on a Redhat system, trying to find the cause of / filling up unexpectedly, I ran into this file named /proc/kcore that was quite big. Mysteriously, it couldn't be deleted, even by root. Which was good, since it turns out that it's actually a device. You'd think that kcore would be a core file that had to do with KDE, but in fact it's a wacky built-in that allows a person to dump active memory as though it were a file (using tools like od). Forums across the tubes are full of people who jumped to the same wrong conclusion that I did, and kind folks who explained the answer in ways interesting enough to preserve links to:
https://lists.ubuntu.com/archives/kubuntu-users/2005-May/000890.html
http://www.justlinux.com/forum/showthread.php?t=94027
http://www.linuxforums.org/forum/suse-linux-help/145869-kcore-file.html
http://www.linuxquestions.org/questions/ubuntu-63/prockcore-file-is-getting-bigger-and-bigger.-626078/
http://www.unix.com/unix-advanced-expert-users/107375-can-we-delete-kcore-file.html
