I have never installed KDE4 on this machine, which has been running KDE3 on openSuSE v11.1 64bit.

Last night I evidently did something, I do not know what, that caused the machine to boot this morning to a KDE4.1 desktop. I do not know how to return to the use of KDE3, and thereby to be able to run my KDE3 apps and access my data through them. Or, alternately, to get the KDE4 desktop to run the KDE3 apps. I would be very grateful for assistance.

hanasi

Log out in kde4 and choice kde3 see session type or something like that
Just log out do not reboot
If kde3 is gone reinstall using yast ore yum

KDE3 can be started from here

That gets me the following response:

$DISPLAY is not set or cannot connect to the X server.

Well, if kde 4 has never been installed, you won't be able to run kde 4, but you can.

Do you have a 'chooser' when you boot? that is, when the boot process goes through to a graphical splash screen, do you get the chance to choose the name of the user and to enter a password? If you do, this screen also gives you the choice, perhaps a little too well hidden, of choosing which GUI you will use for the immediate session.

In general, the default for the chooser is to give you (you = the user that you select, and therefore the GUI can't be selected before the user is selected) is to use the GUI that the particular user used on their last log in. If you do accidentally change things here, it will stay (should stay, anyway) the same until you change it.

To change it, select the user and then check the bottom of the screen.

Mostly this 'sort-of' works. kde4 can run kde3 programs, or has equivalents (although there are problems with stuff that gets too close to the hardware, like k3b), but quite a number of bits and pieces don't work; mainly irritations, but there are some show stoppers. However, it sounds like you have something like kde 4.1.2 as your kde 4, which is the version that came as default with 11.1. This version is really inadequate and under no circumstances, other than the most peculiar of perversions, would I advise that this would be good version to stay with; if you can't get into the 4.3.x range (pref at least 4.3.2, which is OK-ish), its too buggy....sorry should have called that full of interesting and distracting features.

If you are seeing it in your screen, it's installed. There's no spontaneous way that kde4 could just suddenly exist where it didn't exist before. The question is not if it has or not been installed. The right question that you should be formulating is "how".

I can't add anything that hasn't been already said above. Only add one bit: kde3 is still there, otherwise, this:

Would have returned a command not found error. The error it gave you means you probably ran it outside X, and kde can't run outside X of course. If you are using "startx" to start your session, you should put that command inside your ~/.xinitrc file, which is the script that will be launched each time you do "startx". If you are using a login manager, then you should see an option to boot whatever WMs or DEs you have available.

The way it happened to me was when I selected a package that requires the KDE4 libraries. Find the package you installed prior to the KDE change, and remove it. There may be an older version of that package that uses the KDE3 libraries. You have to be careful and watch the dependencies that are required.