cmd/tailscaled: run off internal state autonomously.

With this change, tailscaled can be restarted and reconnect
without interaction from `tailscale`, and `tailscale` is merely
there to provide login assistance and adjust preferences.

Signed-off-by: David Anderson <dave@natulte.net>

cmd/tailscaled/tailscaled.go

@@ -23,6 +23,15 @@ import (
 	"tailscale.com/wgengine/magicsock"
 )
 
+// globalStateKey is the ipn.StateKey that tailscaled loads on
+// startup.
+//
+// We have to support multiple state keys for other OSes (Windows in
+// particular), but right now Unix daemons run with a single
+// node-global state. To keep open the option of having per-user state
+// later, the global state key doesn't look like a username.
+const globalStateKey = "_daemon"
+
 func main() {
 	fake := getopt.BoolLong("fake", 0, "fake tunnel+routing instead of tuntap")
 	debug := getopt.StringLong("debug", 0, "", "Address of debug server")
@@ -43,6 +52,10 @@ func main() {
 		log.Fatalf("too many non-flag arguments: %#v", getopt.Args()[0])
 	}
 
+	if *statepath == "" {
+		log.Fatalf("--state is required")
+	}
+
 	if *debug != "" {
 		go runDebugServer(*debug)
 	}
@@ -60,6 +73,7 @@ func main() {
 
 	opts := ipnserver.Options{
 		StatePath:          *statepath,
+		AutostartStateKey:  globalStateKey,
 		SurviveDisconnects: true,
 	}
 	err = ipnserver.Run(context.Background(), logf, pol.PublicID.String(), opts, e)