cmd/tailscale{,d}: combine into a single binaryonebinary

To reduce size, combine tailscaled and tailscale into a single
binary which will figure out what it should do based on argv[0].

Signed-off-by: Denton Gentry <dgentry@tailscale.com>

19 files changed, 5000 insertions, 1 deletions

diff --git a/cmd/tailscaled/cli/bugreport.go b/cmd/tailscaled/cli/bugreport.go
new file mode 100644
index 000000000..46c32bf96
--- /dev/null
+++ b/cmd/tailscaled/cli/bugreport.go
@@ -0,0 +1,38 @@
+// Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package cli
+
+import (
+	"context"
+	"errors"
+	"fmt"
+
+	"github.com/peterbourgon/ff/v2/ffcli"
+	"tailscale.com/client/tailscale"
+)
+
+var bugReportCmd = &ffcli.Command{
+	Name:       "bugreport",
+	Exec:       runBugReport,
+	ShortHelp:  "Print a shareable identifier to help diagnose issues",
+	ShortUsage: "bugreport [note]",
+}
+
+func runBugReport(ctx context.Context, args []string) error {
+	var note string
+	switch len(args) {
+	case 0:
+	case 1:
+		note = args[0]
+	default:
+		return errors.New("unknown argumets")
+	}
+	logMarker, err := tailscale.BugReport(ctx, note)
+	if err != nil {
+		return err
+	}
+	fmt.Println(logMarker)
+	return nil
+}
diff --git a/cmd/tailscaled/cli/cli.go b/cmd/tailscaled/cli/cli.go
new file mode 100644
index 000000000..ab58eb4a3
--- /dev/null
+++ b/cmd/tailscaled/cli/cli.go
@@ -0,0 +1,276 @@
+// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package cli contains the cmd/tailscale CLI code in a package that can be included
+// in other wrapper binaries such as the Mac and Windows clients.
+package cli
+
+import (
+	"context"
+	"errors"
+	"flag"
+	"fmt"
+	"io"
+	"log"
+	"net"
+	"os"
+	"os/signal"
+	"runtime"
+	"strconv"
+	"strings"
+	"syscall"
+	"text/tabwriter"
+
+	"github.com/peterbourgon/ff/v2/ffcli"
+	"tailscale.com/client/tailscale"
+	"tailscale.com/ipn"
+	"tailscale.com/paths"
+	"tailscale.com/safesocket"
+	"tailscale.com/syncs"
+)
+
+// ActLikeCLI reports whether a GUI application should act like the
+// CLI based on os.Args, GOOS, the context the process is running in
+// (pty, parent PID), etc.
+func ActLikeCLI() bool {
+	// This function is only used on macOS.
+	if runtime.GOOS != "darwin" {
+		return false
+	}
+
+	// Escape hatch to let people force running the macOS
+	// GUI Tailscale binary as the CLI.
+	if v, _ := strconv.ParseBool(os.Getenv("TAILSCALE_BE_CLI")); v {
+		return true
+	}
+
+	// If our parent is launchd, we're definitely not
+	// being run as a CLI.
+	if os.Getppid() == 1 {
+		return false
+	}
+
+	// Xcode adds the -NSDocumentRevisionsDebugMode flag on execution.
+	// If present, we are almost certainly being run as a GUI.
+	for _, arg := range os.Args {
+		if arg == "-NSDocumentRevisionsDebugMode" {
+			return false
+		}
+	}
+
+	// Looking at the environment of the GUI Tailscale app (ps eww
+	// $PID), empirically none of these environment variables are
+	// present. But all or some of these should be present with
+	// Terminal.all and bash or zsh.
+	for _, e := range []string{
+		"SHLVL",
+		"TERM",
+		"TERM_PROGRAM",
+		"PS1",
+	} {
+		if os.Getenv(e) != "" {
+			return true
+		}
+	}
+	return false
+}
+
+// Run runs the CLI. The args do not include the binary name.
+func Run(args []string) error {
+	if len(args) == 1 && (args[0] == "-V" || args[0] == "--version") {
+		args = []string{"version"}
+	}
+
+	rootfs := flag.NewFlagSet("tailscale", flag.ExitOnError)
+	rootfs.StringVar(&rootArgs.socket, "socket", paths.DefaultTailscaledSocket(), "path to tailscaled's unix socket")
+
+	rootCmd := &ffcli.Command{
+		Name:       "tailscale",
+		ShortUsage: "tailscale [flags] <subcommand> [command flags]",
+		ShortHelp:  "The easiest, most secure way to use WireGuard.",
+		LongHelp: strings.TrimSpace(`
+For help on subcommands, add --help after: "tailscale status --help".
+
+This CLI is still under active development. Commands and flags will
+change in the future.
+`),
+		Subcommands: []*ffcli.Command{
+			upCmd,
+			downCmd,
+			logoutCmd,
+			netcheckCmd,
+			ipCmd,
+			statusCmd,
+			pingCmd,
+			versionCmd,
+			webCmd,
+			fileCmd,
+			bugReportCmd,
+		},
+		FlagSet:   rootfs,
+		Exec:      func(context.Context, []string) error { return flag.ErrHelp },
+		UsageFunc: usageFunc,
+	}
+	for _, c := range rootCmd.Subcommands {
+		c.UsageFunc = usageFunc
+	}
+
+	// Don't advertise the debug command, but it exists.
+	if strSliceContains(args, "debug") {
+		rootCmd.Subcommands = append(rootCmd.Subcommands, debugCmd)
+	}
+
+	if err := rootCmd.Parse(args); err != nil {
+		return err
+	}
+
+	tailscale.TailscaledSocket = rootArgs.socket
+
+	err := rootCmd.Run(context.Background())
+	if err == flag.ErrHelp {
+		return nil
+	}
+	return err
+}
+
+func fatalf(format string, a ...interface{}) {
+	log.SetFlags(0)
+	log.Fatalf(format, a...)
+}
+
+var rootArgs struct {
+	socket string
+}
+
+var gotSignal syncs.AtomicBool
+
+func connect(ctx context.Context) (net.Conn, *ipn.BackendClient, context.Context, context.CancelFunc) {
+	c, err := safesocket.Connect(rootArgs.socket, 41112)
+	if err != nil {
+		if runtime.GOOS != "windows" && rootArgs.socket == "" {
+			fatalf("--socket cannot be empty")
+		}
+		fatalf("Failed to connect to tailscaled. (safesocket.Connect: %v)\n", err)
+	}
+	clientToServer := func(b []byte) {
+		ipn.WriteMsg(c, b)
+	}
+
+	ctx, cancel := context.WithCancel(ctx)
+
+	go func() {
+		interrupt := make(chan os.Signal, 1)
+		signal.Notify(interrupt, syscall.SIGINT, syscall.SIGTERM)
+		select {
+		case <-interrupt:
+		case <-ctx.Done():
+			// Context canceled elsewhere.
+			signal.Reset(syscall.SIGINT, syscall.SIGTERM)
+			return
+		}
+		gotSignal.Set(true)
+		c.Close()
+		cancel()
+	}()
+
+	bc := ipn.NewBackendClient(log.Printf, clientToServer)
+	return c, bc, ctx, cancel
+}
+
+// pump receives backend messages on conn and pushes them into bc.
+func pump(ctx context.Context, bc *ipn.BackendClient, conn net.Conn) error {
+	defer conn.Close()
+	for ctx.Err() == nil {
+		msg, err := ipn.ReadMsg(conn)
+		if err != nil {
+			if ctx.Err() != nil {
+				return ctx.Err()
+			}
+			if errors.Is(err, io.EOF) || errors.Is(err, net.ErrClosed) {
+				return fmt.Errorf("%w (tailscaled stopped running?)", err)
+			}
+			return err
+		}
+		bc.GotNotifyMsg(msg)
+	}
+	return ctx.Err()
+}
+
+func strSliceContains(ss []string, s string) bool {
+	for _, v := range ss {
+		if v == s {
+			return true
+		}
+	}
+	return false
+}
+
+func usageFunc(c *ffcli.Command) string {
+	var b strings.Builder
+
+	fmt.Fprintf(&b, "USAGE\n")
+	if c.ShortUsage != "" {
+		fmt.Fprintf(&b, "  %s\n", c.ShortUsage)
+	} else {
+		fmt.Fprintf(&b, "  %s\n", c.Name)
+	}
+	fmt.Fprintf(&b, "\n")
+
+	if c.LongHelp != "" {
+		fmt.Fprintf(&b, "%s\n\n", c.LongHelp)
+	}
+
+	if len(c.Subcommands) > 0 {
+		fmt.Fprintf(&b, "SUBCOMMANDS\n")
+		tw := tabwriter.NewWriter(&b, 0, 2, 2, ' ', 0)
+		for _, subcommand := range c.Subcommands {
+			fmt.Fprintf(tw, "  %s\t%s\n", subcommand.Name, subcommand.ShortHelp)
+		}
+		tw.Flush()
+		fmt.Fprintf(&b, "\n")
+	}
+
+	if countFlags(c.FlagSet) > 0 {
+		fmt.Fprintf(&b, "FLAGS\n")
+		tw := tabwriter.NewWriter(&b, 0, 2, 2, ' ', 0)
+		c.FlagSet.VisitAll(func(f *flag.Flag) {
+			var s string
+			name, usage := flag.UnquoteUsage(f)
+			if isBoolFlag(f) {
+				s = fmt.Sprintf("  --%s, --%s=false", f.Name, f.Name)
+			} else {
+				s = fmt.Sprintf("  --%s", f.Name) // Two spaces before --; see next two comments.
+				if len(name) > 0 {
+					s += " " + name
+				}
+			}
+			// Four spaces before the tab triggers good alignment
+			// for both 4- and 8-space tab stops.
+			s += "\n    \t"
+			s += strings.ReplaceAll(usage, "\n", "\n    \t")
+
+			if f.DefValue != "" {
+				s += fmt.Sprintf(" (default %s)", f.DefValue)
+			}
+
+			fmt.Fprintln(&b, s)
+		})
+		tw.Flush()
+		fmt.Fprintf(&b, "\n")
+	}
+
+	return strings.TrimSpace(b.String())
+}
+
+func isBoolFlag(f *flag.Flag) bool {
+	bf, ok := f.Value.(interface {
+		IsBoolFlag() bool
+	})
+	return ok && bf.IsBoolFlag()
+}
+
+func countFlags(fs *flag.FlagSet) (n int) {
+	fs.VisitAll(func(*flag.Flag) { n++ })
+	return n
+}
diff --git a/cmd/tailscaled/cli/cli_test.go b/cmd/tailscaled/cli/cli_test.go
new file mode 100644
index 000000000..fecdb76b2
--- /dev/null
+++ b/cmd/tailscaled/cli/cli_test.go
@@ -0,0 +1,668 @@
+// Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package cli
+
+import (
+	"bytes"
+	"encoding/json"
+	"flag"
+	"fmt"
+	"reflect"
+	"strings"
+	"testing"
+
+	"inet.af/netaddr"
+	"tailscale.com/ipn"
+	"tailscale.com/ipn/ipnstate"
+	"tailscale.com/types/preftype"
+)
+
+// geese is a collection of gooses. It need not be complete.
+// But it should include anything handled specially (e.g. linux, windows)
+// and at least one thing that's not (darwin, freebsd).
+var geese = []string{"linux", "darwin", "windows", "freebsd"}
+
+// Test that checkForAccidentalSettingReverts's updateMaskedPrefsFromUpFlag can handle
+// all flags. This will panic if a new flag creeps in that's unhandled.
+//
+// Also, issue 1880: advertise-exit-node was being ignored. Verify that all flags cause an edit.
+func TestUpdateMaskedPrefsFromUpFlag(t *testing.T) {
+	for _, goos := range geese {
+		var upArgs upArgsT
+		fs := newUpFlagSet(goos, &upArgs)
+		fs.VisitAll(func(f *flag.Flag) {
+			mp := new(ipn.MaskedPrefs)
+			updateMaskedPrefsFromUpFlag(mp, f.Name)
+			got := mp.Pretty()
+			wantEmpty := preflessFlag(f.Name)
+			isEmpty := got == "MaskedPrefs{}"
+			if isEmpty != wantEmpty {
+				t.Errorf("flag %q created MaskedPrefs %s; want empty=%v", f.Name, got, wantEmpty)
+			}
+		})
+	}
+}
+
+func TestCheckForAccidentalSettingReverts(t *testing.T) {
+	tests := []struct {
+		name     string
+		flags    []string // argv to be parsed by FlagSet
+		curPrefs *ipn.Prefs
+
+		curExitNodeIP netaddr.IP
+		curUser       string // os.Getenv("USER") on the client side
+		goos          string // empty means "linux"
+
+		want string
+	}{
+		{
+			name:  "bare_up_means_up",
+			flags: []string{},
+			curPrefs: &ipn.Prefs{
+				ControlURL:  ipn.DefaultControlURL,
+				WantRunning: false,
+				Hostname:    "foo",
+			},
+			want: "",
+		},
+		{
+			name:  "losing_hostname",
+			flags: []string{"--accept-dns"},
+			curPrefs: &ipn.Prefs{
+				ControlURL:       ipn.DefaultControlURL,
+				WantRunning:      false,
+				Hostname:         "foo",
+				CorpDNS:          true,
+				NetfilterMode:    preftype.NetfilterOn,
+				AllowSingleHosts: true,
+			},
+			want: accidentalUpPrefix + " --accept-dns --hostname=foo",
+		},
+		{
+			name:  "hostname_changing_explicitly",
+			flags: []string{"--hostname=bar"},
+			curPrefs: &ipn.Prefs{
+				ControlURL:       ipn.DefaultControlURL,
+				CorpDNS:          true,
+				NetfilterMode:    preftype.NetfilterOn,
+				AllowSingleHosts: true,
+				Hostname:         "foo",
+			},
+			want: "",
+		},
+		{
+			name:  "hostname_changing_empty_explicitly",
+			flags: []string{"--hostname="},
+			curPrefs: &ipn.Prefs{
+				ControlURL:       ipn.DefaultControlURL,
+				CorpDNS:          true,
+				NetfilterMode:    preftype.NetfilterOn,
+				AllowSingleHosts: true,
+				Hostname:         "foo",
+			},
+			want: "",
+		},
+		{
+			// Issue 1725: "tailscale up --authkey=..." (or other non-empty flags) works from
+			// a fresh server's initial prefs.
+			name:     "up_with_default_prefs",
+			flags:    []string{"--authkey=foosdlkfjskdljf"},
+			curPrefs: ipn.NewPrefs(),
+			want:     "",
+		},
+		{
+			name:  "implicit_operator_change",
+			flags: []string{"--hostname=foo"},
+			curPrefs: &ipn.Prefs{
+				ControlURL:       ipn.DefaultControlURL,
+				OperatorUser:     "alice",
+				AllowSingleHosts: true,
+				CorpDNS:          true,
+				NetfilterMode:    preftype.NetfilterOn,
+			},
+			curUser: "eve",
+			want:    accidentalUpPrefix + " --hostname=foo --operator=alice",
+		},
+		{
+			name:  "implicit_operator_matches_shell_user",
+			flags: []string{"--hostname=foo"},
+			curPrefs: &ipn.Prefs{
+				ControlURL:       ipn.DefaultControlURL,
+				AllowSingleHosts: true,
+				CorpDNS:          true,
+				NetfilterMode:    preftype.NetfilterOn,
+				OperatorUser:     "alice",
+			},
+			curUser: "alice",
+			want:    "",
+		},
+		{
+			name:  "error_advertised_routes_exit_node_removed",
+			flags: []string{"--advertise-routes=10.0.42.0/24"},
+			curPrefs: &ipn.Prefs{
+				ControlURL:       ipn.DefaultControlURL,
+				AllowSingleHosts: true,
+				CorpDNS:          true,
+				NetfilterMode:    preftype.NetfilterOn,
+				AdvertiseRoutes: []netaddr.IPPrefix{
+					netaddr.MustParseIPPrefix("10.0.42.0/24"),
+					netaddr.MustParseIPPrefix("0.0.0.0/0"),
+					netaddr.MustParseIPPrefix("::/0"),
+				},
+			},
+			want: accidentalUpPrefix + " --advertise-routes=10.0.42.0/24 --advertise-exit-node",
+		},
+		{
+			name:  "advertised_routes_exit_node_removed_explicit",
+			flags: []string{"--advertise-routes=10.0.42.0/24", "--advertise-exit-node=false"},
+			curPrefs: &ipn.Prefs{
+				ControlURL:       ipn.DefaultControlURL,
+				AllowSingleHosts: true,
+				CorpDNS:          true,
+				NetfilterMode:    preftype.NetfilterOn,
+				AdvertiseRoutes: []netaddr.IPPrefix{
+					netaddr.MustParseIPPrefix("10.0.42.0/24"),
+					netaddr.MustParseIPPrefix("0.0.0.0/0"),
+					netaddr.MustParseIPPrefix("::/0"),
+				},
+			},
+			want: "",
+		},
+		{
+			name:  "advertised_routes_includes_the_0_routes", // but no --advertise-exit-node
+			flags: []string{"--advertise-routes=11.1.43.0/24,0.0.0.0/0,::/0"},
+			curPrefs: &ipn.Prefs{
+				ControlURL:       ipn.DefaultControlURL,
+				AllowSingleHosts: true,
+				CorpDNS:          true,
+				NetfilterMode:    preftype.NetfilterOn,
+				AdvertiseRoutes: []netaddr.IPPrefix{
+					netaddr.MustParseIPPrefix("10.0.42.0/24"),
+					netaddr.MustParseIPPrefix("0.0.0.0/0"),
+					netaddr.MustParseIPPrefix("::/0"),
+				},
+			},
+			want: "",
+		},
+		{
+			name:  "advertise_exit_node", // Issue 1859
+			flags: []string{"--advertise-exit-node"},
+			curPrefs: &ipn.Prefs{
+				ControlURL:       ipn.DefaultControlURL,
+				AllowSingleHosts: true,
+				CorpDNS:          true,
+				NetfilterMode:    preftype.NetfilterOn,
+			},
+			want: "",
+		},
+		{
+			name:  "advertise_exit_node_over_existing_routes",
+			flags: []string{"--advertise-exit-node"},
+			curPrefs: &ipn.Prefs{
+				ControlURL:       ipn.DefaultControlURL,
+				AllowSingleHosts: true,
+				CorpDNS:          true,
+				NetfilterMode:    preftype.NetfilterOn,
+
+				AdvertiseRoutes: []netaddr.IPPrefix{
+					netaddr.MustParseIPPrefix("1.2.0.0/16"),
+				},
+			},
+			want: accidentalUpPrefix + " --advertise-exit-node --advertise-routes=1.2.0.0/16",
+		},
+		{
+			name:  "advertise_exit_node_over_existing_routes_and_exit_node",
+			flags: []string{"--advertise-exit-node"},
+			curPrefs: &ipn.Prefs{
+				ControlURL:       ipn.DefaultControlURL,
+				AllowSingleHosts: true,
+				CorpDNS:          true,
+				NetfilterMode:    preftype.NetfilterOn,
+				AdvertiseRoutes: []netaddr.IPPrefix{
+					netaddr.MustParseIPPrefix("0.0.0.0/0"),
+					netaddr.MustParseIPPrefix("::/0"),
+					netaddr.MustParseIPPrefix("1.2.0.0/16"),
+				},
+			},
+			want: accidentalUpPrefix + " --advertise-exit-node --advertise-routes=1.2.0.0/16",
+		},
+		{
+			name:  "exit_node_clearing", // Issue 1777
+			flags: []string{"--exit-node="},
+			curPrefs: &ipn.Prefs{
+				ControlURL:       ipn.DefaultControlURL,
+				AllowSingleHosts: true,
+				CorpDNS:          true,
+				NetfilterMode:    preftype.NetfilterOn,
+
+				ExitNodeID: "fooID",
+			},
+			want: "",
+		},
+		{
+			name:  "remove_all_implicit",
+			flags: []string{"--force-reauth"},
+			curPrefs: &ipn.Prefs{
+				WantRunning:      true,
+				ControlURL:       ipn.DefaultControlURL,
+				RouteAll:         true,
+				AllowSingleHosts: false,
+				ExitNodeIP:       netaddr.MustParseIP("100.64.5.6"),
+				CorpDNS:          false,
+				ShieldsUp:        true,
+				AdvertiseTags:    []string{"tag:foo", "tag:bar"},
+				Hostname:         "myhostname",
+				ForceDaemon:      true,
+				AdvertiseRoutes: []netaddr.IPPrefix{
+					netaddr.MustParseIPPrefix("10.0.0.0/16"),
+					netaddr.MustParseIPPrefix("0.0.0.0/0"),
+					netaddr.MustParseIPPrefix("::/0"),
+				},
+				NetfilterMode: preftype.NetfilterNoDivert,
+				OperatorUser:  "alice",
+			},
+			curUser: "eve",
+			want:    accidentalUpPrefix + " --force-reauth --accept-dns=false --accept-routes --advertise-exit-node --advertise-routes=10.0.0.0/16 --advertise-tags=tag:foo,tag:bar --exit-node=100.64.5.6 --host-routes=false --hostname=myhostname --netfilter-mode=nodivert --operator=alice --shields-up",
+		},
+		{
+			name:  "remove_all_implicit_except_hostname",
+			flags: []string{"--hostname=newhostname"},
+			curPrefs: &ipn.Prefs{
+				WantRunning:      true,
+				ControlURL:       ipn.DefaultControlURL,
+				RouteAll:         true,
+				AllowSingleHosts: false,
+				ExitNodeIP:       netaddr.MustParseIP("100.64.5.6"),
+				CorpDNS:          false,
+				ShieldsUp:        true,
+				AdvertiseTags:    []string{"tag:foo", "tag:bar"},
+				Hostname:         "myhostname",
+				ForceDaemon:      true,
+				AdvertiseRoutes: []netaddr.IPPrefix{
+					netaddr.MustParseIPPrefix("10.0.0.0/16"),
+				},
+				NetfilterMode: preftype.NetfilterNoDivert,
+				OperatorUser:  "alice",
+			},
+			curUser: "eve",
+			want:    accidentalUpPrefix + " --hostname=newhostname --accept-dns=false --accept-routes --advertise-routes=10.0.0.0/16 --advertise-tags=tag:foo,tag:bar --exit-node=100.64.5.6 --host-routes=false --netfilter-mode=nodivert --operator=alice --shields-up",
+		},
+		{
+			name:  "loggedout_is_implicit",
+			flags: []string{"--hostname=foo"},
+			curPrefs: &ipn.Prefs{
+				ControlURL:       ipn.DefaultControlURL,
+				LoggedOut:        true,
+				AllowSingleHosts: true,
+				CorpDNS:          true,
+				NetfilterMode:    preftype.NetfilterOn,
+			},
+			want: "", // not an error. LoggedOut is implicit.
