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About InstallUtil
Development Guide > Managed CAs > InstallUtil

InstallUtil is often considered as another option for executing MSI custom actions written in managed code. But in most cases it is not the best solution, for a number of reasons.

InstallUtil (in either InstallUtil.exe or InstallUtilLib.dll form) is a .NET Framework tool for executing the System.Configuration.Installer classes that are implemented in an assembly. That way the assembly can contain any special code required to install itself and uninstall itself. Essentially it is the .NET replacement for COM self-registration aka DllRegisterServer.

Self-reg or System.Configuration.Installer is convenient for development use in order to test code without creating an actual setup package, or for an IDE which wants to generate self-installing code. But experienced setup developers and the Windows Installer documentation all agree that self-reg is a bad practice for a production-quality setup. The current theory of state-of-the-art setup is that it should be as data-driven as possible. That is, the setup package describes as fully as possible the desired state of the system, and then the installer engine calculates the necessary actions to install, uninstall, patch, etc.

S.C.I encourages developers to write code for things such as registering services or registering COM classes or other things which are more appropriately done using built-in MSI functionality (the ServiceInstall and Registry tables). The Visual Studio .NET wizards also tend to generate this kind of install code. Again, that is nice for development but not good for real installations. You end up with similar but slightly different code in many places for doing the same thing. And that code is a black-box to the installer engine.

An ideal MSI custom action is a logical extension of the setup engine, meaning it is data-driven and written in a very generic way to read from existing or custom tables in the MSI database, following a very similar pattern to the built-in actions. This makes the CA re-usable, and makes the installation more transparent. S.C.I custom actions invoked by InstallUtil cannot be data-driven because they don't have full access to the install session or database. They also cannot write to the install session's regular MSI log, but instead use a separate log which is bad for supportability.

InstallUtil also requires that the assembly be installed before the CA is able to execute. This is a problem for CAs that need to execute during the UI phase, or gather information before installation. For that purpose MSI allows custom action binaries to be embedded as non-installed files, but InstallUtil cannot make use of those.

Custom actions developed with DTF have none of the limitations of InstallUtil, giving a setup developer full capabilities to write well-designed custom actions, only now in managed code.