Just recently installed Slack 12 where I selected an ext3 filesystem.
My main partition was already formatted ext3 by Qparted; I did not
format it during install.

I want to determine which block size Qparted established and have learned
that dumpe2fs is the way to do it. All I have read suggests that I init
to single user mode (init 1) so that my partition will be mounted ro
instead of rw and I can then run dumpe2fs to gather information.

However, after entering single user mode, the partition, as well as a
few other items are still mounted rw.

I would rather run dump from within a running system rather than using
a rescue disk. I think I will somehow have to unmount the partition
from root and remount it ro, but I am not quite sure how to do it.

How should this be done?

If you mean to use 'dumpe2fs -h /dev/device' it's the same as using 'tune2fs -l /dev/device' (or if you like some LQ code: Osor posted http://www.linuxquestions.org/questi...7/#post2878170). I'm pretty sure none of those need runlevel one because you're not *writing* anything to it and you're not requesting anything volatile a multi-user runlevel could skew.