LaTeX Forum

%% tikzext.tex
\documentclass[draft]{article}
\usepackage{xltxtra}
\defaultfontfeatures{Mapping=tex-text}
\usepackage{polyglossia}
\setdefaultlanguage[spelling=new]{german}

\usepackage{tikz}
\usetikzlibrary{external}
\tikzexternalize

\begin{document}
\begin{tikzpicture}
    \draw (1,1) -- (2,2);
\end{tikzpicture}
\end{document}

...
! Package tikz Warning: The key 'up to date check=md5' is impossible, there is 
no macro to compute MD5. Falling back to 'up to date check=diff'.
===== 'mode=convert with system call': Invoking 'xelatex -halt-on-error -intera
ction=batchmode -jobname "tikzext-figure0" "\def\tikzexternalrealjob{tikzext}\i
nput{tikzext}"' ========

! Package tikz Error: Sorry, the system call 'xelatex -halt-on-error -interacti
on=batchmode -jobname "tikzext-figure0" "\def\tikzexternalrealjob{tikzext}\inpu
t{tikzext}"' did NOT result in a usable output file 'tikzext-figure0' (expected
 one of .pdf:.jpg:.jpeg:.png:.bmp:). Please verify that you have enabled system
 calls. For pdflatex, this is 'pdflatex -shell-escape'. Sometimes it is also na
med 'write 18' or something like that. Or maybe the command simply failed? Erro
r messages can be found in 'tikzext-figure0.log'. If you continue now, I'll try
 to typeset the picture.

See the tikz package documentation for explanation.

tikzset{external/up to date check=simple}