Migration from CentOS7 to RHEL9

The computing platform’s operating system is currently being migrated from CentOS7 to RHEL9.

25% of the computing servers are providing the RHEL9 operating system. The rest of the platform remains on CentOS7.

Please find on this page all the information required to use both operating systems during this transition period.

Interactive access

To access an interactive server in RHEL9, please use the alias cca9:

% ssh -Y username@cca9.in2p3.fr

The same best practices rules for the use of interactive servers apply.

Submit a job

To switch to a RHEL9 computing server, you will need to add the --constraint el9 option to the submission command.

% sbatch -n 1 -t 01:00:00 --mem 3G --constraint el9 job.sh

If the --constraint argument is not specified, the job automatically switches to CentOS7.

To avoid being limited to a single segment of the computing platform and if the job can run on either CentOS7 or RHEL9, you can use --constraint "el7|el9" (the quotes are important to avoid bash interpreting the |). For example:

% sbatch -n 1 -t 01:00:00 --mem 3G --constraint "el7|el9" job.sh

This way, the scheduler can place the job on any available server on the computing platform.


Only htc, htc_interactive and gpu partitions are currently concerned. This option may thus be added to the following submission type syntaxes:

Software environment

The software environment, in particular the softwares provided by CC-IN2P3, depends on the operating system.

Slurm transports your environment from the submission server to your allocated computing server. It is therefore recommended that you submit your jobs from an interactive server running the same operating system, if you want to ensure having the required environment on the computing server (you can also define, and export, thanks to the submission script, the environment variables you need).


If you have pre-defined environment variables, or configuration files, such as the local Environment Modules configuration file, there could be incompatibilities if the software is loaded from an CentOS7 configuration instead of from RHEL9.

Please do not hesitate to contact user support to report any software issue encountered.