[vbox-dev] [PROPOSAL] Userdata Interface

Klaus Espenlaub klaus.espenlaub at oracle.com
Fri Sep 16 11:15:23 GMT 2016

Hi Alex,

apologies for spreading incorrect information below. The guest 
properties have much lower size restrictions than I thought.

The limit for the guest property key length is 128 bytes (including the 
string termination), and for the guest property value it's 256 bytes.


On 15.09.2016 17:34, Alex Crawford wrote:
> On 09/15, Klaus Espenlaub wrote:
>> On 15.09.2016 09:12, Ivo Smits wrote:
>>> VirtualBox has Guest Properties, which I think are very similar to
>>> VMware's GuestVariables. You can use Guest Properties via the command
>>> line: https://forums.virtualbox.org/viewtopic.php?t=10823
>>> Or via the COM API:
>>> https://www.virtualbox.org/sdkref/interface_i_machine.html#a9f2fffade4b897eb659cc4602694676d
>> Right, Guest Properties sounds like a suitable mechanism. It has
>> reasonably high limits (can easily handle several 100KB), and handles
>> anything which is valid UTF-8. Don't try to abuse it as a way to pass
>> binary data directly, because then you'll run into 'random' failures
>> when the UTF-8 validation sets off the alarm. Oh, and if you pass large
>> data it's probably a good idea to mark the guest property as transient
>> so that it doesn't cause VM settings bloat.
> Yes, this is exactly the functionality I need. I don't understand how I
> could have missed this in the docs... Thank you for pointing this out.
>>> On the guest side you'll probably need the VirtualBox Guest Additions
>>> including its kernel module to be able to access the properties.
>> Not "probably", Guest Additions in the VM are a must have if you're
>> intending to use Guest Properties.
> Noted. Thank you both again.
> -Alex

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