Description of the Windows Update Standalone Installer in Windows

Use WUSA to install an update package

When you use Wusa.exe to install an update package, Wusa.exe expands the contents of the .msu file to a temporary folder. Then, Wusa.exe performs the following steps:

1. Wusa.exe uses the Windows Update metadata in the .msu file to search for applicable updates.

2. Wusa.exe copies the contents of the applicable updates to the Windows Update sandbox. The Windows Update sandbox is a protected folder.

3. Wusa.exe calls the appropriate function in the Windows Update Agent API according to the mode in which you start Wusa.exe.

4. When the Windows Update wizard finishes the installation, the Windows Update Agent API returns a status. Then, Wusa.exe works synchronously with the Windows Update Agent API.

Note Each update in an .msu update package is installed in a separate session. Only one instance of Wusa.exe runs when you use Wusa.exe. Wusa.exe does not change the contents of the updates in .msu files. The Windows Update infrastructure performs the required actions according to the contents of the update.

When you start Wusa.exe in interactive mode, a welcome screen displays high-level information about the update. If you continue to install the update, Wusa.exe calls the appropriate function in the Windows Update Agent API to start the Windows Update wizard. The Windows Update wizard displays the Microsoft Software License Terms that are associated with the update package. Wusa.exe calls the Windows Update Agent API to continue the installation. Then, Wusa.exe waits until the Windows Update wizard finishes the installation.

To install an .msu update package, run Wusa.exe together with the full path of the file.

For example, if the Windows6.0-KB934307-x86.msu file is in the D:\934307 folder, type the following command at a command prompt to install the update package:

Note You can also double-click the .msu file to install the update package.

WUSA Switches

You can use the following switches together with Wusa.exe.

Note The .msu files can be installed to an offline image by using the DISM.exe /Add-Package option together with the Windows OEM Preinstallation Kit (OPK) or the Windows Automated Installation Kit (AIK). For more information, see Operating System Package Servicing Command-Line Options.

WUSA Event log

To view the Windows Update Standalone Installer event log, follow these steps:

1. Click Start, type event viewer in the Search box, and then click Event Viewer.
   
   If you are prompted for an administrator password or for confirmation, type the password, or click Continue.

2. In Event Viewer, expand Windows Logs, and then click Setup. Setup events appear in the middle pane.

3. In the Actions pane, click Filter Current Log.

4. In the Event sources list, click to select the WUSA check box, and then click OK.

Checkpoint cumulative updates

Windows quality updates use servicing technology and are built cumulatively from the time when a new Windows OS was released to manufacturing (RTM). These monthly updates include all the changes since RTM in the form of binary differentials computed from the initial version of those binaries.

With Windows 11, version 24H2 and Windows Server 2025, Microsoft introduced a new concept of checkpoint cumulative updates. This change allows you to get features and security enhancements via the latest cumulative update through smaller, incremental differentials containing only the changes since the previous checkpoint cumulative update. This change means that you can save time, bandwidth, and hard drive space.

Going forward, Microsoft might periodically release cumulative updates as checkpoints. The subsequent updates will then consist of:

• The update package files associated with the checkpoints, and

• New update package files that contain incremental binary differentials against the version of binaries in the last checkpoint.

This process might be repeated multiple times, thereby generating multiple checkpoints during the lifecycle of a given Windows release. The Windows 11, version 24H2 and Windows Server 2025 servicing stack can merge all the checkpoints and only download and install content that is missing on the device.

If any checkpoint cumulative updates precede a target update, a device or image needs to take all prior checkpoint cumulative updates before it can take the target update. In other words, a post-checkpoint latest cumulative update can be applied to images/devices that are on that checkpoint or on a subsequent latest cumulative update. For updates sourced from WU and WSUS this process happens seamlessly. You can continue to use the same tools and processes that you currently use for approving and deploying updates. We expect that your experience updating through a checkpoint cumulative update will position you to efficiently take future checkpoint cumulative updates.

Applicability

A checkpoint cumulative update is just another monthly security update that informs how subsequent updates are built. There is no policy change or new requirement around when you must take these updates, though it is best practice to take monthly security updates at the earliest opportunity to keep your devices protected and productive.

Finding prior checkpoint cumulative updates

For a given update, you can look up the KB article and find all preceding checkpoints, if any, listed under the Catalog release channel. For instance, the 2024-12 monthly security update (KB5048667) has one preceding checkpoint cumulative update per December 10, 2024-KB5048667 (OS Build 26100.2605).

Install each MSU file individually, in order

Download and install each MSU file individually either using DISM or Windows Update Standalone Installer in the following order:

• windows11.0-kb5043080-x64_953449672073f8fb99badb4cc6d5d7849b9c83e8.msu

• windows11.0-kb5048667-x64_d4ad0ca69de9a02bc356757581e0e0d6960c9f93.msu

Alternately, you can search for the KB number in the Microsoft Update Catalog and select the Download button for the selected architecture. The download pop-up shows all prior checkpoints for the update so that you can conveniently download all .msu files and apply them to their image or device. For instance, Microsoft Update Catalog shows the 2024-12 cumulative update (KB5048667) has one preceding checkpoint cumulative update, KB5043080.

Updating through checkpoint cumulative updates

​​​​​​​When installing a given monthly security or optional nonsecurity preview update, Microsoft Update Catalog users can determine and download the prior checkpoint cumulative updates and apply them together using WUSA or DISM, or apply them sequentially under certain situations. This section covers WUSA usage. This functionality is available on devices that have the KB5060829 or a subsequent update installed.

Devices that aren't on the latest checkpoint cumulative update can install all needed cumulative updates in the right sequence using WUSA in one go:

1. Copy the .msu files of the latest cumulative update (the target) and all prior checkpoint cumulative updates to a local folder. Make sure there are no other .msu files present.

2. Double-click the latest .msu file. This installs all missing MSUs in the right sequence followed by the latest .msu file.

If there are total four checkpoint cumulative updates available and the device already has the first one installed, WUSA applies the remaining three checkpoint cumulative updates in the right order followed by the target cumulative update together.

Alternately, if Language pack or region Features on Demand (FOD) customization is not needed, you can apply each required .msu file one at a time by double-clicking it in the right sequence.