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Editorial Team
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Asked: 2026-05-19T09:01:15+00:00

I’ve got a component that runs a couple of XmlConfig actions: one on install

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I’ve got a component that runs a couple of XmlConfig actions: one on install and one on uninstall:

  <Component Id="machine.config.Update" Guid="573DF5B0-438D-498d-8919-C4B96835C1EF">
    <RegistryKey Root="HKLM" Key="[REGISTRYKEY]\Settings\[TITLE]" Action="createAndRemoveOnUninstall">
      <RegistryValue Action="write" Type="integer" Name="MACHINEMEMORYLIMIT" Value="1" KeyPath="yes"/>
    </RegistryKey>
    <util:XmlConfig
      Id="CacheNode.memoryLimit.add"
      File="[WindowsFolder]\Microsoft.NET\[FRAMEWORKDIR]\v2.0.50727\CONFIG\machine.Config"
      Action="create"
      ElementPath="/configuration/system.web/processModel"
      Name="memoryLimit"
      Node="value"
      On="install"
      Value="90" />
    <util:XmlConfig
      Id="CacheNode.memoryLimit.remove"
      File="[WindowsFolder]\Microsoft.NET\[FRAMEWORKDIR]\v2.0.50727\CONFIG\machine.Config"
      Action="delete"
      ElementPath="/configuration/system.web/processModel"
      VerifyPath="/configuration/system.web/processModel"
      Name="memoryLimit"
      Node="value"
      On="uninstall" />
  </Component>

The component is part of a patch that I can install and roll back. The problem is that the uninstall action doesn’t fire when I uninstall the patch. The odd part is that the same XmlConfig action does execute if I change it to be On="install". I see that the registry key is properly removed on uninstall. Why isn’t the XmlConfig action firing as well? I checked the logs and did not see any errors or explanation of why it didn’t happen.

Update:
The XmlConfig action works when doing a full uninstall. Just not on a patch rollback.

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1 Answer

  1. Editorial Team

    Got an answer from the wix-users mailing list.

    Rob Mensching:
    “Adding custom actions in patches doesn’t work out so well. Patches essentially apply transform to the existing MSI then repair the MSI. In the case of uninstalling a patch, the transform is removed and the MSI is repaired. Obviously, if the custom action is removed with the transform then it has no chance to run.

    The Windows Installer does special magic to keep track of the state of the MSI before and after the transform so they can properly remove data.”

    They also talked about how there was a feature in MSI 4.5 that may let you do it but WIX needed to stay compatible with earlier versions and there were still some data storage problems around it.

    So in short, custom actions on patch uninstall don’t work in WIX.

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