5.4. Linux and X11 Guests

5.4.1. Linux Guests May Cause a High CPU load

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, 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.

5.4.2. Buggy Linux 2.6 Kernel Versions

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 System Settings, or upgrade the guest to a newer kernel.

    See http://www.mail-archive.com/git-commits-head@vger.kernel.org/msg30813.html for details about the kernel fix.

5.4.3. Shared Clipboard, Auto-Resizing, and Seamless Desktop in X11 Guests

Guest desktop services in guests running the X11 window system such as Oracle Solaris and Linux, are provided by a guest service called VBoxClient, 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.

The 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.