File descriptor exhaustion
Host-wide file descriptor usage at or above 80% of fs.file-max OR a single process at or above 80% of its RLIMIT_NOFILE soft limit. The per-process path activates with Crucible v0.11.0+; older agents only emit on the host-wide path.
Remediation
When this rule fires on one of your servers, the dashboard alert detail page renders the full remediation guidance: the command to run, what to verify after, and Furnace's annotation for your specific distro + hardware. Sign in at app.glassmkr.com to see the live alert.