# Configuring virtual machines

Whereas gave you a quick introduction to VirtualBox and how to get your first virtual machine running, the following chapter describes in detail how to configure virtual machines.

You have considerable latitude in deciding what virtual hardware will be provided to the guest. The virtual hardware can be used for communicating with the host system or with other guests. For instance, if you provide VirtualBox with the image of a CD-ROM in an ISO file, VirtualBox can present this image to a guest system as if it were a physical CD-ROM. Similarly, you can give a guest system access to the real network via its virtual network card, and, if you so choose, give the host system, other guests, or computers on the Internet access to the guest system.

## Supported guest operating systems

Since VirtualBox is designed to provide a generic virtualization environment for x86 systems, it may run operating systems of any kind, even those not listed here. However, the focus is to optimize VirtualBox for the following guest systems:

Windows NT 4.0

  All versions, editions and service packs are fully supported; however, there are some issues with older service packs. We recommend to install service pack 6a. Guest Additions are available with a limited feature set.

Windows 2000 / XP / Server 2003 / Vista / Server 2008 / Windows 7

  All versions, editions and service packs are fully supported (including 64-bit versions, under the preconditions listed below). Guest Additions are available.

DOS / Windows 3.x / 95 / 98 / ME

  Limited testing has been performed. Use beyond legacy installation mechanisms not recommended. No Guest Additions available.

Linux 2.4

  Limited support.

Linux 2.6

  All versions/editions are fully supported (32 bits and 64 bits). Guest Additions are available.

  We strongly recommend using a Linux kernel version 2.6.13 or higher for better performance.

  Certain Linux kernel releases have bugs that prevent them from executing in a virtual environment; please see for details.

Solaris 10, OpenSolaris

  Fully supported (32 bits and 64 bits). Guest Additions are available.

FreeBSD

  Requires hardware virtualization to be enabled. Limited support. Guest Additions are not available yet.

OpenBSD

  Requires hardware virtualization to be enabled. Versions 3.7 and later are supported. Guest Additions are not available yet.

OS/2 Warp 4.5

  Requires hardware virtualization to be enabled. We officially support MCP2 only; other OS/2 versions may or may not work. Guest Additions are available with a limited feature set. See .

Mac OS X Server

  VirtualBox 3.2 added experimental support for Mac OS X Server guests, but this comes with restrictions. Please see the following section as well as .

### Mac OS X Server guests

Starting with version 3.2, VirtualBox has experimental support for Mac OS X Server guests. This allows you to install and execute unmodified versions of Mac OS X Server on supported host hardware.

Whereas competing solutions perform modifications to the Mac OS X Server install DVDs (e.g. different boot loader and replaced files), VirtualBox is the first product to provide the modern PC architecture expected by OS X without requiring any "hacks".

You should be aware of a number of important issues before attempting to install a Mac OS X Server guest:

1. Mac OS X is commercial, licensed software and contains both license and technical restrictions that limit its use to certain hardware and usage scenarios. It is important that you understand and obey these restrictions.

   In particular, for most versions of Mac OS X Server, Apple prohibits installing them on non-Apple hardware. Also, only the server versions of Mac OS X are designed to be used in a virtual environment; as a result, VirtualBox does not support client versions of Mac OS X as a guest.

   These license restrictions are also enforced on a technical level. Mac OS X Server verifies whether it is running on Apple hardware, and most DVDs that that come with Apple hardware even check for an exact model. These restrictions are not circumvented by VirtualBox and continue to apply.

2. Only CPUs known and tested by Apple are supported. As a result, if your Intel CPU is newer than the build of Mac OS X Server, or if you have a non-Intel CPU, it will most likely panic during bootup with an "Unsupported CPU" exception. It is generally best to use the Mac OS X Server DVD that came with your Apple hardware.

3. The Mac OS X Server installer expects the harddisk to be partitioned so when it does not offer a selection, you have to launch the Disk Utility from the "Tools" menu and partition the hard disk. Then close the Disk Utility and proceed with the installation.

