You could use kpathsea to check the locations.
Type this at the command prompt to get the main path of your TeX installation:
kpsewhich --var-value=TEXMFMAIN
kpsewhich can provide more information, just type kpsewhich --help to learn more about it.
Further you could use the which tool to locate executables:
which tex
You may also check the versions of TeX, pdfTeX, LaTeX etc.:
tex -version
latex -version
All can be done at the command prompt, i.e. within a terminal window.
Further there are of course package managing tools of your distribution for look-up which packages are installed - Synaptic, dpkg-query -l etc.
If you're still not sure: just go ahead, compile a LaTeX file. Afterwards read the first line of the .log file produced by LaTeX, within the same directory. The first line may look like:
This is pdfTeX, Version 3.1415926-1.40.10 (Web2C 2009) (format=pdflatex 2010.6.25)
12 DEC 2010 16:47
So you know if you're using a current version. The package manager which you used for installation should have taken care of all, so texlive would be used. The questions 'What' and 'Where' can be answered by the mentioned kpsewhich, using various parameters, which does path look-up and file-look-up and presents the actually 'active' file.
You can find all locations that TeX will search for files using
kpsepath tex
The format is a bit weird: items are separated by colons, directories that should be searched using a ls-R index file start with !!, directories to be searched recursively end with //. To clean it up, we can process the output a bit:
kpsepath tex | tr ':' '\n' | perl -ne 'm-^(!!)?(/.*?)(//)?$- && print "$2\n"'
For each of those paths, you can find out which installed packages have put files under those paths using dlocate:
dlocate --package-only /path
(if you don't have dlocate, install it and make sure to run sudo update-dlocatedb). Putting it all together and eliminating duplicate package names from the output:
kpsepath tex | tr ':' '\n' | perl -ne 'm-^(!!)?(/.*?)(//)?$- && print "$2\n"' | while read path; do dlocate --package-only $path ; done | sort -u
For example, on my system, that prints:
asymptote
cm-super-minimal
context
dblatex
feynmf
gnuplot-x11
latex-beamer
latex-cjk-common
latex-make
latex-xcolor
latex2html
lgrind
lilypond-data
lmodern
pgf
preview-latex-style
tex-common
tex-gyre
tex4ht-common
texinfo
texlive-base
texlive-bibtex-extra
texlive-extra-utils
texlive-font-utils
texlive-fonts-extra
texlive-fonts-recommended
texlive-generic-recommended
texlive-lang-other
texlive-latex-base
texlive-latex-extra
texlive-latex-recommended
texlive-luatex
texlive-math-extra
texlive-metapost
texlive-pictures
texlive-pstricks
texlive-science
texlive-xetex
texpower
tipa
There's some stuff there that I wouldn't have expected, like gnuplot-x11, but dpkg -L shows that it includes a gnuplot-lua-tikz.sty. Who knew?!
Best Answer
Use
pdflatex --versionto tell which version of Latex you're using.