+		},
+		{
+			// Test that a pre-1.8 version of Tailscale with bogus NoSNAT pref
+			// values is able to enable exit nodes without warnings.
+			name:  "make_windows_exit_node",
+			flags: []string{"--advertise-exit-node"},
+			curPrefs: &ipn.Prefs{
+				ControlURL:       ipn.DefaultControlURL,
+				AllowSingleHosts: true,
+				CorpDNS:          true,
+
+				// And assume this no-op accidental pre-1.8 value:
+				NoSNAT: true,
+			},
+			goos: "windows",
+			want: "", // not an error
+		},
+		{
+			name:  "ignore_netfilter_change_non_linux",
+			flags: []string{"--accept-dns"},
+			curPrefs: &ipn.Prefs{
+				ControlURL:       ipn.DefaultControlURL,
+				AllowSingleHosts: true,
+
+				NetfilterMode: preftype.NetfilterNoDivert, // we never had this bug, but pretend it got set non-zero on Windows somehow
+			},
+			goos: "windows",
+			want: "", // not an error
+		},
+		{
+			name:  "operator_losing_routes_step1", // https://twitter.com/EXPbits/status/1390418145047887877
+			flags: []string{"--operator=expbits"},
+			curPrefs: &ipn.Prefs{
+				ControlURL:       ipn.DefaultControlURL,
+				AllowSingleHosts: true,
+				CorpDNS:          true,
+				NetfilterMode:    preftype.NetfilterOn,
+				AdvertiseRoutes: []netaddr.IPPrefix{
+					netaddr.MustParseIPPrefix("0.0.0.0/0"),
+					netaddr.MustParseIPPrefix("::/0"),
+					netaddr.MustParseIPPrefix("1.2.0.0/16"),
+				},
+			},
+			want: accidentalUpPrefix + " --operator=expbits --advertise-exit-node --advertise-routes=1.2.0.0/16",
+		},
+		{
+			name:  "operator_losing_routes_step2", // https://twitter.com/EXPbits/status/1390418145047887877
+			flags: []string{"--operator=expbits", "--advertise-routes=1.2.0.0/16"},
+			curPrefs: &ipn.Prefs{
+				ControlURL:       ipn.DefaultControlURL,
+				AllowSingleHosts: true,
+				CorpDNS:          true,
+				NetfilterMode:    preftype.NetfilterOn,
+				AdvertiseRoutes: []netaddr.IPPrefix{
+					netaddr.MustParseIPPrefix("0.0.0.0/0"),
+					netaddr.MustParseIPPrefix("::/0"),
+					netaddr.MustParseIPPrefix("1.2.0.0/16"),
+				},
+			},
+			want: accidentalUpPrefix + " --advertise-routes=1.2.0.0/16 --operator=expbits --advertise-exit-node",
+		},
+		{
+			name:  "errors_preserve_explicit_flags",
+			flags: []string{"--reset", "--force-reauth=false", "--authkey=secretrand"},
+			curPrefs: &ipn.Prefs{
+				ControlURL:       ipn.DefaultControlURL,
+				WantRunning:      false,
+				CorpDNS:          true,
+				NetfilterMode:    preftype.NetfilterOn,
+				AllowSingleHosts: true,
+
+				Hostname: "foo",
+			},
+			want: accidentalUpPrefix + " --authkey=secretrand --force-reauth=false --reset --hostname=foo",
+		},
+		{
+			name:  "error_exit_node_omit_with_ip_pref",
+			flags: []string{"--hostname=foo"},
+			curPrefs: &ipn.Prefs{
+				ControlURL:       ipn.DefaultControlURL,
+				AllowSingleHosts: true,
+				CorpDNS:          true,
+				NetfilterMode:    preftype.NetfilterOn,
+
+				ExitNodeIP: netaddr.MustParseIP("100.64.5.4"),
+			},
+			want: accidentalUpPrefix + " --hostname=foo --exit-node=100.64.5.4",
+		},
+		{
+			name:          "error_exit_node_omit_with_id_pref",
+			flags:         []string{"--hostname=foo"},
+			curExitNodeIP: netaddr.MustParseIP("100.64.5.7"),
+			curPrefs: &ipn.Prefs{
+				ControlURL:       ipn.DefaultControlURL,
+				AllowSingleHosts: true,
+				CorpDNS:          true,
+				NetfilterMode:    preftype.NetfilterOn,
+
+				ExitNodeID: "some_stable_id",
+			},
+			want: accidentalUpPrefix + " --hostname=foo --exit-node=100.64.5.7",
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			goos := "linux"
+			if tt.goos != "" {
+				goos = tt.goos
+			}
+			var upArgs upArgsT
+			flagSet := newUpFlagSet(goos, &upArgs)
+			flagSet.Parse(tt.flags)
+			newPrefs, err := prefsFromUpArgs(upArgs, t.Logf, new(ipnstate.Status), goos)
+			if err != nil {
+				t.Fatal(err)
+			}
+			applyImplicitPrefs(newPrefs, tt.curPrefs, tt.curUser)
+			var got string
+			if err := checkForAccidentalSettingReverts(flagSet, tt.curPrefs, newPrefs, upCheckEnv{
+				goos:          goos,
+				curExitNodeIP: tt.curExitNodeIP,
+			}); err != nil {
+				got = err.Error()
+			}
+			if strings.TrimSpace(got) != tt.want {
+				t.Errorf("unexpected result\n got: %s\nwant: %s\n", got, tt.want)
+			}
+		})
+	}
+}
+
+func upArgsFromOSArgs(goos string, flagArgs ...string) (args upArgsT) {
+	fs := newUpFlagSet(goos, &args)
+	fs.Parse(flagArgs) // populates args
+	return
+}
+
+func TestPrefsFromUpArgs(t *testing.T) {
+	tests := []struct {
+		name     string
+		args     upArgsT
+		goos     string           // runtime.GOOS; empty means linux
+		st       *ipnstate.Status // or nil
+		want     *ipn.Prefs
+		wantErr  string
+		wantWarn string
+	}{
+		{
+			name: "default_linux",
+			goos: "linux",
+			args: upArgsFromOSArgs("linux"),
+			want: &ipn.Prefs{
+				ControlURL:       ipn.DefaultControlURL,
+				WantRunning:      true,
+				NoSNAT:           false,
+				NetfilterMode:    preftype.NetfilterOn,
+				CorpDNS:          true,
+				AllowSingleHosts: true,
+			},
+		},
+		{
+			name: "default_windows",
+			goos: "windows",
+			args: upArgsFromOSArgs("windows"),
+			want: &ipn.Prefs{
+				ControlURL:       ipn.DefaultControlURL,
+				WantRunning:      true,
+				CorpDNS:          true,
+				AllowSingleHosts: true,
+				NetfilterMode:    preftype.NetfilterOn,
+			},
+		},
+		{
+			name: "advertise_default_route",
+			args: upArgsFromOSArgs("linux", "--advertise-exit-node"),
+			want: &ipn.Prefs{
+				ControlURL:       ipn.DefaultControlURL,
+				WantRunning:      true,
+				AllowSingleHosts: true,
+				CorpDNS:          true,
+				AdvertiseRoutes: []netaddr.IPPrefix{
+					netaddr.MustParseIPPrefix("0.0.0.0/0"),
+					netaddr.MustParseIPPrefix("::/0"),
+				},
+				NetfilterMode: preftype.NetfilterOn,
+			},
+		},
+		{
+			name: "error_advertise_route_invalid_ip",
+			args: upArgsT{
+				advertiseRoutes: "foo",
+			},
+			wantErr: `"foo" is not a valid IP address or CIDR prefix`,
+		},
+		{
+			name: "error_advertise_route_unmasked_bits",
+			args: upArgsT{
+				advertiseRoutes: "1.2.3.4/16",
+			},
+			wantErr: `1.2.3.4/16 has non-address bits set; expected 1.2.0.0/16`,
+		},
+		{
+			name: "error_exit_node_bad_ip",
+			args: upArgsT{
+				exitNodeIP: "foo",
+			},
+			wantErr: `invalid IP address "foo" for --exit-node: ParseIP("foo"): unable to parse IP`,
+		},
+		{
+			name: "error_exit_node_allow_lan_without_exit_node",
+			args: upArgsT{
+				exitNodeAllowLANAccess: true,
+			},
+			wantErr: `--exit-node-allow-lan-access can only be used with --exit-node`,
+		},
+		{
+			name: "error_tag_prefix",
+			args: upArgsT{
+				advertiseTags: "foo",
+			},
+			wantErr: `tag: "foo": tags must start with 'tag:'`,
+		},
+		{
+			name: "error_long_hostname",
+			args: upArgsT{
+				hostname: strings.Repeat("a", 300),
+			},
+			wantErr: `hostname too long: 300 bytes (max 256)`,
+		},
+		{
+			name: "error_linux_netfilter_empty",
+			args: upArgsT{
+				netfilterMode: "",
+			},
+			wantErr: `invalid value --netfilter-mode=""`,
+		},
+		{
+			name: "error_linux_netfilter_bogus",
+			args: upArgsT{
+				netfilterMode: "bogus",
+			},
+			wantErr: `invalid value --netfilter-mode="bogus"`,
+		},
+		{
+			name: "error_exit_node_ip_is_self_ip",
+			args: upArgsT{
+				exitNodeIP: "100.105.106.107",
+			},
+			st: &ipnstate.Status{
+				TailscaleIPs: []netaddr.IP{netaddr.MustParseIP("100.105.106.107")},
+			},
+			wantErr: `cannot use 100.105.106.107 as the exit node as it is a local IP address to this machine, did you mean --advertise-exit-node?`,
+		},
+		{
+			name: "warn_linux_netfilter_nodivert",
+			goos: "linux",
+			args: upArgsT{
+				netfilterMode: "nodivert",
+			},
+			wantWarn: "netfilter=nodivert; add iptables calls to ts-* chains manually.",
+			want: &ipn.Prefs{
+				WantRunning:   true,
+				NetfilterMode: preftype.NetfilterNoDivert,
+				NoSNAT:        true,
+			},
+		},
+		{
+			name: "warn_linux_netfilter_off",
+			goos: "linux",
+			args: upArgsT{
+				netfilterMode: "off",
+			},
+			wantWarn: "netfilter=off; configure iptables yourself.",
+			want: &ipn.Prefs{
+				WantRunning:   true,
+				NetfilterMode: preftype.NetfilterOff,
+				NoSNAT:        true,
+			},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			var warnBuf bytes.Buffer
+			warnf := func(format string, a ...interface{}) {
+				fmt.Fprintf(&warnBuf, format, a...)
+			}
+			goos := tt.goos
+			if goos == "" {
+				goos = "linux"
+			}
+			st := tt.st
+			if st == nil {
+				st = new(ipnstate.Status)
+			}
+			got, err := prefsFromUpArgs(tt.args, warnf, st, goos)
+			gotErr := fmt.Sprint(err)
+			if tt.wantErr != "" {
+				if tt.wantErr != gotErr {
+					t.Errorf("wrong error.\n got error: %v\nwant error: %v\n", gotErr, tt.wantErr)
+				}
+				return
+			}
+			if err != nil {
+				t.Fatal(err)
+			}
+			if tt.want == nil {
+				t.Fatal("tt.want is nil")
+			}
+			if !got.Equals(tt.want) {
+				jgot, _ := json.MarshalIndent(got, "", "\t")
+				jwant, _ := json.MarshalIndent(tt.want, "", "\t")
+				if bytes.Equal(jgot, jwant) {
+					t.Logf("prefs differ only in non-JSON-visible ways (nil/non-nil zero-length arrays)")
+				}
+				t.Errorf("wrong prefs\n got: %s\nwant: %s\n\ngot: %s\nwant: %s\n",
+					got.Pretty(), tt.want.Pretty(),
+					jgot, jwant,
+				)
+
+			}
+		})
+	}
+
+}
+
+func TestPrefFlagMapping(t *testing.T) {
+	prefHasFlag := map[string]bool{}
+	for _, pv := range prefsOfFlag {
+		for _, pref := range pv {
+			prefHasFlag[pref] = true
+		}
+	}
+
+	prefType := reflect.TypeOf(ipn.Prefs{})
+	for i := 0; i < prefType.NumField(); i++ {
+		prefName := prefType.Field(i).Name
+		if prefHasFlag[prefName] {
+			continue
+		}
+		switch prefName {
+		case "WantRunning", "Persist", "LoggedOut":
+			// All explicitly handled (ignored) by checkForAccidentalSettingReverts.
+			continue
+		case "OSVersion", "DeviceModel":
+			// Only used by Android, which doesn't have a CLI mode anyway, so
+			// fine to not map.
