enhance systemd integration

* log level identification
* manual activation with flag
* automatic systemd launch detection

fs/log.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"log"
 
+	sysdjournald "github.com/iguanesolutions/go-systemd/v5/journald"
 	"github.com/pkg/errors"
 	"github.com/sirupsen/logrus"
 )
@@ -70,7 +71,28 @@ func (l *LogLevel) Type() string {
 
 // LogPrint sends the text to the logger of level
 var LogPrint = func(level LogLevel, text string) {
-	text = fmt.Sprintf("%-6s: %s", level, text)
+	var prefix string
+	if Config.LogSystemdSupport {
+		switch level {
+		case LogLevelDebug:
+			prefix = sysdjournald.DebugPrefix
+		case LogLevelInfo:
+			prefix = sysdjournald.InfoPrefix
+		case LogLevelNotice:
+			prefix = sysdjournald.NoticePrefix
+		case LogLevelWarning:
+			prefix = sysdjournald.WarningPrefix
+		case LogLevelError:
+			prefix = sysdjournald.ErrPrefix
+		case LogLevelCritical:
+			prefix = sysdjournald.CritPrefix
+		case LogLevelAlert:
+			prefix = sysdjournald.AlertPrefix
+		case LogLevelEmergency:
+			prefix = sysdjournald.EmergPrefix
+		}
+	}
+	text = fmt.Sprintf("%s%-6s: %s", prefix, level, text)
 	_ = log.Output(4, text)
 }