\headheight Problem

Question

I'm using LuaLaTeX of latest TexLive 2014 on Windows 7.

I want to overlap headers (page numbers) and documents.

My code is as below:

\documentclass[a4, 10pt]{article}
\usepackage{fancyhdr}

\setlength{\headheight}{0mm}
\setlength{\headsep}{0mm}

\pagestyle{fancy}
\rhead{\thepage{}}

\begin{document}
test1
\clearpage
test2
\end{document}

When I typeset the code, 2 pages are generated.
But these layouts are different.
"test1" is above the header line, but "test2" is below.

How can I raise the text after 2nd page?

Answer 1

Check the console or the .log file, package fancyhdr is telling you, what is happening:

Package Fancyhdr Warning: \headheight is too small (0.0pt): 
 Make it at least 12.0pt.
 We now make it that large for the rest of the document.
 This may cause the page layout to be inconsistent, however.

Solution: set \headheight to 12pt in the preamble. Manually:

\setlength{\headheight}{12pt}

Or if package geometry is already used:

\usepackage[
  headheight=12pt,
  % other options
]{geometry}

BTW: There is a typo (two times) in the MWE: \0mm → 0mm.