client/systray: add startup script generator for systemd (#16801)

Updates #1708

Signed-off-by: Claus Lensbøl <claus@tailscale.com>

client/systray/startup-creator.go

@@ -0,0 +1,76 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+//go:build cgo || !darwin
+
+// Package systray provides a minimal Tailscale systray application.
+package systray
+
+import (
+	"bufio"
+	"bytes"
+	_ "embed"
+	"fmt"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strings"
+)
+
+//go:embed tailscale-systray.service
+var embedSystemd string
+
+func InstallStartupScript(initSystem string) error {
+	switch initSystem {
+	case "systemd":
+		return installSystemd()
+	default:
+		return fmt.Errorf("unsupported init system '%s'", initSystem)
+	}
+}
+
+func installSystemd() error {
+	// Find the path to tailscale, just in case it's not where the example file
+	// has it placed, and replace that before writing the file.
+	tailscaleBin, err := exec.LookPath("tailscale")
+	if err != nil {
+		return fmt.Errorf("failed to find tailscale binary %w", err)
+	}
+
+	var output bytes.Buffer
+	scanner := bufio.NewScanner(strings.NewReader(embedSystemd))
+	for scanner.Scan() {
+		line := scanner.Text()
+		if strings.HasPrefix(line, "ExecStart=") {
+			line = fmt.Sprintf("ExecStart=%s systray", tailscaleBin)
+		}
+		output.WriteString(line + "\n")
+	}
+
+	configDir, err := os.UserConfigDir()
+	if err != nil {
+		homeDir, err := os.UserHomeDir()
+		if err != nil {
+			return fmt.Errorf("unable to locate user home: %w", err)
+		}
+		configDir = filepath.Join(homeDir, ".config")
+	}
+
+	systemdDir := filepath.Join(configDir, "systemd", "user")
+	if err := os.MkdirAll(systemdDir, 0o755); err != nil {
+		return fmt.Errorf("failed creating systemd uuser dir: %w", err)
+	}
+
+	serviceFile := filepath.Join(systemdDir, "tailscale-systray.service")
+
+	if err := os.WriteFile(serviceFile, output.Bytes(), 0o755); err != nil {
+		return fmt.Errorf("failed writing systemd user service: %w", err)
+	}
+
+	fmt.Printf("Successfully installed systemd service to: %s\n", serviceFile)
+	fmt.Println("To enable and start the service, run:")
+	fmt.Println("  systemctl --user daemon-reload")
+	fmt.Println("  systemctl --user enable --now tailscale-systray")
+
+	return nil
+}

client/systray/tailscale-systray.service

@@ -0,0 +1,10 @@
+[Unit]
+Description=Tailscale System Tray
+After=systemd.service
+
+[Service]
+Type=simple
+ExecStart=/usr/bin/tailscale systray
+
+[Install]
+WantedBy=default.target