4. In addition, as Mac OS X Server support in VirtualBox is currently still experimental, please refer also to .

### 64-bit guests

VirtualBox supports 64-bit guest operating systems, even on 32-bit host operating systems, 64-bit guest support was added with VirtualBox 2.0; support for 64-bit guests on 32-bit hosts was added with VirtualBox 2.1. provided that the following conditions are met:

1. You need a 64-bit processor with hardware virtualization support (see ).

2. You must enable hardware virtualization for the particular VM for which you want 64-bit support; software virtualization is not supported for 64-bit VMs.

3. If you want to use 64-bit guest support on a 32-bit host operating system, you must also select a 64-bit operating system for the particular VM. Since supporting 64 bits on 32-bit hosts incurs additional overhead, VirtualBox only enables this support upon explicit request.

   On 64-bit hosts (which typically come with hardware virtualization support), 64-bit guest operating systems are always supported regardless of settings, so you can simply install a 64-bit operating system in the guest.

On any host, you should enable the I/O APIC for virtual machines that you intend to use in 64-bit mode. This is especially true for 64-bit Windows VMs. See . In addition, for 64-bit Windows guests, you should make sure that the VM uses the Intel networking device, since there is no 64-bit driver support for the AMD PCNet card; see .

If you use the "Create VM" wizard of the VirtualBox graphical user interface (see ), VirtualBox will automatically use the correct settings for each selected 64-bit operating system type.

## Emulated hardware

VirtualBox virtualizes nearly all hardware of the host. Depending on a VM's configuration, the guest will see the following virtual hardware:

- Input devices. By default, VirtualBox emulates a standard PS/2 keyboard and mouse. These devices are supported by almost all past and present operating systems.

  In addition, VirtualBox can provide virtual USB input devices to avoid having to capture mouse and keyboard, as described in .

- Graphics. The VirtualBox graphics device (sometimes referred to as VGA device) is, unlike nearly all other emulated devices, not based on any physical counterpart. It is a simple, synthetic device which provides compatibility with standard VGA and several extended registers used by the VESA BIOS Extensions (VBE).

- Storage. VirtualBox currently emulates the standard ATA interface found on Intel PIIX3/PIIX4 chips, the SATA (AHCI) interface, and two SCSI adapters (LSI Logic and BusLogic); see for details. Whereas providing one of these would be enough for VirtualBox by itself, this multitude of storage adapters is required for compatibility with other hypervisors. Windows is particularly picky about its boot devices, and migrating VMs between hypervisors is very difficult or impossible if the storage controllers are different.

- Networking. See .

- USB. VirtualBox emulates two USB host controllers, EHCI and OHCI. There is a need for two host controllers because OHCI only handles USB low- and full-speed devices (both USB 1.x and 2.0), while EHCI only handles high-speed devices (USB 2.0 only). The emulated USB controllers do not communicate directly with devices on the host but rather with a virtual USB layer which abstracts the USB protocol and allows the use of remote USB devices.

- Audio. See .

## General settings

In the Settings window, under "General", you can configure the most fundamental aspects of the virtual machine such as memory and essential hardware. There are three tabs, "Basic", "Advanced" and "Description".

### "Basic" tab

Under the "Basic" tab of the "General" settings category, you can find these settings:

Name

  The name under which the VM is shown in the list of VMs in the main window. Under this name, VirtualBox also saves the VM's configuration files. By changing the name, VirtualBox renames these files as well. As a result, you can only use characters which are allowed in your host operating system's file names.

  Note that internally, VirtualBox uses unique identifiers (UUIDs) to identify virtual machines. You can display these with `VBoxManage`.

Operating system / version

  The type of the guest operating system that is (or will be) installed in the VM. This is the same setting that was specified in the "New Virtual Machine" wizard, as described in .

  Whereas the default settings of a newly created VM depend on the selected operating system type, changing the type later has no effect on VM settings; this value is then purely informational and decorative.

### "Advanced" tab

Snapshot folder

  By default, VirtualBox saves snapshot data together with your other VirtualBox configuration data; see . With this setting, you can specify any other folder for each VM.

