12 Troubleshooting 12.3.4 How to record bluescreen information from Windows guests 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. VirtualBox provides a method of halting a guest when it wants to perform a reset. In order to enable this feature, issue the following command: VBoxManage setextradata "VM name" "VBoxInternal/PDM/HaltOnReset" 1 12.3.5 No networking in Windows Vista guests With Windows Vista, Microsoft dropped support for the AMD PCNet card that VirtualBox used to provide as the default virtual network card before version 1.6.0. For Windows Vista guests, VirtualBox now uses an Intel E1000 card by default. If, for some reason, you still want to use the AMD card, VirtualBox ships a 32-bit driver for that card with the Windows Guest Additions see chapter 4.2.1.5, Windows Vista networking, page 56. 12.3.6 Windows guests may cause a high CPU load 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. 12.3.7 Long delays when accessing shared folders The performance for accesses to shared folders from a Windows guest might be decreased due to delays during the resolution of the VirtualBox shared folders name service. To fix these de- lays, add the following entries to the file \windows\system32\drivers\etc\lmhosts 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. 12.4 Linux and X11 guests 12.4.1 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 (RHEL) as of release 4.7 and 5.1 as well as kernels of related Linux distributions (for instance CentOS and Oracle Enterprise Linux) support a kernel parameter divider=N. Hence, such kernels support a lower timer frequency without recompilation. We suggest to add the kernel parameter divider=10 to select a guest kernel timer frequency of 100Hz. 171