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How do you "log a reason" using PowerCLI when rebooting or shutting down ESXi host?

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I am sure many of you have seen this UI prompt asking you to specify a reason before issuing a reboot or shutdown of an ESXi host and I assume most of you spend a few seconds to type in a useful message and not just random characters, right? 😉


Have you ever tried performing the same reboot or shutdown operation using the vSphere API or PowerCLI (which leverages the API)? Have noticed, there is not a way to specify a message like you can in the UI?

Here is a table of the PowerCLI cmdlets and the respective vSphere API that is used to perform these two operations:

Operation Cmdlet vSphere API
Reboot  Restart-VMHost  RebootHost_Task
Shutdown  Stop-VMHost  ShutdownHost_Task

When looking at either the PowerCLI and/or vSphere API documentation, we can confirm that there are no fields to specify a message which can lead to an assumption that this is simply not possible or that the functionality might be provided by a private API. Fortunately, this is not the case and the functionality is in fact in the public vSphere API and has been for quite some time.

When you specify a message prior to rebooting or shutting down, this message is actually persisted and implemented as an Event within vCenter Server as shown in the screenshot below.

Instead of being able to specify a message that is only applicable to an ESXi host, I believe the original vSphere API designers thought that this functionality could also be useful and applied more broadly across any number of the vSphere Inventory objects, not just ESXi hosts. As such, this functionality which the vSphere UI uses is provided by the LogUserEvent() method which is part of the EventManager API. Customers or solutions can leverage this mechanism to log custom user defined events which is then persisted with the lifecycle fo the vSphere Inventory Object or as far back as your retention period for vCenter Server Events.

Going back to our original question, if you want to specify a message prior to rebooting or shutting down an ESXi host, the following snippet below demonstrates the use of the vSphere API via PowerCLI:

$eventManager = Get-View eventManager
$vmhost = Get-VMHost -Name 192.168.30.11
$message = "This message will be logged"

$eventManager.LogUserEvent($vmhost.ExtensionData.MoRef,$message)

How to simulate Persistent Memory (PMem) in vSphere 6.7 for educational purposes? 

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A really cool new capability that was introduced in vSphere 6.7 is the support for the extremely fast memory technology known as non-volatile memory (NVM), also known as persistent memory (PMem). Customers can now benefit from the high data transfer rate of volatile memory with the persistence and resiliency of traditional storage. As of this blog post, both Dell and HP have Persistent Memory support and you can see the list of supported devices and systems here and here.


PMem can be consumed in one of two methods:

  • Virtual PMem (vPMem) - In this mode, the GuestOS is actually PMem-aware and can consume the physical PMem device on the ESXi host as standard, byte-addressable memory. In addition to using an OS that supports PMem, you will also need to ensure that the VM is running the latest Virtual Hardware 14
  • Virtual PMem Disks (vPMemDisk) - In this mode, the GuestOS is NOT PMem-aware and does not have access to the physical PMem device. Instead, a new virtual PMem hard disk can be created and attached to a VM. To ensure the PMem hard disk is placed on the PMem Datastore as part of this workflow, a new PMem VM Storage Policy will be applied automatically. There are no additional GuestOS or VM Virtual Hardware requirement for this scenario, this is great for legacy OS that are not PMem-aware

Customers who may want to familiarize themselves with these new PMem workflows, especially for Automation or educational purposes, could definitely benefit from the ability to simulate PMem in their vSphere environment prior to obtaining a physical PMem device. Fortunately, this is something you can actually do if you have some additional spare memory from your physical ESXi host.

Disclaimer: This is not officially supported by VMware. Unlike a real physical PMem device where your data will be persisted upon a reboot, the simulated method will NOT persist your data. Please use this at your own risk and do not place important or critical VMs using this method.

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Quick Tip - What hashing algorithm is supported for ESXi Kickstart password?

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I had a question the other day asking whether the encrypted password which can be specified within an ESXi Kickstart file (denoted by the --isencrypted flag) can use a different hashing algorithm other than MD5? The answer is absolutely yes. In fact, MD5 as a default hashing algorithm has NOT been used for a number of releases, probably dating back to classic ESX (you know, the version that had the Service Console).

For all recent releases of ESXi including 5.5 to 6.7, the default hashing algorithm has been SHA512 for quite some time now. Below are two ways in which you can check which default hashing algorithm is currently being used:

Option 1 - SSH to ESXi host and take a look at /etc/pam.d/passwd


Option 2 - SSH to ESXi host and take a look at /etc/shadow and look at the field prior to the salt.

As a reference:

  • $1$ - MD5
  • $5$ - SHA256
  • $6$ - SHA512