Table of Contents
This chapter provides answers to commonly asked questions. In order to improve your user experience with Oracle VM VirtualBox, it is recommended to read this section to learn more about common pitfalls and get recommendations on how to use the product.
More often than not, a virtualized guest behaves like a physical system. Any problems that a physical machine would encounter, a virtual machine will encounter as well. If, for example, Internet connectivity is lost due to external issues, virtual machines will be affected just as much as physical ones.
If a true Oracle VM VirtualBox problem is encountered, it helps to categorize and isolate the problem first. Here are some of the questions that should be answered before reporting a problem:
Is the problem specific to a certain guest OS? Or a specific release of a guest OS? Especially with Linux guest related problems, the issue may be specific to a certain distribution and version of Linux.
Is the problem specific to a certain host OS? Problems are usually not host OS specific, because most of the Oracle VM VirtualBox code base is shared across all supported platforms, but especially in the areas of networking and USB support, there are significant differences between host platforms. Some GUI related issues are also host specific.
Is the problem specific to certain host hardware? This category of issues is typically related to the host CPU. Because of significant differences between VT-x and AMD-V, problems may be specific to one or the other technology. The exact CPU model may also make a difference, even for software virtualization, because different CPUs support different features, which may affect certain aspects of guest CPU operation.
Is the problem specific to a certain virtualization mode? Some problems may only occur in software virtualization mode, others may be specific to hardware virtualization.
Is the problem specific to guest SMP? That is, is it related to the number of virtual CPUs (VCPUs) in the guest? Using more than one CPU usually significantly affects the internal operation of a guest OS.
Is the problem specific to the Guest Additions? In some cases, this is obvious, such as a shared folders problem. In other cases such as display problems, it may be less obvious. If the problem is Guest Additions specific, is it also specific to a certain version of the Guest Additions?
Is the problem specific to a certain environment? Some problems are related to a particular environment external to the VM. This usually involves network setup. Certain configurations of external servers such as DHCP or PXE may expose problems which do not occur with other, similar servers.
Is the problem a regression? Knowing that an issue is a regression usually makes it significantly easier to find the solution. In this case, it is crucial to know which version is affected and which is not.
For problem determination, it is often important to collect debugging information which can be analyzed by Oracle VM VirtualBox support. This section contains information about what kind of information can be obtained.
Every time Oracle VM VirtualBox starts up a VM, a so-called
release log file is created, containing
lots of information about the VM configuration and runtime
events. The log file is called
VBox.log and resides in the VM
log file folder. Typically this will be a directory as follows:
When starting a VM, the configuration file of the last run will
be renamed to
.1, up to
.3. Sometimes when there is a
problem, it is useful to have a look at the logs. Also when
requesting support for Oracle VM VirtualBox, supplying the
corresponding log file is mandatory.
For convenience, for each virtual machine, the VirtualBox Manager window can show these logs in a window. To access it, select a virtual machine from the list on the left and select Show Log from the Machine menu.
The release log file, VBox.log, contains a wealth of diagnostic information, such as Host OS type and version, Oracle VM VirtualBox version and build (32-bit or 64-bit). It also includes a complete dump of the guest's configuration (CFGM), detailed information about the host CPU type and supported features, whether hardware virtualization is enabled, information about VT-x/AMD-V setup, state transitions (such as creating, running, paused, stopping), guest BIOS messages, Guest Additions messages, device-specific log entries and, at the end of execution, final guest state and condensed statistics.
In case of crashes, it is very important to collect crash dumps. This is true for both host and guest crashes. For information about enabling core dumps on Linux, Oracle Solaris, and OS X systems, refer to the following core dump article on the Oracle VM VirtualBox website:
You can also use VBoxManage debugvm to create a dump of a complete virtual machine. See Section 8.42, “VBoxManage debugvm”.
For network related problems, it is often helpful to capture a trace of network traffic. If the traffic is routed through an adapter on the host, it is possible to use Wireshark or a similar tool to capture the traffic there. However, this often also includes a lot of traffic unrelated to the VM.
Oracle VM VirtualBox provides an ability to capture network traffic only on a specific VM's network adapter. Refer to the following network tracing article on the Oracle VM VirtualBox website for information on enabling this capture:
The trace files created by Oracle VM VirtualBox are in
.pcap format and can be easily
analyzed with Wireshark.
Oracle VM VirtualBox includes a built-in VM debugger, which advanced users may find useful. This debugger enables you to examine and, to some extent, control the VM state.
Use the VM debugger at your own risk. There is no support for it, and the following documentation is only made available for advanced users with a very high level of familiarity with the x86/AMD64 machine instruction set, as well as detailed knowledge of the PC architecture. A degree of familiarity with the internals of the guest OS in question may also be very helpful.
The VM debugger is available in all regular production versions of Oracle VM VirtualBox, but it is disabled by default because the average user will have little use for it. There are two ways to access the debugger:
Using a debugger console window displayed alongside the VM
on port 5000
The debugger can be enabled in the following ways:
Start the VM directly using VirtualBox
--startvm, with an additional
argument. See the VirtualBox command
usage help for details.
environment variable to
true before launching the
Oracle VM VirtualBox process. Setting these variables, only their
presence is checked, is effective even when the first
Oracle VM VirtualBox process is the VM selector window. VMs
subsequently launched from the selector will have the
extra data item to
before launching the VM. This can be set globally or on a
per VM basis.
