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1200+ undocumented .vmx parameters

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Recently while performing some skunkworks testing in my personal lab, I came across a slew of documented and undocumented virtual machine .vmx configuration parameters. Using one of my favorite UNIX/Linux utility strings, I was able to uncover some interesting things in the /usr/lib/vmware/bin/vmware-vmx binary which is used to load a virtual machines configuration file.

Here are some of the interesting observations I have made:


vSphere is hypervisor aware?

%s: %s detected by CPUID
%s: VMware detected
Microsoft Hyper-V
%s: Xen detected by hypercall
Xen detected but hypervisor unrecognized (Xen variant?)

I noticed the following strings around detecting certain guest hypervisors, is this a hint that VMware is going to support other virtual "hypervisors", specifically Microsoft and Xen?

vSphere to support Mac OSX?

Linux Host
Windows Host
Mac OS Host

There were some text that listed the various types of host, including Mac OSX.

Make sure that you have installed all available Mac OS X software updates.
@&!*@*@(msg.cdrom.darwindisconnect)Your Mac OS guest is using this CD-ROM device. The safest way to disconnect this virtual CD-ROM is by pressing %s, then ej
ecting the media from inside the guest%s. To continue anyway, press %s.%s
@&!*@*@(msg.Backdoor.OsNotMacOSXServer)The guest operating system is not Mac OS X Server.
@&!*@*@(msg.cpuid.darwinWithBTHV)Mac OS X is not supported with software virtualization. Change the execution mode to automatic.
@&!*@*@(msg.cpuid.darwinWithBT)Mac OS X is not supported with software virtualization. To run Mac OS X you need a host on which %s supports hardware virtuali
zation.
isolation.bios.IsGOS.Darwin

There were some text that listed various messages regarding Mac OSX

sbios
vbios
bios440
efi32
efi64
nvram
lsibios
nbios
nxbios
nx3bios
e1000bios
vmibios
vmmmods
sas1068bios
pvscsibios

As you can see, there is mention of EFI support which is required to boot Mac OSX. Does this mean future version of vSphere will support virtualizing Mac OSX?

New guestOS types?

darwin10
darwin10-64
darwin-64
mandrake-64
opensuse
opensuse-64
winServer2008Cluster-32
winServer2008Cluster-64
winServer2008Datacenter-32
winServer2008Datacenter-64
winServer2008DatacenterCore-32
winServer2008DatacenterCore-64
winServer2008Enterprise-32
winServer2008Enterprise-64
winServer2008EnterpriseCore-32
winServer2008EnterpriseCore-64
winServer2008SmallBusiness-32
winServer2008SmallBusiness-64
winServer2008SmallBusinessPremium-32
winServer2008SmallBusinessPremium-64
winServer2008Standard-32
winServer2008Standard-64
winServer2008StandardCore-32
winServer2008StandardCore-64
winServer2008Web-32
winServer2008Web-64
XenVMMXenVMM

There was a section that I came across which listed all supported guestOS types, here you can see there have been a few more that were added between vSphere 4.0 and 4.1. One interesting thing that I am not sure if a lot of people have noticed, is the VirtualMachineGuestOsIdentifier in the vSphere API. This basically provides the guestos identifier that is supported in each release of VI/vSphere. Interesting enough, a darwin guestos support has been documented as of vSphere 4.0:

Though we all know we can not run Mac OSX on ESX(i) ... at least not just yet from what the above is hinting at.

These were just a few of the interesting things I found while parsing through the strings output when looking at the ESX 4.1's vmware-vmx binary.

Here is a collection of over 1200+ documented and undocumented .vmx configuration parameters.

**** These are not documented by VMware, use at your own risk! ****

http://https://s3.amazonaws.com/virtuallyghetto-download/hidden_vmx_params.html

**** These are not documented by VMware, use at your own risk! ****

Some of these hidden .vmx entries have been shared by the VMware and the community, here are just a few:

How to control maximum number of VMware snapshots

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There are currently no methods of controlling the number of VMware snapshots using vCenter or ESX(i) permissions today, you either provide the snapshot privilege or you deny it all together. I recently discovered an undocumented .vmx entry that allows you to control the maximum number of VMware snapshots for a given virtual machine. By default, a virtual machine can have a snapshot tree depth of 31, in the worse case scenario supporting up to a maximum of 496 snapshots.

