ginuerzh/gost · error

%s: %v

Error message

%s: %v

What it means

On macOS, createTun configures the newly created TUN interface by shelling out to ifconfig ('ifconfig <ifc> inet <addr> <peer> mtu <mtu> up'). If exec.Command(...).Run() fails, the error is wrapped as '<full command>: <underlying error>' and returned from createTun, aborting TUN creation.

Source

Thrown at tuntap_darwin.go:41

	if err != nil {
		return
	}

	mtu := cfg.MTU
	if mtu <= 0 {
		mtu = DefaultMTU
	}

	peer := cfg.Peer
	if peer == "" {
		peer = ip.String()
	}
	cmd := fmt.Sprintf("ifconfig %s inet %s %s mtu %d up",
		ifce.Name(), cfg.Addr, peer, mtu)
	log.Log("[tun]", cmd)
	args := strings.Split(cmd, " ")
	if er := exec.Command(args[0], args[1:]...).Run(); er != nil {
		err = fmt.Errorf("%s: %v", cmd, er)
		return
	}

	if err = addTunRoutes(ifce.Name(), cfg.Routes...); err != nil {
		return
	}

	itf, err = net.InterfaceByName(ifce.Name())
	if err != nil {
		return
	}

	conn = &tunTapConn{
		ifce: ifce,
		addr: &net.IPAddr{IP: ip},
	}
	return
}

View on GitHub (pinned to a33fdbf4c9)

Solutions

1. Run the process with elevated privileges (sudo) so ifconfig can configure the interface
2. Validate cfg.Addr/peer values and the ifce.Name() returned by the TUN device open
3. Run the failing ifconfig command manually to see the raw error
4. Check that the utun device was created successfully before configuration

Example fix

// before
$ ./gost -L 'tun://...'   # fails: ifconfig ... : operation not permitted
// after
$ sudo ./gost -L 'tun://...'

// check privileges before attempting TUN setup
if os.Geteuid() != 0 {
    return errors.New("creating a TUN interface on macOS requires root")
}

ifce, err := createTun(cfg)
if err != nil {
    if strings.Contains(err.Error(), "ifconfig") {
        return fmt.Errorf("tun setup failed (are you root?): %w", err)
    }
    return err
}

When it happens

Trigger: Starting a TUN-based service on macOS where the ifconfig command fails — typically because the process lacks root privileges, the interface vanished, or the address/peer arguments are invalid.

Common situations: Running the app without sudo (macOS TUN setup requires root); missing or invalid tun.address/tun.netmask/peer config; ifconfig not present or PATH issues; OS denying utun operations.

Related errors

• %s: %v
• accept on closed listener
• listener has been closed
• not a packet connection
• tap is not supported on darwin

AI-assisted analysis of ginuerzh/gost@a33fdbf4c9 (2026-09-02). Data as JSON: /api/errors/eac0c5c830636260. Report an issue: GitHub.