Activate stopping and starting of Plex

See #6 (comment)
for a write-up of the thinking behind this change. Resolves #5,
resolves #6.

README.md

@@ -3,12 +3,22 @@
 [![Build Status](https://travis-ci.org/gebn/plexbackup.svg?branch=master)](https://travis-ci.org/gebn/plexbackup)
 [![GoDoc](https://godoc.org/github.com/gebn/plexbackup?status.svg)](https://godoc.org/github.com/gebn/plexbackup)
 
-This tool backs up [Plex](https://www.plex.tv)'s server data to S3.
-The entire `Plex Media Server` directory (sans `Cache`) is snapshotted, stopping the server beforehand and restarting it after to ensure consistency.
-It is `tar`red, `gz`ipped then piped to S3 without writing to disk.
+This tool backs up the [`Plex Media Server`](https://www.plex.tv) directory (sans `Cache`) to S3.
+It is `tar`red, `gz`ipped and uploaded without writing to disk.
 The tool is envisaged to be run as a cron job, preferably soon after the configured maintenance period.
 The process is usually CPU-bound on the compression, so [`pigz`](https://zlib.net/pigz/) will be used in place of `gz` if available on the `$PATH`.
 
+## Setup
+
+In order to ensure consistency of the backup, Plex is stopped then started once the process is complete.
+This tool effectively runs `sudo systemctl stop|start <unit>` to do this (Polkit was also considered but [ultimately rejected](https://github.com/gebn/plexbackup/issues/6#issuecomment-452899467)).
+Assuming a vanilla installation, this can be made to work by allowing the `plex` user to execute the two required commands without having to re-authenticate:
+
+    # cat <<EOF > /etc/sudoers.d/10-plex-backup
+    plex ALL=NOPASSWD: /bin/systemctl stop plexmediaserver.service
+    plex ALL=NOPASSWD: /bin/systemctl start plexmediaserver.service
+    EOF
+
 ## Usage
 
     $ plexbackup --help
@@ -21,6 +31,8 @@ The process is usually CPU-bound on the compression, so [`pigz`](https://zlib.ne
       --prefix="plex/"      Location within the bucket to upload to; a trailing slash is added if not present.
                             The backup object is stored under this prefix as <RFC3339 date>.tar.xz, e.g.
                             "2019-01-06T22:38:21Z.tar.xz".
+      --no-pause            Do not stop Plex while the backup is performed. This is not recommended, as it risks
+                            an inconsistent backup.
       --service="plexmediaserver.service"  
                             Name of the Plex systemd unit to stop while the backup is performed.
       --directory=/var/lib/plexmediaserver/Library/Application Support/Plex Media Server

backup/backup.go

@@ -17,6 +17,12 @@ import (
 // Opts encapsulates parameters for backing up Plex's database.
 type Opts struct {
 
+	// NoPause takes the backup without stopping Plex. The server will remain
+	// available throughout, but the backup may be unusable.
+	// It is specified negatively in order to default to false, which is the
+	// recommended setting.
+	NoPause bool
+
 	// Service is the name of Plex's systemd unit, e.g. plexmediaserver.service
 	Service string
 
@@ -83,9 +89,11 @@ func (o *Opts) Run(svc *s3.S3) error {
 		return fmt.Errorf("failed to retrieve oldest backup: %v", err)
 	}
 
-	//if err = exec.Command("systemctl", "stop", plexService).Run(); err != nil {
-	//	return fmt.Errorf("failed to stop plex: %v", err)
-	//}
+	if !o.NoPause {
+		if err = exec.Command("sudo", "systemctl", "stop", o.Service).Run(); err != nil {
+			return fmt.Errorf("failed to stop plex: %v", err)
+		}
+	}
 
 	tar := exec.Command(
 		"tar", "-cf", "-",
@@ -125,9 +133,11 @@ func (o *Opts) Run(svc *s3.S3) error {
 		}{gzStdout},
 	})
 
-	//if err = exec.Command("systemctl", "start", plexService).Run(); err != nil {
-	//	return fmt.Errorf("failed to start plex: %v", err)
-	//}
+	if !o.NoPause {
+		if err = exec.Command("sudo", "systemctl", "start", o.Service).Run(); err != nil {
+			return fmt.Errorf("failed to start plex: %v", err)
+		}
+	}
 
 	// TODO unclear whether this is necessary; the example uses it
 	if err = tar.Wait(); err != nil {

main.go

@@ -23,6 +23,8 @@ var (
 		Default("plex/").
 		String()
 
+	noPause = kingpin.Flag("no-pause", "Do not stop Plex while the backup is performed. This is not recommended, as it risks an inconsistent backup.").
+		Bool()
 	service = kingpin.Flag("service", "Name of the Plex systemd unit to stop while the backup is performed.").
 		Default("plexmediaserver.service").
 		String()
@@ -39,6 +41,7 @@ func main() {
 	svc := s3.New(sess)
 
 	opts := &backup.Opts{
+		NoPause:   !*noPause,
 		Service:   *service,
 		Directory: *directory,
 		Bucket:    *bucket,