# EESSI hackathon (Dec'21) - docs on installing software on top of EESSI

## Goals

- installing your own software packages on top of what's provided in EESSI
- examples:
- customized software
- software that's not freely available as open source

## Problems

- /cvmfs/pilot.eessi-hpc.org is read-only
- isolation from the host is required, must only link to compat layer
⇨ build must be done in stripped down Prefix environment
- RPATH linking complicates things (especially when not using properly configured EasyBuild)

## Workflow (manual)

- drop into Prefix environment
- use RPATH linking (see work on including RPATH wrapper scripts with compilers installed in EESSI software layer)

### What is needed to properly configure EasyBuild?

Highligth what needs to be changed in the EB config file

From: https://eessi.github.io/docs/pilot/#easybuild-configuration

- `robot`: to point to your own repo (first) + EESSI path
- `sourcepath`: prepend your source path, for example for non-opensource apps - so that it is not in your repo, and you can store it safely
- `prefix`: the local prefix for EB to install the app, this must then be prepend to the `$MODULEPATH`
- other best practise EB variables (for example `enforce-checksums = 1`)