# Enabling YJIT via Template Doesn't Work
**URL:** https://meta.discourse.org/t/enabling-yjit-via-template-doesnt-work/401815
**Category:** Support
**Created:** [29 april 2026 om 14:26 UTC](https://meta.discourse.org/t/enabling-yjit-via-template-doesnt-work/401815 "2026-04-29T14:26:31Z")
**Posts on this page:** 7
**Page:** 1
### Author:  [@cedric\_chin](https://meta.discourse.org/u/cedric_chin)
#### Post date: [29 april 2026 om 14:26 UTC](https://meta.discourse.org/t/enabling-yjit-via-template-doesnt-work/401815/1 "2026-04-29T14:26:32Z")
Hi there,
I run a self hosted Discourse install (2026.5.0-latest). Today I tried to turn YJIT on. I added `"templates/enable-ruby-yjit.yml"` to `containers/app.yml` and rebuilt the app.
After the rebuild was done, something interesting happened. Inside the Docker container, I ran `env | grep RUBY_YJIT_ENABLE` and got `RUBY_YJIT_ENABLE=1`. So far so good. But then I ran `sudo -u discourse RAILS_ENV=production bundle exec rails runner 'puts "YJIT enabled: #{RubyVM::YJIT.enabled?}"; puts RUBY_DESCRIPTION'` … I got:
```bash
YJIT enabled: false
ruby 3.4.7 (2025-10-08 revision 7a5688e2a2) +PRISM [x86_64-linux]
```
So YJIT was not enabled, despite adding the `enable-ruby-yjit.yml` template. Then, when I ran `sudo -u discourse RAILS_ENV=production bundle exec rails runner 'puts "GlobalSetting.yjit_enabled=#{GlobalSetting.yjit_enabled}"'` I got `GlobalSetting.yjit_enabled=` — a nil value!
Anyway, after futzing around with it a bit more, I finally got YJIT enabled by adding the following to `containers/app.yml`:
```yaml
env:
DISCOURSE_YJIT_ENABLED: true
```
I’m sure there’s a bug somewhere (`GlobalSetting.yjit_enabled` _shouldn’t_ ever return nil) but setting the env variable worked, and I hope someone Googling for this will find this topic.
---
### Author:  [@Falco](https://meta.discourse.org/u/Falco)
#### Post date: [29 april 2026 om 18:36 UTC](https://meta.discourse.org/t/enabling-yjit-via-template-doesnt-work/401815/2 "2026-04-29T18:36:16Z")
> [@cedric\_chin](#):
>
> `sudo -u discourse RAILS_ENV=production bundle exec rails runner 'puts "YJIT enabled: #{RubyVM::YJIT.enabled?}"; puts RUBY_DESCRIPTION'`
Isn’t that a misdiagnose? You are checking the ENV of a brand new spawned ruby proccess instead of the one running the actual web server.
If you inspect the `/proc//environ` of the Pitchfork mold process you will see the YJIT env var there.
```plaintext
root@raspberrypi5:/var/discourse# cat /proc/3331660/environ | tr '\0' '\n' | grep -i yjit
RUBY_YJIT_ENABLE=1
```
---
### Author:  [@cedric\_chin](https://meta.discourse.org/u/cedric_chin)
#### Post date: [29 april 2026 om 23:48 UTC](https://meta.discourse.org/t/enabling-yjit-via-template-doesnt-work/401815/3 "2026-04-29T23:48:22Z")
Looking at the presence of an env var doesn’t tell you anything about whether Ruby is currently running with YJIT enabled. In this particular case, the env var is set but something else was clobbering the variable Rails uses to enable (or disable) YJIT on startup! (Or at least … that’s my suspicion).
There’s no other explanation for why `GlobalSetting.yjit_enabled=` returns nil, even on a new Rails instance. There’s also no reason why YJIT should be turned off on a new Rails instance.
After adding the DISCOURSE\_YJIT\_ENABLED env var to my containers/app.yml,
1. `sudo -u discourse RAILS_ENV=production bundle exec rails runner 'puts “YJIT enabled: #{RubyVM::YJIT.enabled?}”; puts RUBY_DESCRIPTION’`returns `YJIT enabled: true `
2. Memory usage on my server finally goes up (a little).
3. I finally see a real speed up on my forum.
It should be easy to replicate my findings. Just add the template and see.
