From 24406969613f4119a98e4e54dd1e302345825b55 Mon Sep 17 00:00:00 2001
From: pasquier-s <pasquier.simon@gmail.com>
Date: Mon, 11 Dec 2017 14:01:53 +0100
Subject: [PATCH] Log file descriptor limits at startup (#3567)

Fixes #3564
---
 cmd/prometheus/fdlimits_default.go | 32 ++++++++++++++++++++++++++++++
 cmd/prometheus/fdlimits_windows.go | 21 ++++++++++++++++++++
 cmd/prometheus/main.go             |  1 +
 3 files changed, 54 insertions(+)
 create mode 100644 cmd/prometheus/fdlimits_default.go
 create mode 100644 cmd/prometheus/fdlimits_windows.go

diff --git a/cmd/prometheus/fdlimits_default.go b/cmd/prometheus/fdlimits_default.go
new file mode 100644
index 000000000..197810e28
--- /dev/null
+++ b/cmd/prometheus/fdlimits_default.go
@@ -0,0 +1,32 @@
+// Copyright 2017 The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// +build !windows
+
+package main
+
+import (
+	"fmt"
+	"log"
+	"syscall"
+)
+
+// FdLimits returns the soft and hard limits for file descriptors
+func FdLimits() string {
+	flimit := syscall.Rlimit{}
+	err := syscall.Getrlimit(syscall.RLIMIT_NOFILE, &flimit)
+	if err != nil {
+		log.Fatal("Error!")
+	}
+	return fmt.Sprintf("(soft=%d, hard=%d)", flimit.Cur, flimit.Max)
+}
diff --git a/cmd/prometheus/fdlimits_windows.go b/cmd/prometheus/fdlimits_windows.go
new file mode 100644
index 000000000..3fcff4905
--- /dev/null
+++ b/cmd/prometheus/fdlimits_windows.go
@@ -0,0 +1,21 @@
+// Copyright 2017 The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// +build windows
+
+package main
+
+// FdLimits not supported on Windows
+func FdLimits() string {
+	return "N/A"
+}
diff --git a/cmd/prometheus/main.go b/cmd/prometheus/main.go
index e278f5a4b..b03db5891 100644
--- a/cmd/prometheus/main.go
+++ b/cmd/prometheus/main.go
@@ -220,6 +220,7 @@ func main() {
 	level.Info(logger).Log("msg", "Starting Prometheus", "version", version.Info())
 	level.Info(logger).Log("build_context", version.BuildContext())
 	level.Info(logger).Log("host_details", Uname())
+	level.Info(logger).Log("fd_limits", FdLimits())
 
 	var (
 		localStorage  = &tsdb.ReadyStorage{}