+			continue
+		case "NotepadURLs":
+			// TODO(bradfitz): https://github.com/tailscale/tailscale/issues/1830
+			continue
+		}
+		t.Errorf("unexpected new ipn.Pref field %q is not handled by up.go (see addPrefFlagMapping and checkForAccidentalSettingReverts)", prefName)
+	}
+}
+
+func TestFlagAppliesToOS(t *testing.T) {
+	for _, goos := range geese {
+		var upArgs upArgsT
+		fs := newUpFlagSet(goos, &upArgs)
+		fs.VisitAll(func(f *flag.Flag) {
+			if !flagAppliesToOS(f.Name, goos) {
+				t.Errorf("flagAppliesToOS(%q, %q) = false but found in %s set", f.Name, goos, goos)
+			}
+		})
+	}
+}
diff --git a/cmd/tailscaled/cli/debug.go b/cmd/tailscaled/cli/debug.go
new file mode 100644
index 000000000..851bb97de
--- /dev/null
+++ b/cmd/tailscaled/cli/debug.go
@@ -0,0 +1,129 @@
+// Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package cli
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"flag"
+	"fmt"
+	"io"
+	"log"
+	"os"
+	"runtime"
+	"strings"
+
+	"github.com/peterbourgon/ff/v2/ffcli"
+	"tailscale.com/client/tailscale"
+	"tailscale.com/ipn"
+	"tailscale.com/paths"
+	"tailscale.com/safesocket"
+)
+
+var debugCmd = &ffcli.Command{
+	Name: "debug",
+	Exec: runDebug,
+	FlagSet: (func() *flag.FlagSet {
+		fs := flag.NewFlagSet("debug", flag.ExitOnError)
+		fs.BoolVar(&debugArgs.goroutines, "daemon-goroutines", false, "If true, dump the tailscaled daemon's goroutines")
+		fs.BoolVar(&debugArgs.ipn, "ipn", false, "If true, subscribe to IPN notifications")
+		fs.BoolVar(&debugArgs.prefs, "prefs", false, "If true, dump active prefs")
+		fs.BoolVar(&debugArgs.pretty, "pretty", false, "If true, pretty-print output (for --prefs)")
+		fs.BoolVar(&debugArgs.netMap, "netmap", true, "whether to include netmap in --ipn mode")
+		fs.BoolVar(&debugArgs.localCreds, "local-creds", false, "print how to connect to local tailscaled")
+		fs.StringVar(&debugArgs.file, "file", "", "get, delete:NAME, or NAME")
+		return fs
+	})(),
+}
+
+var debugArgs struct {
+	localCreds bool
+	goroutines bool
+	ipn        bool
+	netMap     bool
+	file       string
+	prefs      bool
+	pretty     bool
+}
+
+func runDebug(ctx context.Context, args []string) error {
+	if len(args) > 0 {
+		return errors.New("unknown arguments")
+	}
+	if debugArgs.localCreds {
+		port, token, err := safesocket.LocalTCPPortAndToken()
+		if err == nil {
+			fmt.Printf("curl -u:%s http://localhost:%d/localapi/v0/status\n", token, port)
+			return nil
+		}
+		if runtime.GOOS == "windows" {
+			fmt.Printf("curl http://localhost:41112/localapi/v0/status\n")
+			return nil
+		}
+		fmt.Printf("curl --unix-socket %s http://foo/localapi/v0/status\n", paths.DefaultTailscaledSocket())
+		return nil
+	}
+	if debugArgs.prefs {
+		prefs, err := tailscale.GetPrefs(ctx)
+		if err != nil {
+			return err
+		}
+		if debugArgs.pretty {
+			fmt.Println(prefs.Pretty())
+		} else {
+			j, _ := json.MarshalIndent(prefs, "", "\t")
+			fmt.Println(string(j))
+		}
+		return nil
+	}
+	if debugArgs.goroutines {
+		goroutines, err := tailscale.Goroutines(ctx)
+		if err != nil {
+			return err
+		}
+		os.Stdout.Write(goroutines)
+		return nil
+	}
+	if debugArgs.ipn {
+		c, bc, ctx, cancel := connect(ctx)
+		defer cancel()
+
+		bc.SetNotifyCallback(func(n ipn.Notify) {
+			if !debugArgs.netMap {
+				n.NetMap = nil
+			}
+			j, _ := json.MarshalIndent(n, "", "\t")
+			fmt.Printf("%s\n", j)
+		})
+		bc.RequestEngineStatus()
+		pump(ctx, bc, c)
+		return errors.New("exit")
+	}
+	if debugArgs.file != "" {
+		if debugArgs.file == "get" {
+			wfs, err := tailscale.WaitingFiles(ctx)
+			if err != nil {
+				log.Fatal(err)
+			}
+			e := json.NewEncoder(os.Stdout)
+			e.SetIndent("", "\t")
+			e.Encode(wfs)
+			return nil
+		}
+		delete := strings.HasPrefix(debugArgs.file, "delete:")
+		if delete {
+			return tailscale.DeleteWaitingFile(ctx, strings.TrimPrefix(debugArgs.file, "delete:"))
+		}
+		rc, size, err := tailscale.GetWaitingFile(ctx, debugArgs.file)
+		if err != nil {
+			return err
+		}
+		log.Printf("Size: %v\n", size)
+		io.Copy(os.Stdout, rc)
+		return nil
+	}
+	return nil
+}
diff --git a/cmd/tailscaled/cli/down.go b/cmd/tailscaled/cli/down.go
new file mode 100644
index 000000000..c0a9034fe
--- /dev/null
+++ b/cmd/tailscaled/cli/down.go
@@ -0,0 +1,46 @@
+// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package cli
+
+import (
+	"context"
+	"fmt"
+	"log"
+	"os"
+
+	"github.com/peterbourgon/ff/v2/ffcli"
+	"tailscale.com/client/tailscale"
+	"tailscale.com/ipn"
+)
+
+var downCmd = &ffcli.Command{
+	Name:       "down",
+	ShortUsage: "down",
+	ShortHelp:  "Disconnect from Tailscale",
+
+	Exec: runDown,
+}
+
+func runDown(ctx context.Context, args []string) error {
+	if len(args) > 0 {
+		log.Fatalf("too many non-flag arguments: %q", args)
+	}
+
+	st, err := tailscale.Status(ctx)
+	if err != nil {
+		return fmt.Errorf("error fetching current status: %w", err)
+	}
+	if st.BackendState == "Stopped" {
+		fmt.Fprintf(os.Stderr, "Tailscale was already stopped.\n")
+		return nil
+	}
+	_, err = tailscale.EditPrefs(ctx, &ipn.MaskedPrefs{
+		Prefs: ipn.Prefs{
+			WantRunning: false,
+		},
+		WantRunningSet: true,
+	})
+	return err
+}
diff --git a/cmd/tailscaled/cli/file.go b/cmd/tailscaled/cli/file.go
new file mode 100644
index 000000000..01dc68d83
--- /dev/null
+++ b/cmd/tailscaled/cli/file.go
@@ -0,0 +1,444 @@
+// Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package cli
+
+import (
+	"bytes"
+	"context"
+	"errors"
+	"flag"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"log"
+	"mime"
+	"net/http"
+	"net/url"
+	"os"
+	"path/filepath"
+	"strconv"
+	"strings"
+	"time"
+	"unicode/utf8"
+
+	"github.com/peterbourgon/ff/v2/ffcli"
+	"golang.org/x/time/rate"
+	"inet.af/netaddr"
+	"tailscale.com/client/tailscale"
+	"tailscale.com/client/tailscale/apitype"
+	"tailscale.com/ipn"
+	"tailscale.com/net/tsaddr"
+	"tailscale.com/version"
+)
+
+var fileCmd = &ffcli.Command{
+	Name:       "file",
+	ShortUsage: "file <cp|get> ...",
+	ShortHelp:  "Send or receive files",
+	Subcommands: []*ffcli.Command{
+		fileCpCmd,
+		fileGetCmd,
+	},
+	Exec: func(context.Context, []string) error {
+		// TODO(bradfitz): is there a better ffcli way to
+		// annotate subcommand-required commands that don't
+		// have an exec body of their own?
+		return errors.New("file subcommand required; run 'tailscale file -h' for details")
+	},
+}
+
+var fileCpCmd = &ffcli.Command{
+	Name:       "cp",
+	ShortUsage: "file cp <files...> <target>:",
+	ShortHelp:  "Copy file(s) to a host",
+	Exec:       runCp,
+	FlagSet: (func() *flag.FlagSet {
+		fs := flag.NewFlagSet("cp", flag.ExitOnError)
+		fs.StringVar(&cpArgs.name, "name", "", "alternate filename to use, especially useful when <file> is \"-\" (stdin)")
+		fs.BoolVar(&cpArgs.verbose, "verbose", false, "verbose output")
+		fs.BoolVar(&cpArgs.targets, "targets", false, "list possible file cp targets")
+		return fs
+	})(),
+}
+
+var cpArgs struct {
+	name    string
+	verbose bool
+	targets bool
+}
+
+func runCp(ctx context.Context, args []string) error {
+	if cpArgs.targets {
+		return runCpTargets(ctx, args)
+	}
+	if len(args) < 2 {
+		//lint:ignore ST1005 no sorry need that colon at the end
+		return errors.New("usage: tailscale file cp <files...> <target>:")
+	}
+	files, target := args[:len(args)-1], args[len(args)-1]
+	if !strings.HasSuffix(target, ":") {
+		return fmt.Errorf("final argument to 'tailscale file cp' must end in colon")
+	}
+	target = strings.TrimSuffix(target, ":")
+	hadBrackets := false
+	if strings.HasPrefix(target, "[") && strings.HasSuffix(target, "]") {
+		hadBrackets = true
+		target = strings.TrimSuffix(strings.TrimPrefix(target, "["), "]")
+	}
+	if ip, err := netaddr.ParseIP(target); err == nil && ip.Is6() && !hadBrackets {
+		return fmt.Errorf("an IPv6 literal must be written as [%s]", ip)
+	} else if hadBrackets && (err != nil || !ip.Is6()) {
+		return errors.New("unexpected brackets around target")
+	}
+	ip, err := tailscaleIPFromArg(ctx, target)
+	if err != nil {
+		return err
+	}
+
+	peerAPIBase, lastSeen, isOffline, err := discoverPeerAPIBase(ctx, ip)
+	if err != nil {
+		return fmt.Errorf("can't send to %s: %v", target, err)
+	}
+	if isOffline {
+		fmt.Fprintf(os.Stderr, "# warning: %s is offline\n", target)
+	} else if !lastSeen.IsZero() && time.Since(lastSeen) > lastSeenOld {
+		fmt.Fprintf(os.Stderr, "# warning: %s last seen %v ago\n", target, time.Since(lastSeen).Round(time.Minute))
+	}
+
+	if len(files) > 1 {
+		if cpArgs.name != "" {
+			return errors.New("can't use --name= with multiple files")
+		}
+		for _, fileArg := range files {
+			if fileArg == "-" {
+				return errors.New("can't use '-' as STDIN file when providing filename arguments")
+			}
+		}
+	}
+
+	for _, fileArg := range files {
+		var fileContents io.Reader
+		var name = cpArgs.name
+		var contentLength int64 = -1
+		if fileArg == "-" {
+			fileContents = os.Stdin
+			if name == "" {
+				name, fileContents, err = pickStdinFilename()
+				if err != nil {
+					return err
+				}
+			}
+		} else {
+			f, err := os.Open(fileArg)
+			if err != nil {
+				if version.IsSandboxedMacOS() {
+					return errors.New("the GUI version of Tailscale on macOS runs in a macOS sandbox that can't read files")
+				}
+				return err
+			}
+			defer f.Close()
+			fi, err := f.Stat()
+			if err != nil {
+				return err
+			}
+			if fi.IsDir() {
+				return errors.New("directories not supported")
+			}
+			contentLength = fi.Size()
+			fileContents = io.LimitReader(f, contentLength)
+			if name == "" {
+				name = filepath.Base(fileArg)
+			}
+
+			if slow, _ := strconv.ParseBool(os.Getenv("TS_DEBUG_SLOW_PUSH")); slow {
+				fileContents = &slowReader{r: fileContents}
+			}
+		}
+
+		dstURL := peerAPIBase + "/v0/put/" + url.PathEscape(name)
+		req, err := http.NewRequestWithContext(ctx, "PUT", dstURL, fileContents)
+		if err != nil {
+			return err
+		}
+		req.ContentLength = contentLength
+		if cpArgs.verbose {
+			log.Printf("sending to %v ...", dstURL)
+		}
+		res, err := http.DefaultClient.Do(req)
+		if err != nil {
+			return err
+		}
+		if res.StatusCode == 200 {
+			io.Copy(ioutil.Discard, res.Body)
+			res.Body.Close()
+			continue
+		}
+		io.Copy(os.Stdout, res.Body)
+		res.Body.Close()
+		return errors.New(res.Status)
+	}
+	return nil
+}
+
+func discoverPeerAPIBase(ctx context.Context, ipStr string) (base string, lastSeen time.Time, isOffline bool, err error) {
+	ip, err := netaddr.ParseIP(ipStr)
+	if err != nil {
+		return "", time.Time{}, false, err
+	}
+	fts, err := tailscale.FileTargets(ctx)
+	if err != nil {
+		return "", time.Time{}, false, err
+	}
+	for _, ft := range fts {
+		n := ft.Node
+		for _, a := range n.Addresses {
+			if a.IP() != ip {
+				continue
+			}
+			if n.LastSeen != nil {
+				lastSeen = *n.LastSeen
+			}
+			isOffline = n.Online != nil && !*n.Online
+			return ft.PeerAPIURL, lastSeen, isOffline, nil
+		}
+	}
+	return "", time.Time{}, false, fileTargetErrorDetail(ctx, ip)
+}
+
+// fileTargetErrorDetail returns a non-nil error saying why ip is an
+// invalid file sharing target.
+func fileTargetErrorDetail(ctx context.Context, ip netaddr.IP) error {
+	found := false
+	if st, err := tailscale.Status(ctx); err == nil && st.Self != nil {
+		for _, peer := range st.Peer {
+			for _, pip := range peer.TailscaleIPs {
+				if pip == ip {
+					found = true
+					if peer.UserID != st.Self.UserID {
+						return errors.New("owned by different user; can only send files to your own devices")
+					}
+				}
+			}
+		}
+	}
+	if found {
+		return errors.New("target seems to be running an old Tailscale version")
+	}
+	if !tsaddr.IsTailscaleIP(ip) {
+		return fmt.Errorf("unknown target; %v is not a Tailscale IP address", ip)
+	}
+	return errors.New("unknown target; not in your Tailnet")
+}
+
+const maxSniff = 4 << 20
+
+func ext(b []byte) string {
+	if len(b) < maxSniff && utf8.Valid(b) {
+		return ".txt"
+	}
+	if exts, _ := mime.ExtensionsByType(http.DetectContentType(b)); len(exts) > 0 {
+		return exts[0]
+	}
+	return ""
+}
+
+// pickStdinFilename reads a bit of stdin to return a good filename
+// for its contents. The returned Reader is the concatenation of the
+// read and unread bits.
+func pickStdinFilename() (name string, r io.Reader, err error) {
+	sniff, err := io.ReadAll(io.LimitReader(os.Stdin, maxSniff))
+	if err != nil {
+		return "", nil, err
+	}
+	return "stdin" + ext(sniff), io.MultiReader(bytes.NewReader(sniff), os.Stdin), nil
+}
+
+type slowReader struct {
+	r  io.Reader
+	rl *rate.Limiter
+}
+
+func (r *slowReader) Read(p []byte) (n int, err error) {
+	const burst = 4 << 10
+	plen := len(p)
+	if plen > burst {
+		plen = burst
+	}
+	if r.rl == nil {
+		r.rl = rate.NewLimiter(rate.Limit(1<<10), burst)
+	}
+	n, err = r.r.Read(p[:plen])
+	r.rl.WaitN(context.Background(), n)
+	return
+}
+
+const lastSeenOld = 20 * time.Minute
+
+func runCpTargets(ctx context.Context, args []string) error {
+	if len(args) > 0 {
+		return errors.New("invalid arguments with --targets")
+	}
+	fts, err := tailscale.FileTargets(ctx)
+	if err != nil {
+		return err
+	}
+	for _, ft := range fts {
+		n := ft.Node
+		var detail string
+		if n.Online != nil {
+			if !*n.Online {
+				detail = "offline"
+			}
+		} else {
+			detail = "unknown-status"
+		}
+		if detail != "" && n.LastSeen != nil {
+			d := time.Since(*n.LastSeen)
+			detail += fmt.Sprintf("; last seen %v ago", d.Round(time.Minute))
+		}
+		if detail != "" {
+			detail = "\t" + detail
+		}
+		fmt.Printf("%s\t%s%s\n", n.Addresses[0].IP(), n.ComputedName, detail)
+	}
+	return nil
+}
+
+var fileGetCmd = &ffcli.Command{
+	Name:       "get",
+	ShortUsage: "file get [--wait] [--verbose] <target-directory>",
+	ShortHelp:  "Move files out of the Tailscale file inbox",
+	Exec:       runFileGet,
+	FlagSet: (func() *flag.FlagSet {
+		fs := flag.NewFlagSet("get", flag.ExitOnError)
+		fs.BoolVar(&getArgs.wait, "wait", false, "wait for a file to arrive if inbox is empty")
+		fs.BoolVar(&getArgs.verbose, "verbose", false, "verbose output")
+		return fs
+	})(),
+}
+
+var getArgs struct {
+	wait    bool
+	verbose bool
+}
+
+func runFileGet(ctx context.Context, args []string) error {
+	if len(args) != 1 {
+		return errors.New("usage: file get <target-directory>")
+	}
+	log.SetFlags(0)
+
+	dir := args[0]
+	if dir == "/dev/null" {
+		return wipeInbox(ctx)
+	}
+
+	if fi, err := os.Stat(dir); err != nil || !fi.IsDir() {
+		return fmt.Errorf("%q is not a directory", dir)
+	}
+
+	var wfs []apitype.WaitingFile
+	var err error
+	for {
+		wfs, err = tailscale.WaitingFiles(ctx)
+		if err != nil {
+			return fmt.Errorf("getting WaitingFiles: %v", err)
+		}
+		if len(wfs) != 0 || !getArgs.wait {
+			break
+		}
+		if getArgs.verbose {
+			log.Printf("waiting for file...")
+		}
+		if err := waitForFile(ctx); err != nil {
+			return err
+		}
+	}
+
+	deleted := 0
+	for _, wf := range wfs {
+		rc, size, err := tailscale.GetWaitingFile(ctx, wf.Name)
+		if err != nil {
+			return fmt.Errorf("opening inbox file %q: %v", wf.Name, err)
+		}
+		targetFile := filepath.Join(dir, wf.Name)
+		of, err := os.OpenFile(targetFile, os.O_RDWR|os.O_CREATE|os.O_EXCL, 0644)
+		if err != nil {
+			if _, err := os.Stat(targetFile); err == nil {
+				return fmt.Errorf("refusing to overwrite %v", targetFile)
+			}
+			return err
+		}
+		_, err = io.Copy(of, rc)
+		rc.Close()
+		if err != nil {
+			return fmt.Errorf("failed to write %v: %v", targetFile, err)
+		}
+		if err := of.Close(); err != nil {
+			return err
+		}
+		if getArgs.verbose {
+			log.Printf("wrote %v (%d bytes)", wf.Name, size)
+		}
+		if err := tailscale.DeleteWaitingFile(ctx, wf.Name); err != nil {
+			return fmt.Errorf("deleting %q from inbox: %v", wf.Name, err)
+		}
+		deleted++
+	}
+	if getArgs.verbose {
+		log.Printf("moved %d files", deleted)
+	}
+	return nil
+}
+
+func wipeInbox(ctx context.Context) error {
+	if getArgs.wait {
+		return errors.New("can't use --wait with /dev/null target")
+	}
+	wfs, err := tailscale.WaitingFiles(ctx)
+	if err != nil {
+		return fmt.Errorf("getting WaitingFiles: %v", err)
+	}
+	deleted := 0
+	for _, wf := range wfs {
+		if getArgs.verbose {
+			log.Printf("deleting %v ...", wf.Name)
+		}
+		if err := tailscale.DeleteWaitingFile(ctx, wf.Name); err != nil {
+			return fmt.Errorf("deleting %q: %v", wf.Name, err)
+		}
+		deleted++
+	}
+	if getArgs.verbose {
+		log.Printf("deleted %d files", deleted)
+	}
+	return nil
+}
+
+func waitForFile(ctx context.Context) error {
+	c, bc, pumpCtx, cancel := connect(ctx)
+	defer cancel()
+	fileWaiting := make(chan bool, 1)
+	bc.SetNotifyCallback(func(n ipn.Notify) {
+		if n.ErrMessage != nil {
+			log.Fatal(*n.ErrMessage)
+		}
+		if n.FilesWaiting != nil {
+			select {
+			case fileWaiting <- true:
+			default:
+			}
+		}
+	})
+	go pump(pumpCtx, bc, c)
+	select {
+	case <-fileWaiting:
+		return nil
+	case <-pumpCtx.Done():
+		return pumpCtx.Err()
+	case <-ctx.Done():
+		return ctx.Err()
+	}
+}
diff --git a/cmd/tailscaled/cli/ip.go b/cmd/tailscaled/cli/ip.go
new file mode 100644
index 000000000..2122d6022
--- /dev/null
+++ b/cmd/tailscaled/cli/ip.go
@@ -0,0 +1,105 @@
+// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package cli
+
+import (
+	"context"
+	"errors"
+	"flag"
+	"fmt"
+
+	"github.com/peterbourgon/ff/v2/ffcli"
+	"inet.af/netaddr"
+	"tailscale.com/client/tailscale"
+	"tailscale.com/ipn/ipnstate"
+)
+
+var ipCmd = &ffcli.Command{
+	Name:       "ip",
+	ShortUsage: "ip [-4] [-6] [peername]",
+	ShortHelp:  "Show current Tailscale IP address(es)",
+	LongHelp:   "Shows the Tailscale IP address of the current machine without an argument. With an argument, it shows the IP of a named peer.",
+	Exec:       runIP,
+	FlagSet: (func() *flag.FlagSet {
+		fs := flag.NewFlagSet("ip", flag.ExitOnError)
+		fs.BoolVar(&ipArgs.want4, "4", false, "only print IPv4 address")
+		fs.BoolVar(&ipArgs.want6, "6", false, "only print IPv6 address")
+		return fs
+	})(),
+}
+
+var ipArgs struct {
+	want4 bool
+	want6 bool
+}
+
+func runIP(ctx context.Context, args []string) error {
+	if len(args) > 1 {
+		return errors.New("unknown arguments")
+	}
+	var of string
+	if len(args) == 1 {
+		of = args[0]
+	}
+
+	v4, v6 := ipArgs.want4, ipArgs.want6
+	if v4 && v6 {
+		return errors.New("tailscale up -4 and -6 are mutually exclusive")
+	}
+	if !v4 && !v6 {
+		v4, v6 = true, true
+	}
+	st, err := tailscale.Status(ctx)
+	if err != nil {
+		return err
+	}
+	ips := st.TailscaleIPs
+	if of != "" {
+		ip, err := tailscaleIPFromArg(ctx, of)
+		if err != nil {
+			return err
+		}
+		peer, ok := peerMatchingIP(st, ip)
+		if !ok {
+			return fmt.Errorf("no peer found with IP %v", ip)
+		}
+		ips = peer.TailscaleIPs
+	}
+	if len(ips) == 0 {
+		return fmt.Errorf("no current Tailscale IPs; state: %v", st.BackendState)
+	}
+
+	match := false
+	for _, ip := range ips {
+		if ip.Is4() && v4 || ip.Is6() && v6 {
+			match = true
+			fmt.Println(ip)
+		}
+	}
+	if !match {
+		if ipArgs.want4 {
+			return errors.New("no Tailscale IPv4 address")
+		}
+		if ipArgs.want6 {
+			return errors.New("no Tailscale IPv6 address")
+		}
+	}
+	return nil
+}
+
+func peerMatchingIP(st *ipnstate.Status, ipStr string) (ps *ipnstate.PeerStatus, ok bool) {
+	ip, err := netaddr.ParseIP(ipStr)
+	if err != nil {
+		return
+	}
+	for _, ps = range st.Peer {
+		for _, pip := range ps.TailscaleIPs {
+			if ip == pip {
+				return ps, true
+			}
+		}
+	}
+	return nil, false
+}
diff --git a/cmd/tailscaled/cli/logout.go b/cmd/tailscaled/cli/logout.go
new file mode 100644
index 000000000..6356b2452
--- /dev/null
+++ b/cmd/tailscaled/cli/logout.go
@@ -0,0 +1,34 @@
+// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package cli
+
+import (
+	"context"
+	"log"
+	"strings"
+
+	"github.com/peterbourgon/ff/v2/ffcli"
+	"tailscale.com/client/tailscale"
+)
+
+var logoutCmd = &ffcli.Command{
+	Name:       "logout",
+	ShortUsage: "logout [flags]",
+	ShortHelp:  "Disconnect from Tailscale and expire current node key",
+
+	LongHelp: strings.TrimSpace(`
+"tailscale logout" brings the network down and invalidates
+the current node key, forcing a future use of it to cause
+a reauthentication.
