Event ID 21 — WUA Update Installation

Applies To: Windows Server 2008 R2

Windows Update Agent installs updates from Windows Update, Microsoft Update, or Windows Server Update Services.

Windows Update Agent detects updates every day at the user configured time or by default at 3:00 A.M. If the computer is configured for Automatic Updates to take place, the downloading and installation of updates also take place at this time.

Event Details

Product: Windows Operating System
ID: 21
Source: Microsoft-Windows-WindowsUpdateClient
Version: 6.1
Message: Reboot required: To complete the installation of the following updates, the computer must be restarted. Until this computer has been restarted, Windows cannot search for or download new updates: %1


Restart the system

If updates are available but are not automatically downloaded, restart the system.


To confirm Windows Update Agent has installed updates:

  1. Open an elevated the Command Prompt window. Click Start, point to All Programs, click Accessories, right-click Command Prompt, and then click Run as administrator.
  2. At the command prompt, type eventvwr.msc, and press ENTER to open Event Viewer.
  3. To check for events in Event Viewer:
    1. In the left panel of Event Viewer, click Application and Service Logs.
    2. Expand Microsoft, and then expand Windows.
    3. Click WindowsUpdateClient, and then click Operational.
    4. Check to see if Event ID 19 is present in the event list to confirm that Windows Update Agent has successfully installed the updates.

WUA Update Installation

Windows Update