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Like previous generation UI HPC systems, Argon uses environment modules for managing the shell environment needed by software packages. Argon uses LMod rather than the TCL modules used in previous generation UI HPC systems. More information about Lmod can be found in the Lmod: A New Environment Module System — Lmod 6.0 documentation. Briefly, Lmod provides improvements over TCL modules in some key ways. One is that Lmod will automatically load and/or swap dependent environment modules when higher level modules are changed in the environment. It can also temporarily deactivate modules if a suitable alternative is not found, and can reactivate those modules when the environment changes back. We are not using all of the features that Lmod is capable of so the modules behavior should be very close to previous systems but with a more robust way of handling dependencies. There is a module spider command that can be used to list modules but the module avail command is present as well. The module spider command is really designed for a hierarchical module layout, which Argon does not use, so there is little benefit to using module spider versus module avail to list the installed module files on Argon. An important point needs to be made for those who like to load modules in their shell startup files, ie., ~/.bashrc. One of the things that environment modules sets up is the $LD_LIBRARY_PATH. However, when a setuid/setgid program runs it unsets $LD_LIBRARY_PATH for security reasons. One such setgid program is the duo login program that runs as part of an ssh session. This will leave you with a partially broken environment as a module is loaded, sets $LD_LIBRARY_PATH but then has it get unset before shell initialization is complete. This is worked around on previous systems by always forcing a reload of the environment module but this is not very efficient. This scenario should not be an issue on Argon as all software is built with RPATH support, meaning the library paths are embedded in the binaries. In theory, $LD_LIBRARY_PATH would not be needed but this is something to keep in mind if you are loading modules from your ~/.bashrc or similar.
Lmod provides a mechanism to save a set of modules that can then be restored. For those who wish to load modules at shell startup this provides a better mechanism than calling individual module files. The reasons are that
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