+`),
+	Exec: runLogout,
+}
+
+func runLogout(ctx context.Context, args []string) error {
+	if len(args) > 0 {
+		log.Fatalf("too many non-flag arguments: %q", args)
+	}
+	return tailscale.Logout(ctx)
+}
diff --git a/cmd/tailscaled/cli/netcheck.go b/cmd/tailscaled/cli/netcheck.go
new file mode 100644
index 000000000..09ce664cd
--- /dev/null
+++ b/cmd/tailscaled/cli/netcheck.go
@@ -0,0 +1,178 @@
+// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package cli
+
+import (
+	"context"
+	"encoding/json"
+	"flag"
+	"fmt"
+	"log"
+	"os"
+	"sort"
+	"strings"
+	"time"
+
+	"github.com/peterbourgon/ff/v2/ffcli"
+	"tailscale.com/derp/derpmap"
+	"tailscale.com/net/netcheck"
+	"tailscale.com/net/portmapper"
+	"tailscale.com/tailcfg"
+	"tailscale.com/types/logger"
+)
+
+var netcheckCmd = &ffcli.Command{
+	Name:       "netcheck",
+	ShortUsage: "netcheck",
+	ShortHelp:  "Print an analysis of local network conditions",
+	Exec:       runNetcheck,
+	FlagSet: (func() *flag.FlagSet {
+		fs := flag.NewFlagSet("netcheck", flag.ExitOnError)
+		fs.StringVar(&netcheckArgs.format, "format", "", `output format; empty (for human-readable), "json" or "json-line"`)
+		fs.DurationVar(&netcheckArgs.every, "every", 0, "if non-zero, do an incremental report with the given frequency")
+		fs.BoolVar(&netcheckArgs.verbose, "verbose", false, "verbose logs")
+		return fs
+	})(),
+}
+
+var netcheckArgs struct {
+	format  string
+	every   time.Duration
+	verbose bool
+}
+
+func runNetcheck(ctx context.Context, args []string) error {
+	c := &netcheck.Client{
+		UDPBindAddr: os.Getenv("TS_DEBUG_NETCHECK_UDP_BIND"),
+		PortMapper:  portmapper.NewClient(logger.WithPrefix(log.Printf, "portmap: ")),
+	}
+	if netcheckArgs.verbose {
+		c.Logf = logger.WithPrefix(log.Printf, "netcheck: ")
+		c.Verbose = true
+	} else {
+		c.Logf = logger.Discard
+	}
+
+	if strings.HasPrefix(netcheckArgs.format, "json") {
+		fmt.Fprintln(os.Stderr, "# Warning: this JSON format is not yet considered a stable interface")
+	}
+
+	dm := derpmap.Prod()
+	for {
+		t0 := time.Now()
+		report, err := c.GetReport(ctx, dm)
+		d := time.Since(t0)
+		if netcheckArgs.verbose {
+			c.Logf("GetReport took %v; err=%v", d.Round(time.Millisecond), err)
+		}
+		if err != nil {
+			log.Fatalf("netcheck: %v", err)
+		}
+		if err := printReport(dm, report); err != nil {
+			return err
+		}
+		if netcheckArgs.every == 0 {
+			return nil
+		}
+		time.Sleep(netcheckArgs.every)
+	}
+}
+
+func printReport(dm *tailcfg.DERPMap, report *netcheck.Report) error {
+	var j []byte
+	var err error
+	switch netcheckArgs.format {
+	case "":
+		break
+	case "json":
+		j, err = json.MarshalIndent(report, "", "\t")
+	case "json-line":
+		j, err = json.Marshal(report)
+	default:
+		return fmt.Errorf("unknown output format %q", netcheckArgs.format)
+	}
+	if err != nil {
+		return err
+	}
+	if j != nil {
+		j = append(j, '\n')
+		os.Stdout.Write(j)
+		return nil
+	}
+
+	fmt.Printf("\nReport:\n")
+	fmt.Printf("\t* UDP: %v\n", report.UDP)
+	if report.GlobalV4 != "" {
+		fmt.Printf("\t* IPv4: yes, %v\n", report.GlobalV4)
+	} else {
+		fmt.Printf("\t* IPv4: (no addr found)\n")
+	}
+	if report.GlobalV6 != "" {
+		fmt.Printf("\t* IPv6: yes, %v\n", report.GlobalV6)
+	} else if report.IPv6 {
+		fmt.Printf("\t* IPv6: (no addr found)\n")
+	} else {
+		fmt.Printf("\t* IPv6: no\n")
+	}
+	fmt.Printf("\t* MappingVariesByDestIP: %v\n", report.MappingVariesByDestIP)
+	fmt.Printf("\t* HairPinning: %v\n", report.HairPinning)
+	fmt.Printf("\t* PortMapping: %v\n", portMapping(report))
+
+	// When DERP latency checking failed,
+	// magicsock will try to pick the DERP server that
+	// most of your other nodes are also using
+	if len(report.RegionLatency) == 0 {
+		fmt.Printf("\t* Nearest DERP: unknown (no response to latency probes)\n")
+	} else {
+		fmt.Printf("\t* Nearest DERP: %v\n", dm.Regions[report.PreferredDERP].RegionName)
+		fmt.Printf("\t* DERP latency:\n")
+		var rids []int
+		for rid := range dm.Regions {
+			rids = append(rids, rid)
+		}
+		sort.Slice(rids, func(i, j int) bool {
+			l1, ok1 := report.RegionLatency[rids[i]]
+			l2, ok2 := report.RegionLatency[rids[j]]
+			if ok1 != ok2 {
+				return ok1 // defined things sort first
+			}
+			if !ok1 {
+				return rids[i] < rids[j]
+			}
+			return l1 < l2
+		})
+		for _, rid := range rids {
+			d, ok := report.RegionLatency[rid]
+			var latency string
+			if ok {
+				latency = d.Round(time.Millisecond / 10).String()
+			}
+			r := dm.Regions[rid]
+			var derpNum string
+			if netcheckArgs.verbose {
+				derpNum = fmt.Sprintf("derp%d, ", rid)
+			}
+			fmt.Printf("\t\t- %3s: %-7s (%s%s)\n", r.RegionCode, latency, derpNum, r.RegionName)
+		}
+	}
+	return nil
+}
+
+func portMapping(r *netcheck.Report) string {
+	if !r.AnyPortMappingChecked() {
+		return "not checked"
+	}
+	var got []string
+	if r.UPnP.EqualBool(true) {
+		got = append(got, "UPnP")
+	}
+	if r.PMP.EqualBool(true) {
+		got = append(got, "NAT-PMP")
+	}
+	if r.PCP.EqualBool(true) {
+		got = append(got, "PCP")
+	}
+	return strings.Join(got, ", ")
+}
diff --git a/cmd/tailscaled/cli/ping.go b/cmd/tailscaled/cli/ping.go
new file mode 100644
index 000000000..25470aa69
--- /dev/null
+++ b/cmd/tailscaled/cli/ping.go
@@ -0,0 +1,179 @@
+// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package cli
+
+import (
+	"context"
+	"errors"
+	"flag"
+	"fmt"
+	"log"
+	"net"
+	"strings"
+	"time"
+
+	"github.com/peterbourgon/ff/v2/ffcli"
+	"tailscale.com/client/tailscale"
+	"tailscale.com/ipn"
+	"tailscale.com/ipn/ipnstate"
+)
+
+var pingCmd = &ffcli.Command{
+	Name:       "ping",
+	ShortUsage: "ping <hostname-or-IP>",
+	ShortHelp:  "Ping a host at the Tailscale layer, see how it routed",
+	LongHelp: strings.TrimSpace(`
+
+The 'tailscale ping' command pings a peer node at the Tailscale layer
+and reports which route it took for each response. The first ping or
+so will likely go over DERP (Tailscale's TCP relay protocol) while NAT
+traversal finds a direct path through.
+
+If 'tailscale ping' works but a normal ping does not, that means one
+side's operating system firewall is blocking packets; 'tailscale ping'
+does not inject packets into either side's TUN devices.
+
+By default, 'tailscale ping' stops after 10 pings or once a direct
+(non-DERP) path has been established, whichever comes first.
+
+The provided hostname must resolve to or be a Tailscale IP
+(e.g. 100.x.y.z) or a subnet IP advertised by a Tailscale
+relay node.
+
+`),
+	Exec: runPing,
+	FlagSet: (func() *flag.FlagSet {
+		fs := flag.NewFlagSet("ping", flag.ExitOnError)
+		fs.BoolVar(&pingArgs.verbose, "verbose", false, "verbose output")
+		fs.BoolVar(&pingArgs.untilDirect, "until-direct", true, "stop once a direct path is established")
+		fs.BoolVar(&pingArgs.tsmp, "tsmp", false, "do a TSMP-level ping (through IP + wireguard, but not involving host OS stack)")
+		fs.IntVar(&pingArgs.num, "c", 10, "max number of pings to send")
+		fs.DurationVar(&pingArgs.timeout, "timeout", 5*time.Second, "timeout before giving up on a ping")
+		return fs
+	})(),
+}
+
+var pingArgs struct {
+	num         int
+	untilDirect bool
+	verbose     bool
+	tsmp        bool
+	timeout     time.Duration
+}
+
+func runPing(ctx context.Context, args []string) error {
+	c, bc, ctx, cancel := connect(ctx)
+	defer cancel()
+
+	if len(args) != 1 || args[0] == "" {
+		return errors.New("usage: ping <hostname-or-IP>")
+	}
+	var ip string
+	prc := make(chan *ipnstate.PingResult, 1)
+	bc.SetNotifyCallback(func(n ipn.Notify) {
+		if n.ErrMessage != nil {
+			log.Fatal(*n.ErrMessage)
+		}
+		if pr := n.PingResult; pr != nil && pr.IP == ip {
+			prc <- pr
+		}
+	})
+	pumpErr := make(chan error, 1)
+	go func() { pumpErr <- pump(ctx, bc, c) }()
+
+	hostOrIP := args[0]
+	ip, err := tailscaleIPFromArg(ctx, hostOrIP)
+	if err != nil {
+		return err
+	}
+
+	if pingArgs.verbose && ip != hostOrIP {
+		log.Printf("lookup %q => %q", hostOrIP, ip)
+	}
+
+	n := 0
+	anyPong := false
+	for {
+		n++
+		bc.Ping(ip, pingArgs.tsmp)
+		timer := time.NewTimer(pingArgs.timeout)
+		select {
+		case <-timer.C:
+			fmt.Printf("timeout waiting for ping reply\n")
+		case err := <-pumpErr:
+			return err
+		case pr := <-prc:
+			timer.Stop()
+			if pr.Err != "" {
+				return errors.New(pr.Err)
+			}
+			latency := time.Duration(pr.LatencySeconds * float64(time.Second)).Round(time.Millisecond)
+			via := pr.Endpoint
+			if pr.DERPRegionID != 0 {
+				via = fmt.Sprintf("DERP(%s)", pr.DERPRegionCode)
+			}
+			if pingArgs.tsmp {
+				// TODO(bradfitz): populate the rest of ipnstate.PingResult for TSMP queries?
+				// For now just say it came via TSMP.
+				via = "TSMP"
+			}
+			anyPong = true
+			extra := ""
+			if pr.PeerAPIPort != 0 {
+				extra = fmt.Sprintf(", %d", pr.PeerAPIPort)
+			}
+			fmt.Printf("pong from %s (%s%s) via %v in %v\n", pr.NodeName, pr.NodeIP, extra, via, latency)
+			if pingArgs.tsmp {
+				return nil
+			}
+			if pr.Endpoint != "" && pingArgs.untilDirect {
+				return nil
+			}
+			time.Sleep(time.Second)
+		case <-ctx.Done():
+			return ctx.Err()
+		}
+		if n == pingArgs.num {
+			if !anyPong {
+				return errors.New("no reply")
+			}
+			if pingArgs.untilDirect {
+				return errors.New("direct connection not established")
+			}
+			return nil
+		}
+	}
+}
+
+func tailscaleIPFromArg(ctx context.Context, hostOrIP string) (ip string, err error) {
+	// If the argument is an IP address, use it directly without any resolution.
+	if net.ParseIP(hostOrIP) != nil {
+		return hostOrIP, nil
+	}
+
+	// Otherwise, try to resolve it first from the network peer list.
+	st, err := tailscale.Status(ctx)
+	if err != nil {
+		return "", err
+	}
+	for _, ps := range st.Peer {
+		if hostOrIP == dnsOrQuoteHostname(st, ps) || hostOrIP == ps.DNSName {
+			if len(ps.TailscaleIPs) == 0 {
+				return "", errors.New("node found but lacks an IP")
+			}
+			return ps.TailscaleIPs[0].String(), nil
+		}
+	}
+
+	// Finally, use DNS.
+	var res net.Resolver
+	if addrs, err := res.LookupHost(ctx, hostOrIP); err != nil {
+		return "", fmt.Errorf("error looking up IP of %q: %v", hostOrIP, err)
+	} else if len(addrs) == 0 {
+		return "", fmt.Errorf("no IPs found for %q", hostOrIP)
+	} else {
+		return addrs[0], nil
+	}
+}
diff --git a/cmd/tailscaled/cli/status.go b/cmd/tailscaled/cli/status.go
new file mode 100644
index 000000000..af887f427
--- /dev/null
+++ b/cmd/tailscaled/cli/status.go
@@ -0,0 +1,226 @@
+// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package cli
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"flag"
+	"fmt"
+	"net"
+	"net/http"
+	"os"
+	"strings"
+	"time"
+
+	"github.com/peterbourgon/ff/v2/ffcli"
+	"github.com/toqueteos/webbrowser"
+	"inet.af/netaddr"
+	"tailscale.com/client/tailscale"
+	"tailscale.com/ipn"
+	"tailscale.com/ipn/ipnstate"
+	"tailscale.com/net/interfaces"
+	"tailscale.com/util/dnsname"
+)
+
+var statusCmd = &ffcli.Command{
+	Name:       "status",
+	ShortUsage: "status [--active] [--web] [--json]",
+	ShortHelp:  "Show state of tailscaled and its connections",
+	Exec:       runStatus,
+	FlagSet: (func() *flag.FlagSet {
+		fs := flag.NewFlagSet("status", flag.ExitOnError)
+		fs.BoolVar(&statusArgs.json, "json", false, "output in JSON format (WARNING: format subject to change)")
+		fs.BoolVar(&statusArgs.web, "web", false, "run webserver with HTML showing status")
+		fs.BoolVar(&statusArgs.active, "active", false, "filter output to only peers with active sessions (not applicable to web mode)")
+		fs.BoolVar(&statusArgs.self, "self", true, "show status of local machine")
+		fs.BoolVar(&statusArgs.peers, "peers", true, "show status of peers")
+		fs.StringVar(&statusArgs.listen, "listen", "127.0.0.1:8384", "listen address for web mode; use port 0 for automatic")
+		fs.BoolVar(&statusArgs.browser, "browser", true, "Open a browser in web mode")
+		return fs
+	})(),
+}
+
+var statusArgs struct {
+	json    bool   // JSON output mode
+	web     bool   // run webserver
+	listen  string // in web mode, webserver address to listen on, empty means auto
+	browser bool   // in web mode, whether to open browser
+	active  bool   // in CLI mode, filter output to only peers with active sessions
+	self    bool   // in CLI mode, show status of local machine
+	peers   bool   // in CLI mode, show status of peer machines
+}
+
+func runStatus(ctx context.Context, args []string) error {
+	st, err := tailscale.Status(ctx)
+	if err != nil {
+		return err
+	}
+	if statusArgs.json {
+		if statusArgs.active {
+			for peer, ps := range st.Peer {
+				if !peerActive(ps) {
+					delete(st.Peer, peer)
+				}
+			}
+		}
+		j, err := json.MarshalIndent(st, "", "  ")
+		if err != nil {
+			return err
+		}
+		fmt.Printf("%s", j)
+		return nil
+	}
+	if statusArgs.web {
+		ln, err := net.Listen("tcp", statusArgs.listen)
+		if err != nil {
+			return err
+		}
+		statusURL := interfaces.HTTPOfListener(ln)
+		fmt.Printf("Serving Tailscale status at %v ...\n", statusURL)
+		go func() {
+			<-ctx.Done()
+			ln.Close()
+		}()
+		if statusArgs.browser {
+			go webbrowser.Open(statusURL)
+		}
+		err = http.Serve(ln, http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			if r.RequestURI != "/" {
+				http.NotFound(w, r)
+				return
+			}
+			st, err := tailscale.Status(ctx)
+			if err != nil {
+				http.Error(w, err.Error(), 500)
+				return
+			}
+			w.Header().Set("Content-Type", "text/html; charset=utf-8")
+			st.WriteHTML(w)
+		}))
+		if ctx.Err() != nil {
+			return ctx.Err()
+		}
+		return err
+	}
+
+	switch st.BackendState {
+	default:
+		fmt.Fprintf(os.Stderr, "unexpected state: %s\n", st.BackendState)
+		os.Exit(1)
+	case ipn.Stopped.String():
+		fmt.Println("Tailscale is stopped.")
+		os.Exit(1)
+	case ipn.NeedsLogin.String():
+		fmt.Println("Logged out.")
+		if st.AuthURL != "" {
+			fmt.Printf("\nLog in at: %s\n", st.AuthURL)
+		}
+		os.Exit(1)
+	case ipn.NeedsMachineAuth.String():
+		fmt.Println("Machine is not yet authorized by tailnet admin.")
+		os.Exit(1)
+	case ipn.Running.String():
+		// Run below.