A new Debug menu entry is added to the Oracle VM VirtualBox application. This menu enables the user to open the debugger console.
The VM debugger command syntax is loosely modeled on Microsoft and IBM debuggers used on DOS, OS/2, and Windows. Users familiar with symdeb, CodeView, or the OS/2 kernel debugger will find the Oracle VM VirtualBox VM debugger familiar.
The most important command is help. This will print brief usage help for all debugger commands. The set of commands supported by the VM debugger changes frequently and the help command is always up-to-date.
A brief summary of frequently used commands is as follows:
stop: Stops the VM
execution and enables single stepping
g: Continue VM execution
t: Single step an
rg/rh/r: Print the
kg/kh/k: Print the
guest/hypervisor/current call stack
memory contents as ASCII/bytes/words/dwords/qwords
u: Unassemble memory
dg: Print the guest's GDT
di: Print the guest's IDT
dl: Print the guest's LDT
dt: Print the guest's TSS
dp*: Print the guest's page
bp/br: Set a
bl: List breakpoints
bc: Clear a breakpoint
writecore: Write a VM core
file to disk. See Section 12.1.4, “VM Core Format”
See the built-in
help for other
The VM debugger supports symbolic debugging, although symbols
for guest code are often not available. For Oracle Solaris
guests, the detect command automatically
determines the guest OS version and locates kernel symbols in
guest's memory. Symbolic debugging is then available. For Linux
guests, the detect commands also determines
the guest OS version, but there are no symbols in the guest's
memory. Kernel symbols are available in the file
/proc/kallsyms on Linux guests.
This file must be copied to the host, for example using
scp. The loadmap debugger
command can be used to make the symbol information available to
the VM debugger. Note that the
kallsyms file contains the
symbols for the currently loaded modules. If the guest's
configuration changes, the symbols will change as well and must
For all guests, a simple way to verify that the correct symbols are loaded is the k command. The guest is normally idling and it should be clear from the symbolic information that the guest operating system's idle loop is being executed.
Another group of debugger commands is the set of info commands. Running info help provides complete usage information. The information commands provide ad-hoc data pertinent to various emulated devices and aspects of the VMM. There is no general guideline for using the info commands, the right command to use depends entirely on the problem being investigated. Some of the info commands are as follows:
cfgm: Print a branch of the
cpuid: Display the guest
ioport: Print registered
I/O port ranges
mmio: Print registered MMIO
mode -- print the current
pit: Print the i8254 PIT
pic: Print the i8259A PIC
ohci/ehci/xhci: Print a
subset of the OHCI/EHCI/xHCI USB controller state
pcnet0: Print the PCnet
vgatext: Print the contents
of the VGA framebuffer formatted as standard text mode
timers: Print all VM timers
The output of the info commands generally requires in-depth knowledge of the emulated device or Oracle VM VirtualBox VMM internals. However, when used properly, the information provided can be invaluable.
Oracle VM VirtualBox uses the 64-bit ELF format for its VM core files created by VBoxManage debugvm, see Section 8.42, “VBoxManage debugvm”. The VM core file contain the memory and CPU dumps of the VM and can be useful for debugging your guest OS. The 64-bit ELF object format specification can be obtained at:
The overall layout of the VM core format is as follows:
[ ELF 64 Header] [ Program Header, type PT_NOTE ] → offset to COREDESCRIPTOR [ Program Header, type PT_LOAD ] - one for each contiguous physical memory range → Memory offset of range → File offset [ Note Header, type NT_VBOXCORE ] [ COREDESCRIPTOR ] → Magic → VM core file version → VBox version → Number of vCPUs etc. [ Note Header, type NT_VBOXCPU ] - one for each vCPU [ vCPU 1 Note Header ] [ DBGFCORECPU - vCPU 1 dump ] [ Additional Notes + Data ] - currently unused [ Memory dump ]
The memory descriptors contain physical addresses relative to the guest and not virtual addresses. Regions of memory such as MMIO regions are not included in the core file.
The relevant data structures and definitions can be found in the
Oracle VM VirtualBox sources under the following header files:
The VM core file can be inspected using
elfdump and GNU
readelf or other similar
Occasionally, some host file systems provide very poor writing performance and as a consequence cause the guest to time out IDE/SATA commands. This is normal behavior and should normally cause no real problems, as the guest should repeat commands that have timed out. However, guests such as some Linux versions have severe problems if a write to an image file takes longer than about 15 seconds. Some file systems however require more than a minute to complete a single write, if the host cache contains a large amount of data that needs to be written.
The symptom for this problem is that the guest can no longer access its files during large write or copying operations, usually leading to an immediate hang of the guest.
In order to work around this problem, the true fix is to use a faster file system that does not exhibit such unacceptable write performance, it is possible to flush the image file after a certain amount of data has been written. This interval is normally infinite, but can be configured individually for each disk of a VM.
