Golang utils.GetResolvConf函數代碼示例

func (runtime *Runtime) checkLocaldns() error {
	resolvConf, err := utils.GetResolvConf()
	if err != nil {
		return err
	}
	if len(runtime.config.Dns) == 0 && utils.CheckLocalDns(resolvConf) {
		log.Printf("Local (127.0.0.1) DNS resolver found in resolv.conf and containers can't use it. Using default external servers : %v\n", DefaultDns)
		runtime.config.Dns = DefaultDns
	}
	return nil
}

func (container *Container) setupContainerDns() error {
	if container.ResolvConfPath != "" {
		return nil
	}
	var (
		config  = container.hostConfig
		runtime = container.runtime
	)
	resolvConf, err := utils.GetResolvConf()
	if err != nil {
		return err
	}
	// If custom dns exists, then create a resolv.conf for the container
	if len(config.Dns) > 0 || len(runtime.config.Dns) > 0 || len(config.DnsSearch) > 0 || len(runtime.config.DnsSearch) > 0 {
		var (
			dns       = utils.GetNameservers(resolvConf)
			dnsSearch = utils.GetSearchDomains(resolvConf)
		)
		if len(config.Dns) > 0 {
			dns = config.Dns
		} else if len(runtime.config.Dns) > 0 {
			dns = runtime.config.Dns
		}
		if len(config.DnsSearch) > 0 {
			dnsSearch = config.DnsSearch
		} else if len(runtime.config.DnsSearch) > 0 {
			dnsSearch = runtime.config.DnsSearch
		}
		container.ResolvConfPath = path.Join(container.root, "resolv.conf")
		f, err := os.Create(container.ResolvConfPath)
		if err != nil {
			return err
		}
		defer f.Close()
		for _, dns := range dns {
			if _, err := f.Write([]byte("nameserver " + dns + "\n")); err != nil {
				return err
			}
		}
		if len(dnsSearch) > 0 {
			if _, err := f.Write([]byte("search " + strings.Join(dnsSearch, " ") + "\n")); err != nil {
				return err
			}
		}
	} else {
		container.ResolvConfPath = "/etc/resolv.conf"
	}
	return nil
}

func postContainersCreate(srv *Server, version float64, w http.ResponseWriter, r *http.Request, vars map[string]string) error {
	if err := parseForm(r); err != nil {
		return nil
	}
	config := &Config{}
	out := &APIRun{}
	name := r.Form.Get("name")

	if err := json.NewDecoder(r.Body).Decode(config); err != nil {
		return err
	}

	resolvConf, err := utils.GetResolvConf()
	if err != nil {
		return err
	}

	if !config.NetworkDisabled && len(config.Dns) == 0 && len(srv.runtime.config.Dns) == 0 && utils.CheckLocalDns(resolvConf) {
		out.Warnings = append(out.Warnings, fmt.Sprintf("Docker detected local DNS server on resolv.conf. Using default external servers: %v", defaultDns))
		config.Dns = defaultDns
	}

	id, warnings, err := srv.ContainerCreate(config, name)
	if err != nil {
		return err
	}
	out.ID = id
	for _, warning := range warnings {
		out.Warnings = append(out.Warnings, warning)
	}

	if config.Memory > 0 && !srv.runtime.capabilities.MemoryLimit {
		log.Println("WARNING: Your kernel does not support memory limit capabilities. Limitation discarded.")
		out.Warnings = append(out.Warnings, "Your kernel does not support memory limit capabilities. Limitation discarded.")
	}
	if config.Memory > 0 && !srv.runtime.capabilities.SwapLimit {
		log.Println("WARNING: Your kernel does not support swap limit capabilities. Limitation discarded.")
		out.Warnings = append(out.Warnings, "Your kernel does not support memory swap capabilities. Limitation discarded.")
	}

	if !config.NetworkDisabled && srv.runtime.capabilities.IPv4ForwardingDisabled {
		log.Println("Warning: IPv4 forwarding is disabled.")
		out.Warnings = append(out.Warnings, "IPv4 forwarding is disabled.")
	}

