# Trace doesn't work

**URL:** https://swi-prolog.discourse.group/t/trace-doesnt-work/9413
**Category:** General
**Created:** [December 4, 2025, 7:57am UTC](https://swi-prolog.discourse.group/t/trace-doesnt-work/9413 "2025-12-04T07:57:19Z")
**Posts on this page:** 4
**Page:** 1

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### Author: ![szeredi](https://avatars.discourse-cdn.com/v4/letter/s/a3d4f5/32.png) [@szeredi](https://swi-prolog.discourse.group/u/szeredi)
#### Post date: [December 4, 2025, 7:57am UTC](https://swi-prolog.discourse.group/t/trace-doesnt-work/9413/1 "2025-12-04T07:57:19Z")

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Trace does no seem to work for me. Any ideas ? Thanks.

Péter

trace, X= 1.

```prolog
Unknown procedure: thread_util:ep_has_console/1
In:
   [2] trace
   [1] '<meta-call>'((trace,...)) <foreign>

```

---

<div class="post-metadata">

### Author: ![jan](https://yyz2.discourse-cdn.com/free1/user_avatar/swi-prolog.discourse.group/jan/32/4_2.png) [@jan](https://swi-prolog.discourse.group/u/jan)
#### Post date: [December 4, 2025, 8:15am UTC](https://swi-prolog.discourse.group/t/trace-doesnt-work/9413/2 "2025-12-04T08:15:43Z")

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> [@szeredi](#):
>
> `Unknown procedure: thread_util:ep_has_console/1`

Looks like a broken installation.

```prolog
36 ?- trace, X= 1.
   Call: (13) _32050=1 ? creep
   Exit: (13) 1=1 ? creep
X = 1.

[trace] 37 ?- 

```

So, which version? Which OS? How was it installed? Using the terminal or `swipl-win` (the app)?

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<div class="post-metadata">

### Author: ![szeredi](https://avatars.discourse-cdn.com/v4/letter/s/a3d4f5/32.png) [@szeredi](https://swi-prolog.discourse.group/u/szeredi)
#### Post date: [December 4, 2025, 8:31am UTC](https://swi-prolog.discourse.group/t/trace-doesnt-work/9413/3 "2025-12-04T08:31:01Z")

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It’s Swish. Sorry for missing this.

Péter

Jan Wielemaker via SWI-Prolog \<[notifications@swiprolog.discoursemail.com](mailto:notifications@swiprolog.discoursemail.com)\> ezt írta (időpont: 2025. dec. 4., Cs 9:25):

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<div class="post-metadata">

### Author: ![jan](https://yyz2.discourse-cdn.com/free1/user_avatar/swi-prolog.discourse.group/jan/32/4_2.png) [@jan](https://swi-prolog.discourse.group/u/jan)
#### Post date: [December 4, 2025, 9:19am UTC](https://swi-prolog.discourse.group/t/trace-doesnt-work/9413/4 "2025-12-04T09:19:04Z")

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> [@szeredi](#):
>
> It’s [Swish](https://swish.swi-prolog.org/). Sorry for missing this.

I see. Fixed and restarted the SWISH backends. Thanks for reporting!