+	}
+
+	var buf bytes.Buffer
+	f := func(format string, a ...interface{}) { fmt.Fprintf(&buf, format, a...) }
+	printPS := func(ps *ipnstate.PeerStatus) {
+		active := peerActive(ps)
+		f("%-15s %-20s %-12s %-7s ",
+			firstIPString(ps.TailscaleIPs),
+			dnsOrQuoteHostname(st, ps),
+			ownerLogin(st, ps),
+			ps.OS,
+		)
+		relay := ps.Relay
+		anyTraffic := ps.TxBytes != 0 || ps.RxBytes != 0
+		if !active {
+			if ps.ExitNode {
+				f("idle; exit node")
+			} else if anyTraffic {
+				f("idle")
+			} else {
+				f("-")
+			}
+		} else {
+			f("active; ")
+			if ps.ExitNode {
+				f("exit node; ")
+			}
+			if relay != "" && ps.CurAddr == "" {
+				f("relay %q", relay)
+			} else if ps.CurAddr != "" {
+				f("direct %s", ps.CurAddr)
+			}
+		}
+		if anyTraffic {
+			f(", tx %d rx %d", ps.TxBytes, ps.RxBytes)
+		}
+		f("\n")
+	}
+
+	if statusArgs.self && st.Self != nil {
+		printPS(st.Self)
+	}
+	if statusArgs.peers {
+		var peers []*ipnstate.PeerStatus
+		for _, peer := range st.Peers() {
+			ps := st.Peer[peer]
+			if ps.ShareeNode {
+				continue
+			}
+			peers = append(peers, ps)
+		}
+		ipnstate.SortPeers(peers)
+		for _, ps := range peers {
+			active := peerActive(ps)
+			if statusArgs.active && !active {
+				continue
+			}
+			printPS(ps)
+		}
+	}
+	os.Stdout.Write(buf.Bytes())
+	return nil
+}
+
+// peerActive reports whether ps has recent activity.
+//
+// TODO: have the server report this bool instead.
+func peerActive(ps *ipnstate.PeerStatus) bool {
+	return !ps.LastWrite.IsZero() && time.Since(ps.LastWrite) < 2*time.Minute
+}
+
+func dnsOrQuoteHostname(st *ipnstate.Status, ps *ipnstate.PeerStatus) string {
+	baseName := dnsname.TrimSuffix(ps.DNSName, st.MagicDNSSuffix)
+	if baseName != "" {
+		return baseName
+	}
+	return fmt.Sprintf("(%q)", dnsname.SanitizeHostname(ps.HostName))
+}
+
+func ownerLogin(st *ipnstate.Status, ps *ipnstate.PeerStatus) string {
+	if ps.UserID.IsZero() {
+		return "-"
+	}
+	u, ok := st.User[ps.UserID]
+	if !ok {
+		return fmt.Sprint(ps.UserID)
+	}
+	if i := strings.Index(u.LoginName, "@"); i != -1 {
+		return u.LoginName[:i+1]
+	}
+	return u.LoginName
+}
+
+func firstIPString(v []netaddr.IP) string {
+	if len(v) == 0 {
+		return ""
+	}
+	return v[0].String()
+}
diff --git a/cmd/tailscaled/cli/up.go b/cmd/tailscaled/cli/up.go
new file mode 100644
index 000000000..d8e24a095
--- /dev/null
+++ b/cmd/tailscaled/cli/up.go
@@ -0,0 +1,775 @@
+// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package cli
+
+import (
+	"context"
+	"errors"
+	"flag"
+	"fmt"
+	"os"
+	"reflect"
+	"runtime"
+	"sort"
+	"strings"
+	"sync"
+
+	shellquote "github.com/kballard/go-shellquote"
+	"github.com/peterbourgon/ff/v2/ffcli"
+	"inet.af/netaddr"
+	"tailscale.com/client/tailscale"
+	"tailscale.com/ipn"
+	"tailscale.com/ipn/ipnstate"
+	"tailscale.com/safesocket"
+	"tailscale.com/tailcfg"
+	"tailscale.com/types/logger"
+	"tailscale.com/types/preftype"
+	"tailscale.com/version/distro"
+)
+
+var upCmd = &ffcli.Command{
+	Name:       "up",
+	ShortUsage: "up [flags]",
+	ShortHelp:  "Connect to Tailscale, logging in if needed",
+
+	LongHelp: strings.TrimSpace(`
+"tailscale up" connects this machine to your Tailscale network,
+triggering authentication if necessary.
+
+With no flags, "tailscale up" brings the network online without
+changing any settings. (That is, it's the opposite of "tailscale
+down").
+
+If flags are specified, the flags must be the complete set of desired
+settings. An error is returned if any setting would be changed as a
+result of an unspecified flag's default value, unless the --reset
+flag is also used.
+`),
+	FlagSet: upFlagSet,
+	Exec:    runUp,
+}
+
+var upFlagSet = newUpFlagSet(runtime.GOOS, &upArgs)
+
+func newUpFlagSet(goos string, upArgs *upArgsT) *flag.FlagSet {
+	upf := flag.NewFlagSet("up", flag.ExitOnError)
+
+	upf.BoolVar(&upArgs.forceReauth, "force-reauth", false, "force reauthentication")
+	upf.BoolVar(&upArgs.reset, "reset", false, "reset unspecified settings to their default values")
+
+	upf.StringVar(&upArgs.server, "login-server", ipn.DefaultControlURL, "base URL of control server")
+	upf.BoolVar(&upArgs.acceptRoutes, "accept-routes", false, "accept routes advertised by other Tailscale nodes")
+	upf.BoolVar(&upArgs.acceptDNS, "accept-dns", true, "accept DNS configuration from the admin panel")
+	upf.BoolVar(&upArgs.singleRoutes, "host-routes", true, "install host routes to other Tailscale nodes")
+	upf.StringVar(&upArgs.exitNodeIP, "exit-node", "", "Tailscale IP of the exit node for internet traffic")
+	upf.BoolVar(&upArgs.exitNodeAllowLANAccess, "exit-node-allow-lan-access", false, "Allow direct access to the local network when routing traffic via an exit node")
+	upf.BoolVar(&upArgs.shieldsUp, "shields-up", false, "don't allow incoming connections")
+	upf.StringVar(&upArgs.advertiseTags, "advertise-tags", "", "comma-separated ACL tags to request; each must start with \"tag:\" (e.g. \"tag:eng,tag:montreal,tag:ssh\")")
+	upf.StringVar(&upArgs.authKey, "authkey", "", "node authorization key")
+	upf.StringVar(&upArgs.hostname, "hostname", "", "hostname to use instead of the one provided by the OS")
+	upf.StringVar(&upArgs.advertiseRoutes, "advertise-routes", "", "routes to advertise to other nodes (comma-separated, e.g. \"10.0.0.0/8,192.168.0.0/24\")")
+	upf.BoolVar(&upArgs.advertiseDefaultRoute, "advertise-exit-node", false, "offer to be an exit node for internet traffic for the tailnet")
+	if safesocket.GOOSUsesPeerCreds(goos) {
+		upf.StringVar(&upArgs.opUser, "operator", "", "Unix username to allow to operate on tailscaled without sudo")
+	}
+	switch goos {
+	case "linux":
+		upf.BoolVar(&upArgs.snat, "snat-subnet-routes", true, "source NAT traffic to local routes advertised with --advertise-routes")
+		upf.StringVar(&upArgs.netfilterMode, "netfilter-mode", defaultNetfilterMode(), "netfilter mode (one of on, nodivert, off)")
+	case "windows":
+		upf.BoolVar(&upArgs.forceDaemon, "unattended", false, "run in \"Unattended Mode\" where Tailscale keeps running even after the current GUI user logs out (Windows-only)")
+	}
+	return upf
+}
+
+func defaultNetfilterMode() string {
+	if distro.Get() == distro.Synology {
+		return "off"
+	}
+	return "on"
+}
+
+type upArgsT struct {
+	reset                  bool
+	server                 string
+	acceptRoutes           bool
+	acceptDNS              bool
+	singleRoutes           bool
+	exitNodeIP             string
+	exitNodeAllowLANAccess bool
+	shieldsUp              bool
+	forceReauth            bool
+	forceDaemon            bool
+	advertiseRoutes        string
+	advertiseDefaultRoute  bool
+	advertiseTags          string
+	snat                   bool
+	netfilterMode          string
+	authKey                string
+	hostname               string
+	opUser                 string
+}
+
+var upArgs upArgsT
+
+func warnf(format string, args ...interface{}) {
+	fmt.Printf("Warning: "+format+"\n", args...)
+}
+
+var (
+	ipv4default = netaddr.MustParseIPPrefix("0.0.0.0/0")
+	ipv6default = netaddr.MustParseIPPrefix("::/0")
+)
+
+// prefsFromUpArgs returns the ipn.Prefs for the provided args.
+//
+// Note that the parameters upArgs and warnf are named intentionally
+// to shadow the globals to prevent accidental misuse of them. This
+// function exists for testing and should have no side effects or
+// outside interactions (e.g. no making Tailscale local API calls).
+func prefsFromUpArgs(upArgs upArgsT, warnf logger.Logf, st *ipnstate.Status, goos string) (*ipn.Prefs, error) {
+	routeMap := map[netaddr.IPPrefix]bool{}
+	var default4, default6 bool
+	if upArgs.advertiseRoutes != "" {
+		advroutes := strings.Split(upArgs.advertiseRoutes, ",")
+		for _, s := range advroutes {
+			ipp, err := netaddr.ParseIPPrefix(s)
+			if err != nil {
+				return nil, fmt.Errorf("%q is not a valid IP address or CIDR prefix", s)
+			}
+			if ipp != ipp.Masked() {
+				return nil, fmt.Errorf("%s has non-address bits set; expected %s", ipp, ipp.Masked())
+			}
+			if ipp == ipv4default {
+				default4 = true
+			} else if ipp == ipv6default {
+				default6 = true
+			}
+			routeMap[ipp] = true
+		}
+		if default4 && !default6 {
+			return nil, fmt.Errorf("%s advertised without its IPv6 counterpart, please also advertise %s", ipv4default, ipv6default)
+		} else if default6 && !default4 {
+			return nil, fmt.Errorf("%s advertised without its IPv6 counterpart, please also advertise %s", ipv6default, ipv4default)
+		}
+	}
+	if upArgs.advertiseDefaultRoute {
+		routeMap[netaddr.MustParseIPPrefix("0.0.0.0/0")] = true
+		routeMap[netaddr.MustParseIPPrefix("::/0")] = true
+	}
+	routes := make([]netaddr.IPPrefix, 0, len(routeMap))
+	for r := range routeMap {
+		routes = append(routes, r)
+	}
+	sort.Slice(routes, func(i, j int) bool {
+		if routes[i].Bits() != routes[j].Bits() {
+			return routes[i].Bits() < routes[j].Bits()
+		}
+		return routes[i].IP().Less(routes[j].IP())
+	})
+
+	var exitNodeIP netaddr.IP
+	if upArgs.exitNodeIP != "" {
+		var err error
+		exitNodeIP, err = netaddr.ParseIP(upArgs.exitNodeIP)
+		if err != nil {
+			return nil, fmt.Errorf("invalid IP address %q for --exit-node: %v", upArgs.exitNodeIP, err)
+		}
+	} else if upArgs.exitNodeAllowLANAccess {
+		return nil, fmt.Errorf("--exit-node-allow-lan-access can only be used with --exit-node")
+	}
+
+	if upArgs.exitNodeIP != "" {
+		for _, ip := range st.TailscaleIPs {
+			if exitNodeIP == ip {
+				return nil, fmt.Errorf("cannot use %s as the exit node as it is a local IP address to this machine, did you mean --advertise-exit-node?", upArgs.exitNodeIP)
+			}
+		}
+	}
+
+	var tags []string
+	if upArgs.advertiseTags != "" {
+		tags = strings.Split(upArgs.advertiseTags, ",")
+		for _, tag := range tags {
+			err := tailcfg.CheckTag(tag)
+			if err != nil {
+				return nil, fmt.Errorf("tag: %q: %s", tag, err)
+			}
+		}
+	}
+
+	if len(upArgs.hostname) > 256 {
+		return nil, fmt.Errorf("hostname too long: %d bytes (max 256)", len(upArgs.hostname))
+	}
+
+	prefs := ipn.NewPrefs()
+	prefs.ControlURL = upArgs.server
+	prefs.WantRunning = true
+	prefs.RouteAll = upArgs.acceptRoutes
+	prefs.ExitNodeIP = exitNodeIP
+	prefs.ExitNodeAllowLANAccess = upArgs.exitNodeAllowLANAccess
+	prefs.CorpDNS = upArgs.acceptDNS
+	prefs.AllowSingleHosts = upArgs.singleRoutes
+	prefs.ShieldsUp = upArgs.shieldsUp
+	prefs.AdvertiseRoutes = routes
+	prefs.AdvertiseTags = tags
+	prefs.Hostname = upArgs.hostname
+	prefs.ForceDaemon = upArgs.forceDaemon
+	prefs.OperatorUser = upArgs.opUser
+
+	if goos == "linux" {
+		prefs.NoSNAT = !upArgs.snat
+
+		switch upArgs.netfilterMode {
+		case "on":
+			prefs.NetfilterMode = preftype.NetfilterOn
+		case "nodivert":
+			prefs.NetfilterMode = preftype.NetfilterNoDivert
+			warnf("netfilter=nodivert; add iptables calls to ts-* chains manually.")
+		case "off":
+			prefs.NetfilterMode = preftype.NetfilterOff
+			warnf("netfilter=off; configure iptables yourself.")
+		default:
+			return nil, fmt.Errorf("invalid value --netfilter-mode=%q", upArgs.netfilterMode)
+		}
+	}
+	return prefs, nil
+}
+
+func runUp(ctx context.Context, args []string) error {
+	if len(args) > 0 {
+		fatalf("too many non-flag arguments: %q", args)
+	}
+
+	st, err := tailscale.Status(ctx)
+	if err != nil {
+		fatalf("can't fetch status from tailscaled: %v", err)
+	}
+	origAuthURL := st.AuthURL
+
+	// printAuthURL reports whether we should print out the
+	// provided auth URL from an IPN notify.
+	printAuthURL := func(url string) bool {
+		if upArgs.authKey != "" {
+			// Issue 1755: when using an authkey, don't
+			// show an authURL that might still be pending
+			// from a previous non-completed interactive
+			// login.
+			return false
+		}
+		if upArgs.forceReauth && url == origAuthURL {
+			return false
+		}
+		return true
+	}
+
+	if distro.Get() == distro.Synology {
+		notSupported := "not yet supported on Synology; see https://github.com/tailscale/tailscale/issues/451"
+		if upArgs.acceptRoutes {
+			return errors.New("--accept-routes is " + notSupported)
+		}
+		if upArgs.exitNodeIP != "" {
+			return errors.New("--exit-node is " + notSupported)
+		}
+		if upArgs.netfilterMode != "off" {
+			return errors.New("--netfilter-mode values besides \"off\" " + notSupported)
+		}
+	}
+
+	prefs, err := prefsFromUpArgs(upArgs, warnf, st, runtime.GOOS)
+	if err != nil {
+		fatalf("%s", err)
+	}
+
+	if len(prefs.AdvertiseRoutes) > 0 {
+		if err := tailscale.CheckIPForwarding(context.Background()); err != nil {
+			warnf("%v", err)
+		}
+	}
+
+	curPrefs, err := tailscale.GetPrefs(ctx)
+	if err != nil {
+		return err
+	}
+
+	if !upArgs.reset {
+		applyImplicitPrefs(prefs, curPrefs, os.Getenv("USER"))
+
+		if err := checkForAccidentalSettingReverts(upFlagSet, curPrefs, prefs, upCheckEnv{
+			goos:          runtime.GOOS,
+			curExitNodeIP: exitNodeIP(prefs, st),
+		}); err != nil {
+			fatalf("%s", err)
+		}
+	}
+
+	controlURLChanged := curPrefs.ControlURL != prefs.ControlURL
+	if controlURLChanged && st.BackendState == ipn.Running.String() && !upArgs.forceReauth {
+		fatalf("can't change --login-server without --force-reauth")
+	}
+
+	// If we're already running and none of the flags require a
+	// restart, we can just do an EditPrefs call and change the
+	// prefs at runtime (e.g. changing hostname, changing
+	// advertised tags, routes, etc)
+	justEdit := st.BackendState == ipn.Running.String() &&
+		!upArgs.forceReauth &&
+		!upArgs.reset &&
+		upArgs.authKey == "" &&
+		!controlURLChanged
+	if justEdit {
+		mp := new(ipn.MaskedPrefs)
+		mp.WantRunningSet = true
+		mp.Prefs = *prefs
+		upFlagSet.Visit(func(f *flag.Flag) {
+			updateMaskedPrefsFromUpFlag(mp, f.Name)
+		})
+
+		_, err := tailscale.EditPrefs(ctx, mp)
+		return err
+	}
+
+	// simpleUp is whether we're running a simple "tailscale up"
+	// to transition to running from a previously-logged-in but
+	// down state, without changing any settings.
+	simpleUp := upFlagSet.NFlag() == 0 &&
+		curPrefs.Persist != nil &&
+		curPrefs.Persist.LoginName != "" &&
+		st.BackendState != ipn.NeedsLogin.String()
+
+	// At this point we need to subscribe to the IPN bus to watch
+	// for state transitions and possible need to authenticate.
+	c, bc, pumpCtx, cancel := connect(ctx)
+	defer cancel()
+
+	startingOrRunning := make(chan bool, 1) // gets value once starting or running
+	gotEngineUpdate := make(chan bool, 1)   // gets value upon an engine update
+	pumpErr := make(chan error, 1)
+	go func() { pumpErr <- pump(pumpCtx, bc, c) }()
+
+	printed := !simpleUp
+	var loginOnce sync.Once
+	startLoginInteractive := func() { loginOnce.Do(func() { bc.StartLoginInteractive() }) }
+
+	bc.SetNotifyCallback(func(n ipn.Notify) {
+		if n.Engine != nil {
+			select {
+			case gotEngineUpdate <- true:
+			default:
+			}
+		}
+		if n.ErrMessage != nil {
+			msg := *n.ErrMessage
+			if msg == ipn.ErrMsgPermissionDenied {
+				switch runtime.GOOS {
+				case "windows":
+					msg += " (Tailscale service in use by other user?)"
+				default:
+					msg += " (try 'sudo tailscale up [...]')"
+				}
+			}
+			fatalf("backend error: %v\n", msg)
+		}
+		if s := n.State; s != nil {
+			switch *s {
+			case ipn.NeedsLogin:
+				printed = true
+				startLoginInteractive()
+			case ipn.NeedsMachineAuth:
+				printed = true
+				fmt.Fprintf(os.Stderr, "\nTo authorize your machine, visit (as admin):\n\n\t%s/admin/machines\n\n", upArgs.server)
+			case ipn.Starting, ipn.Running:
+				// Done full authentication process
+				if printed {
+					// Only need to print an update if we printed the "please click" message earlier.
+					fmt.Fprintf(os.Stderr, "Success.\n")
+				}
+				select {
+				case startingOrRunning <- true:
+				default:
+				}
+				cancel()
+			}
+		}
+		if url := n.BrowseToURL; url != nil && printAuthURL(*url) {
+			printed = true
+			fmt.Fprintf(os.Stderr, "\nTo authenticate, visit:\n\n\t%s\n\n", *url)
+		}
+	})
+	// Wait for backend client to be connected so we know
+	// we're subscribed to updates. Otherwise we can miss
+	// an update upon its transition to running. Do so by causing some traffic
+	// back to the bus that we then wait on.
+	bc.RequestEngineStatus()
+	select {
+	case <-gotEngineUpdate:
+	case <-pumpCtx.Done():
+		return pumpCtx.Err()
+	case err := <-pumpErr:
+		return err
+	}
+
+	// Special case: bare "tailscale up" means to just start
+	// running, if there's ever been a login.
