Understanding File Overwrite Rules

InstallShield 2025

Project: This information applies to the following project types:

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Basic MSI

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InstallScript MSI

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MSI Database

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Transform

The Windows Installer service uses several file overwrite rules, by default, to determine whether a file included in an upgrade should overwrite a file that already exists on the target system. The rules apply when the REINSTALLMODE property uses the o setting to install over older files on the target system. To change this behavior, you can replace the o option with one of the following values:

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p—Reinstall only if there is no equivalent file on the target system.

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e—Reinstall if the file is missing or if it is an earlier or equal version.

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d—Reinstall if file is missing or different.

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a—Reinstall all files, regardless of version.

Note that the setting for REINSTALLMODE applies to all of the features being installed; it cannot be set for an individual feature. In addition, setting REINSTALLMODE to include a will likely cause prompts for the original installation source during the application of a patch.