Here is what a VM looks like with 496 snapshots (unexpanded):

 

Note: If you are interested in what this looks like fully expanded, take a look at the screenshot at the very bottom of this post.

If you like to prevent the above or at least control the maximum number of snapshots for a given virtual machine, you can add the following into a VM's .vmx configuration file. Ideally, this is deployed using vSphere API as there is no need to directly edit the VMX's file and this can also be applied to a live running VM (another benefit of using the vSphere API).

Here is an example using PowerCLI:

$vm = Get-VM -Name TestVM
New-AdvancedSetting -Name snapshot.maxSnapshots -Value 1 -Entity $vm

For those that prefer using another vSphere SDK, you just need to use the ReconfigVM_Task() to add the VM Advanced Setting. Please take a look at this sample for here for how to add/update VM Advanced Settings.

snapshot.maxSnapshots = "n"

where n = max number of snapshots and n <= 496

Here is a screenshot of adding this .vmx parameter using the vSphere Client:

The virtual machine above already has one snapshot and per the configuration change, we should not be able to take any additional snapshots:

Next, we will try to take a second snapshot:

As you can see, an error is thrown that we have reached the maximum number of permitted snapshots. If you would like to disable snapshots all together, you can set the value to be 0 and this will prevent anyone from taking snapshots, including administrators.

Here is a an screenshot of the expanded view of a VM with 496 snapshots:

Note: These snapshots were created with a VM running in an vESXi host and script to exhaust the maximum snapshot depth of 31. Each snapshot level was also exhausted with the maximum number of snapshots. Starting from level-1: it was the maximum depth minus 1, level-2: it was maximum depth minus 2, and so fourth. This was just a test to see what the system could handle, you should not try this a home or on a production VM 😉 Use at your own risk

Where are the "Power" Perf Metrics in the vSphere API?

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A recent question was posed on the VMTN developer forum on how to obtain the new power utilization metrics using the vSphere API. This new performance metric was introduced with the release of vSphere 4.x and can be seen using either esxtop or resxtop and specifying the "p" option for power if you are on an ESX or ESXi host.

You can also get these counters by using the vSphere Client and using the Advanced Charts:

This actually seemed like a simple enough question, pointing the user over to the vSphere API reference documentation under the perfManager. Though after taking a second look, it appears that no such metric exists in the documentation from VMware:

After a few minutes of digging around, I found that Power metrics actually do in fact exists but were not properly documented when they were first introduced. I wrote a quick vSphere SDK for Perl script called perfQuery.pl looking for metrics that were related to "power" and I identified the following:

As you can see these match up to those seen using the vSphere Client and I output the metrics using its rollup type, units, internal name and metric description. While writing this script, I also noticed there were two other performance metric types that existed and were not documented by VMware. Here is a mapping of the API performance metric keys to vSphere API perfManager, the last two including power metric types are undocumented by VMware:

vSphere Client Chart Option vSphere API Perf Metric Key Documented
Cluster Services clusterServices yes
CPU cpu yes
Management Agent managementAgent yes
Memory mem yes
Network net yes
Resource Scheduler rescpu yes
Storage Capacity disk yes
Datastore datastore yes
Disk disk yes
Virtual Disk virtualDisk yes
Storage Adapter storageAdapter yes
Storage Path storagePath yes
System sys yes
Virtual Machine Operations vmop yes
Power power no
vCenter Resources vcResources no
vCenter Debug Info vcDebugInfo no

Using the script and the performance metric key, you can actually query either all or a specific metric type that you are interested in. This is helpful, for those metrics that have not been publicly documented by VMware. However, the power metric should have been documented and I believe this to be a documentation bug that was missed by VMware.

Download: perfQuery.pl

If you are interested in learning more about the vSphere statistics and performance monitoring, I highly recommend checking out Luc Dekens three part series (Part1, Part2 and Part3) on vSphere performance monitoring. Even though his posts are specific to PowerCLI, all the concepts discussed apply to all the vSphere SDKs when dealing with performance monitoring using the vSphere APIs.