[CentOS] startx on console 2

I seem to recall that there is some special option to run X11 on <Alt-F2>

On this ClearOS system, their console sits on the default console. You have to <Alt-F2> (etc.) to get a text login. Now that I have Xfce kind of installed, I want to see it on the system console, and I thought that just running startx would work.

It doesn't. Got some errors. And then I remembered years back where there was some extra options used to run startx on one of the other consoles.

But it has been too many years and I can't find any notes on it. The manpage says something about a DISPLAY option, but its use is very unclear.

thanks