2.32. PC Speaker Passthrough

As an experimental feature, primarily due to being limited to Linux host only and unknown Linux distribution coverage, Oracle VM VirtualBox supports passing through the PC speaker to the host. The PC speaker, sometimes called the system speaker, is a way to produce audible feedback such as beeps without the need for regular audio and sound card support.

The PC speaker passthrough feature in Oracle VM VirtualBox handles beeps only. Advanced PC speaker use by the VM, such as PCM audio, will not work, resulting in undefined host behavior.

Producing beeps on Linux is a very complex topic. Oracle VM VirtualBox offers a collection of options, in an attempt to make this work deterministically and reliably on as many Linux distributions and system configurations as possible. These are summarized in the following table.

Table 2.4 PC Speaker Configuration Options

Code

Device

Notes

1

/dev/input/by-path/platform-pcspkr-event-spkr

Direct host PC speaker use.

2

/dev/tty

Uses the terminal association of the VM process. VM needs to be started on a virtual console.

3

/dev/tty0 or /dev/vc/0

Can only be used by user root or users with cap_sys_tty_config capability.

9

A user-specified console or evdev device path.

As for codes 1 to 3, but with a custom device path.

70

/dev/tty

Standard beep only. Loses frequency and length. See code 2.

79

A user-specified terminal device path.

As for code 70, but with a custom device path.

100

All of the above.

Tries all the available codes.


To enable PC speaker passthrough use the following command:

VBoxManage setextradata "VM name" "VBoxInternal/Devices/i8254/0/Config/PassthroughSpeaker" N

Replace N with the code representing the case you want to use. Changing this setting will take effect when the VM is started next. It is safe to enable PC speaker passthrough on all host OSes. It will only have an effect on Linux.

The VM log file, VBox.log, will contain lines with the prefix PIT: speaker: showing the PC speaker passthrough setup activities. It gives hints which device it picked or why it failed.

Enabling PC speaker passthrough for the VM is usually the simple part. The real difficulty is making sure that Oracle VM VirtualBox can access the necessary device, because in a typical Linux install most of them can only be accessed by user root. You should follow the preferred way to persistently change this, such as by referring to your distribution's documentation. Since there are countless Linux distribution variants, we can only give the general hints that there is often a way to give the X11 session user access to additional devices, or you need to find a working solution using a udev configuration file. If everything fails you might try setting the permissions using a script which is run late enough in the host system startup.

Sometimes additional rules are applied by the kernel to limit access. For example, that the VM process must have the same controlling terminal as the device configured to be used for beeping, something which is often very difficult to achieve for GUI applications such as Oracle VM VirtualBox. The table above contains some hints, but in general refer to the Linux documentation.

If you have trouble getting any beeps even if the device permissions are set up and VBox.log confirms that it uses evdev or console for the PC speaker control, check if your system has a PC speaker. Some systems do not have one. Other complications can arise from Linux rerouting the PC speaker output to a sound card. Check if the beeps are audible if you connect speakers to your sound card. Today almost all systems have one. Finally, check if the audio mixer control has a channel named "beep", which could be hidden in the mixer settings, and that it is not muted.