Shared clipboard

  You can select here whether the clipboard of the guest operating system should be shared with that of your host. If you select "Bidirectional", then VirtualBox will always make sure that both clipboards contain the same data. If you select "Host to guest" or "Guest to host", then VirtualBox will only ever copy clipboard data in one direction.

  Clipboard sharing requires that the VirtualBox Guest Additions be installed. As a result, this setting has no effect otherwise; see for details.

Removable media: remember runtime changes

  If this is checked, VirtualBox will save the state of what media has been mounted between several runs of a virtual machine.

Mini toolbar

  In full screen or seamless mode, VirtualBox can display a small toolbar that contains some of the items that are normally available from the virtual machine's menu bar. This toolbar reduces itself to a small gray line unless you move the mouse over it. With the toolbar, you can return from full screen or seamless mode, control machine execution or enable certain devices. If you don't want to see the toolbar, disable this setting.

### "Description" tab

Here you can enter any description for your virtual machine, if you want. This has no effect on the functionality of the machine, but you may find this space useful to note down things like the configuration of a virtual machine and the software that has been installed into it.

## System settings

The "System" category groups various settings that are related to the basic hardware that is presented to the virtual machine.

As the activation mechanism of Microsoft Windows is sensitive to hardware changes, if you are changing hardware settings for a Windows guest, some of these changes may trigger a request for another activation with Microsoft.

### "Motherboard" tab

On the "Motherboard" tab, you can influence virtual hardware that would normally be on the motherboard of a real computer.

Base memory

  This sets the amount of RAM that is allocated and given to the VM when it is running. The specified amount of memory will be requested from the host operating system, so it must be available or made available as free memory on the host when attempting to start the VM and will not be available to the host while the VM is running. This is the same setting that was specified in the "New Virtual Machine" wizard, as described with guidelines under above.

  Generally, it is possible to change the memory size after installing the guest operating system (provided you do not reduce the memory to an amount where the operating system would no longer boot).

Boot order

  This setting determines the order in which the guest operating system will attempt to boot from the various virtual boot devices. Analogous to a real PC's BIOS setting, VirtualBox can tell a guest OS to start from the virtual floppy, the virtual CD/DVD drive, the virtual hard drive (each of these as defined by the other VM settings), the network, or none of these.

  If you select "Network", the VM will attempt to boot from a network via the PXE mechanism. This needs to be configured in detail on the command line; please see .

Chipset

  Here you can select which chipset will be presented to the virtual machine. Before VirtualBox 4.0, PIIX3 was the only available option here. For modern guest operating systems such as Mac OS X server, that old chipset is no longer well supported. As a result, VirtualBox 4.0 introduced an emulation of the more modern ICH9 chipset, which supports PCI express, three PCI buses, PCI-to-PCI bridges and Message Signalled Interrupts (MSI). This allows modern operating systems to address more PCI devices and no longer requires IRQ sharing.

Enable I/O APIC

  Advanced Programmable Interrupt Controllers (APICs) are a newer x86 hardware feature that have replaced old-style Programmable Interrupt Controllers (PICs) in recent years. With an I/O APIC, operating systems can use more than 16 interrupt requests (IRQs) and therefore avoid IRQ sharing for improved reliability.

  Enabling the I/O APIC is required for 64-bit guest operating systems, especially Windows Vista; it is also required if you want to use more than one virtual CPU in a virtual machine.

  However, software support for I/O APICs has been unreliable with some operating systems other than Windows. Also, the use of an I/O APIC slightly increases the overhead of virtualization and therefore slows down the guest OS a little.

  All Windows operating systems starting with Windows 2000 install different kernels depending on whether an I/O APIC is available. As with ACPI, the I/O APIC therefore must not be turned off after installation of a Windows guest OS. Turning it on after installation will have no effect however.

Enable EFI

  This enables Extensible Firmware Interface (EFI), which replaces the legacy BIOS and may be useful for certain advanced use cases. Please refer to for details.

Hardware clock in UTC time

  If checked, VirtualBox will report the system time in UTC format to the guest instead of local (host) time. This affects how the virtual real-time clock (RTC) operates and may be useful for Unix-like guest operating systems, which typically expect the hardware clock to be set to UTC.

