From 5f07da4854e73181e21c7d1d90191db5d65f2675 Mon Sep 17 00:00:00 2001
From: Brad Fitzpatrick <bradfitz@tailscale.com>
Date: Thu, 17 Dec 2020 12:59:05 -0800
Subject: [PATCH] util/systemd: don't log warnings when not running under
 systemd

It caused our integration tests to fail, which prohibit logging to
os.Stderr for test cleanliness reasons.
---
 util/systemd/systemd_linux.go | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/util/systemd/systemd_linux.go b/util/systemd/systemd_linux.go
index 133bf520f..f33c35730 100644
--- a/util/systemd/systemd_linux.go
+++ b/util/systemd/systemd_linux.go
@@ -8,6 +8,7 @@ package systemd
 
 import (
 	"log"
+	"os"
 	"sync"
 
 	"github.com/mdlayher/sdnotify"
@@ -35,8 +36,13 @@ var (
 
 func notifier() *sdnotify.Notifier {
 	getNotifyOnce.Do(func() {
+		sock := os.Getenv(sdnotify.Socket)
+		if sock == "" {
+			// Not running under systemd probably. Bail out before logging.
+			return
+		}
 		var err error
-		getNotifyOnce.v, err = sdnotify.New()
+		getNotifyOnce.v, err = sdnotify.Open(sock)
 		if err != nil {
 			log.Printf("systemd: systemd-notifier error: %v", err)
 		}