Hi,
when I enter something in Krunner sometimes weird txt files, such as cmake, packages and other pop up as result. I guess these are system files which are searched for and within (because I didn't enter packages or make).

So searching for files and also within files is nice, but I would actually like to restrict this to my files (i.e. under /home), because these other results they always confuse me and also they make my hdd spin like mad.

So is it possible to restrict the search and how?
I look already in the plugin list, but I couldn't find such option there.

The locations which are indexed by Nepomuk, and thus searched through KRunner can be configured in System Settings > Desktop Search > Desktop Query, select "Customise index folders".

Ok, this works. Would have been nice tho restrict it just for krunner...

Because I just found out about this index setting:
I have an extra partition with music and video files, which isn't checked in the indexing. When I search with dolphin from my home and check "search everywhere" it doesn't find any files on this partiton. However when I go on the partition with dolphin and choose "search here" it finds the files. Is this because of the (missing) indexing?

Yes, this is likely due to the missing indexing - or the location where your drive is mounted is non-standard, and seen as part of the system, rather than containing user data.