Enable absolute pointing device

  If enabled, VirtualBox reports to the virtual machine that a USB tablet device is present and communicates mouse events to the virtual machine through this device. If disabled, mouse events are communicated through a traditional PS/2 virtual mouse device.

  Using the virtual USB tablet has the advantage that movements are reported in absolute coordinates (instead of as relative position changes), which allows VirtualBox to translate mouse events over the VM window into tablet events without having to "capture" the mouse in the guest as described in . This makes using the VM less tedious even if Guest Additions are not installed. The virtual USB tablet was added with VirtualBox 3.2. Depending on the guest operating system selected, this is now enabled by default for new virtual machines.

In addition, you can turn off the Advanced Configuration and Power Interface (ACPI) which VirtualBox presents to the guest operating system by default. ACPI is the current industry standard to allow operating systems to recognize hardware, configure motherboards and other devices and manage power. As all modern PCs contain this feature and Windows and Linux have been supporting it for years, it is also enabled by default in VirtualBox. It can only be turned off on the command line; see .

All Windows operating systems starting with Windows 2000 install different kernels depending on whether ACPI is available, so ACPI must not be turned off after installation of a Windows guest OS. Turning it on after installation will have no effect however.

### "Processor" tab

On the "Processor" tab, you can set how many virtual CPU cores the guest operating systems should see. Starting with version 3.0, VirtualBox supports symmetrical multiprocessing (SMP) and can present up to 32 virtual CPU cores to each virtual machine.

You should not, however, configure virtual machines to use more CPU cores than you have available physically.

In addition, the "Enable PAE/NX" setting determines whether the PAE and NX capabilities of the host CPU will be exposed to the virtual machine. PAE stands for "Physical Address Extension". Normally, if enabled and supported by the operating system, then even a 32-bit x86 CPU can access more than 4 GB of RAM. This is made possible by adding another 4 bits to memory addresses, so that with 36 bits, up to 64 GB can be addressed. Some operating systems (such as Ubuntu Server) require PAE support from the CPU and cannot be run in a virtual machine without it.

With virtual machines running modern server operating systems, VirtualBox also supports CPU hot-plugging. For details about this, please refer to .

### "Acceleration" tab

On this page, you can determine whether and how VirtualBox should use hardware virtualization extensions that your host CPU may support. This is the case with most CPUs built after 2006.

You can select for each virtual machine individually whether VirtualBox should use software or hardware virtualization. Prior to VirtualBox version 2.2, software virtualization was the default; starting with version 2.2, VirtualBox will enable hardware virtualization by default for new virtual machines that you create. (Existing virtual machines are not automatically changed for compatibility reasons, and the default can of course be changed for each virtual machine.)

In most cases, the default settings will be fine; VirtualBox will have picked sensible defaults depending on the operating system that you selected when you created the virtual machine. In certain situations, however, you may want to change these preconfigured defaults.

Advanced users may be interested in technical details about software vs. hardware virtualization; please see .

If your host's CPU supports the nested paging (AMD-V) or EPT (Intel VT-x) features, then you can expect a significant performance increase by enabling nested paging in addition to hardware virtualization. For technical details, see .

## Display settings

Video memory size

  This sets the size of the memory provided by the virtual graphics card available to the guest, in MB. As with the main memory, the specified amount will be allocated from the host's resident memory. Based on the amount of video memory, higher resolutions and color depths may be available.

Monitor count

  With this setting VirtualBox can provide more than one virtual monitor to a virtual machine. If a guest operating system (such as Windows) supports multiple attached monitors, VirtualBox can pretend that multiple virtual monitors are present. Multiple monitor support was added with VirtualBox 3.2. Up to 8 such virtual monitors are supported.

  The output of the multiple monitors will be displayed on the host in multiple VM windows which are running side by side.

  However, in fullscreen and seamless mode, they will use the available physical monitors attached to the host. As a result, for fullscreen and seamless modes to work with multiple monitors, you will need at least as many physical monitors as you have virtual monitors configured, or VirtualBox will report an error. You can configure the relationship between guest and host monitors using the view menu by pressing Host key + Home when you are in fullscreen or seamless mode.