+	if simpleUp {
+		_, err := tailscale.EditPrefs(ctx, &ipn.MaskedPrefs{
+			Prefs: ipn.Prefs{
+				WantRunning: true,
+			},
+			WantRunningSet: true,
+		})
+		if err != nil {
+			return err
+		}
+	} else {
+		opts := ipn.Options{
+			StateKey:    ipn.GlobalDaemonStateKey,
+			AuthKey:     upArgs.authKey,
+			UpdatePrefs: prefs,
+		}
+		// On Windows, we still run in mostly the "legacy" way that
+		// predated the server's StateStore. That is, we send an empty
+		// StateKey and send the prefs directly. Although the Windows
+		// supports server mode, though, the transition to StateStore
+		// is only half complete. Only server mode uses it, and the
+		// Windows service (~tailscaled) is the one that computes the
+		// StateKey based on the connection identity. So for now, just
+		// do as the Windows GUI's always done:
+		if runtime.GOOS == "windows" {
+			// The Windows service will set this as needed based
+			// on our connection's identity.
+			opts.StateKey = ""
+			opts.Prefs = prefs
+		}
+
+		bc.Start(opts)
+		if upArgs.forceReauth {
+			startLoginInteractive()
+		}
+	}
+
+	select {
+	case <-startingOrRunning:
+		return nil
+	case <-pumpCtx.Done():
+		select {
+		case <-startingOrRunning:
+			return nil
+		default:
+		}
+		return pumpCtx.Err()
+	case err := <-pumpErr:
+		return err
+	}
+}
+
+var (
+	prefsOfFlag = map[string][]string{} // "exit-node" => ExitNodeIP, ExitNodeID
+)
+
+func init() {
+	// Both these have the same ipn.Pref:
+	addPrefFlagMapping("advertise-exit-node", "AdvertiseRoutes")
+	addPrefFlagMapping("advertise-routes", "AdvertiseRoutes")
+
+	// And this flag has two ipn.Prefs:
+	addPrefFlagMapping("exit-node", "ExitNodeIP", "ExitNodeID")
+
+	// The rest are 1:1:
+	addPrefFlagMapping("accept-dns", "CorpDNS")
+	addPrefFlagMapping("accept-routes", "RouteAll")
+	addPrefFlagMapping("advertise-tags", "AdvertiseTags")
+	addPrefFlagMapping("host-routes", "AllowSingleHosts")
+	addPrefFlagMapping("hostname", "Hostname")
+	addPrefFlagMapping("login-server", "ControlURL")
+	addPrefFlagMapping("netfilter-mode", "NetfilterMode")
+	addPrefFlagMapping("shields-up", "ShieldsUp")
+	addPrefFlagMapping("snat-subnet-routes", "NoSNAT")
+	addPrefFlagMapping("exit-node-allow-lan-access", "ExitNodeAllowLANAccess")
+	addPrefFlagMapping("unattended", "ForceDaemon")
+	addPrefFlagMapping("operator", "OperatorUser")
+}
+
+func addPrefFlagMapping(flagName string, prefNames ...string) {
+	prefsOfFlag[flagName] = prefNames
+	prefType := reflect.TypeOf(ipn.Prefs{})
+	for _, pref := range prefNames {
+		// Crash at runtime if there's a typo in the prefName.
+		if _, ok := prefType.FieldByName(pref); !ok {
+			panic(fmt.Sprintf("invalid ipn.Prefs field %q", pref))
+		}
+	}
+}
+
+// preflessFlag reports whether flagName is a flag that doesn't
+// correspond to an ipn.Pref.
+func preflessFlag(flagName string) bool {
+	switch flagName {
+	case "authkey", "force-reauth", "reset":
+		return true
+	}
+	return false
+}
+
+func updateMaskedPrefsFromUpFlag(mp *ipn.MaskedPrefs, flagName string) {
+	if preflessFlag(flagName) {
+		return
+	}
+	if prefs, ok := prefsOfFlag[flagName]; ok {
+		for _, pref := range prefs {
+			reflect.ValueOf(mp).Elem().FieldByName(pref + "Set").SetBool(true)
+		}
+		return
+	}
+	panic(fmt.Sprintf("internal error: unhandled flag %q", flagName))
+}
+
+const accidentalUpPrefix = "Error: changing settings via 'tailscale up' requires mentioning all\n" +
+	"non-default flags. To proceed, either re-run your command with --reset or\n" +
+	"use the command below to explicitly mention the current value of\n" +
+	"all non-default settings:\n\n" +
+	"\ttailscale up"
+
+// upCheckEnv are extra parameters describing the environment as
+// needed by checkForAccidentalSettingReverts and friends.
+type upCheckEnv struct {
+	goos          string
+	curExitNodeIP netaddr.IP
+}
+
+// checkForAccidentalSettingReverts (the "up checker") checks for
+// people running "tailscale up" with a subset of the flags they
+// originally ran it with.
+//
+// For example, in Tailscale 1.6 and prior, a user might've advertised
+// a tag, but later tried to change just one other setting and forgot
+// to mention the tag later and silently wiped it out. We now
+// require --reset to change preferences to flag default values when
+// the flag is not mentioned on the command line.
+//
+// curPrefs is what's currently active on the server.
+//
+// mp is the mask of settings actually set, where mp.Prefs is the new
+// preferences to set, including any values set from implicit flags.
+func checkForAccidentalSettingReverts(flagSet *flag.FlagSet, curPrefs, newPrefs *ipn.Prefs, env upCheckEnv) error {
+	if curPrefs.ControlURL == "" {
+		// Don't validate things on initial "up" before a control URL has been set.
+		return nil
+	}
+
+	flagIsSet := map[string]bool{}
+	flagSet.Visit(func(f *flag.Flag) {
+		flagIsSet[f.Name] = true
+	})
+
+	if len(flagIsSet) == 0 {
+		// A bare "tailscale up" is a special case to just
+		// mean bringing the network up without any changes.
+		return nil
+	}
+
+	// flagsCur is what flags we'd need to use to keep the exact
+	// settings as-is.
+	flagsCur := prefsToFlags(env, curPrefs)
+	flagsNew := prefsToFlags(env, newPrefs)
+
+	var missing []string
+	for flagName := range flagsCur {
+		valCur, valNew := flagsCur[flagName], flagsNew[flagName]
+		if flagIsSet[flagName] {
+			continue
+		}
+		if reflect.DeepEqual(valCur, valNew) {
+			continue
+		}
+		missing = append(missing, fmtFlagValueArg(flagName, valCur))
+	}
+	if len(missing) == 0 {
+		return nil
+	}
+	sort.Strings(missing)
+
+	// Compute the stringification of the explicitly provided args in flagSet
+	// to prepend to the command to run.
+	var explicit []string
+	flagSet.Visit(func(f *flag.Flag) {
+		type isBool interface {
+			IsBoolFlag() bool
+		}
+		if ib, ok := f.Value.(isBool); ok && ib.IsBoolFlag() {
+			if f.Value.String() == "false" {
+				explicit = append(explicit, "--"+f.Name+"=false")
+			} else {
+				explicit = append(explicit, "--"+f.Name)
+			}
+		} else {
+			explicit = append(explicit, fmtFlagValueArg(f.Name, f.Value.String()))
+		}
+	})
+
+	var sb strings.Builder
+	sb.WriteString(accidentalUpPrefix)
+
+	for _, a := range append(explicit, missing...) {
+		fmt.Fprintf(&sb, " %s", a)
+	}
+	sb.WriteString("\n\n")
+	return errors.New(sb.String())
+}
+
+// applyImplicitPrefs mutates prefs to add implicit preferences. Currently
+// this is just the operator user, which only needs to be set if it doesn't
+// match the current user.
+//
+// curUser is os.Getenv("USER"). It's pulled out for testability.
+func applyImplicitPrefs(prefs, oldPrefs *ipn.Prefs, curUser string) {
+	if prefs.OperatorUser == "" && oldPrefs.OperatorUser == curUser {
+		prefs.OperatorUser = oldPrefs.OperatorUser
+	}
+}
+
+func flagAppliesToOS(flag, goos string) bool {
+	switch flag {
+	case "netfilter-mode", "snat-subnet-routes":
+		return goos == "linux"
+	case "unattended":
+		return goos == "windows"
+	}
+	return true
+}
+
+func prefsToFlags(env upCheckEnv, prefs *ipn.Prefs) (flagVal map[string]interface{}) {
+	ret := make(map[string]interface{})
+
+	exitNodeIPStr := func() string {
+		if !prefs.ExitNodeIP.IsZero() {
+			return prefs.ExitNodeIP.String()
+		}
+		if prefs.ExitNodeID.IsZero() || env.curExitNodeIP.IsZero() {
+			return ""
+		}
+		return env.curExitNodeIP.String()
+	}
+
+	fs := newUpFlagSet(env.goos, new(upArgsT) /* dummy */)
+	fs.VisitAll(func(f *flag.Flag) {
+		if preflessFlag(f.Name) {
+			return
+		}
+		set := func(v interface{}) {
+			if flagAppliesToOS(f.Name, env.goos) {
+				ret[f.Name] = v
+			} else {
+				ret[f.Name] = nil
+			}
+		}
+		switch f.Name {
+		default:
+			panic(fmt.Sprintf("unhandled flag %q", f.Name))
+		case "login-server":
+			set(prefs.ControlURL)
+		case "accept-routes":
+			set(prefs.RouteAll)
+		case "host-routes":
+			set(prefs.AllowSingleHosts)
+		case "accept-dns":
+			set(prefs.CorpDNS)
+		case "shields-up":
+			set(prefs.ShieldsUp)
+		case "exit-node":
+			set(exitNodeIPStr())
+		case "exit-node-allow-lan-access":
+			set(prefs.ExitNodeAllowLANAccess)
+		case "advertise-tags":
+			set(strings.Join(prefs.AdvertiseTags, ","))
+		case "hostname":
+			set(prefs.Hostname)
+		case "operator":
+			set(prefs.OperatorUser)
+		case "advertise-routes":
+			var sb strings.Builder
+			for i, r := range withoutExitNodes(prefs.AdvertiseRoutes) {
+				if i > 0 {
+					sb.WriteByte(',')
+				}
+				sb.WriteString(r.String())
+			}
+			set(sb.String())
+		case "advertise-exit-node":
+			set(hasExitNodeRoutes(prefs.AdvertiseRoutes))
+		case "snat-subnet-routes":
+			set(!prefs.NoSNAT)
+		case "netfilter-mode":
+			set(prefs.NetfilterMode.String())
+		case "unattended":
+			set(prefs.ForceDaemon)
+		}
+	})
+	return ret
+}
+
+func fmtFlagValueArg(flagName string, val interface{}) string {
+	if val == true {
+		return "--" + flagName
+	}
+	if val == "" {
+		return "--" + flagName + "="
+	}
+	return fmt.Sprintf("--%s=%v", flagName, shellquote.Join(fmt.Sprint(val)))
+}
+
+func hasExitNodeRoutes(rr []netaddr.IPPrefix) bool {
+	var v4, v6 bool
+	for _, r := range rr {
+		if r.Bits() == 0 {
+			if r.IP().Is4() {
+				v4 = true
+			} else if r.IP().Is6() {
+				v6 = true
+			}
+		}
+	}
+	return v4 && v6
+}
+
+// withoutExitNodes returns rr unchanged if it has only 1 or 0 /0
+// routes. If it has both IPv4 and IPv6 /0 routes, then it returns
+// a copy with all /0 routes removed.
+func withoutExitNodes(rr []netaddr.IPPrefix) []netaddr.IPPrefix {
+	if !hasExitNodeRoutes(rr) {
+		return rr
+	}
+	var out []netaddr.IPPrefix
+	for _, r := range rr {
+		if r.Bits() > 0 {
+			out = append(out, r)
+		}
+	}
+	return out
+}
+
+// exitNodeIP returns the exit node IP from p, using st to map
+// it from its ID form to an IP address if needed.
+func exitNodeIP(p *ipn.Prefs, st *ipnstate.Status) (ip netaddr.IP) {
+	if p == nil {
+		return
+	}
+	if !p.ExitNodeIP.IsZero() {
+		return p.ExitNodeIP
+	}
+	id := p.ExitNodeID
+	if id.IsZero() {
+		return
+	}
+	for _, p := range st.Peer {
+		if p.ID == id {
+			if len(p.TailscaleIPs) > 0 {
+				return p.TailscaleIPs[0]
+			}
+			break
+		}
+	}
+	return
+}
diff --git a/cmd/tailscaled/cli/version.go b/cmd/tailscaled/cli/version.go
new file mode 100644
index 000000000..2c6f97a3b
--- /dev/null
+++ b/cmd/tailscaled/cli/version.go
@@ -0,0 +1,51 @@
+// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package cli
+
+import (
+	"context"
+	"flag"
+	"fmt"
+	"log"
+
+	"github.com/peterbourgon/ff/v2/ffcli"
+	"tailscale.com/client/tailscale"
+	"tailscale.com/version"
+)
+
+var versionCmd = &ffcli.Command{
+	Name:       "version",
+	ShortUsage: "version [flags]",
+	ShortHelp:  "Print Tailscale version",
+	FlagSet: (func() *flag.FlagSet {
+		fs := flag.NewFlagSet("version", flag.ExitOnError)
+		fs.BoolVar(&versionArgs.daemon, "daemon", false, "also print local node's daemon version")
+		return fs
+	})(),
+	Exec: runVersion,
+}
+
+var versionArgs struct {
+	daemon bool // also check local node's daemon version
+}
+
+func runVersion(ctx context.Context, args []string) error {
+	if len(args) > 0 {
+		log.Fatalf("too many non-flag arguments: %q", args)
+	}
+	if !versionArgs.daemon {
+		fmt.Println(version.String())
+		return nil
+	}
+
+	fmt.Printf("Client: %s\n", version.String())
+
+	st, err := tailscale.StatusWithoutPeers(ctx)
+	if err != nil {
+		return err
+	}
+	fmt.Printf("Daemon: %s\n", st.Version)
+	return nil
+}
diff --git a/cmd/tailscaled/cli/web.css b/cmd/tailscaled/cli/web.css
new file mode 100644
index 000000000..64672224d
--- /dev/null
+++ b/cmd/tailscaled/cli/web.css
@@ -0,0 +1,1337 @@
+*,
+::before,
+::after {
+	box-sizing: border-box;
+	border-width: 0;
+	border-style: solid;
+	border-color: #e5e7eb;
+}
+
+html {
+	font-family: ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont,
+		"Segoe UI", Roboto, "Helvetica Neue", Arial, "Noto Sans", sans-serif,
+		"Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol", "Noto Color Emoji";
+	line-height: 1.5;
+	-webkit-text-size-adjust: 100%;
+}
+
+::selection {
+	background-color: rgba(97, 122, 255, 0.2);
+}
+
+body {
+	margin: 0;
+	font-family: inherit;
+	line-height: inherit;
+}
+
+hr {
+	height: 0;
+	color: inherit;
+	border-top-width: 1px;
+}
+
+code,
+kbd,
+samp,
+pre {
+	font-family: ui-monospace, SFMono-Regular, Consolas, "Liberation Mono", Menlo,
+		monospace;
+	font-size: 1em;
+}
+
+img,
+svg,
+video,
+canvas,
+audio,
+iframe,
+embed,
+object {
+	display: block;
+	vertical-align: middle;
+}
+
+img,
+video {
+	max-width: 100%;
+	height: auto;
+}
+
+button,
+input,
+optgroup,
+select,
+textarea {
+	font-family: inherit;
+	font-size: 100%;
+	line-height: 1.15;
+	margin: 0;
+}
+
+button,
+select {
+	text-transform: none;
+}
+
+button,
+[type="button"],
+[type="submit"] {
+	-webkit-appearance: button;
+}
+
+blockquote,
+dl,
+dd,
+h1,
+h2,
+h3,
+h4,
+h5,
+h6,
+hr,
+figure,
+p,
+pre {
+	margin: 0;
+}
+
+button,
+input,
+optgroup,
+select,
+textarea {
+	padding: 0;
+	line-height: inherit;
+	color: inherit;
+}
+
+button {
+	cursor: pointer;
+	background-color: transparent;
+	background-image: none;
+}
+
+button:focus {
+	outline: 1px dotted;
+	outline: 5px auto -webkit-focus-ring-color;
+}
+
+fieldset {
+	margin: 0;
+	padding: 0;
+}
+
+ol,
+ul {
+	list-style: none;
+	margin: 0;
+	padding: 0;
+}
+
+textarea {
+	resize: vertical;
+}
+
+input::-moz-placeholder,
