catch journalctl exit (#754)

Author: DmitryRomanov

plugin/input/journalctl/README.idoc.md

@@ -1,5 +1,9 @@
 # Journal.d plugin
 @introduction
 
+### Warning
+
+**Important:** If the `journalctl` process is stopped or killed, the `file.d` application will also be stopped.
+
 ### Config params
 @config-params|description

plugin/input/journalctl/README.md

@@ -1,6 +1,10 @@
 # Journal.d plugin
 Reads `journalctl` output.
 
+### Warning
+
+**Important:** If the `journalctl` process is stopped or killed, the `file.d` application will also be stopped.
+
 ### Config params
 **`offsets_file`** *`string`* *`required`* 
 

plugin/input/journalctl/reader.go

@@ -7,6 +7,7 @@ import (
 	"io"
 	"os/exec"
 	"strings"
+	"syscall"
 
 	"github.com/prometheus/client_golang/prometheus"
 	"go.uber.org/zap"
@@ -94,10 +95,15 @@ func (r *journalReader) start() error {
 	}
 
 	go r.readLines(out, r.config)
+	go func() {
+		if err := r.cmd.Wait(); err != nil {
+			r.config.logger.Fatal("journalctl command exited with error", zap.Error(err))
+		}
+	}()
 
 	return nil
 }
 
 func (r *journalReader) stop() error {
-	return r.cmd.Process.Kill()
+	return r.cmd.Process.Signal(syscall.SIGTERM)
 }