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How to extract host information from within a VM?

01.15.2011 by William Lam // 34 Comments

From time to time, I see this question come up asking how one might be able to extract a certain piece of information from either ESX(i) or the management APIs (vSphere API) from within a virtual machine. The simple answer is you can not, by default the guest operating system has no idea of the underlying hypervisor nor does it have the access to the management APIs. This of course, assumes you are following VMware's best practices in isolated and segregating off your management network from your virtual machine network.

Having said that, there are certain bits of information that you can extract about your ESX(i) host from within the guestOS using some of the utilities that is installed with VMware Tools. The first utility is called VMware Toolbox command which can be found on both UNIX/Linux and Windows systems that have tools installed.

[Read more...]

Categories // Automation, OVFTool, vSphere Tags // guestinfo, vmtoolsd, vmware tools, vmware-cmd

How to control maximum number of VMware snapshots

10.31.2010 by William Lam // 21 Comments

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

Categories // Automation, vSphere Tags // snapshot

How to unregister vCenter plugin/extension using the MOB

07.09.2010 by William Lam // 20 Comments

I saw a post on the VMTN forums the other day about unregistering a vCenter plugin. The user had a bad installation of an early preview of NetApp's VSC utility. After uninstalling the plugin, the user was still unable to unlink the plugin from vCenter. There is actually a pretty simple solution to this problem which can be accomplished by using the vSphere MOB.

UPDATE (10/16/22) - As of vSphere 8, you can now easily unregister vCenter plugins within the vSphere UI. Select the specific plugin and then click on remove button.

Here are the instructions to remove a specific plugin/extension from your vCenter server:

1. Point your web browser to your vCenter server: https://your_vc_server/mob and login.

2. Click on content:

3. Locate and click on ExtensionManager:

4. Click on the plugin you are interested in removing:

5. Record the plugin key id which will be used to remove the plugin:

6. Now, go back to previous page and at the bottom click on the function "UnregisterExtension". A new window will open and ask for the plugin key id which was recorded from above. Enter the key and click on the "Invoke Method" to remove the plugin

You can now refresh the page and you will see that the plugin is no longer available. You can restart your vSphere Client to see that the plugin has now been removed.

The following operation can also be performed using a script, here is a vSphere SDK for Perl script that does just that: pluginExtensionManager.pl

Categories // Career, vSphere, vSphere Web Client Tags // Managed Object Browser, mob, plugin, vcenter, vsphere client, vSphere MOB

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Author

William Lam is a Senior Staff Solution Architect working in the VMware Cloud team within the Cloud Infrastructure Business Group (CIBG) at VMware. He focuses on Cloud Native, Automation, Integration and Operation for the VMware Cloud based Software Defined Datacenters (SDDC) across Private, Hybrid and Public Cloud

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