Learn from a particle physicist

Dec 22, 2021 learning LaTeX ORNL COHERENT Linux HPC

For various reasons, default programs on a Linux High Performance Computing (HPC) cluster are normally quite outdated. LaTeX may be one of them. SSH into your cluster and run latex --version to find out how old yours is. There are two problems with an old LaTeX installation. First, many new LaTeX packages widely used may not be included. Second, sometimes, the installation is too old to even allow you to add new packages to it to fix the first problem.

Before we talk about ways to fix the two problems, we need to think whether it is necessary to use LaTeX on a Linux cluster at all. After all, the main purpose of a Linux cluster is for computing, not typesetting a document. Beside, there are online LaTeX platforms to allow you to write articles in LaTeX together with your collaborators, such as Overleaf. However, I do find it convenient to write scientific papers with LaTeX on a cluster, which normally include many figures as the results of complex data analyses that are normally done directly on a cluster. You can download those figures from the cluster to your own computer, from where you upload them to Overleaf. This is painful if you have a lot of figures and you need to update them from time to time as your analyses progress. A better way to deal with this is to git clone your LaTeX project from Overleaf or other places to your cluster, save your analysis scripts and resulting figures in the project, and git push them to remote servers like Overleaf so that your colleagues can work on top of your update. But before that, you may want to check if you can compile your updated LaTeX project on the cluster and whether the resulting paper is satisfactory. This is where a working LaTeX installation on your cluster comes in handy.

Local LaTeX configuration

Now, let’s provide two solutions to the first problem, that is, how to deal with missing packages in an old LaTeX installation. If you see error messages complaining about missing .sty, .cls, or .bst, etc. files when you run latex yourPaper.tex, search that file on Google to find out which LaTeX package contains it, then go to CTAN to download that package and unpack it to your LaTeX project directory. The drawback of this solution is that your LaTeX project would include many files that is not related to your work.

A better solution is to save the missing package to another directory and tell LaTeX where to find it so that it will be kept separated from your personal LaTeX project. Meanwhile, this package can be reused for your other LaTeX projects. LaTeX allows a normal Linux user (without root privilege) to save his or her LaTeX packages and configurations in a particular folder in the user’s home directory. This folder is defined by an environment variable called TEXMFHOME. You can check the definition of TEXMFHOME in your system TeX configuration file by running

kpsewhich texmf.cnf # locate system TeX config file
cat /path/to/system/texmf.cnf | grep TEXMFHOME

or simply

kpsewhich --var-value TEXMFHOME

If you don’t have that folder, you can create it by yourself. If you don’t like the default location of that folder, you can also change it by redefining the environment variable TEXMFHOME:

export TEXMFHOME=/a/folder/that/you/like

Remember to put the code above to your SHELL configuration file (.bashrc, .profile, .zshrc, etc.) to make the change permanent.

Now you can put missing packages into this folder specified in $TEXMFHOME and run

cd /path/specified/in/TEXMFHOME
texhash . # or mktexlsr .

to create an index file that tells LaTeX what’s in this folder. NOTE: .cls and .sty files should go to $TEXMFHOME/tex/latex/, while .bst files should go to $TEXMFHOME/bibtex/bst/. Those files won’t be found if you don’t follow this conventional path specification.

It is very easy to make mistakes here or there if you manually install missing packages. Fortunately, if the LaTeX installation is new enough (later than 2013), you can use a command called tlmgr (texlive manager) in usermode to automatically pull packages from CTAN to your $TEXMFHOME:

# create directory defined in $TEXMFHOME (only need to be run once)
tlmgr --init-usertree
# pull missing_package from CTAN to your $TEXMFHOME and update the index file
tlmgr --usermode install missing_package

Local LaTeX installation

If the LaTeX installation on your cluster is too old, it may not be able to handle new packages that you put in your $TEXMFHOME directory. In that case, you can install the entire LaTeX program in your home directory (Yes, LaTeX can be installed without the root privilege). You can follow the documentation of texlive to achieve that. If you install texlive in ~/texlive, the latex command can be found in folder ~/texlive/20xx/bin/x86_64-linux/. Another useful command in the same folder is tlmgr. You can use it to install any missing package without being in the usermode:

tlmgr install missing_package

This sounds like a very attractive solution. However, it takes a lot of time and disk space as well as command-line experience. Before you resort to this solution, ask around. It is very likely that some experienced user on the same cluster has already done that. All you need to do is to use his/her LaTeX installation instead of the system one.

LaTeX on an ORNL HPC cluster

Now let me explain how to use a LaTeX installation that is not in the standard location. I will use an HPC cluster at ORNL called hcdata as an example. I have installed texlive 2019 in my home directory on hcdata. It is not the latest version, but is new enough to handle all scientific paper writings I have to do so far. To use it, put the following environment variable settings in your ~/.bashrc file:

export PATH=~jingliu/texlive/2019/bin/x86_64-linux:$PATH
export MANPATH=~jingliu/texlive/2019/texmf-dist/doc/man:$MANPATH
export INFOPATH=~jingliu/texlive/2019/texmf-dist/doc/info:$INFOPATH

You need to log out and then back into your terminal to let the new settings take effect. Run which latex to make sure that you are using my LaTeX instead of the system one. As an example, you can download a LaTeX project from the MARS group and try to compile it with my LaTeX installation:

git clone https://code.ornl.gov/CASA/MARS.git
cd MARS/docs/papers/2021_MARSCharacterization
latexmk # a Perl script that automates latex compilations

You should be able to generate a pdf file MARSCharacterization.pdf upon a successful LaTeX compilation.