Add open file descriptor monitoring (#5655)

scripts/fd-monitor.sh

@@ -0,0 +1,20 @@
+#!/usr/bin/env bash
+#
+# Reports open file descriptors for the current user
+#
+set -e
+
+[[ $(uname) == Linux ]] || exit 0
+
+cd "$(dirname "$0")"
+
+# shellcheck source=scripts/configure-metrics.sh
+source configure-metrics.sh
+
+while true; do
+  count=$(lsof -u $UID | wc -l)
+  ./metrics-write-datapoint.sh "open-files,hostname=$HOSTNAME count=$count"
+  sleep 10
+done
+
+exit 1