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How to configure EESSI

Why configuration is necessary

Just installing EESSI is enough to get started with the EESSI software stack on a CPU-based system. However, additional configuration is necessary in many other cases, such as - enabling GPU support on GPU-based systems - site-specific configuration / tuning of the MPI libraries provided by EESSI - overriding EESSI's MPI library with an ABI compatible host MPI

To allow such site-specific configuration, the EESSI repository includes a special directory where system administrations can install files that can be picked up by the software installations included in EESSI. This special directory is located in /cvmfs/software.eessi.io/host_injections, and it is a CernVM-FS Variant Symlink: a symbolic link for which the target can be controlled by the CernVM-FS client configuration (for more info, see 'Variant Symlinks' in the official CernVM-FS documentation).

Default target for host_injections variant symlink

Unless otherwise configured in the CernVM-FS client configuration for the EESSI repository, the host_injections symlink points to /opt/eessi on the client system: 

$ ls -l /cvmfs/software.eessi.io/host_injections
lrwxrwxrwx 1 cvmfs cvmfs 10 Oct  3 13:51 /cvmfs/software.eessi.io/host_injections -> /opt/eessi

The target for this symlink can be controlled by setting the EESSI_HOST_INJECTIONS variable in your local CVMFS configuration for EESSI. E.g. 

sudo bash -c "echo 'EESSI_HOST_INJECTIONS=/shared_fs/path/to/host/injections/' > /etc/cvmfs/domain.d/eessi.io.local"

Don't forget to reload the CernVM-FS configuration

After making a change to a CernVM-FS configuration file, you also need to reload the configuration: 

sudo cvmfs_config reload

On a heterogeneous system, you may want to use different targets for the variant symlink for different node types. For example, you might have two types of GPU nodes (gpu1 and gpu2) for which the GPU drivers are not in the same location, or not of the same version. Since those are both things we configure under host_injections, you'll need separate host_injections directories for each node type. That can easily be achieved by putting e.g.

sudo bash -c "echo 'EESSI_HOST_INJECTIONS=/shared_fs/path/to/host/injections/gpu1/' > /etc/cvmfs/domain.d/eessi.io.local"

in the CVMFS config on the gpu1 nodes, and

sudo bash -c "echo 'EESSI_HOST_INJECTIONS=/shared_fs/path/to/host/injections/gpu2/' > /etc/cvmfs/domain.d/eessi.io.local"
in the CVMFS config on the gpu2 nodes.