	return writeJSON(w, http.StatusCreated, out)
}

func postContainersCreate(srv *Server, version float64, w http.ResponseWriter, r *http.Request, vars map[string]string) error {
	if err := parseForm(r); err != nil {
		return nil
	}
	out := &APIRun{}
	job := srv.Eng.Job("create", r.Form.Get("name"))
	if err := job.DecodeEnv(r.Body); err != nil {
		return err
	}
	resolvConf, err := utils.GetResolvConf()
	if err != nil {
		return err
	}
	if !job.GetenvBool("NetworkDisabled") && len(job.Getenv("Dns")) == 0 && len(srv.runtime.config.Dns) == 0 && utils.CheckLocalDns(resolvConf) {
		out.Warnings = append(out.Warnings, fmt.Sprintf("Docker detected local DNS server on resolv.conf. Using default external servers: %v", defaultDns))
		job.SetenvList("Dns", defaultDns)
	}
	// Read container ID from the first line of stdout
	job.Stdout.AddString(&out.ID)
	// Read warnings from stderr
	warnings := &bytes.Buffer{}
	job.Stderr.Add(warnings)
	if err := job.Run(); err != nil {
		return err
	}
	// Parse warnings from stderr
	scanner := bufio.NewScanner(warnings)
	for scanner.Scan() {
		out.Warnings = append(out.Warnings, scanner.Text())
	}
	if job.GetenvInt("Memory") > 0 && !srv.runtime.capabilities.MemoryLimit {
		log.Println("WARNING: Your kernel does not support memory limit capabilities. Limitation discarded.")
		out.Warnings = append(out.Warnings, "Your kernel does not support memory limit capabilities. Limitation discarded.")
	}
	if job.GetenvInt("Memory") > 0 && !srv.runtime.capabilities.SwapLimit {
		log.Println("WARNING: Your kernel does not support swap limit capabilities. Limitation discarded.")
		out.Warnings = append(out.Warnings, "Your kernel does not support memory swap capabilities. Limitation discarded.")
	}

	if !job.GetenvBool("NetworkDisabled") && srv.runtime.capabilities.IPv4ForwardingDisabled {
		log.Println("Warning: IPv4 forwarding is disabled.")
		out.Warnings = append(out.Warnings, "IPv4 forwarding is disabled.")
	}

	return writeJSON(w, http.StatusCreated, out)
}

func postContainersCreate(srv *Server, version float64, w http.ResponseWriter, r *http.Request, vars map[string]string) error {
	config := &Config{}
	out := &APIRun{}

	if err := json.NewDecoder(r.Body).Decode(config); err != nil {
		return err
	}

	resolvConf, err := utils.GetResolvConf()
	if err != nil {
		return err
	}

	if len(config.Dns) == 0 && len(srv.runtime.Dns) == 0 && utils.CheckLocalDns(resolvConf) {
		out.Warnings = append(out.Warnings, fmt.Sprintf("Docker detected local DNS server on resolv.conf. Using default external servers: %v", defaultDns))
		config.Dns = defaultDns
	}

	id, err := srv.ContainerCreate(config)
	if err != nil {
		return err
	}
	out.ID = id

	if config.Memory > 0 && !srv.runtime.capabilities.MemoryLimit {
		log.Println("WARNING: Your kernel does not support memory limit capabilities. Limitation discarded.")
		out.Warnings = append(out.Warnings, "Your kernel does not support memory limit capabilities. Limitation discarded.")
	}
	if config.Memory > 0 && !srv.runtime.capabilities.SwapLimit {
		log.Println("WARNING: Your kernel does not support swap limit capabilities. Limitation discarded.")
		out.Warnings = append(out.Warnings, "Your kernel does not support memory swap capabilities. Limitation discarded.")
	}

	b, err := json.Marshal(out)
	if err != nil {
		return err
	}
	w.WriteHeader(http.StatusCreated)
	writeJSON(w, b)
	return nil
}

