The Mystery of the Changing Citrix Registry Key

Updated: Sep 21, 2018

by Matt Tran

At a site I recently talked with – and where I had once worked – the technical team stumbled upon an issue where specific Cerner registry keys were being changed by an application on the Citrix servers. Users were reporting that they would log into Millennium®, but nothing would happen following the login splash screen. The technical team would identify which server the users were logging onto and begin its troubleshooting. Analysts were able to identify that the registry values were not the default values from their image. Once they corrected the registry values, the applications worked fine. With no knowledge as to why the registry values had changed, however, analysts couldn’t resolve the issue. They just waited for another user to call in the problem and then wait while they corrected it.

Back when I worked at this site, we had a similar issue. So I wrote a script that monitored for registry changes to specific keys and then emailed/paged our on-call analyst when these changes occurred. This notification allowed our analysts to quickly log onto the server and correct the registry keys before our end users were impacted. Additionally, the notification provided a log of all these occurrences and allowed us to capture more information.

This very basic script allows you to specify the registry keys you wish to monitor and the email address where notifications will be sent. If you are interested in using this script, please send your request to with Registry Listener Script in the subject line. We will be happy to share it with you. If you have encountered or resolved this issue in the past, please comment below.

Prognosis: Early detection and quick response to registry changes can reduce user frustration and calls to the help desk.

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