# ParaView headless server crashes with OpenFOAM's non-conformal coupling interface (NCC)

**URL:** https://discourse.paraview.org/t/paraview-headless-server-crashes-with-openfoams-non-conformal-coupling-interface-ncc/15496
**Category:** ParaView Support
**Tags:** openfoam
**Created:** [October 4, 2024, 11:41am UTC](https://discourse.paraview.org/t/paraview-headless-server-crashes-with-openfoams-non-conformal-coupling-interface-ncc/15496 "2024-10-04T11:41:15Z")
**Posts on this page:** 10
**Page:** 1

<div class="post-metadata">

### Author: ![peth](https://discourse.paraview.org/letter_avatar_proxy/v4/letter/p/258eb7/32.png) [@peth](https://discourse.paraview.org/u/peth)
#### Post date: [October 4, 2024, 11:41am UTC](https://discourse.paraview.org/t/paraview-headless-server-crashes-with-openfoams-non-conformal-coupling-interface-ncc/15496/1 "2024-10-04T11:41:15Z")

</div>

client:  
OS: arch linux  
paraview 5.13.1

host:  
OS: ubuntu 22.04 LTS / arch linux (tested on both systems)  
paraview headless 5.13.1, downloaded from ParaView website

host command (from paraview’s bin dir):  
./pvserver  
OpenFOAM version: OpenFOAM 12, OpenFOAM Foundation version, downloaded from GitHub and installed manually

description:  
ParaView shows warnings with OpenFOAM’s new non-conformal-coupling (NCC) interface. A warning message appears from Paraview as “vtkOpenFOAMReader.cxx:8826 ERR| vtkOpenFOAMReaderPrivate …: Number of cells/points in mesh and field do not match: mesh = 0, field = 23805 in T”.  
If I understand correctly the problem is related to the NCC interface, as it looks in OpenFOAM’s mesh directory in constant/polyMesh/boundary that these kind of interfaces have 0 faces. However, on these interfaces the faces will be actually generated with OpenFOAM’s command “createNonconformalCouples”, which are stored in constant/fvMesh, i.e. in a different subfolder. See more details in [Using NCC in OpenFOAM | CFD Direct](https://cfd.direct/openfoam/free-software/using-non-conformal-coupling/)  
The problem is that these warnings can cause segfault crash using the headless server in certain cases. I tried to narrow down the cause of this issue. It seems that for a small number of fields and/or boundaries the warning message pops up, but overall ParaView can handle the mesh. However, in case of a lot of boundaries and/or physical fields the headless server crashes with segfault. I guess it crashes because of the high number of warning messages.  
I tried to create simple simulation case to highlight the issue with only one NCC boundary. In this case the simulation:  
- it can be read when there is only one field  
- but it crashes when there are 30 different fields and the NCC interface is selected. (The crash also happens when there are less fields but more NCC boundaries.)  
I can share these sample simulation folders, if needed.

note: The crash does not happen, when the simulation is opened with the ParaView application, i.e. for me it happens only with the headless server.

---

<div class="post-metadata">

### Author: ![mwestphal](https://discourse.paraview.org/user_avatar/discourse.paraview.org/mwestphal/32/17_2.png) [@mwestphal](https://discourse.paraview.org/u/mwestphal)
#### Post date: [October 4, 2024, 12:09pm UTC](https://discourse.paraview.org/t/paraview-headless-server-crashes-with-openfoams-non-conformal-coupling-interface-ncc/15496/2 "2024-10-04T12:09:10Z")

</div>

FYI @olesenm

@peth Please share your data.

---

<div class="post-metadata">

### Author: ![peth](https://discourse.paraview.org/letter_avatar_proxy/v4/letter/p/258eb7/32.png) [@peth](https://discourse.paraview.org/u/peth)
#### Post date: [October 4, 2024, 1:36pm UTC](https://discourse.paraview.org/t/paraview-headless-server-crashes-with-openfoams-non-conformal-coupling-interface-ncc/15496/3 "2024-10-04T13:36:58Z")

</div>

The simulations are accessible here:  
[https://www.eet.bme.hu/~palovics/](https://www.eet.bme.hu/~palovics/)

Steps to reproduce:

- run paraview 5.13 headless ./pvserver
- connect from a client
- open simulation dir in client by selecting the foam.foam file in the folder
- set Case Type to “Reconstructed Case”
- set Label size to “64 bit”
- unselect all mesh regions except one: the container/patch/container-cube

for some reason the crash now happens also with only one field, so possibly I was incorrect regarding the number of fields or boundaries. Nevertheless I upload two cases:  
- one with only one field (test\_cube\_paraview.tar.gz)  
- another one with 31 fields. These fields are just simply the duplicate of T (test\_cube\_paraview\_morefields.tar.gz )

---

<div class="post-metadata">

### Author: ![mwestphal](https://discourse.paraview.org/user_avatar/discourse.paraview.org/mwestphal/32/17_2.png) [@mwestphal](https://discourse.paraview.org/u/mwestphal)
#### Post date: [October 4, 2024, 2:04pm UTC](https://discourse.paraview.org/t/paraview-headless-server-crashes-with-openfoams-non-conformal-coupling-interface-ncc/15496/4 "2024-10-04T14:04:33Z")

</div>

I reproduce the warning but **not the crash** , with non-distributed and distributed egl headless server 5.13.1 binary release and linux client 5.13.1 binary release.

