Rocky 9 migration#

We plan to update the KU Leuven Tier-2 cluster wICE to Rocky Linux 9.6 as the operating system. Important differences at the system level are listed below.

Packages

Rocky Linux 8

Rocky Linux 9

kernel

4.18.0-553.58.1

5.14.0-570.42.2

bash

4.4.20

5.1.8

gcc

8.5.0

11.5.0

glibc

2.28

2.34

Centrally installed modules have already been made available for Rocky 9, starting from toolchain 2021a.

Timing#

  • The open pilot phase starts from Wednesday 4th until Tuesday 17th of February 2026.

  • The actual migration will take place on Wednesday 18 February 2026. On this day, wICE will be unavailable, but the jobs in the queue stay in pending state until the migration is completed and the machine is released.

Reserved hardware#

During the open pilot phase, you can use the following reservations to test your application on nodes which already have the new OS:

  • rocky9_icelake allows you to use up to 12 Icelake nodes

  • rocky9_sapphirerapids allows you to use up to 12 Sapphire Rapids nodes

  • rocky9_a100 allows you to use one A100 GPU node

Note that we do not plan to reserve H100 GPU nodes for piloting.

Prepare before testing#

If you are only using centrally installed modules, your module load commands will automatically load the appropriate modules (e.g. the ones installed for Rocky 9 if you are on a node with Rocky 9). Note that this may not apply if you are manually modifying your module path (if in doubt, please consult The module system on Leuven clusters).

If you have been compiling your own software on Rocky 8, it is possible that this software will not run on Rocky 9. If this is the case or if you have any doubts, we recommend to recompile on a node with the new OS. When doing so, it can be convenient to use the ${VSC_OS_LOCAL} variable which describes the node’s operating system (i.e. “rocky8” or “rocky9”).

Keep in mind that also Python or R package installations may involve compiling steps for extensions and may need to be redone for Rocky 9.

Conda environments created on Rocky 8 will normally continue to work on Rocky 9 (at least if the compiled components are provided by Conda packages, as is normally the case).

Using reserved nodes#

In order to prepare your software, you need to use one of the target reservations:

  • add --reservation=<ReservationName> to your srun or sbatch commands on the command line, or

  • add #SBATCH --reservation=<ReservationName> to your jobscripts, or

  • specify the <ReservationName> in the text field ‘Reservation’ in the Open OnDemand form for any app

Expected impact#

We have learned from the first migration attempt that the impact of this upgrade will be small for most users. Currently the CPU cores are unable to reach the maximal (‘turbo’) frequency. Compared to nodes with Rocky 8, you may therefore see somewhat lower performance if only a few cores are active while the other cores are idling. This issue is still being investigated.