For IDE disks use the following command:
VBoxManage setextradata "VM name" "VBoxInternal/Devices/piix3ide/0/LUN#[x]/Config/FlushInterval" [b]
For SATA disks use the following command:
VBoxManage setextradata "VM name" "VBoxInternal/Devices/ahci/0/LUN#[x]/Config/FlushInterval" [b]
The value [x] that selects the disk for IDE is 0 for the master device on the first channel, 1 for the slave device on the first channel, 2 for the master device on the second channel or 3 for the slave device on the second channel. For SATA use values between 0 and 29. Only disks support this configuration option; it must not be set for CD/DVD drives.
The unit of the interval [b] is the number of bytes written since the last flush. The value for it must be selected so that the occasional long write delays do not occur. Since the proper flush interval depends on the performance of the host and the host filesystem, finding the optimal value that makes the problem disappear requires some experimentation. Values between 1000000 and 10000000 (1 to 10 megabytes) are a good starting point. Decreasing the interval both decreases the probability of the problem and the write performance of the guest. Setting the value unnecessarily low will cost performance without providing any benefits. An interval of 1 will cause a flush for each write operation and should solve the problem in any case, but has a severe write performance penalty.
Providing a value of 0 for [b] is treated as an infinite flush interval, effectively disabling this workaround. Removing the extra data key by specifying no value for [b] has the same effect.
If desired, the virtual disk images can be flushed when the guest issues the IDE FLUSH CACHE command. Normally these requests are ignored for improved performance. The parameters below are only accepted for disk drives. They must not be set for DVD drives.
To enable flushing for IDE disks, issue the following command:
VBoxManage setextradata "VM name" "VBoxInternal/Devices/piix3ide/0/LUN#[x]/Config/IgnoreFlush" 0
The value [x] that selects the disk is 0 for the master device on the first channel, 1 for the slave device on the first channel, 2 for the master device on the second channel or 3 for the master device on the second channel.
To enable flushing for SATA disks, issue the following command:
VBoxManage setextradata "VM name" "VBoxInternal/Devices/ahci/0/LUN#[x]/Config/IgnoreFlush" 0
The value [x] that selects the disk can be a value between 0 and 29.
Note that this does not affect the flushes performed according to the configuration described in 12.2.1. Restoring the default of ignoring flush commands is possible by setting the value to 1 or by removing the key.
Many newer multi-core processors support some form of frequency boosting, which means that if only one core is utilized, it can run possibly 50% faster or even more than the rated CPU frequency. This causes measured performance to vary somewhat as a function of the momentary overall system load. The exact behavior depends strongly on the specific processor model.
As a consequence, benchmarking on systems which utilize frequency boosting may produce unstable and non-repeatable results. This is especially true if benchmark runs are short, of the order of seconds. To obtain stable results, benchmarks must be run over longer periods of time and with a constant system load apart from the VM being tested.
On some hardware platforms and operating systems, CPU frequency scaling may cause CPU usage reporting to be highly misleading. This happens in situations when the host CPU load is significant but not heavy, such as 15-30% of the maximum.
Most operating systems determine CPU usage in terms of time spent, measuring for example how many nanoseconds the systems or a process was active within one second. However, in order to save energy, modern systems can significantly scale down CPU speed when the system is not fully loaded. Naturally, when the CPU is running at for example one half of its maximum speed, the same number of instructions will take roughly twice as long to execute compared to running at full speed.
Depending on the specific hardware and host OS, this effect can very significantly skew the CPU usage reported by the OS. The reported CPU usage can be several times higher than what it would have been had the CPU been running at full speed. The effect can be observed both on the host OS and in a guest OS.
CPU usage reporting tools which come with Windows, such as Task Manager or Resource Monitor, do not take the time spent processing hardware interrupts into account. If the interrupt load is heavy, with thousands of interrupts per second, CPU usage may be significantly underreported.
This problem affects Windows as both host and guest OS. Sysinternals tools, such as Process Explorer, do not suffer from this problem.
On some hardware platforms and operating systems, virtualization performance is negatively affected by host CPU power management. The symptoms may be choppy audio in the guest or erratic guest clock behavior.
Some of the problems may be caused by firmware and/or host operating system bugs. Therefore, updating the firmware and applying operating systems fixes is recommended.
For optimal virtualization performance, the C1E power state
support in the system's BIOS should be disabled, if such a
setting is available. Not all systems support the C1E power
state. On Intel systems, the
State setting should be disabled. Disabling
other power management settings may also improve performance.
However, a balance between performance and power consumption
must always be considered.
To use 2D Video Acceleration within Oracle VM VirtualBox, your host's video card should support certain OpenGL extensions. On startup, Oracle VM VirtualBox checks for those extensions, and, if the test fails, this option is silently grayed out.
To find out why it has failed, you can manually execute the following command:
VBoxTestOGL --log "log_file_name" --test 2D
It will list the required OpenGL extensions one by one and will show you which one failed the test. This usually means that you are running an outdated or misconfigured OpenGL driver on your host. It can also mean that your video chip is lacking required functionality.
If a Windows 7 or Windows Server 2008 R2 guest is configured for USB 3.0 (xHCI) support, the guest OS will not have any USB support at all. This happens because Windows 7 predates USB 3.0 and therefore does not ship with any xHCI drivers. Microsoft also does not offer any vendor-provided xHCI drivers through Windows Update.
