macOS High Sierra – How to Install csrutil or New Recovery Partition

Default Location
When the macOS High Sierra Installer is downloaded from the Mac AppStore, it, like any other application downloaded through the Mac AppStore, ends up in the Applications folder. The name should be "Install macOS High Sierra.app" (or its equivalent in your language).

Typical Auto-Installation Prevention
Since the first Mac AppStore-based Operating System (Mac OS X Lion) was available to download, the way to prevent an automated installation upon completing the download was to cancel (quit) the installer, open the Applications folder and move (not copy) the installer to another location such as the desktop. Having done this every time, including High Sierra (in September 2017), I can verify that it worked then too.

Why might it be beneficial?
Apple has always been known for staying top of security, rather than playing a slow game of catch-up. It's thus only natural that the latest macOS version is somewhat "forced" onto the user's computer. Afterall, for the majority of users, making the conscious decision of clicking the download button means they intend to install it right away. Unfortunately, though, there are many people who think that clicking the download button is all there is to it - that's where the application opens and a window pops up to tell them otherwise, showing them what must be done. To you and me, this is very annoying because we don't fall into the "negligent" category, but just imagine if people think they have the latest version and are up-to-date with Apple's latest technologies and security only to find out they were just half way there.

What could you try next?

I think we can both agree that if it hints at the High Sierra option at startup, it's most likely that High Sierra has been downloaded and does indeed reside somewhere on the mac.

• I would firstly suggest using Spotlight: Command + Space Bar to make a search for "High Sierra", "Install macOS High Sierra" or any variations of it both in English and your own language (should it be different). I have always had more success with Spotlight than the traditional Finder search bar.

ADDITIONS

1. Please upload an image of the prompt you get upon restarting.

2. Perhaps something went wrong during the download procedure and the installer is not complete as a whole, yet some part of it thinks it is (perhaps a property file was written to too early), making it seem as though the update is ready to install when in fact isn't.

   For this, I would first like you to navigate to the App Store folder at /Users/<USERNAME>/Library/Application Support/AppStore and check that directory (including subfolders) for anything that may be High Sierra related. You may wish to consider this article to resolve download issues. It may seem a little far fetched but worth a go if all else fails.

3. Check under the Purchases tab in the Mac App Store, that High Sierra actually appears. Are you sure you downloaded it, or are you simply getting notifications that the upgrade is available (as your comment may hint at)?

Let me know how you make out and I'd be more than happy to assist further.

3 Solutions, or more likely workarounds
(Found them myself, but thanks to Thorbjørn Ravn Andersen anyways!)

To reiterate and clarify: I want to start in recovery mode of El Capitan on a MacBook Pro 2011 which has said OS as a partition and on another the ("factory set") Snow Leopard. Since El Capitan had - for an for me unknown reason?! - no recovery partition installed, my actual goal was to start internet recovery mode of El Capitan. This did not work since whenever I pressed [Cmd + R] at the chime, it started into recovery mode of Snow Leopard, which doesn't contain the wanted terminal command "csrutil" yet.

I went with option E)2. (above) and installed OS El Capitan on an empty external disk. After rebooting and holding the [Opt key] at the chime, I was able to choose the recovery partition of the newly installed system on the external drive, and afterwards disable SIP.

Thorbjørn Ravn Andersens solution will probably work too: A bootable USB stick - that's essentially the same as I did, but might be faster (?)... A third solution is probably (E)2.) reinstalling El Capitan to get the recovery partition (again?).

But even though those solutions (might) work, all of them include the time and space consuming (re-)installing of El Capitan. Since El Capitan should also have a internet recovery mode option it's unfortunate that one does not seem to be able to boot into that, if you have multiple (and older and "factory set") OS installed. (Option D)2., change the default start up disk to El Capitan and hit [(Opt +) Cmd + R] at the chime, should be working, but doesn't...)

So my Question is actually not solved completely, so I'll leave it open...
Thanks to every one who can give further advise! :D