当您卸载一个程序时，“合理的”期望是从您的系统中删除它的所有痕迹，但事实往往不是这样。为什么？今天的超级用户问答帖子回答了一位好奇的读者的问题。

今天的问答环节是由SuperUser提供的，SuperUser是Stack Exchange的一个分支，是一个由社区驱动的问答网站分组。

由wandersick（Flickr）提供的屏幕截图。

问题

超级用户读者Mark Boulder想知道为什么在正常软件卸载后，某些注册表值始终保留：

Expanding on the SuperUser topic How do I remove residual traces of uninstalled software from the registry, why is it that every time I uninstall a program and then later look it up via RegEdit, it is still there?

Why are the majority of Windows applicati*** so intent on leaving tiny little traces of themselves in the registry? Does the fault lie with Windows or with the developers?

为什么在正常卸载软件后注册表值通常被“留下”？

答案

超级用户贡献者Lukas Rieger和Keltari为我们提供了答案。首先，卢卡斯·里格尔：

Because it is impossible. The registry has multiple root nodes but only two interesting ones: LocalMachine and CurrentUser. Normally, the setup writes values into LocalMachine, and the running program only writes into CurrentUser (actually, unless the setup messes with the permissi***, the running program cannot write into LocalMachine).

While keeping leftovers in LocalMachine is laziness (as pointed out by the other answers), it is not possible to clean the CurrentUser part.

If a program is installed per machine (which most are) and multiple users use it, what should the uninstaller do? It could safely remove the user settings of the current account, but the current account might not be your account. This happens if you started the uninstaller from a non-admin account and then entered the credentials of an admin account, the setup is now running under that account, not the first one.

What about the other users? It could try to enumerate all users, but their registry keys might not be loaded (Windows is lazy and only loads the things it needs).

But you should not even try that. If you use roaming profiles (i.e. terminal services) and then delete all settings on uninstall, you could really mess up and delete stuff that is actually still in use. A terminal server is basically one Windows machine where multiple users log-in at the same time and use applicati***. Say you have two terminal servers running one application. You uninstall the application on TS1, now all the settings for all users are gone on TS2 because you have roaming profiles. Oops.

The same also applies to files in the per-user directories. In the setup of my company’s programs, I delete the per-machine stuff but do not touch the per-user stuff, not even of the user currently running the setup.

接着是凯尔塔里的回答：

There are many reas*** why this is the case, however, it is not the fault of Microsoft or the Windows operating system.

The following is a list of some cases and reas*** why registry entries are left behind:

Bad Programming – The developer did not write the application uninstaller properly and the registry entries are left behind. In addition to that, the uninstaller might not have/use the proper permissi*** to remove the registry entries. It could also be that there is more than one application that uses those keys. For instance, two applicati*** from the same developer that write to the same keys.

Left On Purpose – As one comment mentioned, these entries could have been left on purpose. Some applicati*** have a trial period and, after that period, you might choose to remove the application. If you choose to reinstall the application later, those keys give the application information on when it was installed. In addition to that, some developers might choose to leave those keys in case you choose to reinstall the application. If the developer used registry keys to store your customizati***, they might leave them there so that when you reinstall the application, all of your customizati*** persist. In the grand scheme of things, registry keys only take up a few bytes.

Should you remove the keys? That depends. The Windows registry is a dangerous place to mess around in. You can inadvertently break your system. Leaving the extraneous keys will not hurt the system. Some people will say cleaning/defragging the registry will speed up your system, but that has been proven false repeatedly.

If you really want to get rid of those programs, there are some uninstaller tools that can remove every trace of a program. These programs will watch the installer of another program and record all the acti*** done to the file system and registry, then completely remove those acti***. One issue with these tools is that it is possible they can remove things you might want to keep.

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