 ![image](https://discourse.paraview.org/uploads/default/original/2X/6/6acf33b8450f67481a71a18e6fb27374025feca4.jpeg)

---

<div class="post-metadata">

### Author: ![peth](https://discourse.paraview.org/letter_avatar_proxy/v4/letter/p/258eb7/32.png) [@peth](https://discourse.paraview.org/u/peth)
#### Post date: [October 4, 2024, 3:17pm UTC](https://discourse.paraview.org/t/paraview-headless-server-crashes-with-openfoams-non-conformal-coupling-interface-ncc/15496/5 "2024-10-04T15:17:40Z")

</div>

The crash happens with the osmesa headless version. Sorry that I did not specified it before.  
I tried now with the egl version and it indeed does not crash with this version. Thanks for the hint.

Another (smaller) issue with the osmesa version: when the simulation block is deleted in ParaView the client GUI closes immediately, while the server side also abruptly closes with the message:  
vtkSocketCommunicator.c:774 ERR| vtkSocketCommunicator (…): Could not receive tag. 1  
vtkTCPNetworkAccessMana:284 ERR| vtkTCPNetworkAccessManager (…): Some error in socket processing.  
This error does not occur with the egl version.

---

<div class="post-metadata">

### Author: ![mwestphal](https://discourse.paraview.org/user_avatar/discourse.paraview.org/mwestphal/32/17_2.png) [@mwestphal](https://discourse.paraview.org/u/mwestphal)
#### Post date: [October 4, 2024, 3:29pm UTC](https://discourse.paraview.org/t/paraview-headless-server-crashes-with-openfoams-non-conformal-coupling-interface-ncc/15496/6 "2024-10-04T15:29:20Z")

</div>

> [@peth](#):
>
> The crash happens with the osmesa headless version. Sorry that I did not specified it before.  
> I tried now with the egl version and it indeed does not crash with this version. Thanks for the hint.

Does the osmesa version works at all for you?

See this: [I'm using Ubuntu and ParaView osmesa binary crashes on rendering](https://discourse.paraview.org/t/im-using-ubuntu-and-paraview-osmesa-binary-crashes-on-rendering/14046)

---

<div class="post-metadata">

### Author: ![peth](https://discourse.paraview.org/letter_avatar_proxy/v4/letter/p/258eb7/32.png) [@peth](https://discourse.paraview.org/u/peth)
#### Post date: [October 4, 2024, 3:58pm UTC](https://discourse.paraview.org/t/paraview-headless-server-crashes-with-openfoams-non-conformal-coupling-interface-ncc/15496/7 "2024-10-04T15:58:08Z")

</div>

I used osmesa version with two different cases:

- In an ubuntu 22.02 (remote) system, where I used the headless binary downloaded from paraview webpage  
here I ran: ./pvserver from its bin directory  
or in some cases parallel ./mpiexec -np 24 ./pvserver  
both of them listening on the defult port (11111)  
I connected to the system from a paraview client, which is installed in an arch linux OS
- for investigating the crash issue I also ran the headless version on the arch linux OS, and connected locally with the client on the same machine.

I have the described issues:  
- crash and the warnings with the NCC boundary,  
- sudden exit after simulation block delete  
- also a third one: the SaveScreenshot python command did not work on the remote system.  
Other than these problems the osmesa version seemed to work, but I have not tested it yet so much.  
So all in all should I use the egl version, and not osmesa as glibc version is 2.35 in my case on the ubuntu system?

---

<div class="post-metadata">

### Author: ![mwestphal](https://discourse.paraview.org/user_avatar/discourse.paraview.org/mwestphal/32/17_2.png) [@mwestphal](https://discourse.paraview.org/u/mwestphal)
#### Post date: [October 7, 2024, 7:11am UTC](https://discourse.paraview.org/t/paraview-headless-server-crashes-with-openfoams-non-conformal-coupling-interface-ncc/15496/8 "2024-10-07T07:11:23Z")

</div>

Please test with the simple reproducer provided in the link above.

---

<div class="post-metadata">

### Author: ![peth](https://discourse.paraview.org/letter_avatar_proxy/v4/letter/p/258eb7/32.png) [@peth](https://discourse.paraview.org/u/peth)
#### Post date: [October 7, 2024, 11:02am UTC](https://discourse.paraview.org/t/paraview-headless-server-crashes-with-openfoams-non-conformal-coupling-interface-ncc/15496/9 "2024-10-07T11:02:15Z")

</div>

I tested both of the sample cases with the EGL version, and the crash did not happen in them. Thanks for the help.

one additional note: if possible, please consider adjusting ParaView’s OpenFOAM reader to the new NCC interface to avoid the warning messages at the beginning. As I have written before, although the warning message is technically true, I think the 0 face issue does not represent a problem in this case.

---

<div class="post-metadata">

### Author: ![mwestphal](https://discourse.paraview.org/user_avatar/discourse.paraview.org/mwestphal/32/17_2.png) [@mwestphal](https://discourse.paraview.org/u/mwestphal)
#### Post date: [October 7, 2024, 11:22am UTC](https://discourse.paraview.org/t/paraview-headless-server-crashes-with-openfoams-non-conformal-coupling-interface-ncc/15496/10 "2024-10-07T11:22:11Z")

</div>

> [@peth](#):
>
> onsider adjusting ParaView’s OpenFOAM reader to the new NCC interface to avoid the warning messages at the beginning. As I have written before, although the warning message is technically true, I think the 0 face issue does not represent a problem in this case.

This is a @olesenm question