// CreateBridgeIface creates a network bridge interface on the host system with the name `ifaceName`,
// and attempts to configure it with an address which doesn't conflict with any other interface on the host.
// If it can't find an address which doesn't conflict, it will return an error.
func CreateBridgeIface(config *DaemonConfig) error {
	addrs := []string{
		// Here we don't follow the convention of using the 1st IP of the range for the gateway.
		// This is to use the same gateway IPs as the /24 ranges, which predate the /16 ranges.
		// In theory this shouldn't matter - in practice there's bound to be a few scripts relying
		// on the internal addressing or other stupid things like that.
		// The shouldn't, but hey, let's not break them unless we really have to.
		"172.17.42.1/16", // Don't use 172.16.0.0/16, it conflicts with EC2 DNS 172.16.0.23
		"10.0.42.1/16",   // Don't even try using the entire /8, that's too intrusive
		"10.1.42.1/16",
		"10.42.42.1/16",
		"172.16.42.1/24",
		"172.16.43.1/24",
		"172.16.44.1/24",
		"10.0.42.1/24",
		"10.0.43.1/24",
		"192.168.42.1/24",
		"192.168.43.1/24",
		"192.168.44.1/24",
	}

	nameservers := []string{}
	resolvConf, _ := utils.GetResolvConf()
	// we don't check for an error here, because we don't really care
	// if we can't read /etc/resolv.conf. So instead we skip the append
	// if resolvConf is nil. It either doesn't exist, or we can't read it
	// for some reason.
	if resolvConf != nil {
		nameservers = append(nameservers, utils.GetNameserversAsCIDR(resolvConf)...)
	}

	var ifaceAddr string
	for _, addr := range addrs {
		_, dockerNetwork, err := net.ParseCIDR(addr)
		if err != nil {
			return err
		}
		routes, err := netlink.NetworkGetRoutes()
		if err != nil {
			return err
		}
		if err := checkRouteOverlaps(routes, dockerNetwork); err == nil {
			if err := checkNameserverOverlaps(nameservers, dockerNetwork); err == nil {
				ifaceAddr = addr
				break
			}
		} else {
			utils.Debugf("%s: %s", addr, err)
		}
	}
	if ifaceAddr == "" {
		return fmt.Errorf("Could not find a free IP address range for interface '%s'. Please configure its address manually and run 'docker -b %s'", config.BridgeIface, config.BridgeIface)
	}
	utils.Debugf("Creating bridge %s with network %s", config.BridgeIface, ifaceAddr)

	if err := netlink.NetworkLinkAdd(config.BridgeIface, "bridge"); err != nil {
		return fmt.Errorf("Error creating bridge: %s", err)
	}
	iface, err := net.InterfaceByName(config.BridgeIface)
	if err != nil {
		return err
	}
	ipAddr, ipNet, err := net.ParseCIDR(ifaceAddr)
	if err != nil {
		return err
	}
	if netlink.NetworkLinkAddIp(iface, ipAddr, ipNet); err != nil {
		return fmt.Errorf("Unable to add private network: %s", err)
	}
	if err := netlink.NetworkLinkUp(iface); err != nil {
		return fmt.Errorf("Unable to start network bridge: %s", err)
	}

	if config.EnableIptables {
		// Enable NAT
		if output, err := iptables.Raw("-t", "nat", "-A", "POSTROUTING", "-s", ifaceAddr,
			"!", "-d", ifaceAddr, "-j", "MASQUERADE"); err != nil {
			return fmt.Errorf("Unable to enable network bridge NAT: %s", err)
		} else if len(output) != 0 {
			return fmt.Errorf("Error iptables postrouting: %s", output)
		}

		// Accept incoming packets for existing connections
		if output, err := iptables.Raw("-I", "FORWARD", "-o", config.BridgeIface, "-m", "conntrack", "--ctstate", "RELATED,ESTABLISHED", "-j", "ACCEPT"); err != nil {
			return fmt.Errorf("Unable to allow incoming packets: %s", err)
		} else if len(output) != 0 {
			return fmt.Errorf("Error iptables allow incoming: %s", output)
		}

		// Accept all non-intercontainer outgoing packets
		if output, err := iptables.Raw("-I", "FORWARD", "-i", config.BridgeIface, "!", "-o", config.BridgeIface, "-j", "ACCEPT"); err != nil {
			return fmt.Errorf("Unable to allow outgoing packets: %s", err)
		} else if len(output) != 0 {
			return fmt.Errorf("Error iptables allow outgoing: %s", output)
		}

	}
//.........這裏部分代碼省略.........

