Major OS Update on Theta

In order to make newer software versions available and to improve security and reliability—as well as to help pave the way for Theta to connect with the coming global filesystem—we will be updating Theta’s major OS versions during the week of July 13, 2020. We will upgrade ALCF-Theta from its current SLES12/CNL6 configuration to SLES15/CNL7. This necessary enhancement will be the last major OS version update of Theta. 

This will require most user codes to be rebuilt and/or relinked.


  • Newer versions of system software will offer better support for user software.
  • Newer compiler versions will become available.
  • New builds will be valid though Theta's end-of-life.

Known impacts and remediations

We are taking measures to minimize impacts and ensure continuity of available software. The current list of known impacts and remediations:

  • Cray will no longer be supporting HDF5 1.8.x versions. We will deploy our own build of 1.8.16. 
  • Intel compilers and software products are not expected to be affected.
  • Python support under Intel python should be minimally affected, similarly for conda or user-provided pythons. However, if any of a code's underlying dependencies are reliant upon packages the Cray programming environment or upon specific versions of system libraries, they *may* be affected. The upgraded OS will support both python 2.7.17 and 3.6.10. 
  • This will require a clean wipe of the current programming environment, including spack-built software.
  • Many user codes will need to be re-built and/or re-linked against the newer versions of programming environment and spack provided dependencies.
  • Some older versions of cray-built packages will no longer be available. In some instances this may require migrating to a newer version of a dependency, or sanctioning a spack-built replacement for the cray package.

As much as is practical, we are encouraging users to migrate to newer versions. Our users are a tremendous resource and we are reaching out for feedback during this process so that we can address and test migration issues in a timely matter.

Here is the before-vs-after diff of the OS upgrade.