12 Troubleshooting set VBOX_DISABLE_HOST_DISK_CACHE=1 VirtualBox While this will decrease guest disk performance (especially writes), it does not affect the per- formance of other applications running on the host. 12.5.5 Bridged networking adapters missing 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: VBoxNetCfgWinInstallComponent: Install failed, hr (0x8004a029) You can try to increase the maximum filter count in the Windows registry at the following key: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Network\MaxNumFilters The maximum number allowed is 14. After a reboot, try to re-install VirtualBox. • The INF cache is corrupt. In this case, the install log (%windir%\inf\setupapi.log on XP or %windir%\inf\setupapi.dev.log on Vista or later) would typically men- tion the failure to find a suitable driver package for either the sun_VBoxNetFlt or sun_VBoxNetFltmp components. The solution then is to uninstall VirtualBox, remove the INF cache (%windir%\inf\INFCACHE.1), reboot and try to re-install VirtualBox 12.5.6 Host-only networking adapters cannot be created If host-only adapter cannot be created (either via the Manager or VBoxManage), then the INF cache is probably corrupt. In this case, the install log (%windir%\inf\setupapi.log on XP or %windir%\inf\setupapi.dev.log on Vista or later) would typically mention the failure to find a suitable driver package for the sun_VBoxNetAdp component. Again, as with the bridged networking problem described above, the solution is to uninstall VirtualBox, remove the INF cache (%windir%\inf\INFCACHE.1), reboot and try to re-install VirtualBox. 12.6 Linux hosts 12.6.1 Linux kernel module refuses to load If the VirtualBox kernel module (vboxdrv) refuses to load, i.e. you get an “Error inserting vboxdrv: Invalid argument”, check (as root) the output of the dmesg command to find out why the load failed. Most probably the kernel disagrees with the version of the gcc used to compile the module. Make sure that you use the same compiler as used to build the kernel. 12.6.2 Linux host CD/DVD drive not found 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 (/dev/hdc or /dev/scd0 or /dev/cdrom or similar). On most distributions, the user must be added to a corresponding group (usually called cdrom or cdrw). 174