Use the find command to find files in your root directory that are large.
Quote from my "UNIX CD Bookshelf":
To search for files using a range of file sizes, a minus or plus sign can be specified before the number. The minus sign (-) means less than, and the plus sign (+) means greater than. This next example lists all files that are greater than 10,000 bytes, but less than 32,000 bytes:
find . -size +10000c -size -32000c -print
You can just put
find . -size +10000c -print to give you any file over a certain size. Increase it to at least 1,000,000 (no commas in find command) or maybe 5,000,000 to find the culprit.
Also, do a finger to see who is on the box right now someone maybe testing something and directed the output to root by accident.
Also, check to see how you box is partitioned. If /var or /tmp are in your root partition that maybe your problem area.
Also, do a man find to see what options you have for your UNIX OS. If you have the -prune option, you can limit the depth of your search with find or else it will search your entire box from the root directory!
Hope this helps.
