Recently while researching for my recent blog post on ‘Methods to identify historical Time Zone configuration associated with a Windows PC’, I found myself hunting for Regback data within Windows 10 systems with limited success.
Specifically, across multiple system installed with Windows 10 1607, 1703 and 1803 I was finding hives within the C:\Windows\System32\config\RegBack which were 0 bytes in size, as below:
|RegBack folder with 0 Byte Hives
Many of the systems I was using were fresh windows 10 VMs and as such it may not be a surprise that backups of the registry had yet to be created. Nevertheless, two of the Win 10 1803 systems I was looking at were a longstanding VM that I already had, and my main Windows PC. So, I decided to dig a bit deeper.
Spoiler alert: this post doesn’t have all the answers, it records what I have observed and asks others to confirm whether my observations are consistent with theirs or whether they have an explanation.
The Scheduled task associated with registry backup is ‘RegIdleBackup’ and is located at ‘C:\Windows\System32\Tasks\Microsoft\Windows\Registry\RegIdleBackup’. Examination of various Windows versions 1507, 1511, 1607, 1703, 1709 and 1803 confirmed the scheduled task to be identical in all instances, it is as below:
The task references regidle.dll' which is responsible for the backup process and the ‘UseUnifiedSchedulingEngine’ field is set to ‘TRUE’ which specifies that the generic task scheduling engine is used to manage the task. The ‘Period’ and ‘Deadline’ values of 'P10D' and 'P14D' within ‘MaintenanceSettings’ instruct Task Scheduler to execute the task every 10 Days during regular Automatic maintenance and if it fails for 14 Days, to start attempting the task during the emergency Automatic maintenance. Further information on ‘maintenancesettingstype’ is available here.
I've performed some testing and this confirmed that initiating System Maintenance in any version of Windows 10 prior to 1803 has caused the RegIdleBackup Scheduled Task to be Queued and then Run. This causes the backup copies of the registry hives to be created in the RegBack folder. The same result is seen if we manually run the task.
On my Win 10 1803 test systems, running System Maintenances or manually starting the task will both cause the scheduled task to be executed. The below screenshot shows tasks queued after running System Maintainance on a Win 10 1803 system:
|Queued RegIdleBackup task
But despite the scheduled task being initiated, for some reason it completes immediately (without reporting errors), and the backup files are not updated. Recently when examining ‘Plug and Play Clean-up’ a similar depreciation was observed but in that case systems which were upgraded still retained the task, but fresh installs had dropped it. In this case a fresh install of Windows 10 1803 will still have the ‘RegIdleBackup’ scheduled task and it will still run during System Maintenance, but no backup copies of the registry hives appear to be created.
Earlier I noted that the task references a DLL located at ‘%systemroot%\system32\regidle.dll’. Reviewing this DLL within each version of Windows 10 confirms that each one has a different MD5, indicating differences in all versions.
I don’t have an overwhelming desire to try to reverse engineer the different versions of the DLL to attempt to determine the difference(s) and whether these are the reason that backup copies to be created, but if that particular challenge takes your fancy don’t let me stop you!
Additionally, if anyone on a Windows 10 1803 box has a spare 5 minutes I would appreciated feedback as to whether you have registry backups in your Regback folder and whether initiating system maintenance or starting the scheduled task causes them to be update.