  Please see also.

Enable 3D acceleration

  If a virtual machine has Guest Additions installed, you can select here whether the guest should support accelerated 3D graphics. Please refer to for details.

Enable 2D video acceleration

  If a virtual machine with Microsoft Windows has Guest Additions installed, you can select here whether the guest should support accelerated 2D video graphics. Please refer to for details.

Remote display

  Under the "Remote display" tab, if the VirtualBox Remote Display Extension (VRDE) is installed, you can enable the VRDP server that is built into VirtualBox. This allows you to connect to the console of the virtual machine remotely with any standard RDP viewer, such as `mstsc.exe` that comes with Microsoft Windows. On Linux and Solaris systems you can use the standard open-source `rdesktop` program. These features are described in detail in .

## Storage settings

The "Storage" category in the VM settings allows you to connect virtual hard disk, CD/DVD and floppy images and drives to your virtual machine.

In a real PC, so-called "storage controllers" connect physical disk drives to the rest of the computer. Similarly, VirtualBox presents virtual storage controllers to a virtual machine. Under each controller, the virtual devices (hard disks, CD/DVD or floppy drives) attached to the controller are shown.

This section can only give you a quick introduction to the VirtualBox storage settings. Since VirtualBox gives you an enormous wealth of options in this area, we have dedicated an entire chapter of this User Manual to explaining all the details: please see .

If you have used the "Create VM" wizard to create a machine, you will normally see something like the following:

Depending on the guest operating system type that you selected when you created the VM, the typical layout of storage devices in a new VM is as follows:

- You will see an IDE controller, to which a virtual CD/DVD drive has been attached (to the "secondary master" port of the IDE controller).

- You will also see a SATA controller, which is a more modern type of storage controller for higher hard disk data throughput, to which the virtual hard disks are attached. Initially you will normally have one such virtual disk, but as you can see in the above screenshot, you can have more than one, each represented by a disk image file (VDI files, in this case).

If you created your VM with an older version of VirtualBox, the default storage layout may differ. You might then only have an IDE controller to which both the CD/DVD drive and the hard disks have been attached. This might also apply if you selected an older operating system type when you created the VM. Since older operating systems do not support SATA without additional drivers, VirtualBox will make sure that no such devices are present initially. Please see for additional information.

VirtualBox also provides a floppy controller, which is special: you cannot add devices other than floppy drives to it. Virtual floppy drives, like virtual CD/DVD drives, can be connected to either a host floppy drive (if you have one) or a disk image, which in this case must be in RAW format.

You can modify these media attachments freely. For example, if you wish to copy some files from another virtual disk that you created, you can connect that disk as a second hard disk, as in the above screenshot. You could also add a second virtual CD/DVD drive, or change where these items are attached. The following options are available:

- To add another virtual hard disk, or a CD/DVD or floppy drive, select the storage controller to which it should be added (IDE, SATA, SCSI, SAS, floppy controller) and then click on the "add disk" button below the tree. You can then either select "Add CD/DVD device" or "Add Hard Disk". (If you clicked on a floppy controller, you can add a floppy drive instead.) Alternatively, right-click on the storage controller and select a menu item there.

  On the right part of the window, you can then set the following:

  1. You can then select to which device slot of the controller the virtual disk should be connected to. IDE controllers have four slots which have traditionally been called "primary master", "primary slave", "secondary master" and "secondary slave". By contrast, SATA and SCSI controllers offer you up to 30 slots to which virtual devices can be attached.

  2. You can select which image file to use.

     - For virtual hard disks, a button with a drop-down list appears on the right, offering you to either select a virtual hard disk file using a standard file dialog or to create a new hard disk (image file), which will bring up the "Create new disk" wizard, which was described in .

       For details on the image file types that are supported, please see .

     - For virtual CD/DVD drives, the image files will typically be in the standard ISO format instead. Most commonly, you will select this option when installing an operating system from an ISO file that you have obtained from the Internet. For example, most Linux distributions are available in this way.