To solve this problem, it is necessary to download and install the Intel xHCI driver in the guest. Intel offers the driver as the USB 3.0 eXtensible Host Controller (xHCI) driver for Intel 7 Series/C216 chipsets.
Note that the driver only supports Windows 7 and Windows Server 2008 R2. The driver package includes support for both 32-bit and 64-bit OS variants.
Changing certain virtual machine settings can cause Windows guests to fail during start up with a bluescreen. This may happen if you change VM settings after installing Windows, or if you copy a disk image with an already installed Windows to a newly created VM which has settings that differ from the original machine.
This applies in particular to the following settings:
The ACPI and I/O APIC settings should never be changed after installing Windows. Depending on the presence of these hardware features, the Windows installation program chooses special kernel and device driver versions and will fail to startup should these hardware features be removed. Enabling them for a Windows VM which was installed without them does not cause any harm. However, Windows will not use these features in this case.
Changing the storage controller hardware will cause bootup failures as well. This might also apply to you if you copy a disk image from an older version of Oracle VM VirtualBox to a virtual machine created with a newer Oracle VM VirtualBox version. The default subtype of IDE controller hardware was changed from PIIX3 to PIIX4 with Oracle VM VirtualBox 2.2. Make sure these settings are identical.
If a VM is configured to have more than one processor (symmetrical multiprocessing, SMP), some configurations of Windows guests crash with an 0x101 error message, indicating a timeout for interprocessor interrupts (IPIs). These interrupts synchronize memory management between processors.
According to Microsoft, this is due to a race condition in Windows. A hotfix is available. See http://support.microsoft.com/kb/955076.
If this does not help, please reduce the number of virtual processors to 1.
When installing Windows 2000 guests, you might run into one of the following issues:
Installation reboots, usually during component registration.
Installation fills the whole hard disk with empty log files.
Installation complains about a failure installing
These problems are all caused by a bug in the hard disk driver of Windows 2000. After issuing a hard disk request, there is a race condition in the Windows driver code which leads to corruption if the operation completes too fast. For example, the hardware interrupt from the IDE controller arrives too soon. With physical hardware, there is a guaranteed delay in most systems so the problem is usually hidden there. However, it should be possible to also reproduce it on physical hardware. In a virtual environment, it is possible for the operation to be done immediately, especially on very fast systems with multiple CPUs, and the interrupt is signaled sooner than on a physical system. The solution is to introduce an artificial delay before delivering such interrupts. This delay can be configured for a VM using the following command:
VBoxManage setextradata "VM name" "VBoxInternal/Devices/piix3ide/0/Config/IRQDelay" 1
This sets the delay to one millisecond. In case this does not help, increase it to a value between 1 and 5 milliseconds. Please note that this slows down disk performance. After installation, you should be able to remove the key, or set it to 0.
When Windows guests run into a kernel crash, they display the infamous bluescreen. Depending on how Windows is configured, the information will remain on the screen until the machine is restarted or it will reboot automatically. During installation, Windows is usually configured to reboot automatically. With automatic reboots, there is no chance to record the bluescreen information which might be important for problem determination.
Oracle VM VirtualBox provides a method of halting a guest when it wants to perform a reset. In order to enable this feature, use the following command:
VBoxManage setextradata "VM name" "VBoxInternal/PDM/HaltOnReset" 1
Certain editions of Windows 2000 and 2003 servers support more than 4 GB RAM on 32-bit systems. The AMD PCnet network driver shipped with Windows Server 2003 fails to load if the 32-bit guest OS uses paging extensions, which will occur with more than approximately 3.5 GB RAM assigned to the VM.
This problem is known to occur with version 18.104.22.168 of the PCnet driver. The issue was fixed in version 22.214.171.124 of the driver, which is available as a separate download. An alternative solution may be changing the emulated NIC type to Intel PRO/1000 MT Desktop (82540EM), or reducing the RAM assigned to the VM to approximately 3.5 GB or less.
With Windows Vista, Microsoft dropped support for the AMD PCNet card that Oracle VM VirtualBox used to provide as the default virtual network card before version 1.6.0. For Windows Vista guests, Oracle VM VirtualBox now uses an Intel E1000 card by default.
If, for some reason, you still want to use the AMD card, you need to download the PCNet driver from the AMD website. This driver is available for 32-bit Windows only. You can transfer it into the virtual machine using a shared folder. See Section 4.3, “Shared Folders”.
Several background applications of Windows guests, especially virus scanners, are known to increases the CPU load notably even if the guest appears to be idle. We recommend to deactivate virus scanners within virtualized guests if possible.
The performance for accesses to shared folders from a Windows
guest might be decreased due to delays during the resolution of
the Oracle VM VirtualBox shared folders name service. To fix these
delays, add the following entries to the file
of the Windows guest:
255.255.255.255 VBOXSVR #PRE 255.255.255.255 VBOXSRV #PRE
After doing this change, a reboot of the guest is required.
If a Windows 98 VM is configured to use the emulated USB tablet (absolute pointing device), the coordinate translation may be incorrect and the pointer is restricted to the upper left quarter of the guest's screen.
