I only have a virtual machine available. No super-user rights.
Can I install Plone 6 in such a situation?
In particular, why does Plone 6 need Docker? Can I do without?
As far as I remember, I could install Plone 5 with two (non-superuser) accounts (plone_daemon, and plone_client) and some minimal super-user requirements. Is that still possible with Plone6? How?
You can install and run a Plone 6 project without Docker.
A description can be found on docs.plone.org
An alternative upcoming way to set up a new Plone 6 project, still alpha but already pretty mature, is 'cookieplone': GitHub - plone/cookieplone: Create Plone projects, addons, documentation with ease!
It is recommended to install as a dedicated user, not root, for security reasons.
Even a custom Python version can be installed. See pyenv. All requirements are explained in docs.plone.org.
In the same way as with Plone in the last 20 years.
There is zero need to install Plone under a privileged user account. All our installation are being done under one normal user account. We always install ZEO server and ZEO client under the same account. root access might be needed for the standard tools/packages that are required to build a Plone installation from scratch. root access might be needed to configure reverse proxying, load balancing etc.. but not for the Plone part. If I see Plone installations under root or evening running as root, I could run away and bang my head on the desk.
Good to know that one can still install plone basically without superuser right. Reverse proxy is OK, but why docker?
However, Create a project – Install — Plone Documentation v6.0 says that one of the prerequisites is docker. Is that really needed and why? Or is this just a convenience for people that control/develop several plone instances.
I only want a simple very basic Plone 6. I would like to stay with Plone, but if the installation it becomes too complicated, then I must switch to something else (not very attractive).
Andreas, I've found this thread Docker and Plone for add-on development where you basically explain that you deploy plone without docker. That was 2017. Is it still valid now?
I somehow miss the UnifiedInstaller to get me started with Plone 6 (without docker).
Installation via buildout or pip is also possible. Docker is not needed.
No idea what I wrote in 2017 
Building containers is a pain in the ***. Building Plone containers is a double pain in the ***.
I deploy even larger systems the "old way" using buildout. Much faster to deploy, much easier to deploy, much easier to maintain....only my personal opinion.
You can run buildout to create the docker image. The point is docker is a way to manage ready to use images (so is k8). Before, you've to build your app. You can use buildout, mxdev, ansible and so on.
It is not "complicated", just study them a little bit or keep with buildout.
@hemmecke what is your use case? From your post, it seems you can use buildout as usual. What you miss is the universal installer, maybe? Just follow the traning and adapt it. Do you need ClassicUI or Volto?
If you want to keep using buildout, we have a buildout template for Plone 6 that we are using in Production right now:
You may need to adapt it to remove some products we add and add yours.
Yes, I am going to study that in more detail and will come back with questions.
My usecase is rather simple. I want easyform and events and need to be able to control what members and non-members can see/edit. And I wrote a script to create members from outsite of plone (which is not totally necessary).
I do not care about the look of the user interface. I take whatever is simpler. So my question actually is whether ClassicUI (which I believe I used for Plone 4 and 5) is still the way I should choose over Volto.
I definitely have no real need for cutomizing the UI (excelpt for the Logo).
My main issue is that I would like to be able to upgrade to any newer version of Plone, so the fewer things I need to add the better. In fact, I am unable to upgrade an old Plone 4 site in which I added and later deleted some products without knowing that deleting a product doesn't bring be back to the state I was before the installation. So I have some leftovers in the DB that prevent me from upgrading at least to Plone 5.
If it's the problem I'm thinking of, there might be a way for you to remove references to old add-ons... Is it something like this? Manually Removing Local Persistent Utilities — Plone Documentation v3.3 or this? wildcard.fixpersistentutilities · PyPI
I may get things thrown at me for saying this, but if you want simple, use classic UI...
I am quite amused to find myself agreeing with Andreas ... I too have an aversion to having to run things inside Docker inside a VM.
IMHO the I don't think there is a problem with staying with plone 6 classic for now.
Why?
BTW, to upgrade a site with broken plugins, doing so via collective.exportimport and recreating a new clean site has it's advantages. Not sure you can do that from plone 4 though...