lmod integration unclear in module documentation

[sjpb]

Having recently installed spack on a system with lmod and built packages with it I was confused that module avail showed no modules. After asking for help on slack I discovered that setup-env.sh only sets MODULEPATH for tcl. I suggested on Slack that the module tutorial wasn't very clear about lmod use but having just gone back and reread the it Hierarchical Module Files section is actually fairly clear, but the details for lmod get a bit lost in a) the length of it and b) issues elsewhere.

Things which are confusing:

• Using module files via Spack suggests to me that lmod should "just work" with no configuration:

  If you have installed a supported module system you should be able to run either module avail or use -l spack to see what module files have been installed.

• Shell support says:

  To enable additional Spack commands for loading and unloading module files, and to add the correct path to MODULEPATH, you need to source the appropriate setup file in the $SPACK_ROOT/share/spack directory.

  with no mention that actually this only applies to tcl.

Additionally the module tutorial:

• starts with lmod
• says in that section:

  Now we can re-source the setup file and Spack modules will be put in our module path

• shows module avail working without changes to MODULEPATH - admittedly this is for non-hierarchical modules, but it is using lmod.

I also note (although its not strictly related) that the module tutorial says that spack load

employed the module files generated automatically by Spack.

which I understand is not true.

Its hard to provide a clean paragraph change which fixes the above, but from a new user point-of-view I think the list of things needed to know to get lmod working as expected (i.e. hierarchically, because that's how lmod is generally used I believe):

• ${SPACK_ROOT}/etc/spack/modules.yaml needs to have lmod: or maybe lmod:: in it.

• You need to load the compiler(s) you want to use, then run spack compiler add.

• You must define at least one Core (i.e. os-defined) compiler in modules.yaml, to form the entry point for the heirarchy.

• You need to run something like this to add Spack's modules into lmod:

  module use ${SPACK_ROOT}/share/spack/lmod/linux-centos7-x86_64/Core/
  

• You need to rebuild Spack's modules using

  spack module lmod refresh --delete-tree -y
  

  (I think?)

[justbennet]

You must define at least one Core (i.e. os-defined) compiler there, to form the entry point for the heirarchy.

Does one have to declare the system compiler as Core? Would Spack be usable for, say, a small bioinformatics cluster that doesn't need newer compilers and only run serial/multicore software?

Just trying to separate a requirement from a usual or recommended practice.

[sjpb]

My understanding - and I may be wrong - is that you have to specify some compiler as Core, else there's no entry point for the module tree. So the system compiler should be in Core, but if that's all you need, fine.