---
### Author:  [@Falco](https://meta.discourse.org/u/Falco)
#### Post date: [30 april 2026 om 15:52 UTC](https://meta.discourse.org/t/enabling-yjit-via-template-doesnt-work/401815/4 "2026-04-30T15:52:21Z")
> [@cedric\_chin](#):
>
> Looking at the presence of an env var doesn’t tell you anything about whether Ruby is currently running with YJIT enabled.
This is wrong. At the Ruby level, the ENV var is one of the official toggles, see the Ruby official documentation about this here
> **[yjit - Documentation for Ruby 3.4](https://docs.ruby-lang.org/en/3.4/yjit/yjit_md.html#:~:text=exits-,Note,practical)**
>
> yjit: yjit. user-images.
> [@cedric\_chin](#):
>
> In this particular case, the env var is set but something else was clobbering the variable Rails uses to enable (or disable) YJIT on startup! (Or at least … that’s my suspicion).
This is wrong as `DISCOURSE_YJIT_ENABLED` only feeds `GlobalSetting.yjit_enabled` → `config.yjit` in `config/application.rb`. Rails uses that to enable YJIT _if it isn’t already on_. It does not disable an already-enabled YJIT. So when the env var is set, `DISCOURSE_YJIT_ENABLED` has nothing to do.
To further prove my point I wrote a plugin that returns if YJIT is enabled on my web process:
[https://discourse-on-a-pi5.falco.dev/ruby-info](https://discourse-on-a-pi5.falco.dev/ruby-info)
You are confused about the Rails level toggle, which is unnecessary as use the Ruby level toggle.
---
### Author:  [@cedric\_chin](https://meta.discourse.org/u/cedric_chin)
#### Post date: [30 april 2026 om 16:24 UTC](https://meta.discourse.org/t/enabling-yjit-via-template-doesnt-work/401815/5 "2026-04-30T16:24:09Z")
Huh! So you’re saying we can reliably use the env var to detect if YJIT is enabled! I didn’t know that; thank you for the link to the Ruby documentation.
I’m a little confused about something though. How is it possible that `env | grep RUBY_YJIT_ENABLE` returns `RUBY_YJIT_ENABLE=1`, but a new Rails instance in the same container when asked to print `#{RubyVM::YJIT.enabled?}` outputs `false`? Shouldn’t it output true since — as you’ve mentioned, this env var works at the Ruby level?
You’re probably really busy and this shouldn’t matter, so no need to answer. I should be able to figure it out on my own server. Could I have your plugin, by any chance? I want a way to be _sure_ that my Discourse server is running on a Ruby with YJIT enabled.
I’ll mark your response as a solution after I’ve replicated.
Thanks in advance!
---
### Author:  [@cedric\_chin](https://meta.discourse.org/u/cedric_chin)
#### Post date: [30 april 2026 om 16:48 UTC](https://meta.discourse.org/t/enabling-yjit-via-template-doesnt-work/401815/6 "2026-04-30T16:48:29Z")
I’m sorry, I’ve figured it out.
`sudo -u discourse` scrubs the env. Using the `-E` flag brings the normal env along, and in that case `sudo -E -u discourse RAILS_ENV=production bundle exec rails runner 'puts "YJIT enabled: #{RubyVM::YJIT.enabled?}"; puts RUBY_DESCRIPTION'` returns
```bash
YJIT enabled: true
ruby 3.4.7 (2025-10-08 revision 7a5688e2a2) +YJIT +PRISM [x86_64-linux]
```
With just the template added.
I apologise for wasting your time, and have marked your response as the solution. Sorry about this. Thank you for investigating and taking the time to respond.
---
### Author:  [@system](https://meta.discourse.org/u/system)
#### Post date: [30 mei 2026 om 16:49 UTC](https://meta.discourse.org/t/enabling-yjit-via-template-doesnt-work/401815/7 "2026-05-30T16:49:14Z")
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