Urgent: fopen() doesn't work!

Hi all,

I am writing a module for Tux and I was hoping to write a file
'/tmp/myfile.txt' (or wherever it would be located). I found out that I can
only open files in the docroot or it's subdirs. I've created a subdir
"testdir" in the docroot and I've written a file "test.txt" in that
directory.
If i call fopen("/testdir/test.txt","r") it works. If I want to access
another file, lets say in the /tmp/ dir (reading or writing) it tells me
that the dir or filename does not exists.
What is causing this and could someone please show me how to get around this
problem in a module?
Thanks in advance!


Robin