Why does MSI require the original .msi file to proceed with an uninstall?

As most of you probably noticed, when uninstalling an MSI package Windows will ask for the original .msi file. Why is that?

I can only see disadvantages to that:

• not resilient to network changes.
• not resilient to local disk changes.
• unexpected by users.
• typically requires users to leave their desk and start a crusade to get the correct CD.
• kind of proves installations are not self-contained.
• promotes the use of unsafe tools such as msizap.
• which in turn promotes the "next time I'll just use a zip file" mentality.

Could someone shed some light on this?

Solution 1:

Fix Broken Uninstall: You can try the newest FixIt Uninstall tool from Microsoft if you have problems uninstalling an MSI. And one more link: Uninstalling an MSI file from the command line without using msiexec (a plethora of different ways to uninstall an MSI).

UPDATE:

This new support tool (this tool is now also deprecated) can be tried on recent Windows versions if you have defunct MSI packages needing uninstall (rather than the outdated, deprecated, unsupported msizap.exe).

Some have suggested to use the tool linked to here by saschabeaumont: Uninstall without an MSI file. If you try it and it works, please be sure to let us know. Feedback in that answer indicates that it works (I don't have any stuck setups to test with as of now).

Why are you asked for the original installation media?:

• The original MSI is not needed for uninstall unless the MSI itself is badly designed - or the cached MSI is missing (see details below).
• All installed MSI files are cached in %SystemRoot%\Installer\*.* using a random hex name.
• The cached MSI file is used for any maintenance, repair and uninstall operations - and it is sufficient for uninstall in the vast majority of cases.
• In some cases this cached file can be missing, and then uninstall is not possible at all in some cases (some theories as to why this can happen - MSI design errors, anti-virus quarantining, system restore, tinkering, developer system in erroneous state from development work, etc...). See more info below - and links to force uninstall or unregistration of the product.
• The original source is only needed if files need to be copied to disk (for a maintenance install), or the MSI does an explicit request to resolve the original source via the standard action ResolveSource or via a custom action (which shouldn't be done in a properly authored package - I think the MS Office package contained this ResolveSource error back in the day, causing everyone to go looking for their installation CDs/DVDs).
• In previous editions of Windows this cached MSI was stripped of all cabs, and hence contained the installer structure only, and no files.
• Starting with Windows 7 (MSI version 5) the MSI files are now cached full size to avoid breaking the file signature which affects the UAC prompt on setup launch (a known Vista problem). This may cause a tremendous increase in disk space consumption (several gigabytes for some systems). Check this article and especially the discussion at the bottom for more intel.
• To prevent caching a huge MSI file, you can run an admin-install of the package before installing. This is how a company with proper deployment in a managed network would do things, and it will strip out the cab files and make a network install point with a small MSI file and files besides it. Note that this may yield a UAC prompt is some cases since the extracted MSI file is no longer signed - this must be tested with your SOE / desktop configuration.
• Read my answer in this thread for the full description of admin installs: What is the purpose of administrative installation initiated using msiexec /a? or this similar but perhaps more accessible answer: admin install and its uses
• In some rare cases the cached MSI (with the random name) can be erroneously missing, and uninstall will then ask for the original MSI in order to complete the uninstall. This does not happen often. It used to be the case that one could use MsiZap.exe to clean out such an install, but this tool is outdated, deprecated and unsupported. Don't use it - there are too many incompatibilities with newer Windows versions and you create new problems. Perhaps try this support tool instead (also deprecated). The only option I can suggest now is this answer from saschabeaumont. If you try this tool, please let us know if it works for you. If you want to figure out what could have caused the cached MSI to be missing, try to read section 12 here: Uninstalling an MSI file from the command line without using msiexec (in short potential causes range from interference with system restore, anti virus and cleanup scripts, to erronous manual tweaking, low disk space, power outages, developer box debugging errors, badly designed MSI files with duplicate package codes, failed patches, etc... Many theories, few certainties I am afraid).
• As a last resort you can try system restore (unless it has been disabled entirely or partly) to go back to a previous installation state and see if this solves your uninstall problem (you can find video demos of this on youtube or a similar site).
• Be aware that system restore might affect Windows Update that must then be re-applied - as well as many other system settings. I have seen new, unsolvable installation problems resulting from a system restore, but normally it works OK. Obviously don't use the feature for fun, it's a last resort and is best used for rollback of new drivers or setups that have just been installed and are found to cause immediate problems and such issues. The longer you go back the more rework you will create for yourself. A lot of self-evident stuff, but I guess it needs to be mentioned.
• Since I mentioned system restore I suppose I should mention the Last Known Good Configuration feature. This feature has nothing to do with uninstall or system restore, but is the last boot configuration that worked or resulted in a running system. It can be used to get your system running again if it bluescreens or halts during booting. This often happens after driver installs. This will do nothing to fix your failing uninstall though (or I would be very surprised).

Related answer:

• Uninstall without an MSI file

In addition to this answer, perhaps this article on various ways of uninstalling MSI packages is of interest. It is a rather popular article with a high number of views:

• Uninstalling an MSI file from the command line without using msiexec.

Solution 2:

There are a few reasons for keeping the original msi:

• The uninstaller uses it to know what files and registry keys were installed and make sure they are all cleaned up.
• The msi may contain special uninstall actions that need to be performed.
• It allows you do to a 'repair' operation from the Add/Remove Programs menu, regardless of whether or not you saved the install file yourself.

The normal way of things is for Windows to keep the file cached for you, so you don't have to think about it. See your %WINDIR%\Installer\ folder. The only reason it would ask your for the original msi is if something is wrong with the saved file. This addresses most of your concerns, though it does raise a new one (disk-space).