Check for OS and root privileges in NewDaemon

Docker-DCO-1.1-Signed-off-by: Solomon Hykes <solomon@docker.com> (github: shykes)

daemon/daemon.go

@@ -761,6 +761,12 @@ func NewDaemon(config *daemonconfig.Config, eng *engine.Engine) (*Daemon, error)
 }
 
 func NewDaemonFromDirectory(config *daemonconfig.Config, eng *engine.Engine) (*Daemon, error) {
+	if runtime.GOOS != "linux" {
+		log.Fatalf("The Docker daemon is only supported on linux")
+	}
+	if os.Geteuid() != 0 {
+		log.Fatalf("The Docker daemon needs to be run as root")
+	}
 	if !config.EnableSelinuxSupport {
 		selinuxSetDisabled()
 	}

docker/docker.go

@@ -114,13 +114,6 @@ func main() {
 	}
 
 	if *flDaemon {
-		if runtime.GOOS != "linux" {
-			log.Fatalf("The Docker daemon is only supported on linux")
-		}
-		if os.Geteuid() != 0 {
-			log.Fatalf("The Docker daemon needs to be run as root")
-		}
-
 		if flag.NArg() != 0 {
 			flag.Usage()
 			return