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Some failed experiments

These failed experiments are documented to avoid making the same mistake twice.

Overwriting a module by putting one with the same name and version earlier in the path may not work

During the development of the LUMI software stack prototype using the 21.04 CPE release on eiger it turned out that the cpe/21.04 module had one nasty habbit: By setting LMOD_MODULERCFILE with the setenv LMOD function rather than by prepending or appending to it using prependpath/append_path, it cleared the modulerc.lua file that the LUMI software setup relies upon.

We tried to cure that by putting a modified copy of the file in a directory earlier in the MODULEPATH and hiding the original Cray module with a

hide_modulefile ( '/opt/cray/pe/lmod/modulefiles/core/cpe/21.04.lua' )
line in the system modulerc.lua file. Though the module was indeed hidden as module avail confirmed, and though there was a cpe/21.04.lua file earlier in the MODULEPATH, module load cpe/21.04 still loaded the wrong version, even with LMOD_IGNORE_CACHE=1.

A clue to what is happening is that when the line that hides the module in modulerc.lua is removed, you will notice that LMOD marks the one in the Cray core/cpe subdirectory as the default and not the one with the same name earlier in the MODULEPATH.

The problem is that

  1. When a full name is used, LMOD can still load a hidden module and does so when that module is marked as the default.

  2. The CPE does mark one of the cpe modules as the default using a .version file in the core/cpe subdirectory.

Luckily HPE-Cray uses a .version file which has the lowest priority. The solution is to mark a module in the overwrite directory as the default using either the symlink method or a .modulerc.lua file in that directory.

A change of visibility of modules is only detected when the module command exits

The idea was to write a module cpe/restore-defaults to restore the defaults rather than calling a script. This didn't entirely work as expected, likely because LMOD only assesses visibility at the start of the execution. Whereas changing MODULEPATH triggers LMOD to reassess the module tree, making changes to LMOD_MODULERCFILE doesn't trigger reassessing the visibility.

To recreate the experiment, take any standard cpe modulefile that doesn't only use those modules with the highest version number, e.g., one that uses an older version of gcc, ( and with the setenv replaced with append_path or prepend_path see the issues with the CPE), and the following cpe/restore-defaults.lua file:

modules = {

if (mode() == "load" or mode() == "show") then
    for _,mod in pairs(modules)
        if (isloaded(mod)) then
Then observe that
module load cpe/21.04
module load cpe/restore-defaults
doesn't produce the same state as
module load cpe/21.04
module unload cpe/21.04
module load cpe/restore-defaults
even though loading cpe/restore-defaults triggers the unloading of cpe/21.04. In the former, lower versions of modules will remain loaded. However, loading cpe/restore-defaults a second time to correct the situation, i.e.,
module load cpe/21.04
module load cpe/restore-defaults
module load cpe/restore-defaults
produces the expected result.