Setting up your environment
Most applications, compilers and libraries rely on environment variables to function properly. These variables are usually set by the operating system, the administrator, or by the user. Typical examples include:
- PATH — location of system commands and user programs
- LD_LIBRARY_PATH — location of the dynamic (=shared) libraries needed by these commands and programs
- MANPATH — location of man (=manual) pages for these commands
- Program specific environment variables
The majority of problems encountered by users are caused by incorrect or missing environment variables. People often copy initialization scripts — .profile, .bashrc, .cshrc — from one machine to the next, without verifying that the variables defined in these scripts are correct (or even meaningful!) on the target system.
If setting environment variables is difficult, modifying them at run-time is even more complex and error-prone. Changing the contents of PATH to use a different compiler than the one set by default, for example, is not for the casual user. The situation can quickly become a nightmare when one has to deal with multiple compilers and libraries (e.g. MPI) at the same time.
Environment modules — modules in short — offer an elegant and user-friendly solution to all these problems. Modules allow a user to load all the settings needed by a particular application on demand, and to unload them when they are no longer needed. Switching from one compiler to the other; or between different releases of the same application; or from one MPI library to another can be done in a snap, using just one command — module.