{"id":92261,"date":"2015-12-03T07:00:00","date_gmt":"2015-12-03T22:00:00","guid":{"rendered":"https:\/\/blogs.msdn.microsoft.com\/oldnewthing\/20151203-00\/?p=92261\/"},"modified":"2019-03-13T12:22:29","modified_gmt":"2019-03-13T19:22:29","slug":"20151203-00","status":"publish","type":"post","link":"https:\/\/devblogs.microsoft.com\/oldnewthing\/20151203-00\/?p=92261","title":{"rendered":"A question about how to detect whether Windows Update needs the system to be restarted turns out to be the wrong question"},"content":{"rendered":"

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A customer wanted to know whether there was a way to detect that Windows Update has recently installed an update that requires a reboot. They explained that their computers are running dedicated software, and the customers are not technically-savvy, so they want to display the “You need to reboot” message more prominently, and let the user choose the best time to reboot. “We have been checking a variety of registry keys, and we have found that the set of keys to check is quite extensive and varies depending on the nature of the update that was installed.” <\/p>\n

There is a fairly straightforward way to check whether Windows Update is waiting for the system to reboot<\/a>, but we asked for more information about the customer’s scenario. Fortunately, the customer was willing to share. <\/p>\n

These computers are in a hospital running critical medical software. The software runs 24\/7 and must not reboot without user consent. <\/p><\/blockquote>\n

If these are critical machines, then asking whether Windows Update is requesting a reboot is the wrong question. By the time you get the answer “Yes”, you are already in trouble: If you reboot the computer as soon as a reboot is required, you interrupt the machine’s critical functioning. If you postpone the reboot, then you leave the computer in a nonstandard configuration wherein an update is partially-installed, and that nonstandard configuration may compromise the machine’s critical function. <\/p>\n

In this specific case, the idea would be to change the design from “Install the update, and then postpone the reboot until a convenient time” to “Wait for a convenient time, then install the update and reboot immediately.” Here’s a sketch of how it could work. (Note: This is a sketch, not a fully-analyzed scenario. Do not implement this design on your critical medical systems before independently validating its efficacy to your satisfaction. In fact, as a general rule, you should not use blog posts as the sole basis for software design decisions for critical medical systems.) <\/p>\n