feat: emit explicit errors for the service command on unsupported OSes

cmd/cloudflared/generic_service.go

@@ -3,11 +3,36 @@
 package main
 
 import (
+	"fmt"
 	"os"
 
 	cli "github.com/urfave/cli/v2"
 )
 
 func runApp(app *cli.App, graceShutdownC chan struct{}) {
+	app.Commands = append(app.Commands, &cli.Command{
+		Name:  "service",
+		Usage: "Manages the cloudflared system service (not supported on this operating system)",
+		Subcommands: []*cli.Command{
+			{
+				Name:   "install",
+				Usage:  "Install cloudflared as a system service (not supported on this operating system)",
+				Action: cliutil.ConfiguredAction(installGenericService),
+			},
+			{
+				Name:   "uninstall",
+				Usage:  "Uninstall the cloudflared service (not supported on this operating system)",
+				Action: cliutil.ConfiguredAction(uninstallGenericService),
+			},
+		},
+	})
 	app.Run(os.Args)
 }
+
+func installGenericService(c *cli.Context) error {
+	return fmt.Errorf("service installation is not supported on this operating system")
+}
+
+func uninstallGenericService(c *cli.Context) error {
+	return fmt.Errorf("service uninstallation is not supported on this operating system")
+}