The USB HID (Human Interface Device) drivers in Windows 98 are very old and do not handle tablets the same way as more recent operating systems do. For example, Windows 2000 and later, Mac OS X, and Oracle Solaris. To work around the problem, use the following command:
VBoxManage setextradata "VM name" "VBoxInternal/USB/HidMouse/0/Config/CoordShift" 0
To restore the default behavior, remove the key or set its value to 1.
If a Windows guest is a member of an Active Directory domain and the snapshot feature of Oracle VM VirtualBox is used, it could happen it loses this status after you restore an older snapshot.
The reason is the automatic machine password changing performed by Windows at regular intervals for security purposes. You can disable this feature by following the instruction of the following article from Microsoft: http://support.microsoft.com/kb/154501
Oracle VM VirtualBox Guest Additions for Windows prior to 4.1.8 did not properly back up the original d3d8.dll and d3d9.dll system files when selecting and installing the experimental Direct3D support. This process replaces both system files with files from the Guest Additions so that Direct3D calls can be handled correctly. Although this issue was fixed with Oracle VM VirtualBox 4.1.8, there is no way the Windows Guest Additions installer can repair these files.
Corruption of these files has no implications if 3D acceleration is enabled and basic Direct3D support is installed. That is, without WDDM on Windows Vista or later, or on older Windows systems like Windows XP. With the basic Direct3D support all Direct3D 8.0 and Direct3D 9.0 applications will utilize Oracle VM VirtualBox Direct3D files directly and thus will run as expected.
For WDDM Direct3D support however, the originally shipped d3d8.dll and d3d9.dll files are required in order to run Direct3D 8.0 and Direct3D 9.0 applications. As a result of the above mentioned system files corruption these applications will not work anymore. See below for a step-by-step guide for restoring the original d3d8.dll and d3d9.dll system files in case the Oracle VM VirtualBox Guest Additions installer warned about those incorrect files or when having trouble running Direct3D applications.
Starting at Windows 7 the 3D desktop, called Aero, uses DirectX 10 for rendering so that corrupted d3d8.dll and d3d9.dll system files will have no effect on the actual rendering.
This is why such a detected file corruption is not considered as fatal for the basic Direct3D installation on all supported Windows guests, and for WDDM Direct3D installation on Windows 7 and later guests.
Extracting d3d8 and d3d9.dll from a Windows XP installation CD:
Download and install the latest version of 7-Zip File Manager.
Browse into the installation CD. For example E:\i386, or E:\amd64 for the 64-bit version.
Locate the entries d3d8.dl_ and d3d9.dl_. Double-click on the file names and extract d3d8.dll and d3d9.dll.
Reboot Windows in Safe mode.
Copy the extracted d3d8.dll and d3d9.dll files to C:\Windows\system32 and C:\Windows\system32\dllcache.
Extracting d3d8 and d3d9.dll from a Windows XP Service pack:
Download and install the latest version of 7-Zip File Manager.
Choose Open Inside, to open WindowsXP-KB936929-SP3-x86.exe as an archive and browse the i386 directory.
Locate the entries d3d8.dl_ and d3d9.dl_. Double-click on the file names and extract d3d8.dll and d3d9.dll.
Reboot Windows in Safe mode.
Copy the extracted d3d8.dll and d3d9.dll files to C:\Windows\system32 and C:\Windows\system32\dllcache.
Extracting d3d8 and d3d9.dll from a Vista/Windows7 installation CD or Service Pack ISO:
Download and install the latest version of 7-Zip File Manager.
Browse into the installation CD. For example E:\sources.
Locate file install.wim and double-click the file. After the 7-Zip utility unzips the file, you will see a few numbered folders. Each numeric subfolder represents a different version of Windows such as Starter or Home Basic.
Open one of the numeric folders and browse to the Windows\System32 directory, or C:\Windows\SysWOW64 for the 64-bit version. Locate and extract the d3d8.dll and d3d9.dll files.
Copy extracted the d3d8.dll and d3d9.dll files to C:\Windows\system32 or C:\Windows\SysWOW64. Files from system32 should go to system32, from SysWOW64 to SysWOW64.
Windows 3.x guests are typically limited to 64 MB RAM, even if a VM is assigned much more memory. While Windows 3.1 is theoretically capable of using up to 512 MB RAM, it only uses memory available through the XMS interface. Versions of HIMEM.SYS, the Microsoft XMS manager, shipped with MS-DOS and Microsoft Windows 3.x can only use up to 64 MB on standard PCs.
This is a HIMEM.SYS limitation documented by Microsoft in Knowledge base article KB 116256. Windows 3.1 memory limits are described in detail in Microsoft Knowledge base article KB 84388.
It is possible for Windows 3.x guests to utilize more than 64 MB RAM if a different XMS provider is used. That could be a newer HIMEM.SYS version, such as that shipped with Windows 98, or a more capable third-party memory manager, such as QEMM.
Some Linux guests may cause a high CPU load even if the guest system appears to be idle. This can be caused by a high timer frequency of the guest kernel. Some Linux distributions, for example Fedora, ship a Linux kernel configured for a timer frequency of 1000Hz. We recommend to recompile the guest kernel and to select a timer frequency of 100Hz.
