Latex - Manually add a package in Ubuntu
Sometimes the packages in Ubuntu are outdated (e.g. the geometry package in Ubuntu 12.04, see this forum) and it is necessary to manually include the package.
The easiest way for me is to just download the package from ctan, e.g. for the geometry package
i.e. either download the .sty file OR both the .dtx and .ins file. Change directory to the download folder, open a terminal (Ctrl + Alt + t) and run following commands
cd /PATH/TO/FILE.dtx latex *.dtx latex *.ins
Some files are generated. Copy the *.sty file (e.g. geometry.sty) into the directory of your .tex file, on which you are currently working on. Then the document should compile using