       For virtual CD/DVD drives, the following additional options are available:

       - If you select "Host drive" from the list, then the physical device of the host computer is connected to the VM, so that the guest operating system can read from and write to your physical device. This is, for instance, useful if you want to install Windows from a real installation CD. In this case, select your host drive from the drop-down list presented.

         If you want to write (burn) CDs or DVDs using the host drive, you need to also enable the "Passthrough" option; see .

       - If you select "Remove disk from virtual drive", VirtualBox will present an empty CD/DVD drive to the guest into which no media has been inserted.

- To remove an attachment, select it and click on the "remove" icon at the bottom (or right-click on it and select the menu item).

Removable media (CD/DVDs and floppies) can be changed while the guest is running. Since the "Settings" dialog is not available at that time, you can also access these settings from the "Devices" menu of your virtual machine window.

## Audio settings

The "Audio" section in a virtual machine's Settings window determines whether the VM will see a sound card connected, and whether the audio output should be heard on the host system.

If audio is enabled for a guest, you can choose between the emulation of an Intel AC'97 controller, an Intel HD Audio controller Intel HD Audio support was added with VirtualBox 4.0 because Windows 7 (32-bit and 64-bit versions) as well as 64-bit Windows Vista do not support the Intel AC'97 controller. or a SoundBlaster 16 card. In any case, you can select what audio driver VirtualBox will use on the host.

On a Linux host, depending on your host configuration, you can also select between the OSS, ALSA or the PulseAudio subsystem. On newer Linux distributions (Fedora 8 and above, Ubuntu 8.04 and above) the PulseAudio subsystem should be preferred.

## Network settings

The "Network" section in a virtual machine's Settings window allows you to configure how VirtualBox presents virtual network cards to your VM, and how they operate.

When you first create a virtual machine, VirtualBox by default enables one virtual network card and selects the "Network Address Translation" (NAT) mode for it. This way the guest can connect to the outside world using the host's networking and the outside world can connect to services on the guest which you choose to make visible outside of the virtual machine.

This default setup is good for probably 95% of VirtualBox users. However, VirtualBox is extremely flexible in how it can virtualize networking. It supports many virtual network cards per virtual machine, the first four of which can be configured in detail in the Manager window. Additional network cards can be configured on the command line with VBoxManage.

Because of the vast array of options available, we have dedicated an entire chapter of this manual to discussing networking configuration; please see .

## Serial ports

VirtualBox fully supports virtual serial ports in a virtual machine in an easy-to-use manner. Serial port support was added with VirtualBox 1.5.

Ever since the original IBM PC, personal computers have been equipped with one or two serial ports (also called COM ports by DOS and Windows). Most importantly, computer mice used to be connected to serial ports before USB became commonplace.

While serial ports are no longer as important as they used to be, there are still some important uses left for them. For example, serial ports can be used to set up a primitive network over a null-modem cable, in case Ethernet is not available. Also, serial ports are indispensable for system programmers needing to do kernel debugging, since kernel debugging software usually interacts with developers over a serial port. With virtual serial ports, system programmers can do kernel debugging on a virtual machine instead of needing a real computer to connect to.

If a virtual serial port is enabled, the guest operating system sees a standard 16450-type device. Both receiving and transmitting data is supported. How this virtual serial port is then connected to the host is configurable, and the details depend on your host operating system.

You can use either the graphical user interface or the command-line `VBoxManage` tool to set up virtual serial ports. For the latter, please refer to ; in that section, look for the `--uart` and `--uartmode` options.

In either case, you can configure up to two virtual serial ports simultaneously. For each such device, you will need to determine

1. what kind of serial port the virtual machine should see by selecting an I/O base address and interrupt (IRQ). For these, we recommend to use the traditional values See, for example, http://en.wikipedia.org/wiki/COM_(hardware_interface). , which are:

   1. COM1: I/O base 0x3F8, IRQ 4

   2. COM2: I/O base 0x2F8, IRQ 3

   3. COM3: I/O base 0x3E8, IRQ 4

   4. COM4: I/O base 0x2E8, IRQ 3

2. Then, you will need to determine what this virtual port should be connected to. For each virtual serial port, you have the following options:

   - You can elect to have the virtual serial port "disconnected", which means that the guest will see the device, but it will behave as if no cable had been connected to it.