Linux kernels shipped with Red Hat Enterprise Linux (RHEL) as of release 4.7 and 5.1 as well as kernels of related Linux distributions, such as CentOS and Oracle Linux, support a kernel parameter divider=N. Hence, such kernels support a lower timer frequency without recompilation. We suggest you add the kernel parameter divider=10 to select a guest kernel timer frequency of 100Hz.
Most Linux-based guests will fail with AMD Phenoms or Barcelona-level Opterons due to a bug in the Linux kernel. Enable the I/O-APIC to work around the problem. See Section 3.5, “System Settings”.
The following bugs in Linux kernels prevent them from executing correctly in Oracle VM VirtualBox, causing VM boot crashes:
The Linux kernel version 2.6.18, and some 2.6.17 versions, introduced a race condition that can cause boot crashes in Oracle VM VirtualBox. Please use a kernel version 2.6.19 or later.
With hardware virtualization and the I/O APIC enabled, kernels before 2.6.24-rc6 may panic on boot with the following message:
Kernel panic - not syncing: IO-APIC + timer doesn't work! Boot with apic=debug and send a report. Then try booting with the 'noapic' option
If you see this message, either disable hardware virtualization or the I/O APIC as described in Section 3.5, “System Settings”, or upgrade the guest to a newer kernel.
See http://email@example.com/msg30813.html for details about the kernel fix.
Guest desktop services in guests running the X11 window system
such as Oracle Solaris and Linux, are provided by a guest
which runs under the ID of the user who started the desktop
session and is automatically started using the following command
lines when your X11 user session is started if you are using a
common desktop environment such as Gnome or KDE.
VBoxClient --clipboard VBoxClient --display VBoxClient --seamless
If a particular desktop service is not working correctly, it is worth checking whether the process which should provide it is running.
VBoxClient processes create
files in the user's home directory with names of the form
.vboxclient-*.pid when they are
running in order to prevent a given service from being started
twice. It can happen due to misconfiguration that these files
are created owned by root and not deleted when the services are
stopped, which will prevent them from being started in future
sessions. If the services cannot be started, you may wish to
check whether these files still exist.
Oracle Solaris 10 releases up to and including Oracle Solaris 10 8/07 incorrectly detect newer Intel processors produced since 2007. This problem leads to the 64-bit Oracle Solaris kernel crashing, and usually causing a triple fault, almost immediately during startup, in both virtualized and physical environments.
The recommended solution is upgrading to at least Oracle Solaris 10 5/08. Alternative solutions include forcing Oracle Solaris to always boot the 32-bit kernel or applying a patch for bug 6574102 while Oracle Solaris is using the 32-bit kernel.
When using more than one CPU, Oracle Solaris 10 5/08, Oracle Solaris 10 10/08, and Oracle Solaris 10 5/09 may take a long time to boot and may print warnings on the system console regarding failures to read from disk. This is a bug in Oracle Solaris 10 which affects specific physical and virtual configurations. It is caused by trying to read microcode updates from the boot disk when the disk interrupt is reassigned to a not yet fully initialized secondary CPU. Disk reads will time out and fail, triggering delays of about 45 seconds and warnings.
The recommended solution is upgrading to at least Oracle Solaris 10 10/09 which includes a fix for this problem. Alternative solutions include restricting the number of virtual CPUs to one or possibly using a different storage controller.
Solaris 2.6, 7 and 8 releases up to and including Solaris 8 4/01 ("S8U4") incorrectly set up Machine Check Exception (MCE) MSRs on Pentium 4 and some later Intel CPUs. The problem leads to the Solaris kernel crashing, and usually causing a triple fault, almost immediately during startup, in both virtualized and physical environments. Solaris 9 and later releases are not affected by this problem, and neither is Solaris 2.5.1 and earlier.
The recommended solution is upgrading to at least Solaris 8 7/01 ("S8U5"). Alternative solutions include applying a patch for bugs 4408508 and 4414557 on an unaffected system.
If xHCI (USB 3.0) emulation is enabled for FreeBSD 10.0 guests, the guest OS will hang. This is caused by the guest OS incorrectly handling systems where Message Signaled Interrupts (MSIs) are not used with the xHCI device.
The problem does not exist in earlier FreeBSD releases and was fixed in FreeBSD 10.1.
Oracle VM VirtualBox makes use of the Microsoft Component Object Model
(COM) for interprocess and intraprocess communication. This
enables Oracle VM VirtualBox to share a common configuration among
different virtual machine processes and provide several user
interface options based on a common architecture. All global
status information and configuration is maintained by the
VBoxSVC.exe, which is
an out-of-process COM server. Whenever an Oracle VM VirtualBox process
is started, it requests access to the COM server and Windows
automatically starts the process. Note that it should never be
started by the end user.
When the last process disconnects from the COM server, it will terminate itself after some seconds. The Oracle VM VirtualBox configuration (XML files) is maintained and owned by the COM server and the files are locked whenever the server runs.
