[Zope] location of tmp-file while uploading a file

hi, while uploading a file through the ZMI, i'd tried to locate this file on the filesystem on my linux box. with 'df' i saw that the space on /var was used. i've tried to locate the file, but i've had no success. then i used a simple "du -sb /var > out1 && sleep 10 && du -sb /var > out2 && diff -a out1 out2" to find the file. but there was no diff!! but meanwhile /var used about 10MB more space. any help? markus