diff --git a/cmd/tailscale/cli/cli.go b/cmd/tailscale/cli/cli.go
index 99d2d694f..87e127b9f 100644
--- a/cmd/tailscale/cli/cli.go
+++ b/cmd/tailscale/cli/cli.go
@@ -173,10 +173,17 @@ change in the future.
 }
 
 func fatalf(format string, a ...interface{}) {
+	if Fatalf != nil {
+		Fatalf(format, a...)
+		return
+	}
 	log.SetFlags(0)
 	log.Fatalf(format, a...)
 }
 
+// Fatalf, if non-nil, is used instead of log.Fatalf.
+var Fatalf func(format string, a ...interface{})
+
 var rootArgs struct {
 	socket string
 }
diff --git a/cmd/tailscale/cli/debug.go b/cmd/tailscale/cli/debug.go
index 3eb8179f6..0d3d7e12b 100644
--- a/cmd/tailscale/cli/debug.go
+++ b/cmd/tailscale/cli/debug.go
@@ -174,7 +174,7 @@ func runDebug(ctx context.Context, args []string) error {
 		if debugArgs.file == "get" {
 			wfs, err := tailscale.WaitingFiles(ctx)
 			if err != nil {
-				log.Fatal(err)
+				fatalf("%v\n", err)
 			}
 			e := json.NewEncoder(Stdout)
 			e.SetIndent("", "\t")
diff --git a/cmd/tailscale/cli/down.go b/cmd/tailscale/cli/down.go
index 90c568bd0..30a2d2f9b 100644
--- a/cmd/tailscale/cli/down.go
+++ b/cmd/tailscale/cli/down.go
@@ -7,7 +7,6 @@ package cli
 import (
 	"context"
 	"fmt"
-	"log"
 
 	"github.com/peterbourgon/ff/v3/ffcli"
 	"tailscale.com/client/tailscale"
@@ -24,7 +23,7 @@ var downCmd = &ffcli.Command{
 
 func runDown(ctx context.Context, args []string) error {
 	if len(args) > 0 {
-		log.Fatalf("too many non-flag arguments: %q", args)
+		return fmt.Errorf("too many non-flag arguments: %q", args)
 	}
 
 	st, err := tailscale.Status(ctx)
diff --git a/cmd/tailscale/cli/file.go b/cmd/tailscale/cli/file.go
index 3c0b01a57..9f42c1d04 100644
--- a/cmd/tailscale/cli/file.go
+++ b/cmd/tailscale/cli/file.go
@@ -415,7 +415,7 @@ func waitForFile(ctx context.Context) error {
 	fileWaiting := make(chan bool, 1)
 	bc.SetNotifyCallback(func(n ipn.Notify) {
 		if n.ErrMessage != nil {
-			log.Fatal(*n.ErrMessage)
+			fatalf("Notify.ErrMessage: %v\n", *n.ErrMessage)
 		}
 		if n.FilesWaiting != nil {
 			select {
diff --git a/cmd/tailscale/cli/logout.go b/cmd/tailscale/cli/logout.go
index a58a0f1ba..3511b9efd 100644
--- a/cmd/tailscale/cli/logout.go
+++ b/cmd/tailscale/cli/logout.go
@@ -6,7 +6,7 @@ package cli
 
 import (
 	"context"
-	"log"
+	"fmt"
 	"strings"
 
 	"github.com/peterbourgon/ff/v3/ffcli"
@@ -28,7 +28,7 @@ a reauthentication.
 
 func runLogout(ctx context.Context, args []string) error {
 	if len(args) > 0 {
-		log.Fatalf("too many non-flag arguments: %q", args)
+		return fmt.Errorf("too many non-flag arguments: %q", args)
 	}
 	return tailscale.Logout(ctx)
 }
diff --git a/cmd/tailscale/cli/netcheck.go b/cmd/tailscale/cli/netcheck.go
index f0b33544e..59e8bc256 100644
--- a/cmd/tailscale/cli/netcheck.go
+++ b/cmd/tailscale/cli/netcheck.go
@@ -82,7 +82,7 @@ func runNetcheck(ctx context.Context, args []string) error {
 			c.Logf("GetReport took %v; err=%v", d.Round(time.Millisecond), err)
 		}
 		if err != nil {
-			log.Fatalf("netcheck: %v", err)
+			return fmt.Errorf("netcheck: %w", err)
 		}
 		if err := printReport(dm, report); err != nil {
 			return err
diff --git a/cmd/tailscale/cli/ping.go b/cmd/tailscale/cli/ping.go
index 8953ff09d..4dc9ee2a1 100644
--- a/cmd/tailscale/cli/ping.go
+++ b/cmd/tailscale/cli/ping.go
@@ -74,7 +74,7 @@ func runPing(ctx context.Context, args []string) error {
 	prc := make(chan *ipnstate.PingResult, 1)
 	bc.SetNotifyCallback(func(n ipn.Notify) {
 		if n.ErrMessage != nil {
-			log.Fatal(*n.ErrMessage)
+			fatalf("Notify.ErrMessage: %v", *n.ErrMessage)
 		}
 		if pr := n.PingResult; pr != nil && pr.IP == ip {
 			prc <- pr
diff --git a/cmd/tailscale/cli/version.go b/cmd/tailscale/cli/version.go
index 1726bac0b..9f3e17594 100644
--- a/cmd/tailscale/cli/version.go
+++ b/cmd/tailscale/cli/version.go
@@ -7,7 +7,7 @@ package cli
 import (
 	"context"
 	"flag"
-	"log"
+	"fmt"
 
 	"github.com/peterbourgon/ff/v3/ffcli"
 	"tailscale.com/client/tailscale"
@@ -32,7 +32,7 @@ var versionArgs struct {
 
 func runVersion(ctx context.Context, args []string) error {
 	if len(args) > 0 {
-		log.Fatalf("too many non-flag arguments: %q", args)
+		return fmt.Errorf("too many non-flag arguments: %q", args)
 	}
 	if !versionArgs.daemon {
 		outln(version.String())
diff --git a/cmd/tailscale/cli/web.go b/cmd/tailscale/cli/web.go
index 003b5af39..399ad05e9 100644
--- a/cmd/tailscale/cli/web.go
+++ b/cmd/tailscale/cli/web.go
@@ -114,7 +114,7 @@ func tlsConfigFromEnvironment() *tls.Config {
 
 func runWeb(ctx context.Context, args []string) error {
 	if len(args) > 0 {
-		log.Fatalf("too many non-flag arguments: %q", args)
+		return fmt.Errorf("too many non-flag arguments: %q", args)
 	}
 
 	if webArgs.cgi {