   - You can connect the virtual serial port to a physical serial port on your host. (On a Windows host, this will be a name like `COM1`; on Linux or Solaris hosts, it will be a device node like `/dev/ttyS0`). VirtualBox will then simply redirect all data received from and sent to the virtual serial port to the physical device.

   - You can tell VirtualBox to connect the virtual serial port to a software pipe on the host. This depends on your host operating system:

     - On a Windows host, data will be sent and received through a named pipe. You can use a helper program called VMware Serial Line Gateway, available for download at `http://www.l4ka.org/91.php` . This tool provides a fixed server mode named pipe at `\\.\pipe\vmwaredebug` and connects incoming TCP connections on port 567 with the named pipe.

     - On a Mac, Linux or OpenSolaris host, a local domain socket is used instead. On Linux there are various tools which can connect to a local domain socket or create one in server mode. The most flexible tool is `socat` and is available as part of many distributions.

     In this case, you can configure whether VirtualBox should create the named pipe (or, on non-Windows hosts, the local domain socket) itself or whether VirtualBox should assume that the pipe (or socket) exists already. With the `VBoxManage` command-line options, this is referred to as "server" or "client" mode, respectively.

Up to two serial ports can be configured simultaneously per virtual machine, but you can pick any port numbers out of the above. For example, you can configure two serial ports to be able to work with COM2 and COM4 in the guest.

## USB support

### USB settings

The "USB" section in a virtual machine's Settings window allows you to configure VirtualBox's sophisticated USB support.

VirtualBox can allow virtual machines to access the USB devices on your host directly. To achieve this, VirtualBox presents the guest operating system with a virtual USB controller. As soon as the guest system starts using a USB device, it will appear as unavailable on the host.

1. Be careful with USB devices that are currently in use on the host! For example, if you allow your guest to connect to your USB hard disk that is currently mounted on the host, when the guest is activated, it will be disconnected from the host without a proper shutdown. This may cause data loss.

2. Solaris hosts have a few known limitations regarding USB support; please see .

In addition to allowing a guest access to your local USB devices, VirtualBox even allows your guests to connect to remote USB devices by use of the VirtualBox Remote Desktop Extension (VRDE). For details about this, see .

In the Settings dialog, you can first configure whether USB is available in the guest at all, and in addition also optionally enable the USB 2.0 (EHCI) controller for the guest. If so, you can determine in detail which devices are available. For this, you must create so-called "filters" by specifying certain properties of the USB device.

The EHCI controller is shipped as a VirtualBox extension package, which must be installed separately. See for more information.

Clicking on the "+" button to the right of the "USB Device Filters" window creates a new filter. You can give the filter a name (for referencing it later) and specify the filter criteria. The more criteria you specify, the more precisely devices will be selected. For instance, if you specify only a vendor ID of 046d, all devices produced by Logitech will be available to the guest. If you fill in all fields, on the other hand, the filter will only apply to a particular device model from a particular vendor, and not even to other devices of the same type with a different revision and serial number.

In detail, the following criteria are available:

1. Vendor and product ID. With USB, each vendor of USB products carries an identification number that is unique world-wide, the "vendor ID". Similarly, each line of products is assigned a "product ID" number. Both numbers are commonly written in hexadecimal (that is, they are composed of the numbers 0-9 and the letters A-F), and a colon separates the vendor from the product ID. For example, `046d:c016` stands for Logitech as a vendor, and the "M-UV69a Optical Wheel Mouse" product.

   Alternatively, you can also specify "Manufacturer" and "Product" by name.

   To list all the USB devices that are connected to your host machine with their respective vendor and product IDs, you can use the following command (see ):

       VBoxManage list usbhost

   On Windows, you can also see all USB devices that are attached to your system in the Device Manager. On Linux, you can use the `lsusb` command.

