ES install: add cgroup v2 compatibility warning for affected versions

[kunisen]

Summary

Adds a cgroup v2 compatibility warning for Elasticsearch versions 8.0.0–8.4.3 and 7.15.1–7.17.6, which fail to start on Linux hosts running pure cgroup v2 due to a bug in the bundled JDK.

This PR adds a new ### Linux cgroups version subsection to the Supported operating systems and JVMs section of the Install Elasticsearch page, and a corresponding bullet in the Important system configuration checklist, both pointing to the KB article for detailed guidance.

Related: elastic/support-tech-lead#1913

Generative AI disclosure

1. Did you use a generative AI (GenAI) tool to assist in creating this contribution?

• Yes
• No

Tool(s) and model(s) used: Claude (Anthropic) via Cowork

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🔍 Preview links for changed docs

• deploy-manage/deploy/cloud-enterprise/ece-software-prereq.md
• deploy-manage/deploy/self-managed/important-system-configuration.md
• deploy-manage/deploy/self-managed/installing-elasticsearch.md

[github-actions]

Elastic Docs Style Checker (Vale)

Summary: 2 suggestions found

💡 Suggestions (2): Optional style improvements. Apply when helpful.

File	Line	Rule	Message
deploy-manage/deploy/self-managed/installing-elasticsearch.md	114	Elastic.Wordiness	Consider using 'sometimes' instead of 'In some cases'.
deploy-manage/deploy/self-managed/installing-elasticsearch.md	114	Elastic.WordChoice	Consider using 'can, might' instead of 'may', unless the term is in the UI.

---

The Vale linter checks documentation changes against the Elastic Docs style guide. To use Vale locally or report issues, refer to Elastic style guide for Vale.

[github-actions]

Docs review summary

Focus areas

• Style and clarity: Two new sentences use literal "Elasticsearch" instead of the {{es}} substitution used consistently throughout both pages — flagged inline with suggested fixes. Also flagged unnecessary "Note that" preamble.
• Jargon: None found — "cgroups" and "JDK" are used in context with a linked man-page reference.
• Frontmatter and applies_to: No frontmatter changes in this PR; existing applies_to/products metadata untouched and still valid for both files.
• Content type fit: Both are how-to/reference pages; the new content is a short warning bullet/subsection consistent with surrounding structure. No mismatch.
• Contradictions: No contradictions found — the new cgroups v2 warning is additive and consistent with Elastic's published KB guidance on this bug.
• Parent issue satisfaction: Satisfied — the PR adds the requested warning in both the installation page and the system configuration checklist, each linking to the KB article.

Nits

• Vale flagged several pre-existing "may" → "can/might" and "In some cases" → "sometimes" suggestions in installing-elasticsearch.md; these are in unchanged surrounding text and not required for this PR.

Notes

• Reviewed only the two eligible changed markdown files per repo-wide-markdown scope.

Generated by Docs review agent for #7983 · sonnet50 · 31.6 AIC · ⌖ 6.64 AIC · ⊞ 17.1K

[kunisen]

FWIW, I got our dev friend's (@jowiho) LGTM here - link.

Could we please have doc friend to review and move forward?
Thanks!

[shainaraskas]

I understand your motivation for opening this PR, but I don't think this is the right place for this information.

[shainaraskas]

we don't need this info for ECE because we don't support cgroups v2 in this case at all

[kunisen]

we don't need this info for ECE because we don't support cgroups v2 in this case at all

I know this is confusing, but @erikjenks is in charge of testing and certifying cgroup v2 support on ECE.
We may tweak this part in near future.
=> In the future, once we get this part changed, I will file another doc PR to remove {ece}} is not supported on Linux distributions that use [cgroups](https://man7.org/linux/man-pages/man7/cgroups.7.html) version 2 when we are ready.

Based on the context, do you think we still don't need to put the content for now? (but put it later when we remove the v2 non-support message?)

[kunisen]

My personal opinion is this is in ECE side and user may still have old stack version running on it and they may indeed hit this issue, so it would be beneficial for us to put here for better explanation and visibility.

[gigerdo]

Yep we are currently in an intermediate state when adding cgroupv2 support. I think it is best to review the docs from now on from the perspective of 'cgroupv2 is supported on latest 4.x'

[shainaraskas]

these docs are 9.x only, so the change likely belongs in the old docs system (althought we would have difficulty editing it): https://www.elastic.co/guide/en/elasticsearch/reference/8.4/setup.html

[kunisen]

@shainaraskas thanks.
I can file the 8.4 doc PR later but wdyt the wording?
I want to make sure the wording is correct so I can do it more quickly.

[shainaraskas]

same note - these docs are 9.x+ so this is not relevant to this docset

[kunisen]

@shainaraskas thanks for this too.
I can file the 8.4 doc PR later but wdyt the wording?
I want to make sure the wording is correct so I can do it more quickly.

[gigerdo]

ECE-side LGTM 👍

[kunisen]

Thanks @gigerdo ! 🙏

Hi @shainaraskas given we got approval from our control plane dev friend, do you think it makes sense we go further with the doc PR on old ES versions?

Do you have handy AI tools to file old version doc PRs? I can do it too but I am not an expert of running PRs on old asciidoc pages... Well I can still try it...