Módulos del Entorno

When one has multiple programs serving the same purpose (for instance SMTP servers such as sendmail, exim and postfix; or print servers such as lprng and cups), it is usual to wrap these using alternatives. Alternatives provides a clean way to have many types of software serving the same purpose installed at the same time and have the commands such as mail and lpr point to the wanted versions.

Sin embargo, cuando hay múltiples variantes que cada una sirve las necesidades de algún usuario y por tanto debe estar disponible simultáneamente por los usuarios, las alternativas del sistema simplemente no es suficiente ya que es por todo el sistema. Esto ha sido realmente en supercomputación y clúster para eones, y múltiples implementaciones de una solución ha sido desarrollada: módulos de entorno y Lmod. Actualmente Fedora emplea esto primariamente para manipular interruptores entre diferentes implementaciones de MPI.

Environment modules are also useful in situations where a package wants to install binaries that use common names and might conflict file in or otherwise pollute /usr/bin. Use must then load an environment module before being able to make use of those programs.

To see what modules are available, run $ module avail. To load a module run e.g. $ module load mpi/openmpi-x86_64. To unload a module, run e.g. $module unload mpi/openmpi-x86_64.

The upstream documentation for the module command is available here or with man module.

To install an environment module, place a module file into %{_modulesdir}, which should evaluate to /usr/share/modulefiles. This macro is available in Fedora and EPEL 7+. The directory /usr/share/Modules/modulefiles is to be used only for internal modules of environment-modules. /etc/modulefiles is available to local system administrator use.

The module files are plain text with optional tcl syntax, for instance an environment module for 64-bit OpenMPI mpi/openmpi-x86_64:

The module file begins with the magic cookie +#%Module +, where is the version of the module file used. The current version is 1.0.

The above commands prepends the path with the bindir of the 64-bit OpenMPI (compiled with GCC) and adds the relevant library path. Then it sets various environment variables.

It is also possible to set CFLAGS and LDFLAGS with the above manner, but in the case of MPI compilers it is not necessary since the compilers are invoked with the mpicc, mpicxx, mpif77 and mpif90 wrappers that already contain the necessary include and library paths. Also, in the case of development packages an override of CFLAGS and/or LDFLAGS is not sane, as it may cause trouble in building RPMs as it overrides %{optflags}.

The upstream documentation for module files is available here or with man modulefile.

Switching between the environment-modules and Lmod implementations is done via alternatives. The shell init scripts /etc/profile.d/modules.\{csh,sh} are links to /etc/alternatives/modules.\{csh.sh} and can be manipulated with the alternatives command.

Lmod is an environment modules implementation written in Lua, and can make use of module files written in Lua as well as Tcl. Such files have a ".lua" extensions. However, such files must not be installed /usr/share/modulefiles so as to not cause issues when the environment-modules package is in use. Instead install into %{_datadir}/lmod/lmod/modulefiles/Core.