Access to this page requires authorization. You can try signing in or changing directories . Access to this page requires authorization. You can try changing directories . Applies to: ✅ Windows 11 , ✅ Windows 10 The following table describes the log files created by Windows Update. When you see that the updates are available but download isn't getting triggered. When updates are downloaded but installation isn't triggered. When updates are installed but reboot isn't triggered. Generating WindowsUpdate.log To merge and convert Windows Update trace files (.etl files) into a single readable WindowsUpdate.log file, see Get-WindowsUpdateLog . When you run the Get-WindowsUpdateLog cmdlet, a copy of WindowsUpdate.log file is created as a static log file. It does not update as the old WindowsUpdate.log unless you run Get-WindowsUpdateLog again. Windows Update log components The Windows Update engine has different component names. The following are some of the most common components that appear in the WindowsUpdate.log file: AGENT- Windows Update agent AU - Automatic Updates is performing this task AUCLNT- Interaction between AU and the logged-on user CDM- Device Manager CMPRESS- Compression agent COMAPI- Windows Update API DRIVER- Device driver information DTASTOR- Handles database transactions EEHNDLER- Expression handler that's used to evaluate update applicability HANDLER- Manages the update installers MISC- General service information OFFLSNC- Detects available updates without network connection PARSER- Parses expression information PT- Synchronizes updates information to the local datastore REPORT- Collects reporting information SERVICE- Startup/shutdown of the Automatic Updates service SETUP- Installs new versions of the Windows Update client when it's available SHUTDWN- Install at shutdown feature WUREDIR- The Windows Update redirector files WUWEB- The Windows Update ActiveX control ProtocolTalker - Client-server sync DownloadManager - Creates and monitors payload downloads Handler, Setup - Installer handlers (CBS, and so on) EEHandler - Evaluating update applicability rules DataStore - Caching update data locally IdleTimer - Tracking active calls, stopping a service Many component log messages are invaluable if you are looking for problems in that specific area. However, they can be useless if you don't filter to exclude irrelevant components so that you can focus on what's important. Windows Update log structure The Windows update log structure is separated into four main identities: Process ID and thread ID Update identifiers Update ID and revision number Revision ID Local ID Inconsistent terminology Update ID and revision number Inconsistent terminology The WindowsUpdate.log structure is discussed in the following sections. The time stamp indicates the time at which the logging occurs. Messages are usually in chronological order, but there may be exceptions.

A pause during a sync can indicate a network problem, even if the scan succeeds. A long pause near the end of a scan can indicate a supersedence chain issue. Process ID and thread ID The Process IDs and Thread IDs are random, and they can vary from log to log and even from service session to service session within the same log. The first four digits, in hex, are the process ID. The next four digits, in hex, are the thread ID. Each component, such as the USO, Windows Update engine, COM API callers, and Windows Update installer handlers, has its own process ID. Search for and identify the components that are associated with the IDs. Different parts of the Windows Update engine have different component names. Some of them are as follows: ProtocolTalker - Client-server sync DownloadManager - Creates and monitors payload downloads Handler, Setup - Installer handlers (CBS, etc.) EEHandler - Evaluating update applicability rules DataStore - Caching update data locally IdleTimer - Tracking active calls, stopping service Update identifiers The following items are update identifiers: Update ID and revision number There are different identifiers for the same update in different contexts. It's important to know the identifier schemes. Update ID: A GUID (indicated in the previous screenshot) assigned to a given update at publication time Revision number: A number incremented every time that a given update (that has a given update ID) is modified and republished on a service Revision numbers are reused from one update to another (not a unique identifier). The update ID and revision number are often shown together as "{GUID}.revision." A Revision ID (don't confuse this value with "revision number") is a serial number issued when an update is initially published or revised on a given service. An existing update that is revised keeps the same update ID (GUID), has its revision number incremented (for example, from 100 to 101), but gets a new revision ID that isn't related to the previous ID. Revision IDs are unique on a given update source, but not across multiple sources. The same update revision might have different revision IDs on Windows Update and WSUS. The same revision ID might represent different updates on Windows Update and WSUS. Local ID is a serial number issued by a given Windows Update client when an update is received from a service. Typically seen in debug logs, especially involving the local cache for update info (Datastore) Different client PCs assign different Local IDs to the same update You can find the local IDs that a client is using by getting the client's %WINDIR%\SoftwareDistribution\Datastore\Datastore.edb file Inconsistent terminology Sometimes the logs use terms inconsistently. For example, the InstalledNonLeafUpdateIDs list actually contains revision IDs, not update IDs. Sometimes the logs use terms inconsistently. For example, the InstalledNonLeafUpdateIDs list actually contains revision IDs, not update IDs. Recognize IDs by form and context: GUIDs are update IDs Small integers that appear alongside an update ID are revision numbers Large integers are typically revision IDs Small integers (especially in Datastore) can be local IDs Recognize IDs by form and context: GUIDs are update IDs Small integers that appear alongside an update ID are revision numbers Large integers are typically revision IDs Small integers (especially in Datastore) can be local IDs Windows Setup log files analysis using SetupDiag tool SetupDiag is a diagnostic tool that can be used for analysis of logs related to installation of Windows Updates. For more information, see SetupDiag . Was this page helpful? Need help with this topic? Want to try using Ask Learn to clarify or guide you through this topic? Additional resources Last updated on 2026-02-11