In some cases, such as when a virtual machine is terminated
unexpectedly, the COM server will not notice that the client is
disconnected and stay active for a longer period of 10 minutes
or so, keeping the configuration files locked. In other rare
cases the COM server might experience an internal error and
subsequently other processes fail to initialize it. In these
situations, it is recommended to use the Windows task manager to
kill the process
In case you have assigned a physical CD/DVD drive to a guest and the guest does not notice when the medium changes, make sure that the Windows media change notification (MCN) feature is not turned off. This is represented by the following key in the Windows registry:
Certain applications may disable this key against Microsoft's advice. If it is set to 0, change it to 1 and reboot your system. Oracle VM VirtualBox relies on Windows notifying it of media changes.
If connecting to a Virtual Machine using the Microsoft RDP client, called a Remote Desktop Connection, there can be large delays between input such as moving the mouse over a menu and output. This is because this RDP client collects input for a certain time before sending it to the RDP server.
The interval can be decreased by setting a Windows registry key to smaller values than the default of 100. The key does not exist initially and must be of type DWORD. The unit for its values is milliseconds. Values around 20 are suitable for low-bandwidth connections between the RDP client and server. Values around 4 can be used for a gigabit Ethernet connection. Generally values below 10 achieve a performance that is very close to that of the local input devices and screen of the host on which the Virtual Machine is running.
Depending whether the setting should be changed for an individual user or for the system, set either of the following.
HKEY_CURRENT_USER\Software\Microsoft\Terminal Server Client\Min Send Interval
HKEY_LOCAL_MACHINE\Software\Microsoft\Terminal Server Client\Min Send Interval
Deadlocks can occur on a Windows host when attempting to access an iSCSI target running in a guest virtual machine with an iSCSI initiator, such as a Microsoft iSCSI Initiator, that is running on the host. This is caused by a flaw in the Windows cache manager component, and causes sluggish host system response for several minutes, followed by a "Delayed Write Failed" error message in the system tray or in a separate message window. The guest is blocked during that period and may show error messages or become unstable.
Setting the environment variable
1 will enable a workaround for this problem until Microsoft
addresses the issue. For example, open a command prompt window
and start Oracle VM VirtualBox like this:
set VBOX_DISABLE_HOST_DISK_CACHE=1 VirtualBox
While this will decrease guest disk performance, especially writes, it does not affect the performance of other applications running on the host.
If no bridged adapters show up in the Networking section of the VM settings, this typically means that the bridged networking driver was not installed properly on your host. This could be due to the following reasons:
The maximum allowed filter count was reached on the host. In
this case, the MSI log would mention the
0x8004a029 error code
returned on NetFlt network component install, as follows:
VBoxNetCfgWinInstallComponent: Install failed, hr (0x8004a029)
You can try to increase the maximum filter count in the Windows registry using the following key:
The maximum number allowed is 14. After a reboot, try to reinstall Oracle VM VirtualBox.
The INF cache is corrupt. In this case, the install log
on XP or
on Vista or later) would typically mention the failure to
find a suitable driver package for either the
components. The solution then is to uninstall
Oracle VM VirtualBox, remove the INF cache
reboot and try to reinstall Oracle VM VirtualBox.
If a host-only adapter cannot be created, either with the
VirtualBox Manager or the VBoxManage command,
then the INF cache is probably corrupt. In this case, the
Windows XP or
on Windows Vista or later) would typically mention the failure
to find a suitable driver package for the
Again, as with the bridged networking problem described above,
the solution is to uninstall Oracle VM VirtualBox, remove the INF
reboot and try to reinstall Oracle VM VirtualBox.
If the Oracle VM VirtualBox kernel module,
vboxdrv, refuses to load you
may see an "Error inserting vboxdrv: Invalid argument" message.
As root, check the output of the dmesg
command to find out why the load failed. Most probably the
kernel disagrees with the version of gcc used
to compile the module. Make sure that you use the same compiler
as used to build the kernel.
If you have configured a virtual machine to use the host's
CD/DVD drive, but this does not appear to work, make sure that
the current user has permission to access the corresponding
Linux device file. This is
/dev/cdrom or similar. On most
distributions, the user must be added to a corresponding group,
On older Linux distributions, if your CD/DVD device has a different name, Oracle VM VirtualBox may be unable to find it. On older Linux hosts, Oracle VM VirtualBox performs the following steps to locate your CD/DVD drives:
Oracle VM VirtualBox checks if the environment variable
VBOX_CDROM is defined. If
so, Oracle VM VirtualBox omits all the following checks.
Oracle VM VirtualBox tests if
Oracle VM VirtualBox checks if any CD/DVD drives are currently
mounted by checking
Oracle VM VirtualBox checks if any of the entries in
/etc/fstab point to CD/DVD
You can set the VBOX_CDROM environment variable to contain a list of your CD/DVD devices, separated by colons. For example:
On modern Linux distributions, Oracle VM VirtualBox uses the hardware abstraction layer (HAL) to locate CD and DVD hardware.
Section 12.8.3, “Linux Host CD/DVD Drive Not Found (Older Distributions)” appplies
also to floppy disks, except that on older distributions
Oracle VM VirtualBox tests for
/dev/fd* devices by default.
