Receiving a SIGUSR2 makes Vault log the running goroutines' stacks. (#6240)

* Receiving a SIGUSR2 makes Vault log the running goroutines' stacks.

command/commands.go

@@ -466,6 +466,7 @@ func initCommands(ui, serverCmdUi cli.Ui, runOpts *RunOptions) {
 				PhysicalBackends:   physicalBackends,
 				ShutdownCh:         MakeShutdownCh(),
 				SighupCh:           MakeSighupCh(),
+				SigUSR2Ch:          MakeSigUSR2Ch(),
 			}, nil
 		},
 		"ssh": func() (cli.Command, error) {
@@ -628,3 +629,20 @@ func MakeSighupCh() chan struct{} {
 	}()
 	return resultCh
 }
+
+// MakeSigUSR2Ch returns a channel that can be used for SIGUSR2
+// goroutine logging. This channel will send a message for every
+// SIGUSR2 received.
+func MakeSigUSR2Ch() chan struct{} {
+	resultCh := make(chan struct{})
+
+	signalCh := make(chan os.Signal, 4)
+	signal.Notify(signalCh, syscall.SIGUSR2)
+	go func() {
+		for {
+			<-signalCh
+			resultCh <- struct{}{}
+		}
+	}()
+	return resultCh
+}