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

[github-actions]

Elastic Docs AI PR menu

Check the box to run an AI review for this pull request.

• Review docs changes (docs-review). Status: queued.

Powered by GitHub Agentic Workflows and docs-actions. For more information, reach out to the docs team.

[github-actions]

🔍 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