# XIOS3 demonstrator configuration failing with segmentation fault

**URL:** <https://nemo-ocean.discourse.group/t/xios3-demonstrator-configuration-failing-with-segmentation-fault/945>\
**Category:** Versions\
**Tags:** XIOS\
**Created:** [28 August 2025 17:43 UTC](https://nemo-ocean.discourse.group/t/xios3-demonstrator-configuration-failing-with-segmentation-fault/945 "2025-08-28T17:43:33Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![jraylmer](https://avatars.discourse-cdn.com/v4/letter/j/c0e974/32.png) [@jraylmer](https://nemo-ocean.discourse.group/u/jraylmer)\
**Post date:** [28 August 2025 17:43 UTC](https://nemo-ocean.discourse.group/t/xios3-demonstrator-configuration-failing-with-segmentation-fault/945/1 "2025-08-28T17:43:33Z")

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Hi,

I am trying to upgrade from using XIOS2 to XIOS3 and initially just trying to get (a minor variation on) the `X3_ORCA2_ICE_PISCES` [demonstrator configuration](https://sites.nemo-ocean.io/user-guide/xios3demo.html) working.

I have successfully compiled XIOS3-trunk (revision: 2825) and a custom configuration based on `X3_ORCA2_ICE_PISCES` in NEMO `branch_5.0.1` (#6f645ba8). The only change is that I do not include`PISCES` and remove the corresponding `*pisces.xml` files and references to them in `context_nemo.xml`. I usually run a custom `ORCA2_ICE` configuration in this way without any issues (with XIOS2) so presumably that doesn’t matter here. If relevant, our system has OpenMPI v4.1.1 and GCC v8.5.0.

Running the job with XIOS in detached mode on 12 processors and NEMO on 32 seems to correctly initialise: I get the usual init. outputs in `ocean.output` and various `xios_server_*` outputs, but the simulation fails with “signal 11 (Segmentation fault)”. I get the same error changing to attached mode. I also get the same behaviour trying all this with NEMO `main` branch and `branch_5.0`. I have tried also a simpler output setup with just ice variables, with NEMO on 8 processors and 3 XIOS servers for the 2 `iwriter` and 1 `igatherer`—no difference.

I tried setting the `info_level` to `100` in `iodef.xml`, which doesn’t seem to give much insight beyond confirming that the XIOS servers are initialised.

I tried recompiling with debugging flags and this gave a bit more insight from the back trace: the segmentation fault occurs after the following series of subroutine calls:

`nemo_gcm → stp_MLF → iom_init_closedef → xios_close_context_definition`

So, it looks like the segmentation fault is arising from within XIOS but seems unlikely to be a bug there or in NEMO since these are recent versions of each and clearly others are using XIOS3 without problems.

**Please does anyone have any suggestions as to what might be causing this? I’m at a loss so any ideas would be welcome!**