Search Docs by Keyword

Table of Contents

CentOS 7 Transition FAQ


With the upgrade of Odyssey2 to Odyssey3 and CentOS 7, there are a few things you may need to know in order to resume your work on the cluster. We’ve assembled an FAQ of common questions/issues.

        • SSH key or ‘DNS spoofing’ errors when connecting to login or other nodes
          WARNING: POSSIBLE DNS SPOOFING DETECTED! and/or The RSA host key for has changed error messages.After an update of nodes, such as the May 2018 upgrade to CentOS 7, the SSH key fingerprint of a node may change. This will, in turn, cause an error when you next try to log into that node as your locally stored key will no longer match. SSH uses this as a way to spot man-in-the-middle attacks or DNS spoofing. However, when a key changes for a valid reason, this does mean you need to clear out the one on your computer in order to be able to re-connect.
          See this FAQ page for further instructions: SSH key error, DNS spoofing message
        • Modules in your .bashrc no longer work or give errors on login
          If you have edited your .bashrc file to include module loads at login, you may find that some CentOS 6 modules will not be found or may not work on CentOS 7. You will need to edit your .bashrc and comment out or remove any such lines going forward. If you can no longer log in because of something in your .bashrc, contact us and we can rename your .bashrc and copy in a default version for you.
          If you’d like to start from scratch, a default .bashrc contains the following:# .bashrc# Source global definitions
          if [ -f /etc/bashrc ]; then
          . /etc/bashrc

          # User specific aliases and functions below

        • Can I remove source from my .bashrc ?
          Yes. It no longer serves a purpose and can be removed. It’s not absolutely necessary for you to remove it, but it’s recommended if you’re comfortable with editing your .bashrc file as it makes for a cleaner login.
        • CentOS 7 modules and searching
          The Portal is the best place to search for modules, and provides far more information that module spider will. By default, the portal will now search for CentOS 7 modules (an option to switch to search old modules is also available):
          Portal Module SearchOur Software On Odyssey Intro has also been updated for the CentOS 7 transition and is worth re-viewing.As always, you have the ability to install your own software in many cases (especially true for R, Python, Anaconda).
          Please see our Installing Software Yourself page.

          For more information and information on legacy CentOS 6 modules, see the Running Jobs page.

        • Singularity
          New to Odyssey3 is the concept and implementation of containerized environments for jobs. We have standardized on Singularity for this and it is available now on Odyssey3. For more detailed information and instructions, see:

          Please Note: You cannot run Singularity on a login node (much like you should not run jobs or heavy software there). You will need to run it from an interactive session. More details in Singularity on the FASRC cluster


        • What about old modules?
          While it is true that some older modules will work on CentOS 7 without recompiling or rebuilding, we do not offer any guarantees on that front. You are free to try, but we have no plans to try to go back and make changes to old modules or to support their use. Use at your own risk.
        • My alternate shell (csh, tcsh, etc.) doesn’t work right
          Having a non-standard default shell will cause problems and does not allow us to set global environmental defaults for everyone. We will no longer change the default shell on any account or support the use of alternate shells as default login shell. Users who do not have bash as their default login shell will need to change back to bash. Users can, of course, still launch an alternate shell once logged in.

Still need help transitioning to CentOS 7?

You can always visit our regular Office Hours which run from roughly late August until the end of May/start of June.
See our Office Hours calendar.

Or send us a help ticket via our Portal (preferred) or by emailing


© The President and Fellows of Harvard College
Except where otherwise noted, this content is licensed under Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International license.