rmarkdown: pandoc: pdflatex not found

For people using ubuntu who get stranded here a better option (because it is 1/5 the size) is to use:

sudo apt-get install texlive-latex-base

Which I found via https://tex.stackexchange.com/a/128309

For those using Dunk's answer(For people using UBUNTU) who get a Font <font> at <size> not loadable: Metric (TFM) file not found. error, you also need:

sudo apt-get install texlive-fonts-recommended texlive-latex-recommended

This does unfortunately expand the size of the texlive install considerably, but it is still about half the size of a texlive-latex-extra install.

This answer on TexExchange might help.

I found I was having issues with pdflatex "missing" after I upgraded to OS X Mavericks (e.g. when checking package builds in RStudio I was getting an error tools::texi2pdf pdflatex missing message).

1. Check that /usr/texbin exists.
   In terminal:

   cd /usr/texbin
   

2. If "No such file or directory" then you will need to create a symbolic link to your installation's texbin. Mine was in /Library/TeX/Distributions/.DefaultTeX/Contents/Programs/texbin
   In terminal:

   ln -s /Library/TeX/Distributions/.DefaultTeX/Contents/Programs/texbin /usr/texbin
   

3. In terminal, check the result of echo $PATH. Make sure that /usr/texbin is present. If it isn't present, then you need to add /usr/texbin to your PATH variable.

If you find yourself having to mess with the PATH variable, installing the latest version of MacTex might be a better solution.

UPDATE: OS X 10.11 El Capitan no longer allows writes to /usr so the latest version of MacTeX (2015) now writes a link to /Library/TeX/texbin instead of /usr/texbin on this system.