This can be overridden with the
If the experimental CD/DVD writer support is enabled with an incorrect Oracle VM VirtualBox, host or guest configuration, it is possible that any attempt to access the CD/DVD writer fails and simply results in guest kernel error messages for Linux guests or application error messages for Windows guests. Oracle VM VirtualBox performs the usual consistency checks when a VM is powered up. In particular, it aborts with an error message if the device for the CD/DVD writer is not writable by the user starting the VM. But Oracle VM VirtualBox cannot detect all misconfigurations. The necessary host and guest OS configuration is not specific for Oracle VM VirtualBox, but a few frequent problems are listed here which occurred in connection with Oracle VM VirtualBox.
Special care must be taken to use the correct device. The
configured host CD/DVD device file name, in most cases
/dev/cdrom, must point to the
device that allows writing to the CD/DVD unit. For CD/DVD writer
units connected to a SCSI controller or to a IDE controller that
interfaces to the Linux SCSI subsystem, common for some SATA
controllers, this must refer to the SCSI device node, such as
/dev/scd0. Even for IDE CD/DVD
writer units this must refer to the appropriate SCSI CD-ROM
device node, such as
ide-scsi kernel module
is loaded. This module is required for CD/DVD writer support
with all Linux 2.4 kernels and some early 2.6 kernels. Many
Linux distributions load this module whenever a CD/DVD writer is
detected in the system, even if the kernel would support CD/DVD
writers without the module. Oracle VM VirtualBox supports the use of
IDE device files, such as
/dev/hdc, provided the kernel
supports this and the
module is not loaded.
Similar rules, except that within the guest the CD/DVD writer is always an IDE device, apply to the guest configuration. Since this setup is very common, it is likely that the default configuration of the guest works as expected.
On Linux, Oracle VM VirtualBox makes use of a custom version of
Mozilla XPCOM (cross platform component object model) for
interprocess and intraprocess communication (IPC). The process
VBoxSVC serves as a
communication hub between different Oracle VM VirtualBox processes and
maintains the global configuration, such as the XML database.
When starting an Oracle VM VirtualBox component, the processes
VBoxXPCOMIPCD are started
automatically. They are only accessible from the user account
they are running under.
owns the Oracle VM VirtualBox configuration database which normally
~/.config/VirtualBox, or the
appropriate configuration directory for your operating system.
While it is running, the configuration files are locked.
Communication between the various Oracle VM VirtualBox components and
VBoxSVC is performed through a
local domain socket residing in
In case there are communication problems, such as an
Oracle VM VirtualBox application cannot communicate with
VBoxSVC, terminate the daemons
and remove the local domain socket directory.
If USB is not working on your Linux host, make sure that the
current user is a member of the
vboxusers group. Please keep in
mind that group membership does not take effect immediately but
rather at the next login. If available, the
newgrp command may avoid the need for a
logout and login.
Linux kernels including the grsec patch, see http://www.grsecurity.net/, and derivates have to disable PAX_MPROTECT for the VBox binaries to be able to start a VM. The reason is that VBox has to create executable code on anonymous memory.
When running a large number of VMs with a lot of RAM on a Linux
system, say 20 VMs with 1 GB of RAM each, additional VMs might
fail to start with a kernel error saying that the vmalloc pool
is exhausted and should be extended. The error message also
tells you to specify
vmalloc=256MB in your kernel
parameter list. If adding this parameter to your GRUB or LILO
configuration makes the kernel fail to boot, with an error
message such as "failed to mount the root partition", then you
have probably run into a memory conflict of your kernel and
initial RAM disk. This can be solved by adding the following
parameter to your GRUB configuration:
The ZFS file system is known to use nearly all available RAM as
cache if the default system settings are not changed. This may
lead to a heavy fragmentation of the host memory preventing
Oracle VM VirtualBox VMs from being started. We recommend to limit the
ZFS cache by adding the following line to /etc/system, where
xxxx bytes is the amount of
memory usable for the ZFS cache.
set zfs:zfs_arc_max = xxxx
32-bit Oracle Solaris 10 hosts (bug 1225025) require swap space equal to, or greater than the host's physical memory size. For example, 8 GB physical memory would require at least 8 GB swap. This can be configured during an Oracle Solaris 10 install by choosing a Custom Install and changing the default partitions.
This restriction applies only to 32-bit Oracle Solaris hosts, 64-bit hosts are not affected.
For existing Oracle Solaris 10 installs, an additional swap image needs to be mounted and used as swap. Hence if you have 1 GB swap and 8 GB of physical memory, you require to add 7 GB more swap. This can be done as follows:
For ZFS, run the following as root user:
zfs create -V 8gb /_<ZFS volume>_/swap swap -a /dev/zvol/dsk/_<ZFS volume>_/swap
To mount if after reboot, add the following line to /etc/vfstab:
/dev/zvol/dsk/_<ZFS volume>_/swap - - swap - no -
Alternatively, you could grow the existing swap using:
zfs set volsize=8G rpool/swap
And reboot the system for the changes to take effect.
For UFS (as root user):
mkfile 7g /path/to/swapfile.img swap -a /path/to/swapfile.img
To mount it after reboot, add the following line to /etc/vfstab:
/path/to/swap.img - - swap - no -