Linux Mint 10 includes geometry.sty version 4.2. In geometry.sty version 5, you get some extra snacks, like changing page layout mid-way.

Install the latest version:

wget ftp://ftp.tex.ac.uk/tex-archive/macros/latex/contrib/geometry/geometry.dtx

wget ftp://ftp.tex.ac.uk/tex-archive/macros/latex/contrib/geometry/geometry.ins

tex geometry.dtx

tex geometry.ins

sudo mv /usr/share/texmf-texlive/tex/latex/geometry/geometry.sty /usr/share/texmf-texlive/tex/latex/geometry/geometry.sty.old

sudo cp geometry.sty /usr/share/texmf-texlive/tex/latex/geometry

Latex code:

newgeometry{margin=2cm}

something

restoregeometry