# Dear all, Question on openmc program using custom\_source example

**URL:** <https://openmc.discourse.group/t/dear-all-question-on-openmc-program-using-custom-source-example/948>\
**Category:** User Support\
**Created:** [January 17, 2021, 6:17am UTC](https://openmc.discourse.group/t/dear-all-question-on-openmc-program-using-custom-source-example/948 "2021-01-17T06:17:37Z")\
**Posts on this page:** 1\
**Showing post:** 8

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**Author:** ![paulromano](https://yyz2.discourse-cdn.com/free1/user_avatar/openmc.discourse.group/paulromano/32/486_2.png) [@paulromano](https://openmc.discourse.group/u/paulromano)\
**Post date:** [February 24, 2021, 1:23pm UTC](https://openmc.discourse.group/t/dear-all-question-on-openmc-program-using-custom-source-example/948/8 "2021-02-24T13:23:30Z")

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I suspect the error you’re seeing may be due to the same problem described here:

> [@How to use external source file in fixed source calculation?](https://openmc.discourse.group/t/how-to-use-external-source-file-in-fixed-source-calculation/996/4):
>
> The internal format used for source sites recently changed (there is now a surf\_id attribute that is used for surface source reading/writing). I’m not sure how you are creating the ADS source file, but if you are using openmc.write\_source\_file, you should make sure that you use that function from the same version of OpenMC that is used to eventually read the source file. Either way, running into a segfault is not ideal behavior. I’m working on adding a check on the source file format to ensure …

If you’re recently updated OpenMC, you may need to regenerate the source file using the `write_source_file` function.

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