Migration of Genius to Rocky 8#

The operating system on Genius nodes was updated from CentOS 7 to Rocky 8, the same operating system running on wICE nodes. This update is strictly necessary because CentOS 7 will be discontinued and this poses security concerns. We have tried to make the migration as transparent as possible for users, but still there are a few changes to take into account. The first important item is that the way you can search for and load modules has changed. This probably affects all users and you are urged to carefully read the section on centrally installed modules. The second item is that users that installed their own software (this includes conda environments), will need to reinstall the software for the new OS. More details are outlined below. If you still encounter problems after reading this documentation page, you can contact the support team.

Searching and loading centrally installed modules#


A lot of scientific software is centrally available on the VSC clusters. To avoid conflicts between different software packages, the installations are offered as modules (specifically, the Lmod system is used). The executables, libraries, headers, … of a certain module can only be used after that module has been loaded. By loading a certain set of modules, you can easily set up an environment that has precisely the software you need.

When an HPC 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 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 module#

One crucial point to understand, is that a module is available only if it is located inside a directory contained in the $MODULEPATH environment variable. The $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, you need to make sure your $MODULEPATH variable contains 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. As a result of this change, you do not need to do module use/unuse in your jobscripts. Such lines can be perfectly removed from your jobscript (unless you deal with an exceptional case).


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.


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 module is a sticky module , which means it is not unloaded with module purge.

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 1 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 is a freely available (GPL) program, ...
  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
      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


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


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:




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

Impact on user-installed software#

If you have installed a software package yourself in your own account, and you did this on a Genius CentOS 7 node, it must be recompiled on Genius on a node with the new OS.

Conda environments#

The Conda environment you installed might need reinstallations. If you already have a Conda environment that works on wICE, it also should work on Genius after the migration. If you only have a Conda environment working on Genius, it is best to create a new Conda installation. If you used pip to install software inside your conda environment and pip has compiled the package from source, you certainly need to recreate your conda environment. In this case, it is recommended to recreate your environment for full compatibility with the new OS. Best practice is to choose a new installation folder with explicit mention of the new OS, e.g.:


In order to install miniconda in a new directory you can

bash Miniconda3-latest-Linux-x86_64.sh -b -p ${VSC_DATA}/miniconda3-rocky8
export PATH="${VSC_DATA}/miniconda3-rocky8/bin:${PATH}