Monitor Windows data with PowerShell scripts

PowerShell is a scripting language that comes with many versions of Windows. It lets you handle Windows operations from a command-line interface. You can create scripts with the language and output the results of those scripts as objects to other scripts.

The Splunk platform supports monitoring events received through PowerShell scripts. You can use the PowerShell input to run a single PowerShell command or reference a PowerShell script. The Splunk platform then indexes the output of these commands or scripts as events.

If you use Splunk Cloud and want to monitor script output, use the universal forwarder to ingest the output from a Windows machine and forward it to your Splunk Cloud deployment.

Requirements

• Splunk Cloud must receive Windows data that comes from PowerShell scripts from a universal forwarder that is installed on a Windows machine.
• The Splunk platform instance must run on Windows. See Install on Windows in the Installation Manual.
• The Splunk platform instance must be configured to use the Local System user to run all PowerShell scripts.
• PowerShell version 3.0 or higher must be installed on the machine. Microsoft .NET version 4.5 or higher must be installed on the machine.
• There might be additional requirements to run PowerShell scripts depending on the version of Windows and PowerShell. See the Microsoft documentation on PowerShell for details.

Configure inputs with configuration files

1. Write a PowerShell command or script to capture the information you want.
2. On the Splunk platform instance that will run the script, open a PowerShell window.
3. Create an inputs.conf configuration file in the %SPLUNK_HOME%\etc\system\local directory.
4. Open the inputs.conf file and edit it to enable a Windows PowerShell input.
5. In the input, specify the command or the full path to your script with the script setting.
6. (Optional) Specify a schedule on which the command or script will run with the schedule setting.
7. Save the inputs.conf file.
8. Restart the Splunk platform to enable the input.

PowerShell input configuration values

The Splunk platform uses the following stanzas in the inputs.conf file to monitor data gathered by PowerShell.

Setting	Description	Default
script	The PowerShell command or script file to run. When you specify a script file (.ps1), prepend the script name with a period and a space (. ).	n/a
schedule	How often the command or script runs. You can specify either a number to indicate the interval, in seconds, or a valid cron schedule format.	Script runs once
disabled	Whether or not to enable the input. Set to 1 to disable and 0 to enable.	0 (enabled)

For information on writing PowerShell scripts, see Write scripts for the PowerShell input later in this topic.

Single command configuration example

This example runs the Get-Process cmdlet and pipes that output to the Select-Object cmdlet using the host name that Splunk software is installed on as an argument. It runs the command every 5 minutes.

    [powershell://Processes-EX1]
    script = Get-Process | Select-Object Handles, NPM, PM, WS, VM, Id, ProcessName, @{n="SplunkHost";e={$Env:SPLUNK_SERVER_NAME}}
    schedule = */5 * * * *
    sourcetype = Windows:Process

Script configuration example

This example runs the getprocesses.ps1 script located in the %SPLUNK_HOME\etc\apps\My-App directory. It sets the source type for these events to Windows:Process. The script runs every 20 minutes from 9:00 AM to 4:40 PM on Mondays to Fridays.

    [powershell://Processes-EX2]
    script = . "$SplunkHome\etc\apps\My-App\bin\getprocesses.ps1"
    schedule = */20 * 9-16 * 1-5
    sourcetype = Windows:Process

Configure inputs with Splunk Web

If you use Splunk Enterprise, you can configure inputs with Splunk Web. To configure the PowerShell input on universal forwarders, see Configure inputs with configuration files earlier in this topic.

Follow these steps to configure inputs with Splunk Web:

1. In Splunk Web, select Settings > Data inputs.
2. Select PowerShell v3 modular input.
3. Click New.
4. Enter an input name in the Name field.
5. Enter a command or path to a script in the Command or Script Path field.
6. Enter an interval or cron schedule in the Cron Schedule field.
7. Click the More Settings checkbox to select the source type, host, and default index.
8. Click Next.

Write scripts for the PowerShell input

The Splunk platform provides one modular PowerShell input handler. The PowerShell handler supports Microsoft PowerShell version 3 and higher.

The PowerShell modular input provides a single-instance, multi-threaded script host that provides a supporting schema, XML configuration through the stdin input/output data stream, and XML streaming output. See Modular inputs overview in Developing Views and Apps for Splunk Web.

You can define many PowerShell stanzas in an input configuration file and run them simultaneously. You can schedule each stanza using the cron syntax. Because all scripts run within the same process, scripts share environment variables such as the current working directory.

The input doesn't set a host variable in your PowerShell environment. When you write a script for the input, do not refer to $host or use the Write-Host or Out-Host PowerShell cmdlets. Instead, use either the Write-Output or Write-Error cmdlets.

The input converts all output to key/value pairs based on public properties that are defined in the schema.

The Splunk platform also includes a PowerShell module called LocalStorage, which exposes three cmdlets:

• Get-LocalStoragePath
• Export-LocalStorage
• Import-LocalStorage

These cmdlets use the Splunk platform checkpoint directory and let you maintain key/value pairs of data between scheduled runs of your script. Normally, data does not persist from one invocation to the next.

Specify paths

The input sets the SplunkHome PowerShell variable so you can address scripts in add-ons by writing paths like this:

    [powershell://MSExchange_Health]
    script=. $SplunkHome/etc/apps/TA-Exchange-2010/powershell/health.ps1

Besides $SplunkHome, there are several other read-only constant variables:

Variable	Description
SplunkServerName	The name configured for this machine to use in events
SplunkServerUri	The Splunk platform REST API address
SplunkSessionKey	The session key or authentication token needed for accessing the Splunk platform REST API
SplunkCheckpointPath	The path for storing persistent state
SplunkServerHost	The name of the Splunk platform instance that you want to communicate with
SplunkStanzaName	The name of the inputs.conf stanza that defined this script

Handle output of PowerShell scripts

The Splunk platform takes each object that your script produces as an output and turns it into an event, wrapped in <event> and <data> tags. The Splunk platform converts the properties of each object into key/value pairs. However, the value can only be a quoted string, converted by calling the .ToString() method. Thus, the output must be simple, and you must flatten any complex nested objects in your script before the script outputs them.

The following special property names have significance for the Splunk platform modular inputs and let you override the defaults in the inputs.conf stanza:

Property	Description
SplunkIndex	Overrides the index that the output is stored in.
SplunkSource	Overrides the source for the output.
SplunkHost	Overrides the host name for the output.
SplunkSourceType	Overrides the sourcetype for the output.
SplunkTime	Overrides the time. If you do not specify this, all objects that your script generates in a single execution get roughly the same timestamp. This is because the script holds the objects for output until it finishes executing, and then marks the objects with the output time. You must specify this value in epoch or POSIX time, which is a positive integer that represents the seconds that elapsed since 0:00 UTC on Thursday, January 1, 1970.

These properties never appear as objects in the key/value output.

If you want to set these properties and override the defaults, use a calculated expression with the Select-Object cmdlet or use the Add-Member cmdlet to add a NoteProperty property.

Caveats for handling PowerShell script output

The input currently requires that any PowerShell scripts it executes produce output objects that do not have any script properties. Pipe output through the Select-Object cmdlet to ensure proper formatting.

The input currently doesn't process the output of scripts until your pipeline and runspace are finished. This means the input does not process ScriptProperty values. It also means that all of your output essentially has the same timestamp, unless you override it using the SplunkTime variable.

When writing your scripts, avoid long-running scripts. Do not write scripts that wait for things to happen unless the scripts exit every time there is output.