PowerShell Pipeline and object filtering

Pipeline is a functionality in PowerShell where it allows the output of a cmdlet to be used as input to the next cmdlet in the pipeline and work with them. By default at the end of a pipeline is a special cmdlet called Out-Default. Let's have a look at the example below.

Get-Service | Where-Object {$_.Status -eq "Running"}

The above example will provide you a list of services that are currently running on your machine. Here whats actually happening is objects that are produced by the first cmdlet (Get-Service) is passed to the next cmdlet in the pipeline. The second cmdlet will filter the services that are having "Running" status and displays the final result. "$_" holds the current object in the pipeline. 

Let's go through another example to get Windows event logs for last 24 hours.

Get-eventlog -LogName System -EntryType Error -After (Get-Date).AddDays(-1) | select EventID, TimeGenerated, Message |  convertto-html | Out-File C:\errorlist.htm

As you can see this example has multiple stages where output produced by one cmdlet is passed to the next cmdlet in the pipeline. Stage 1 filters System event logs with type error in the last 24 hours. The output of stage 1 is passed to next cmdlet in the pipeline which filters EventID, TimeGenerated, and Message. Results from stage 2 are passed to the next cmdlet where it converts the result to HTML and finally passed to the last stage where the final result is written to a file.

Reference video:

PowerCLI to remove orphaned VM from inventory

Recently I came across a situation where one of the VM running on ESXi 6.0 was orphaned. This happened after I updated the ESXi with a patch. All the files associated with that VM was available in the datastore. But the VM was displayed in the inventory as orphaned. There was no option available to remove the VM from inventory from the web console. Inorder to register the original VMX file, the orphaned VM needs to be removed from inventory first.

Steps to resolve this issue:

1. Connect to vCenter server using PowerCLI: Connect-VIServer 192.168.14.15
2. Get list of VMs: Get-VM | Select Name

3. In my case "HCIBench_1.6.5.1_14G" was orphaned.

4. Remove the orphaned VM: Remove-VM HCIBench_1.6.5.1_14G

5. As you can see in the above screenshot, orphaned VM is removed from inventory. Now you can go to the datastore where the original VM files are stored, click on the VMX file and register (In my case, while I tried to register the VM it resulted in an error mentioning that the item already exists. I had to reboot the vCenter server to fix this issue. After rebooting the vCenter I was able to register the VMX file of the VM).

Hope it was helpful to you. Cheers!

Reference: blog.vmtraining.net

Active Directory Audit using PowerShell

Most of the organizations will conduct an audit of their active directory infrastructure once in three or six months as part of a regular clean up and maintenance process. Some of the common activities involved in AD audit process are given below.

• Find all disabled objects like users, computers and service accounts
• Find all accounts which are inactive for the last 90 days
• Find all accounts with a password that will never expire
• Find all users, computers and service accounts that are expired
• Find all users, computers and service accounts that will expire in next 7 days
• Find all accounts that have been locked out

Now let's see how you can use PowerShell to obtain the above information.

Find all disabled objects like users, computers and service accounts:
Search-ADAccount -AccountDisabled | Format-Table Name, ObjectClass -AutoSize

Find all accounts which are inactive for the last 90 days:

Search-ADAccount -AccountInactive -TimeSpan 90.00:00:00 | Format-Table Name, ObjectClass -AutoSize

Find all accounts with a password that will never expire:

Search-ADAccount -PasswordNeverExpires | FT Name, ObjectClass -A

Find all users, computers and service accounts that are expired:

Search-ADAccount -AccountExpired | FT Name, ObjectClass -A

Find all users, computers and service accounts that will expire in next 7 days:

Search-ADAccount -AccountExpiring -TimeSpan 7.00:00:00 | FT Name, ObjectClass -A

Find all accounts that have been locked out:

Search-ADAccount -LockedOut | FT Name, ObjectClass -A

As per company IT policies, rules and regulations they can decide what actions need to be taken against the audited items. 

Reference: docs.microsoft.com

Objects, properties and methods in PowerShell

An object is something which has a set of properties that describes it and set of methods which are the actions you can perform on it. Lets look into an example.

Get the virtual machines from a Hyper-V host: Get-VM

The result shown in the above screenshot is not just text. These are objects and associated parameters. There are 4 virtual machine objects and its associated properties like Name, State, Uptime etc. The output shows only limited properties but there are more number of properties associated with a virtual machine object.

You can find all the properties and methods available for an object using: Get-Member

Example: Get-VM | Get-Member

Here you can see all the properties and methods available. 

Property

You can select the properties as per requirement.

Get-VM | select -Property Name, IsClustered, MemoryDemand, ProcessorCount, NumaAligned, Generation, Path

To retrieve properties of a specific virtual machine object, use the below:

Get-VM -name AD | select -Property Name, IsClustered, MemoryDemand, ProcessorCount, NumaAligned, Generation, Path

You can assign this to a string variable as shown below:

$vm = Get-VM -name AD | select -Property Name, IsClustered, MemoryDemand, ProcessorCount, NumaAligned, Generation, Path

And the individual properties of that object can be retrieved too!

Method

Example: Get-Service -Name bits

To get all the properties and methods for this object: Get-Service -Name bits | gm

Note: 'gm' is alias for Get-Member

In the above screenshot you can see several methods like start, stop, refresh etc. These are actions that can be performed on the service controller object "Bits".

Below screenshot shows how to start and stop "bits" service using Start and Stop methods.

To start bits service: (Get-Service -Name bits).Start()

To stop bits service: (Get-Service -Name bits).Stop()

Hope it was useful to you. Cheers!

Avoid disasters in PowerShell

WhatIf

If you are unsure about the operation or action that is going to happen after executing a PowerShell cmdlet, use "WhatIf". This will tell you what it will do without actually doing it. So that you will have an understanding of what the cmdlet is going to perform. Consider the below PS statement. 

Get-Service | where {$PSItem.name -eq "bits"} | Start-Service

Lets assume that you are unsure of what the above statement will do. Add -WhatIf at the end and execute it.

Get-Service | where {$PSItem.name -eq "bits"} | Start-Service -WhatIf

Example: WhatIf

The above screenshot explains the operation that will perform if you execute the statement. In this case it will start the BITS service. 

Confirm

Lets consider another scenario where you want to confirm the action from the user before actually executing it straight away. You can use "Confirm" in this case. See the below example. 

Clear-EventLog -LogName System -Confirm

Example: Confirm