Fix the inability to start with logger in docker contianer (#178)

* check for docker/lxc in isInteractive() for linux

* more clear logic and function name

* add some tests for linux part

* fix test

* cover coverage

service_linux.go

@@ -5,10 +5,13 @@
 package service
 
 import (
+	"bufio"
 	"os"
 	"strings"
 )
 
+var cgroupFile = "/proc/1/cgroup"
+
 type linuxSystemService struct {
 	name        string
 	detect      func() bool
@@ -62,7 +65,37 @@ func init() {
 
 func isInteractive() (bool, error) {
 	// TODO: This is not true for user services.
-	return os.Getppid() != 1, nil
+	inContainer, err := isInContainer(cgroupFile)
+	if err != nil {
+		return false, err
+	}
+	return os.Getppid() != 1 || inContainer, nil
+}
+
+// isInContainer checks if the service is being executed in docker or lxc
+// container.
+func isInContainer(cgroupPath string) (bool, error) {
+	const maxlines = 5 // maximum lines to scan
+
+	f, err := os.Open(cgroupPath)
+	if err != nil {
+		return false, err
+	}
+	defer f.Close()
+	scan := bufio.NewScanner(f)
+
+	lines := 0
+	for scan.Scan() && !(lines > maxlines) {
+		if strings.Contains(scan.Text(), "docker") || strings.Contains(scan.Text(), "lxc") {
+			return true, nil
+		}
+		lines++
+	}
+	if err := scan.Err(); err != nil {
+		return false, err
+	}
+
+	return false, nil
 }
 
 var tf = map[string]interface{}{