fc-collect-garbage: Warn about unknown/human users with gcroots

[dhnasa]

@flyingcircusio/release-managers

PL-134227

Release process

• Created changelog entry using ./changelog.sh

PR release workflow (internal)

• PR has internal ticket
• internal issue ID (PL-…) part of branch name
• internal issue ID mentioned in PR description text
• ticket is on Platform agile board
• if ticket is more urgent than within the next few days, directly contact a member of the Platform team

• set urgency and risk labels
• ensure the merge bot has determined a merge date
• ensure all checks are green
• get a review from a colleague

Design notes

• Provide a feature toggle if the change might need to be adjusted/reverted quickly depending on context. Consider whether the default should be on or off. Example: rate limiting.
• All customer-facing features and (NixOS) options need to be discoverable from documentation. Add or update relevant documentation such that hosted and guided customers can understand it as well.

Security implications

• Security requirements defined? (WHERE)
  • none
• Security requirements tested? (EVIDENCE)
  • tested on a vm

[ctheune]

looks good, two adjustments please :)

[ctheune]

currently KNOWN users can be reliably as human by checking for membership of GID 100 (users)

[ctheune]

lets help the humans who need to consume this message: explicitly say whether this is an unknown or human user.