+textarea::-moz-placeholder {
+	opacity: 1;
+	color: #9ca3af;
+}
+
+input:-ms-input-placeholder,
+textarea:-ms-input-placeholder {
+	opacity: 1;
+	color: #9ca3af;
+}
+
+input::placeholder,
+textarea::placeholder {
+	opacity: 1;
+	color: #9ca3af;
+}
+
+table {
+	border-collapse: collapse;
+}
+
+h1,
+h2,
+h3,
+h4,
+h5,
+h6 {
+	font-size: inherit;
+	font-weight: inherit;
+}
+
+a {
+	color: inherit;
+	text-decoration: inherit;
+}
+
+.container {
+	width: 100%;
+}
+
+@media (min-width: 640px) {
+	.container {
+		max-width: 640px;
+	}
+}
+
+@media (min-width: 768px) {
+	.container {
+		max-width: 768px;
+	}
+}
+
+@media (min-width: 1024px) {
+	.container {
+		max-width: 1024px;
+	}
+}
+
+@media (min-width: 1280px) {
+	.container {
+		max-width: 1280px;
+	}
+}
+
+@media (min-width: 1536px) {
+	.container {
+		max-width: 1536px;
+	}
+}
+
+.space-x-2 > :not([hidden]) ~ :not([hidden]) {
+	--tw-space-x-reverse: 0;
+	margin-right: calc(0.5rem * var(--tw-space-x-reverse));
+	margin-left: calc(0.5rem * calc(1 - var(--tw-space-x-reverse)));
+}
+
+.bg-white {
+	--tw-bg-opacity: 1;
+	background-color: rgba(255, 255, 255, var(--tw-bg-opacity));
+}
+
+.bg-gray-0 {
+	--tw-bg-opacity: 1;
+	background-color: rgba(250, 249, 248, var(--tw-bg-opacity));
+}
+
+.bg-gray-50 {
+	--tw-bg-opacity: 1;
+	background-color: rgba(249, 247, 246, var(--tw-bg-opacity));
+}
+
+.border-gray-200 {
+	--tw-border-opacity: 1;
+	border-color: rgba(238, 235, 234, var(--tw-border-opacity));
+}
+
+.border-gray-400 {
+	--tw-border-opacity: 1;
+	border-color: rgba(175, 172, 171, var(--tw-border-opacity));
+}
+
+.rounded-md {
+	border-radius: 0.375rem;
+}
+
+.rounded-lg {
+	border-radius: 0.5rem;
+}
+
+.rounded-full {
+	border-radius: 9999px;
+}
+
+.border-dashed {
+	border-style: dashed;
+}
+
+.border {
+	border-width: 1px;
+}
+
+.flex {
+	display: flex;
+}
+
+.table {
+	display: table;
+}
+
+.items-center {
+	align-items: center;
+}
+
+.justify-start {
+	justify-content: flex-start;
+}
+
+.justify-end {
+	justify-content: flex-end;
+}
+
+.justify-center {
+	justify-content: center;
+}
+
+.justify-between {
+	justify-content: space-between;
+}
+
+.justify-around {
+	justify-content: space-around;
+}
+
+.justify-evenly {
+	justify-content: space-evenly;
+}
+
+.flex-shrink-0 {
+	flex-shrink: 0;
+}
+
+.font-medium {
+	font-weight: 500;
+}
+
+.font-semibold {
+	font-weight: 600;
+}
+
+.h-8 {
+	height: 2rem;
+}
+
+.mx-auto {
+	margin-left: auto;
+	margin-right: auto;
+}
+
+.mt-0 {
+	margin-top: 0px;
+}
+
+.mr-0 {
+	margin-right: 0px;
+}
+
+.mb-0 {
+	margin-bottom: 0px;
+}
+
+.ml-0 {
+	margin-left: 0px;
+}
+
+.mt-1 {
+	margin-top: 0.25rem;
+}
+
+.mr-1 {
+	margin-right: 0.25rem;
+}
+
+.mb-1 {
+	margin-bottom: 0.25rem;
+}
+
+.ml-1 {
+	margin-left: 0.25rem;
+}
+
+.mt-2 {
+	margin-top: 0.5rem;
+}
+
+.mr-2 {
+	margin-right: 0.5rem;
+}
+
+.mb-2 {
+	margin-bottom: 0.5rem;
+}
+
+.ml-2 {
+	margin-left: 0.5rem;
+}
+
+.mt-3 {
+	margin-top: 0.75rem;
+}
+
+.mr-3 {
+	margin-right: 0.75rem;
+}
+
+.mb-3 {
+	margin-bottom: 0.75rem;
+}
+
+.ml-3 {
+	margin-left: 0.75rem;
+}
+
+.mt-4 {
+	margin-top: 1rem;
+}
+
+.mr-4 {
+	margin-right: 1rem;
+}
+
+.mb-4 {
+	margin-bottom: 1rem;
+}
+
+.ml-4 {
+	margin-left: 1rem;
+}
+
+.mt-5 {
+	margin-top: 1.25rem;
+}
+
+.mr-5 {
+	margin-right: 1.25rem;
+}
+
+.mb-5 {
+	margin-bottom: 1.25rem;
+}
+
+.ml-5 {
+	margin-left: 1.25rem;
+}
+
+.mt-6 {
+	margin-top: 1.5rem;
+}
+
+.mr-6 {
+	margin-right: 1.5rem;
+}
+
+.mb-6 {
+	margin-bottom: 1.5rem;
+}
+
+.ml-6 {
+	margin-left: 1.5rem;
+}
+
+.mt-7 {
+	margin-top: 1.75rem;
+}
+
+.mr-7 {
+	margin-right: 1.75rem;
+}
+
+.mb-7 {
+	margin-bottom: 1.75rem;
+}
+
+.ml-7 {
+	margin-left: 1.75rem;
+}
+
+.mt-8 {
+	margin-top: 2rem;
+}
+
+.mr-8 {
+	margin-right: 2rem;
+}
+
+.mb-8 {
+	margin-bottom: 2rem;
+}
+
+.ml-8 {
+	margin-left: 2rem;
+}
+
+.mt-9 {
+	margin-top: 2.25rem;
+}
+
+.mr-9 {
+	margin-right: 2.25rem;
+}
+
+.mb-9 {
+	margin-bottom: 2.25rem;
+}
+
+.ml-9 {
+	margin-left: 2.25rem;
+}
+
+.mt-10 {
+	margin-top: 2.5rem;
+}
+
+.mr-10 {
+	margin-right: 2.5rem;
+}
+
+.mb-10 {
+	margin-bottom: 2.5rem;
+}
+
+.ml-10 {
+	margin-left: 2.5rem;
+}
+
+.mt-11 {
+	margin-top: 2.75rem;
+}
+
+.mr-11 {
+	margin-right: 2.75rem;
+}
+
+.mb-11 {
+	margin-bottom: 2.75rem;
+}
+
+.ml-11 {
+	margin-left: 2.75rem;
+}
+
+.mt-12 {
+	margin-top: 3rem;
+}
+
+.mr-12 {
+	margin-right: 3rem;
+}
+
+.mb-12 {
+	margin-bottom: 3rem;
+}
+
+.ml-12 {
+	margin-left: 3rem;
+}
+
+.mt-14 {
+	margin-top: 3.5rem;
+}
+
+.mr-14 {
+	margin-right: 3.5rem;
+}
+
+.mb-14 {
+	margin-bottom: 3.5rem;
+}
+
+.ml-14 {
+	margin-left: 3.5rem;
+}
+
+.mt-16 {
+	margin-top: 4rem;
+}
+
+.mr-16 {
+	margin-right: 4rem;
+}
+
+.mb-16 {
+	margin-bottom: 4rem;
+}
+
+.ml-16 {
+	margin-left: 4rem;
+}
+
+.mt-20 {
+	margin-top: 5rem;
+}
+
+.mr-20 {
+	margin-right: 5rem;
+}
+
+.mb-20 {
+	margin-bottom: 5rem;
+}
+
+.ml-20 {
+	margin-left: 5rem;
+}
+
+.mt-24 {
+	margin-top: 6rem;
+}
+
+.mr-24 {
+	margin-right: 6rem;
+}
+
+.mb-24 {
+	margin-bottom: 6rem;
+}
+
+.ml-24 {
+	margin-left: 6rem;
+}
+
+.mt-28 {
+	margin-top: 7rem;
+}
+
+.mr-28 {
+	margin-right: 7rem;
+}
+
+.mb-28 {
+	margin-bottom: 7rem;
+}
+
+.ml-28 {
+	margin-left: 7rem;
+}
+
+.mt-32 {
+	margin-top: 8rem;
+}
+
+.mr-32 {
+	margin-right: 8rem;
+}
+
+.mb-32 {
+	margin-bottom: 8rem;
+}
+
+.ml-32 {
+	margin-left: 8rem;
+}
+
+.mt-36 {
+	margin-top: 9rem;
+}
+
+.mr-36 {
+	margin-right: 9rem;
+}
+
+.mb-36 {
+	margin-bottom: 9rem;
+}
+
+.ml-36 {
+	margin-left: 9rem;
+}
+
+.mt-40 {
+	margin-top: 10rem;
+}
+
+.mr-40 {
+	margin-right: 10rem;
+}
+
+.mb-40 {
+	margin-bottom: 10rem;
+}
+
+.ml-40 {
+	margin-left: 10rem;
+}
+
+.mt-44 {
+	margin-top: 11rem;
+}
+
+.mr-44 {
+	margin-right: 11rem;
+}
+
+.mb-44 {
+	margin-bottom: 11rem;
+}
+
+.ml-44 {
+	margin-left: 11rem;
+}
+
+.mt-48 {
+	margin-top: 12rem;
+}
+
+.mr-48 {
+	margin-right: 12rem;
+}
+
+.mb-48 {
+	margin-bottom: 12rem;
+}
+
+.ml-48 {
+	margin-left: 12rem;
+}
+
+.mt-52 {
+	margin-top: 13rem;
+}
+
+.mr-52 {
+	margin-right: 13rem;
+}
+
+.mb-52 {
+	margin-bottom: 13rem;
+}
+
+.ml-52 {
+	margin-left: 13rem;
+}
+
+.mt-56 {
+	margin-top: 14rem;
+}
+
+.mr-56 {
+	margin-right: 14rem;
+}
+
+.mb-56 {
+	margin-bottom: 14rem;
+}
+
+.ml-56 {
+	margin-left: 14rem;
+}
+
+.mt-60 {
+	margin-top: 15rem;
+}
+
+.mr-60 {
+	margin-right: 15rem;
+}
+
+.mb-60 {
+	margin-bottom: 15rem;
+}
+
+.ml-60 {
+	margin-left: 15rem;
+}
+
+.mt-64 {
+	margin-top: 16rem;
+}
+
+.mr-64 {
+	margin-right: 16rem;
+}
+
+.mb-64 {
+	margin-bottom: 16rem;
+}
+
+.ml-64 {
+	margin-left: 16rem;
+}
+
+.mt-72 {
+	margin-top: 18rem;
+}
+
+.mr-72 {
+	margin-right: 18rem;
+}
+
+.mb-72 {
+	margin-bottom: 18rem;
+}
+
+.ml-72 {
+	margin-left: 18rem;
+}
+
+.mt-80 {
+	margin-top: 20rem;
+}
+
+.mr-80 {
+	margin-right: 20rem;
+}
+
+.mb-80 {
+	margin-bottom: 20rem;
+}
+
+.ml-80 {
+	margin-left: 20rem;
+}
+
+.mt-96 {
+	margin-top: 24rem;
+}
+
+.mr-96 {
+	margin-right: 24rem;
+}
+
+.mb-96 {
+	margin-bottom: 24rem;
+}
+
+.ml-96 {
+	margin-left: 24rem;
+}
+
+.max-w-lg {
+	max-width: 32rem;
+}
+
+.max-w-xl {
+	max-width: 36rem;
+}
+
+.overflow-hidden {
+	overflow: hidden;
+}
+
+.p-2 {
+	padding: 0.5rem;
+}
+
+.py-0 {
+	padding-top: 0px;
+	padding-bottom: 0px;
+}
+
+.px-0 {
+	padding-left: 0px;
+	padding-right: 0px;
+}
+
+.py-1 {
+	padding-top: 0.25rem;
+	padding-bottom: 0.25rem;
+}
+
+.px-1 {
+	padding-left: 0.25rem;
+	padding-right: 0.25rem;
+}
+
+.py-2 {
+	padding-top: 0.5rem;
+	padding-bottom: 0.5rem;
+}
+
+.px-2 {
+	padding-left: 0.5rem;
+	padding-right: 0.5rem;
+}
+
+.py-3 {
+	padding-top: 0.75rem;
+	padding-bottom: 0.75rem;
+}
+
+.px-3 {
+	padding-left: 0.75rem;
+	padding-right: 0.75rem;
+}
+
+.py-4 {
+	padding-top: 1rem;
+	padding-bottom: 1rem;
+}
+
+.px-4 {
+	padding-left: 1rem;
+	padding-right: 1rem;
+}
+
+.py-5 {
+	padding-top: 1.25rem;
+	padding-bottom: 1.25rem;
+}
+
+.px-5 {
+	padding-left: 1.25rem;
+	padding-right: 1.25rem;
+}
+
+.py-6 {
+	padding-top: 1.5rem;
+	padding-bottom: 1.5rem;
+}
+
+.px-6 {
+	padding-left: 1.5rem;
+	padding-right: 1.5rem;
+}
+
+.py-7 {
+	padding-top: 1.75rem;
+	padding-bottom: 1.75rem;
+}
+
+.px-7 {
+	padding-left: 1.75rem;
+	padding-right: 1.75rem;
+}
+
+.py-8 {
+	padding-top: 2rem;
+	padding-bottom: 2rem;
+}
+
+.px-8 {
+	padding-left: 2rem;
+	padding-right: 2rem;
+}
+
+.py-9 {
+	padding-top: 2.25rem;
+	padding-bottom: 2.25rem;
+}
+
+.px-9 {
+	padding-left: 2.25rem;
+	padding-right: 2.25rem;
+}
+
+.py-10 {
+	padding-top: 2.5rem;
+	padding-bottom: 2.5rem;
+}
+
+.px-10 {
+	padding-left: 2.5rem;
+	padding-right: 2.5rem;
+}
+
+.py-11 {
+	padding-top: 2.75rem;
+	padding-bottom: 2.75rem;
+}
+
+.px-11 {
+	padding-left: 2.75rem;
+	padding-right: 2.75rem;
+}
+
+.py-12 {
+	padding-top: 3rem;
+	padding-bottom: 3rem;
+}
+
+.px-12 {
+	padding-left: 3rem;
+	padding-right: 3rem;
+}
+
+.py-14 {
+	padding-top: 3.5rem;
+	padding-bottom: 3.5rem;
+}
+
+.px-14 {
+	padding-left: 3.5rem;
+	padding-right: 3.5rem;
+}
+
+.py-16 {
+	padding-top: 4rem;
+	padding-bottom: 4rem;
+}
+
+.px-16 {
+	padding-left: 4rem;
+	padding-right: 4rem;
+}
+
+.py-20 {
+	padding-top: 5rem;
+	padding-bottom: 5rem;
+}
+
+.px-20 {
+	padding-left: 5rem;
+	padding-right: 5rem;
+}
+
+.py-24 {
+	padding-top: 6rem;
+	padding-bottom: 6rem;
+}
+
+.px-24 {
+	padding-left: 6rem;
+	padding-right: 6rem;
+}
+
+.py-28 {
+	padding-top: 7rem;
+	padding-bottom: 7rem;
+}
+
+.px-28 {
+	padding-left: 7rem;
+	padding-right: 7rem;
+}
+
+.py-32 {
+	padding-top: 8rem;
+	padding-bottom: 8rem;
+}
+
+.px-32 {
+	padding-left: 8rem;
+	padding-right: 8rem;
+}
+
+.py-36 {
+	padding-top: 9rem;
+	padding-bottom: 9rem;
+}
+
+.px-36 {
+	padding-left: 9rem;
+	padding-right: 9rem;
+}
+
+.pr-3 {
+	padding-right: 0.75rem;
+}
+
+.pl-3 {
+	padding-left: 0.75rem;
+}
+
+.pointer-events-none {
+	pointer-events: none;
+}
+
+.relative {
+	position: relative;
+}
+
+* {
+	--tw-shadow: 0 0 #0000;
+}
+
+.shadow-2xl {
+	--tw-shadow: 0 25px 50px -12px rgba(0, 0, 0, 0.25);
+	box-shadow: var(--tw-ring-offset-shadow, 0 0 #0000),
+		var(--tw-ring-shadow, 0 0 #0000), var(--tw-shadow);
+}
+
+* {
+	--tw-ring-inset: var(--tw-empty, /*!*/ /*!*/);
+	--tw-ring-offset-width: 0px;
+	--tw-ring-offset-color: #fff;
+	--tw-ring-color: rgba(75, 112, 204, 0.5);
+	--tw-ring-offset-shadow: 0 0 #0000;
+	--tw-ring-shadow: 0 0 #0000;
+}
+
+.text-xs {
+	font-size: 0.75rem;
+	line-height: 1rem;
+}
+
+.text-sm {
+	font-size: 0.875rem;
+	line-height: 1.25rem;
+}
+
+.text-base {
+	font-size: 1rem;
+	line-height: 1.5rem;
+}
+
+.text-lg {
+	font-size: 1.125rem;
+	line-height: 1.75rem;
+}
+
+.text-xl {
+	font-size: 1.25rem;
+	line-height: 1.75rem;
+}
+
+.text-2xl {
+	font-size: 1.5rem;
+	line-height: 2rem;
+}
+
+.text-3xl {
+	font-size: 1.875rem;
+	line-height: 2.25rem;
+}
+
+.text-4xl {
+	font-size: 2.25rem;
+	line-height: 2.5rem;
+}
+
+.text-left {
+	text-align: left;
+}
+
+.text-center {
+	text-align: center;
+}
+
+.text-right {
+	text-align: right;
+}
+
+.text-justify {
+	text-align: justify;
+}
+
+.text-gray-500 {
+	--tw-text-opacity: 1;
+	color: rgba(112, 110, 109, var(--tw-text-opacity));
+}
+
+.text-gray-600 {
+	--tw-text-opacity: 1;
+	color: rgba(68, 67, 66, var(--tw-text-opacity));
+}
+
+.text-gray-700 {
+	--tw-text-opacity: 1;
+	color: rgba(46, 45, 45, var(--tw-text-opacity));
+}
+
+.text-gray-800 {
+	--tw-text-opacity: 1;
+	color: rgba(35, 34, 34, var(--tw-text-opacity));
+}
+
+.leading-3 {
+	line-height: 0.75rem;
+}
+
+.leading-4 {
+	line-height: 1rem;
+}
+
+.leading-5 {
+	line-height: 1.25rem;
+}
+
+.leading-6 {
+	line-height: 1.5rem;
+}
+
+.leading-7 {
+	line-height: 1.75rem;
+}
+
+.leading-8 {
+	line-height: 2rem;
+}
+
+.leading-9 {
+	line-height: 2.25rem;
+}
+
+.leading-10 {
+	line-height: 2.5rem;
+}
+
+.leading-none {
+	line-height: 1;
+}
+
+.leading-tight {
+	line-height: 1.25;
+}
+
+.leading-snug {
+	line-height: 1.375;
+}
+
+.leading-normal {
+	line-height: 1.5;
+}
+
+.leading-relaxed {
+	line-height: 1.625;
+}
+
+.leading-loose {
+	line-height: 2;
+}
+
+.truncate {
+	overflow: hidden;
+	text-overflow: ellipsis;
+	white-space: nowrap;
+}
+
+.w-8 {
+	width: 2rem;
+}
+
+.w-1\/2 {
+	width: 50%;
+}
+
+.w-2\/3 {
+	width: 66.666667%;
+}
+
+.w-full {
+	width: 100%;
+}
+
+.hover\:text-gray-0:hover {
+	--tw-text-opacity: 1;
+	color: rgba(250, 249, 248, var(--tw-text-opacity));
+}
+
+.hover\:text-gray-50:hover {
+	--tw-text-opacity: 1;
+	color: rgba(249, 247, 246, var(--tw-text-opacity));
+}
+
+.hover\:text-gray-100:hover {
+	--tw-text-opacity: 1;
+	color: rgba(247, 245, 244, var(--tw-text-opacity));
+}
+
+.hover\:text-gray-200:hover {
+	--tw-text-opacity: 1;
+	color: rgba(238, 235, 234, var(--tw-text-opacity));
+}
+
+.hover\:text-gray-300:hover {
+	--tw-text-opacity: 1;
+	color: rgba(218, 214, 213, var(--tw-text-opacity));
+}
+
+.hover\:text-gray-400:hover {
+	--tw-text-opacity: 1;
+	color: rgba(175, 172, 171, var(--tw-text-opacity));
+}
+
+.hover\:text-gray-500:hover {
+	--tw-text-opacity: 1;
+	color: rgba(112, 110, 109, var(--tw-text-opacity));
+}
+
+.hover\:text-gray-600:hover {
+	--tw-text-opacity: 1;
+	color: rgba(68, 67, 66, var(--tw-text-opacity));
+}
+
+.hover\:text-gray-700:hover {
+	--tw-text-opacity: 1;
+	color: rgba(46, 45, 45, var(--tw-text-opacity));
+}
+
+.hover\:text-gray-800:hover {
+	--tw-text-opacity: 1;
+	color: rgba(35, 34, 34, var(--tw-text-opacity));
+}
+
+.hover\:text-gray-900:hover {
+	--tw-text-opacity: 1;
+	color: rgba(31, 30, 30, var(--tw-text-opacity));
+}
+
+/**
+ * Non-Tailwind styles begin here.
