maximum length of I/O bursts in seconds.

bps_rd=<bps>

Maximum read speed in bytes per second.

bps_rd_max_length=<seconds>

Maximum length of read I/O bursts in seconds.

bps_wr=<bps>

Maximum write speed in bytes per second.

bps_wr_max_length=<seconds>

Maximum length of write I/O bursts in seconds.

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=<cloop | cow | qcow | qcow2 | qed | raw | vmdk>

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 in operations per second.

iops_max=<iops>

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

iops_max_length=<seconds>

Maximum length of I/O bursts in seconds.

iops_rd=<iops>

Maximum read I/O in operations per second.

iops_rd_max=<iops>

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

iops_rd_max_length=<seconds>

Maximum length of read I/O bursts in seconds.

iops_wr=<iops>

Maximum write I/O in operations per second.

iops_wr_max=<iops>

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

iops_wr_max_length=<seconds>

Maximum length of write I/O bursts in seconds.

mbps=<mbps>

Maximum r/w speed in megabytes per second.

mbps_max=<mbps>

Maximum unthrottled r/w pool in megabytes per second.

mbps_rd=<mbps>

Maximum read speed in megabytes per second.

mbps_rd_max=<mbps>

Maximum unthrottled read pool in megabytes per second.

mbps_wr=<mbps>

Maximum write speed in megabytes per second.

mbps_wr_max=<mbps>

Maximum unthrottled write pool in megabytes per second.

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

The drive’s media type.

replicate=<boolean> (default = 1)

Whether the drive should considered for replication jobs.

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_max_length=<seconds>] [,bps_rd=<bps>] [,bps_rd_max_length=<seconds>] [,bps_wr=<bps>] [,bps_wr_max_length=<seconds>] [,cache=<enum>] [,cyls=<integer>] [,detect_zeroes=<1|0>] [,discard=<ignore|on>] [,format=<enum>] [,heads=<integer>] [,iops=<iops>] [,iops_max=<iops>] [,iops_max_length=<seconds>] [,iops_rd=<iops>] [,iops_rd_max=<iops>] [,iops_rd_max_length=<seconds>] [,iops_wr=<iops>] [,iops_wr_max=<iops>] [,iops_wr_max_length=<seconds>] [,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>] [,replicate=<1|0>] [,rerror=<ignore|report|stop>] [,scsiblock=<1|0>] [,secs=<integer>] [,serial=<serial>] [,size=<DiskSize>] [,snapshot=<1|0>] [,trans=<none|lba|auto>] [,werror=<enum>]

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 in bytes per second.

bps_max_length=<seconds>

Maximum length of I/O bursts in seconds.

bps_rd=<bps>

Maximum read speed in bytes per second.

bps_rd_max_length=<seconds>

Maximum length of read I/O bursts in seconds.

bps_wr=<bps>

Maximum write speed in bytes per second.

bps_wr_max_length=<seconds>

Maximum length of write I/O bursts in seconds.

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=<cloop | cow | qcow | qcow2 | qed | raw | vmdk>

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 in operations per second.

iops_max=<iops>

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

iops_max_length=<seconds>

Maximum length of I/O bursts in seconds.

iops_rd=<iops>

Maximum read I/O in operations per second.

iops_rd_max=<iops>

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

iops_rd_max_length=<seconds>

Maximum length of read I/O bursts in seconds.

iops_wr=<iops>

Maximum write I/O in operations per second.

iops_wr_max=<iops>

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

iops_wr_max_length=<seconds>

Maximum length of write I/O bursts in seconds.

iothread=<boolean>

Whether to use iothreads for this drive

mbps=<mbps>

Maximum r/w speed in megabytes per second.

mbps_max=<mbps>

Maximum unthrottled r/w pool in megabytes per second.

mbps_rd=<mbps>

Maximum read speed in megabytes per second.

mbps_rd_max=<mbps>

Maximum unthrottled read pool in megabytes per second.

mbps_wr=<mbps>

Maximum write speed in megabytes per second.

mbps_wr_max=<mbps>

Maximum unthrottled write pool in megabytes per second.

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

The drive’s media type.

queues=<integer> (2 - N)

Number of queues.

replicate=<boolean> (default = 1)

Whether the drive should considered for replication jobs.

rerror=<ignore | report | stop>

Read error action.

scsiblock=<boolean> (default = 0)

whether to use scsi-block for full passthrough of host block device

Warning can lead to I/O errors in combination with low memory or high memory fragmentation on host
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_max_length=<seconds>] [,bps_rd=<bps>] [,bps_rd_max_length=<seconds>] [,bps_wr=<bps>] [,bps_wr_max_length=<seconds>] [,cache=<enum>] [,cyls=<integer>] [,detect_zeroes=<1|0>] [,discard=<ignore|on>] [,format=<enum>] [,heads=<integer>] [,iops=<iops>] [,iops_max=<iops>] [,iops_max_length=<seconds>] [,iops_rd=<iops>] [,iops_rd_max=<iops>] [,iops_rd_max_length=<seconds>] [,iops_wr=<iops>] [,iops_wr_max=<iops>] [,iops_wr_max_length=<seconds>] [,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>] [,replicate=<1|0>] [,rerror=<ignore|report|stop>] [,secs=<integer>] [,serial=<serial>] [,size=<DiskSize>] [,snapshot=<1|0>] [,trans=<none|lba|auto>] [,werror=<enum>]

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 in bytes per second.

bps_max_length=<seconds>

Maximum length of I/O bursts in seconds.

bps_rd=<bps>

Maximum read speed in bytes per second.

bps_rd_max_length=<seconds>

Maximum length of read I/O bursts in seconds.

bps_wr=<bps>

Maximum write speed in bytes per second.

bps_wr_max_length=<seconds>

Maximum length of write I/O bursts in seconds.

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=<cloop | cow | qcow | qcow2 | qed | raw | vmdk>

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 in operations per second.

iops_max=<iops>

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

iops_max_length=<seconds>

Maximum length of I/O bursts in seconds.

iops_rd=<iops>

Maximum read I/O in operations per second.

iops_rd_max=<iops>

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

iops_rd_max_length=<seconds>

Maximum length of read I/O bursts in seconds.

iops_wr=<iops>

Maximum write I/O in operations per second.

iops_wr_max=<iops>

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

iops_wr_max_length=<seconds>

Maximum length of write I/O bursts in seconds.

iothread=<boolean>

Whether to use iothreads for this drive

mbps=<mbps>

Maximum r/w speed in megabytes per second.

mbps_max=<mbps>

Maximum unthrottled r/w pool in megabytes per second.

mbps_rd=<mbps>

Maximum read speed in megabytes per second.

mbps_rd_max=<mbps>

Maximum unthrottled read pool in megabytes per second.

mbps_wr=<mbps>

Maximum write speed in megabytes per second.

mbps_wr_max=<mbps>

Maximum unthrottled write pool in megabytes per second.

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

The drive’s media type.

replicate=<boolean> (default = 1)

Whether the drive should considered for replication jobs.

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=<enum>]

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, snapshots 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>
Caution Only do that if you are sure the action which set the lock is no longer running.