The module system on Leuven clusters#
This page offers additional information about the module system used on the HPC clusters hosted at KU Leuven.
Module organization#
When a cluster is not completely homogeneous (for instance there are differences regarding architecture or operating system between nodes), it is important to use the appropriate modules in your jobs. Using a module that is not suited for the node on which the job is running, can give suboptimal performance or may even completely fail to work.
This is why modules are organized in different software stacks, differentiated by the operating system, the architecture, and the toolchain version. The good news is that in general you do not need to worry too much about this, as in most cases the correct software stack will be made available in a job automatically thanks to the cluster modules, as explained in the next section.
If you are interested in more technical details, you can read the section on manually modifying the modulepath, which is oriented towards advanced users.
The cluster modules#
Background: a given module will only be available if it is located inside a
directory contained in the $MODULEPATH environment variable.
This $MODULEPATH environment variable is a colon-separated list of
directories, and you can list all modules located inside those directories
with the module avail command. The different software stacks mentioned
earlier are located in different directories (see the
next section for more details), so in
order to make sure you are loading modules from the appropriate software stack,
the $MODULEPATH variable needs to contain the appropriate paths for the
node where you want to use a module.
Because working with the different directories containing different software
stacks is cumbersome, we advise users to rely on the cluster module to set
the $MODULEPATH variable. The cluster module can be handled identically
as other modules, but instead of making executables or libraries available,
its only purpose is to set up your environment to make the correct modules
available. The cluster module is always available and you can see which
versions can be loaded by executing module avail cluster.
On the login nodes and inside a job environment, the correct version of the
cluster module will be loaded automatically. This means that for these cases,
you do not need to take any special action: the modules from the appropriate
software stack will be the only ones available to you. There is hence no need
for module use/unuse commands in your jobscripts (unless you deal with an
exceptional case).
Note
The appropriate cluster module is only loaded automatically inside a job environment and on the login nodes. In other cases (for example when you ssh directly into a node), you will need to first load a cluster module yourself in order to make the correct modules available.
Warning
If your jobscript contains the command module --force purge, the
cluster module will be unloaded and your $MODULEPATH will not contain
the directory with the appropriate software stack. It will be necessary to
load the correct cluster module or set your $MODULEPATH in another way.
This is why we advise to not use module --force purge in your jobs,
unless you are well aware of the consequences. Note that it is ok to
execute module purge, since the cluster modules are
sticky.
A common scenario is that you want to search through the installed modules for
a software package you need, while you are on a login node. There are two ways
this can be done. In the example below we assume the commands are executed on
a Genius login node. The software package that is used as an example is
called CP2K.
The first option is to load the cluster module corresponding to the node where you eventually want to use a certain software package. If you are planning to run jobs on the wICE batch partition, the commmand is:
$ module load cluster/wice/batch
Note that the previously loaded cluster module will be automatically unloaded:
at most one cluster module can be loaded at a time. Now you can search for
modules containing CP2K by executing (the search is not case sensitive):
$ module avail CP2K
-- /apps/leuven/rocky8/icelake/2021a/modules/all --
CP2K/8.2-foss-2021a Libint/2.6.0-GCC-10.3.0-lmax-6-cp2k
CP2K/8.2-intel-2021a (D) Libint/2.6.0-iimpi-2021a-lmax-6-cp2k
Libint/2.6.0-intel-compilers-2021.2.0-lmax-6-cp2k (D)
A second approach to search for installed software, is to use the
module spider command. In contrast to the module avail command, with
module spider Lmod will not only search for available modules (meaning
modules inside directories included in the current value of $MODULEPATH),
but additionally will take into account additional entries that would be added
to $MODULEPATH in case a cluster module would be loaded. An example is:
$ module spider CP2K
-------------------------------------
CP2K:
-------------------------------------
Description:
CP2K is a freely available (GPL) program, ...
Versions:
CP2K/5.1-intel-2018a
CP2K/6.1-foss-2018a
CP2K/6.1-intel-2018a
CP2K/7.1-foss-2019b
CP2K/7.1-intel-2019b
CP2K/8.2-foss-2021a
CP2K/8.2-intel-2021a
-------------------------------------
For detailed information about a specific "CP2K" package (including how
to load the modules) use the module's full name.
Note that names that have a trailing (E) are extensions provided by other
modules. For example:
$ module spider CP2K/8.2-intel-2021a
-------------------------------------
As suggested by the output, you can obtain more information about one
of the available versions of the CP2K module by executing:
$ module spider CP2K/8.2-intel-2021a
-------------------------------------
CP2K: CP2K/8.2-intel-2021a
-------------------------------------
Description:
CP2K is a freely available (GPL) program, ...
You will need to load all module(s) on any one of the lines below before
the "CP2K/8.2-intel-2021a" module is available to load
cluster/genius/amd
cluster/genius/amd_long
cluster/genius/batch
...
cluster/wice/batch
...
This command shows which cluster modules will make the CP2K/8.2-intel-2021a
module available. As discussed earlier, loading cluster/wice/batch is one
example of a cluster module that suffices to make CP2K/8.2-intel-2021a
available. For more information about module spider, have a look at the
Lmod documentation page
Note
In contrast to previous behavior, modules from different toolchain versions are now available automatically. On Genius, all modules since 2018a are available, and on wICE, all modules starting from 2021a. For a few legacy modules, installation is impossible on a recent operating system. In such a case, it is recommended to use a replacement module from a newer toolchain version. Alternatively you can consider to run your legacy software inside a container, but this is only the best option in some specific cases.
Manually modifying the modulepath#
As discussed in the previous section, the recommended approach to set your
$MODULEPATH environment variable, is by using the cluster module. This
will make modules from the correct software stack available. It is however
also possible to manually modify the path where modules are searched.
Each software stack is located in a directory with the following hierarchical structure:
/apps/leuven/${VSC_OS_LOCAL}/${VSC_ARCH_LOCAL}${VSC_ARCH_SUFFIX}/TOOLCHAIN_VERSION/modules/all
e.g.:
/apps/leuven/rocky8/skylake/2018a/modules/all
This convention is in line with other VSC sites and will also be used on wICE and future clusters. In order to add such a directory to your modulepath, the following command can be used:
module use /apps/leuven/rocky8/skylake/2018a/modules/all
To remove the entry again:
module unuse /apps/leuven/rocky8/skylake/2018a/modules/all
Keep in mind that also /apps/leuven/common/modules/all is part of your
default $MODULEPATH. This module collection is intended for packages which
have no operating system or toolchain dependencies. Typical examples are
packages which are distributed as precompiled binaries such as FLUENT.