Atto uses dvips to render TeX code and the output is written to our error logs.

You can test it with all editor instances on the site. Just open your apache error log (I prefer "tail"):

tail -f /path/to/error.log

Open a page with editor and type some LaTeX. You will see your log filled with output from dvips:

This is dvips(k) 5.992 Copyright 2012 Radical Eye Software (www.radicaleye.com)

' TeX output 2014.07.15:1437' -> /path/to/moodle-data/temp/latex/c9f2799e49b47d9365bd8b80da49e827.ps

</a/path/taken/texlive/texmf/dvips/base/tex.pro>

</a/path/taken/texlive/texmf/dvips/base/texps.pro>. 

</a/path/taken/texlive/texmf-dist/fonts/type1/public/amsfonts/cm/cmsy10.pfb>

</a/path/taken/texlive/texmf-dist/fonts/type1/public/amsfonts/cm/cmr12.pfb>[1]

Dirty hack is to append "-q" in option "pathdvips", but obviously it says "path", which doesn't include command parameters. So the problem is: Why is it written to error output in the first place?