2. Serial number. While vendor and product ID are already quite specific to identify USB devices, if you have two identical devices of the same brand and product line, you will also need their serial numbers to filter them out correctly.

3. Remote. This setting specifies whether the device will be local only, or remote only (over VRDP), or either.

On a Windows host, you will need to unplug and reconnect a USB device to use it after creating a filter for it.

As an example, you could create a new USB filter and specify a vendor ID of 046d (Logitech, Inc), a manufacturer index of 1, and "not remote". Then any USB devices on the host system produced by Logitech, Inc with a manufacturer index of 1 will be visible to the guest system.

Several filters can select a single device -- for example, a filter which selects all Logitech devices, and one which selects a particular webcam.

You can deactivate filters without deleting them by clicking in the checkbox next to the filter name.

### Implementation notes for Windows and Linux hosts

On Windows hosts, a kernel mode device driver provides USB proxy support. It implements both a USB monitor, which allows VirtualBox to capture devices when they are plugged in, and a USB device driver to claim USB devices for a particular virtual machine. As opposed to VirtualBox versions before 1.4.0, system reboots are no longer necessary after installing the driver. Also, you no longer need to replug devices for VirtualBox to claim them.

On newer Linux hosts, VirtualBox accesses USB devices through special files in the file system. When VirtualBox is installed, these are made available to all users in the `vboxusers` system group. In order to be able to access USB from guest systems, make sure that you are a member of this group.

On older Linux hosts, USB devices are accessed using the `usbfs` file system. Therefore, the user executing VirtualBox needs read and write permission to the USB file system. Most distributions provide a group (e.g. `usbusers`) which the VirtualBox user needs to be added to. Also, VirtualBox can only proxy to virtual machines USB devices which are not claimed by a Linux host USB driver. The `Driver=` entry in `/proc/bus/usb/devices` will show you which devices are currently claimed. Please refer to also for details about `usbfs`.

## Shared folders

Shared folders allow you to easily exchange data between a virtual machine and your host. This feature requires that the VirtualBox Guest Additions be installed in a virtual machine and is described in detail in .

## Alternative firmware (EFI)

Starting with release 3.1, VirtualBox includes experimental support for the Extensible Firmware Interface (EFI), which is a new industry standard intended to eventually replace the legacy BIOS as the primary interface for bootstrapping computers and certain system services later.

By default, VirtualBox uses the BIOS firmware for virtual machines. To use EFI for a given virtual machine, you can enable EFI in the machine's "Settings" dialog (see ). Alternatively, use the `VBoxManage` command line interface like this:

    VBoxManage modifyvm "VM name" --firmware efi

To switch back to using the BIOS, use:

    VBoxManage modifyvm "VM name" --firmware bios

One notable user of EFI is Apple's Mac OS X, but recent Linuxes (such as Fedora 11) and Windows (starting with Vista) offer special versions that can be booted using EFI as well.

Another possible use of EFI in VirtualBox is development and testing of EFI applications, without booting any OS.

Note that the VirtualBox EFI support is experimental and will be enhanced as EFI matures and becomes more widespread. While Mac OS X and Linux guests are known to work fine, Windows guests are currently unable to boot with the VirtualBox EFI implementation.

### Video modes in EFI

EFI provides two distinct video interfaces: GOP (Graphics Output Protocol) and UGA (Universal Graphics Adapter). Mac OS X uses GOP, while Linux tends to use UGA. VirtualBox provides a configuration option to control the framebuffer size for both interfaces.

To control GOP, use the following `VBoxManage` command:

    VBoxManage setextradata "VM name" VBoxInternal2/EfiGopMode N

Where N can be one of 0,1,2,3,4 referring to the 640x480, 800x600, 1024x768, 1280x1024, 1440x900 screen resolution respectively.

To change the UGA resolution:

    VBoxManage setextradata "VM name" VBoxInternal2/UgaHorizontalResolution 1440
    VBoxManage setextradata "VM name" VBoxInternal2/UgaVerticalResolution    900

The video mode for both GOP and UGA can only be changed when the VM is powered off and remains persistent until changed.