I have a
header.tex file sitting in
$TEXMFHOME/tex/latex/ and I tried using
\input in another
.tex file in some other directory. Note that
kpsewhich is able to find
header.tex, printing its full path, and I have also applied
texhash on my
pdflatex does not seem to be able to locate the file.
I have tried going through both the documentation for
pdflatex for pointers. The
pdflatex states that
$TEXINPUTS is the search path for
\input files. And so I appended
$TEXMFHOME to that environment, which I believe I should not need to, but alas.