+ */
+
+html {
+	letter-spacing: -0.015em;
+	text-rendering: optimizeLegibility;
+	-webkit-font-smoothing: antialiased;
+	-moz-osx-font-smoothing: grayscale;
+}
+
+.link {
+	--text-opacity: 1;
+	color: #4b70cc;
+	color: rgba(75, 112, 204, var(--text-opacity));
+}
+
+.link:hover,
+.link:active {
+	--text-opacity: 1;
+	color: #19224a;
+	color: rgba(25, 34, 74, var(--text-opacity));
+}
+
+.button {
+	font-weight: 500;
+	padding-top: 0.45rem;
+	padding-bottom: 0.45rem;
+	padding-left: 1rem;
+	padding-right: 1rem;
+	border-radius: 0.375rem;
+	border-width: 1px;
+	border-color: transparent;
+	transition-property: background-color, border-color, color, box-shadow;
+	transition-duration: 120ms;
+	box-shadow: 0 1px 1px rgba(0, 0, 0, 0.04);
+	min-width: 80px;
+}
+
+.button:focus {
+	outline: 0;
+	box-shadow: 0 0 0 3px rgba(66, 153, 225, 0.5);
+}
+
+.button:disabled {
+	cursor: not-allowed;
+	-webkit-user-select: none;
+	-ms-user-select: none;
+	user-select: none;
+}
+
+.button-blue {
+	--bg-opacity: 1;
+	background-color: #4b70cc;
+	background-color: rgba(75, 112, 204, var(--bg-opacity));
+	--border-opacity: 1;
+	border-color: #4b70cc;
+	border-color: rgba(75, 112, 204, var(--border-opacity));
+	--text-opacity: 1;
+	color: #fff;
+	color: rgba(255, 255, 255, var(--text-opacity));
+}
+
+.button-blue:enabled:hover {
+	--bg-opacity: 1;
+	background-color: #3f5db3;
+	background-color: rgba(63, 93, 179, var(--bg-opacity));
+	--border-opacity: 1;
+	border-color: #3f5db3;
+	border-color: rgba(63, 93, 179, var(--border-opacity));
+}
+
+.button-blue:disabled {
+	--text-opacity: 1;
+	color: #cedefd;
+	color: rgba(206, 222, 253, var(--text-opacity));
+	--bg-opacity: 1;
+	background-color: #6c94ec;
+	background-color: rgba(108, 148, 236, var(--bg-opacity));
+	--border-opacity: 1;
+	border-color: #6c94ec;
+	border-color: rgba(108, 148, 236, var(--border-opacity));
+}
diff --git a/cmd/tailscaled/cli/web.go b/cmd/tailscaled/cli/web.go
new file mode 100644
index 000000000..67de1c29c
--- /dev/null
+++ b/cmd/tailscaled/cli/web.go
@@ -0,0 +1,327 @@
+// Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package cli
+
+import (
+	"bytes"
+	"context"
+	_ "embed"
+	"encoding/json"
+	"flag"
+	"fmt"
+	"html/template"
+	"log"
+	"net/http"
+	"net/http/cgi"
+	"os/exec"
+	"runtime"
+	"strings"
+
+	"github.com/peterbourgon/ff/v2/ffcli"
+	"tailscale.com/client/tailscale"
+	"tailscale.com/ipn"
+	"tailscale.com/tailcfg"
+	"tailscale.com/types/preftype"
+	"tailscale.com/version/distro"
+)
+
+//go:embed web.html
+var webHTML string
+
+//go:embed web.css
+var webCSS string
+
+var tmpl *template.Template
+
+func init() {
+	tmpl = template.Must(template.New("web.html").Parse(webHTML))
+	template.Must(tmpl.New("web.css").Parse(webCSS))
+}
+
+type tmplData struct {
+	Profile      tailcfg.UserProfile
+	SynologyUser string
+	Status       string
+	DeviceName   string
+	IP           string
+}
+
+var webCmd = &ffcli.Command{
+	Name:       "web",
+	ShortUsage: "web [flags]",
+	ShortHelp:  "Run a web server for controlling Tailscale",
+
+	FlagSet: (func() *flag.FlagSet {
+		webf := flag.NewFlagSet("web", flag.ExitOnError)
+		webf.StringVar(&webArgs.listen, "listen", "localhost:8088", "listen address; use port 0 for automatic")
+		webf.BoolVar(&webArgs.cgi, "cgi", false, "run as CGI script")
+		return webf
+	})(),
+	Exec: runWeb,
+}
+
+var webArgs struct {
+	listen string
+	cgi    bool
+}
+
+func runWeb(ctx context.Context, args []string) error {
+	if len(args) > 0 {
+		log.Fatalf("too many non-flag arguments: %q", args)
+	}
+
+	if webArgs.cgi {
+		if err := cgi.Serve(http.HandlerFunc(webHandler)); err != nil {
+			log.Printf("tailscale.cgi: %v", err)
+			return err
+		}
+		return nil
+	}
+	return http.ListenAndServe(webArgs.listen, http.HandlerFunc(webHandler))
+}
+
+func auth() (string, error) {
+	if distro.Get() == distro.Synology {
+		cmd := exec.Command("/usr/syno/synoman/webman/modules/authenticate.cgi")
+		out, err := cmd.CombinedOutput()
+		if err != nil {
+			return "", fmt.Errorf("auth: %v: %s", err, out)
+		}
+		return string(out), nil
+	}
+
+	return "", nil
+}
+
+func synoTokenRedirect(w http.ResponseWriter, r *http.Request) bool {
+	if distro.Get() != distro.Synology {
+		return false
+	}
+	if r.Header.Get("X-Syno-Token") != "" {
+		return false
+	}
+	if r.URL.Query().Get("SynoToken") != "" {
+		return false
+	}
+	if r.Method == "POST" && r.FormValue("SynoToken") != "" {
+		return false
+	}
+	// We need a SynoToken for authenticate.cgi.
+	// So we tell the client to get one.
+	serverURL := r.URL.Scheme + "://" + r.URL.Host
+	fmt.Fprintf(w, synoTokenRedirectHTML, serverURL)
+	return true
+}
+
+const synoTokenRedirectHTML = `<html><body>
+Redirecting with session token...
+<script>
+var serverURL = %q;
+var req = new XMLHttpRequest();
+req.overrideMimeType("application/json");
+req.open("GET", serverURL + "/webman/login.cgi", true);
+req.onload = function() {
+	var jsonResponse = JSON.parse(req.responseText);
+	var token = jsonResponse["SynoToken"];
+	document.location.href = serverURL + "/webman/3rdparty/Tailscale/?SynoToken=" + token;
+};
+req.send(null);
+</script>
+</body></html>
+`
+
+const authenticationRedirectHTML = `
+<html>
+<head>
+	<title>Redirecting...</title>
+	<style>
+		html,
+		body {
+			height: 100%;
+		}
+
+		html {
+			background-color: rgb(249, 247, 246);
+			font-family: ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, "Noto Sans", sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol", "Noto Color Emoji";
+			line-height: 1.5;
+			-webkit-text-size-adjust: 100%;
+			-webkit-font-smoothing: antialiased;
+			-moz-osx-font-smoothing: grayscale;
+		}
+
+		body {
+			display: flex;
+			flex-direction: column;
+			align-items: center;
+			justify-content: center;
+		}
+
+		.spinner {
+			margin-bottom: 2rem;
+			border: 4px rgba(112, 110, 109, 0.5) solid;
+			border-left-color: transparent;
+			border-radius: 9999px;
+			width: 4rem;
+			height: 4rem;
+			-webkit-animation: spin 700ms linear infinite;
+      animation: spin 800ms linear infinite;
+		}
+
+		.label {
+			color: rgb(112, 110, 109);
+			padding-left: 0.4rem;
+		}
+
+		@-webkit-keyframes spin {
+			to {
+				transform: rotate(360deg);
+			}
+		}
+
+		@keyframes spin {
+			to {
+				transform: rotate(360deg);
+			}
+		}
+	</style>
+</head>
+<body>
+	<div class="spinner"></div>
+	<div class="label">Redirecting...</div>
+</body>
+`
+
+func webHandler(w http.ResponseWriter, r *http.Request) {
+	if synoTokenRedirect(w, r) {
+		return
+	}
+
+	user, err := auth()
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusForbidden)
+		return
+	}
+
+	if r.URL.Path == "/redirect" || r.URL.Path == "/redirect/" {
+		w.Write([]byte(authenticationRedirectHTML))
+		return
+	}
+
+	if r.Method == "POST" {
+		type mi map[string]interface{}
+		w.Header().Set("Content-Type", "application/json")
+		url, err := tailscaleUpForceReauth(r.Context())
+		if err != nil {
+			json.NewEncoder(w).Encode(mi{"error": err})
+			return
+		}
+		json.NewEncoder(w).Encode(mi{"url": url})
+		return
+	}
+
+	st, err := tailscale.Status(r.Context())
+	if err != nil {
+		http.Error(w, err.Error(), 500)
+		return
+	}
+
+	profile := st.User[st.Self.UserID]
+	deviceName := strings.Split(st.Self.DNSName, ".")[0]
+	data := tmplData{
+		SynologyUser: user,
+		Profile:      profile,
+		Status:       st.BackendState,
+		DeviceName:   deviceName,
+	}
+	if len(st.TailscaleIPs) != 0 {
+		data.IP = st.TailscaleIPs[0].String()
+	}
+
+	buf := new(bytes.Buffer)
+	if err := tmpl.Execute(buf, data); err != nil {
+		http.Error(w, err.Error(), 500)
+		return
+	}
+	w.Write(buf.Bytes())
+}
+
+// TODO(crawshaw): some of this is very similar to the code in 'tailscale up', can we share anything?
+func tailscaleUpForceReauth(ctx context.Context) (authURL string, retErr error) {
+	prefs := ipn.NewPrefs()
+	prefs.ControlURL = ipn.DefaultControlURL
+	prefs.WantRunning = true
+	prefs.CorpDNS = true
+	prefs.AllowSingleHosts = true
+	prefs.ForceDaemon = (runtime.GOOS == "windows")
+
+	if distro.Get() == distro.Synology {
+		prefs.NetfilterMode = preftype.NetfilterOff
+	}
+
+	st, err := tailscale.Status(ctx)
+	if err != nil {
+		return "", fmt.Errorf("can't fetch status: %v", err)
+	}
+	origAuthURL := st.AuthURL
+
+	// printAuthURL reports whether we should print out the
+	// provided auth URL from an IPN notify.
+	printAuthURL := func(url string) bool {
+		return url != origAuthURL
+	}
+
+	c, bc, pumpCtx, cancel := connect(ctx)
+	defer cancel()
+
+	gotEngineUpdate := make(chan bool, 1) // gets value upon an engine update
+	go pump(pumpCtx, bc, c)
+
+	bc.SetNotifyCallback(func(n ipn.Notify) {
+		if n.Engine != nil {
+			select {
+			case gotEngineUpdate <- true:
+			default:
+			}
+		}
+		if n.ErrMessage != nil {
+			msg := *n.ErrMessage
+			if msg == ipn.ErrMsgPermissionDenied {
+				switch runtime.GOOS {
+				case "windows":
+					msg += " (Tailscale service in use by other user?)"
+				default:
+					msg += " (try 'sudo tailscale up [...]')"
+				}
+			}
+			retErr = fmt.Errorf("backend error: %v", msg)
+			cancel()
+		} else if url := n.BrowseToURL; url != nil && printAuthURL(*url) {
+			authURL = *url
+			cancel()
+		}
+	})
+	// Wait for backend client to be connected so we know
+	// we're subscribed to updates. Otherwise we can miss
+	// an update upon its transition to running. Do so by causing some traffic
+	// back to the bus that we then wait on.
+	bc.RequestEngineStatus()
+	select {
+	case <-gotEngineUpdate:
+	case <-pumpCtx.Done():
+		return authURL, pumpCtx.Err()
+	}
+
+	bc.SetPrefs(prefs)
+
+	bc.Start(ipn.Options{
+		StateKey: ipn.GlobalDaemonStateKey,
+	})
+	bc.StartLoginInteractive()
+
+	if authURL == "" && retErr == nil {
+		return "", fmt.Errorf("login failed with no backend error message")
+	}
+	return authURL, retErr
+}
diff --git a/cmd/tailscaled/cli/web.html b/cmd/tailscaled/cli/web.html
new file mode 100644
index 000000000..2789d1e68
--- /dev/null
+++ b/cmd/tailscaled/cli/web.html
@@ -0,0 +1,143 @@
+<!doctype html>
+<html class="bg-gray-50">
+
+<head>
+	<meta charset="utf-8" />
+	<meta name="viewport" content="width=device-width, initial-scale=1" />
+	<link rel="shortcut icon"
+		href="data:image/png;base64,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" />
+	<title>Tailscale</title>
+	<style>{{template "web.css"}}</style>
+</head>
+
+<body class="py-14">
+<main class="container max-w-lg mx-auto py-6 px-8 bg-white rounded-md shadow-2xl" style="width: 95%">
+	<header class="flex justify-between items-center min-width-0 py-2 mb-8">
+		<svg width="26" height="26" viewBox="0 0 23 23" title="Tailscale" fill="none" xmlns="http://www.w3.org/2000/svg"
+			class="flex-shrink-0 mr-4">
+			<circle opacity="0.2" cx="3.4" cy="3.25" r="2.7" fill="currentColor"></circle>
+			<circle cx="3.4" cy="11.3" r="2.7" fill="currentColor"></circle>
+			<circle opacity="0.2" cx="3.4" cy="19.5" r="2.7" fill="currentColor"></circle>
+			<circle cx="11.5" cy="11.3" r="2.7" fill="currentColor"></circle>
+			<circle cx="11.5" cy="19.5" r="2.7" fill="currentColor"></circle>
+			<circle opacity="0.2" cx="11.5" cy="3.25" r="2.7" fill="currentColor"></circle>
+			<circle opacity="0.2" cx="19.5" cy="3.25" r="2.7" fill="currentColor"></circle>
+			<circle cx="19.5" cy="11.3" r="2.7" fill="currentColor"></circle>
+			<circle opacity="0.2" cx="19.5" cy="19.5" r="2.7" fill="currentColor"></circle>
+		</svg>
+		<div class="flex items-center justify-end space-x-2 w-2/3">
+			{{ with .Profile.LoginName }}
+			<div class="text-right truncate leading-4">
+				<h4 class="truncate">{{.}}</h4>
+				<a href="#" class="text-xs text-gray-500 hover:text-gray-700 js-loginButton">Switch account</a>
+			</div>
+			{{ end }}
+			<div class="relative flex-shrink-0 w-8 h-8 rounded-full overflow-hidden">
+				{{ with .Profile.ProfilePicURL }}
+				<div class="w-8 h-8 flex pointer-events-none rounded-full bg-gray-200"
+					style="background-image: url('{{.}}'); background-size: cover;"></div>
+				{{ else }}
+				<div class="w-8 h-8 flex pointer-events-none rounded-full border border-gray-400 border-dashed"></div>
+				{{ end }}
+			</div>
+		</div>
+	</header>
+	{{ if .IP }}
+	<div
+		class="border border-gray-200 bg-gray-0 rounded-lg p-2 pl-3 pr-3 mb-8 width-full flex items-center justify-between">
+		<div class="flex items-center min-width-0">
+			<svg class="flex-shrink-0 text-gray-600 mr-3 ml-1" xmlns="http://www.w3.org/2000/svg" width="20" height="20"
+				viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round"
+				stroke-linejoin="round">
+				<rect x="2" y="2" width="20" height="8" rx="2" ry="2"></rect>
+				<rect x="2" y="14" width="20" height="8" rx="2" ry="2"></rect>
+				<line x1="6" y1="6" x2="6.01" y2="6"></line>
+				<line x1="6" y1="18" x2="6.01" y2="18"></line>
+			</svg>
+			<h4 class="font-semibold truncate mr-2">{{.DeviceName}}</h4>
+		</div>
+		<h5>{{.IP}}</h5>
+	</div>
+	{{ end }}
+	{{ if or (eq .Status "NeedsLogin") (eq .Status "NoState") }}
+	{{ if .IP }}
+	<div class="mb-6">
+		<p class="text-gray-700">Your device's key has expired. Reauthenticate this device by logging in again, or <a
+				href="https://tailscale.com/kb/1028/key-expiry" class="link" target="_blank">learn more</a>.</p>
+	</div>
+	<a href="#" class="mb-4 js-loginButton" target="_blank">
+		<button class="button button-blue w-full">Reauthenticate</button>
+	</a>
+	{{ else }}
+	<div class="mb-6">
+		<h3 class="text-3xl font-semibold mb-3">Log in</h3>
+		<p class="text-gray-700">Get started by logging in to your Tailscale network. Or,&nbsp;learn&nbsp;more at <a
+				href="https://tailscale.com/" class="link" target="_blank">tailscale.com</a>.</p>
+	</div>
+	<a href="#" class="mb-4 js-loginButton" target="_blank">
+		<button class="button button-blue w-full">Log In</button>
+	</a>
+	{{ end }}
+	{{ else if eq .Status "NeedsMachineAuth" }}
+	<div class="mb-4">
+		This device is authorized, but needs approval from a network admin before it can connect to the network.
+	</div>
+	{{ else }}
+	<div class="mb-4">
+		<p>You are connected! Access this device over Tailscale using the device name or IP address above.</p>
+	</div>
+	<a href="#" class="mb-4 link font-medium js-loginButton" target="_blank">Reauthenticate</a>
+	{{ end }}
+</main>
+<script>(function () {
+let loginButtons = document.querySelectorAll(".js-loginButton");
+let fetchingUrl = false;
+
+function handleClick(e) {
+	e.preventDefault();
+
+	if (fetchingUrl) {
+		return;
+	}
+
+	fetchingUrl = true;
+	const urlParams = new URLSearchParams(window.location.search);
+	const token = urlParams.get("SynoToken");
+	const nextParams = new URLSearchParams({ up: true });
+	if (token) {
+		nextParams.set("SynoToken", token)
+	}
+	const nextUrl = new URL(window.location);
+	nextUrl.search = nextParams.toString()
+	const url = nextUrl.toString();
+
+	fetch(url, {
+		method: "POST",
+		headers: {
+			"Accept": "application/json",
+			"Content-Type": "application/json",
+		}
+	}).then(res => res.json()).then(res => {
+		fetchingUrl = false;
+		const err = res["error"];
+		if (err) {
+			throw new Error(err);
+		}
+		const url = res["url"];
+		if (url) {
+			document.location.href = url;
+		} else {
+			location.reload();
+		}
+	}).catch(err => {
+		alert("Failed to log in: " + err.message);
+	});
+}
+
+Array.from(loginButtons).forEach(el => {
+	el.addEventListener("click", handleClick);
+})
+})();</script>
+</body>
+
+</html>
diff --git a/cmd/tailscaled/main.go b/cmd/tailscaled/main.go
new file mode 100644
index 000000000..5b37f08dc
--- /dev/null
+++ b/cmd/tailscaled/main.go
@@ -0,0 +1,16 @@
+package main
+
+import (
+	"os"
+	"strings"
+)
+
+func main() {
+	if strings.HasSuffix(os.Args[0], "tailscaled") {
+		tailscaled_main()
+	} else if strings.HasSuffix(os.Args[0], "tailscale") {
+		tailscale_main()
+	} else {
+		panic(os.Args[0])
+	}
+}
diff --git a/cmd/tailscaled/tailscale.go b/cmd/tailscaled/tailscale.go
new file mode 100644
index 000000000..94a3563a0
--- /dev/null
+++ b/cmd/tailscaled/tailscale.go
@@ -0,0 +1,27 @@
+// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// The tailscale command is the Tailscale command-line client. It interacts
+// with the tailscaled node agent.
+package main // import "tailscale.com/cmd/tailscaled"
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+
+	"tailscale.com/cmd/tailscaled/cli"
+)
+
+func tailscale_main() {
+	args := os.Args[1:]
+	if name, _ := os.Executable(); strings.HasSuffix(filepath.Base(name), ".cgi") {
+		args = []string{"web", "-cgi"}
+	}
+	if err := cli.Run(args); err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+}
diff --git a/cmd/tailscaled/tailscaled.go b/cmd/tailscaled/tailscaled.go
index 63296204d..1adf9a01e 100644
--- a/cmd/tailscaled/tailscaled.go
+++ b/cmd/tailscaled/tailscaled.go
@@ -101,7 +101,7 @@ var subCommands = map[string]*func([]string) error{
 	"debug":                   &debugModeFunc,
 }
 
-func main() {
+func tailscaled_main() {
 	// We aren't very performance sensitive, and the parts that are
 	// performance sensitive (wireguard) try hard not to do any memory
 	// allocations. So let's be aggressive about garbage collection,