There is a comprehensive Unix course on the tutorialspoint Unix training site.
Online HPC training is available as part of the ARCHER national HPC service. Almost all the material is a generic introduction to HPC with a short additional section that is specific to ARCHER.
For those that have run through the material (including the ARCHER-specific section) there is the option to take the ARCHER Driving Test online. People who complete the test successfully can apply for an account on ARCHER with 1200 kAU (80000 CPUh) to use over 12 months.
The online material can be found at:
and the Driving Test at:
The University of Illinois at Urbana-Champaign has a web site which has courses on parallel/MPI programming. The sites requires an account but it is trivial to register and spam safe. For more information please see here.
The Software Carpentry web site has a set of course notes and discussion documents relevant to scientists and engineers using HPC as part of their research.