Load modules

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Revision as of 09:00, 9 April 2020 by Dijkbvan (talk | contribs) (Load modules)

Load modules

To load a software module, use module load. In the example below, we will use Python 3.

Initially, Python 3 is not loaded. We can test this by using the command which that looks for programs the same way that Bash does. We can use it to tell us where a particular piece of software is stored.

  [me@nodelogin01~]$ which python3
  /usr/bin/which: no python3 in     (/cm/shared/apps/slurm/18.08.4/sbin:/cm/shared/apps/slurm/18.08.4/bin:/cm/local/apps/gcc/8.2.0/bin:/usr/local/bin:/usr/bin:/usr/local/sbin:/usr/sbin:/home/me/.local/bin:/home/me/bin)

We can load the python3 command with module load:

  [me@nodelogin01 ~]$ module load Python/3.7.2-GCCcore-8.2.0
  [me@nodelogin01 ~]$ which python3

So what just happened? To understand the output, first we need to understand the nature of the $PATH environment variable. $PATH is a special environment variable that controls where a Linux operating system (OS) looks for software. Specifically $PATH is a list of directories (separated by :) that the OS searches through for a command. As with all environment variables, we can print it using echo.

  [me@nodelogin01 ~]$ echo $PATH
  /cm/shared/easybuild/software/Python/3.7.2-GCCcore-8.2.0/bin:/cm/shared/easybuild/software/XZ/5.2.4-GCCcore-  8.2.0/bin:/cm/shared/easybuild/software/SQLite/3.27.2-GCCcore-8.2.0/bin:/cm/shared/easybuild/software/Tcl/8.6.9-GCCcore-8.2.0/bin:/cm/shared/easybuild/software/libreadline/8.0-GCCcore-8.2.0/bin:/cm/shared/easybuild/software/ncurses/6.1-GCCcore-8.2.0/bin:/cm/shared/easybuild/software/bzip2/1.0.6- GCCcore-8.2.0/bin:/cm/shared/easybuild/software/GCCcore/8.2.0/bin:/cm/shared/apps/slurm/19.05.1/sbin:/cm/shared/apps/slurm/19.05.1/bin:/cm/local/apps/gcc/8.2.0/bin:/usr/local/bin:/usr/bin:/usr/local/sbin:/usr/sbin:/home/me/.local/bin:/home/me/bin

You’ll notice a similarity to the output of the which command. In this case, there’s only one difference: the /cm/shared/easybuild/software/Python/3.7.2-GCCcore-8.2.0/bin directory at the beginning.

When we used module load Python/3.7.2-GCCcore-8.2.0, it added this directory to the beginning of our $PATH. Let’s examine what is there:

   [me@nodelogin01 ~]$ \ls /cm/shared/easybuild/software/Python/3.7.2-GCCcore-8.2.0/bin
   2to3		  futurize	 pip	      pytest		 python3-config	sphinx-apidoc
   2to3-3.7	  idle3		 pip3	      py.test		 pyvenv		sphinx-autogen
   chardetect	  idle3.7	 pip3.7       python		 pyvenv-3.7	sphinx-build
   cygdb	  netaddr	 pybabel      python3		sphinx-quickstart
   cython	  nosetests	 __pycache__  python3.7		tabulate
   cythonize	  nosetests-3.7  pydoc3       python3.7-config		virtualenv
   easy_install	  pasteurize	 pydoc3.7     python3.7m		wheel
   easy_install-3.7  pbr	 pygmentize   python3.7m-config

Taking this to its conclusion, module load adds software to your $PATH. It “loads” software. A special note on this, depending on which version of the module program that is installed at your site, module load may also load required software dependencies.

   [me@nodelogin01 ~]$ module list
   Currently Loaded Modules:
     1) shared           5) GCCcore/8.2.0               9) libreadline/8.0-GCCcore-8.2.0  13) GMP/6.1.2-GCCcore-8.2.0
     2) DefaultModules   6) bzip2/1.0.6-GCCcore-8.2.0  10) Tcl/8.6.9-GCCcore-8.2.0        14) libffi/3.2.1-GCCcore-8.2.0
     3) gcc/8.2.0        7) zlib/1.2.11-GCCcore-8.2.0  11) SQLite/3.27.2-GCCcore-8.2.0    15) Python/3.7.2-GCCcore-8.2.0
     4) slurm/19.05.1    8) ncurses/6.1-GCCcore-8.2.0  12) XZ/5.2.4-GCCcore-8.2.0