//.........這裏部分代碼省略.........
	}

	var args []string
	var entrypoint string

	if len(config.Entrypoint) != 0 {
		entrypoint = config.Entrypoint[0]
		args = append(config.Entrypoint[1:], config.Cmd...)
	} else {
		entrypoint = config.Cmd[0]
		args = config.Cmd[1:]
	}

	container := &Container{
		// FIXME: we should generate the ID here instead of receiving it as an argument
		ID:              id,
		Created:         time.Now(),
		Path:            entrypoint,
		Args:            args, //FIXME: de-duplicate from config
		Config:          config,
		Image:           img.ID, // Always use the resolved image id
		NetworkSettings: &NetworkSettings{},
		// FIXME: do we need to store this in the container?
		SysInitPath: sysInitPath,
		Name:        name,
	}
	container.root = runtime.containerRoot(container.ID)
	// Step 1: create the container directory.
	// This doubles as a barrier to avoid race conditions.
	if err := os.Mkdir(container.root, 0700); err != nil {
		return nil, nil, err
	}

	resolvConf, err := utils.GetResolvConf()
	if err != nil {
		return nil, nil, err
	}

	if len(config.Dns) == 0 && len(runtime.config.Dns) == 0 && utils.CheckLocalDns(resolvConf) {
		//"WARNING: Docker detected local DNS server on resolv.conf. Using default external servers: %v", defaultDns
		runtime.config.Dns = defaultDns
	}

	// If custom dns exists, then create a resolv.conf for the container
	if len(config.Dns) > 0 || len(runtime.config.Dns) > 0 {
		var dns []string
		if len(config.Dns) > 0 {
			dns = config.Dns
		} else {
			dns = runtime.config.Dns
		}
		container.ResolvConfPath = path.Join(container.root, "resolv.conf")
		f, err := os.Create(container.ResolvConfPath)
		if err != nil {
			return nil, nil, err
		}
		defer f.Close()
		for _, dns := range dns {
			if _, err := f.Write([]byte("nameserver " + dns + "\n")); err != nil {
				return nil, nil, err
			}
		}
	} else {
		container.ResolvConfPath = "/etc/resolv.conf"
	}

//.........這裏部分代碼省略.........

	// Generate default hostname
	// FIXME: the lxc template no longer needs to set a default hostname
	if config.Hostname == "" {
		config.Hostname = id[:12]
	}

	var args []string
	var entrypoint string

	if len(config.Entrypoint) != 0 {
		entrypoint = config.Entrypoint[0]
		args = append(config.Entrypoint[1:], config.Cmd...)
	} else {
		entrypoint = config.Cmd[0]
		args = config.Cmd[1:]
	}

	container := &Container{
		// FIXME: we should generate the ID here instead of receiving it as an argument
		ID:              id,
		Created:         time.Now().UTC(),
		Path:            entrypoint,
		Args:            args, //FIXME: de-duplicate from config
		Config:          config,
		hostConfig:      &runconfig.HostConfig{},
		Image:           img.ID, // Always use the resolved image id
		NetworkSettings: &NetworkSettings{},
		Name:            name,
		Driver:          runtime.driver.String(),
		ExecDriver:      runtime.execDriver.Name(),
	}
	container.root = runtime.containerRoot(container.ID)
	// Step 1: create the container directory.
	// This doubles as a barrier to avoid race conditions.
	if err := os.Mkdir(container.root, 0700); err != nil {
		return nil, nil, err
	}

	initID := fmt.Sprintf("%s-init", container.ID)
	if err := runtime.driver.Create(initID, img.ID); err != nil {
		return nil, nil, err
	}
	initPath, err := runtime.driver.Get(initID)
	if err != nil {
		return nil, nil, err
	}
	defer runtime.driver.Put(initID)

	if err := setupInitLayer(initPath); err != nil {
		return nil, nil, err
	}

	if err := runtime.driver.Create(container.ID, initID); err != nil {
		return nil, nil, err
	}
	resolvConf, err := utils.GetResolvConf()
	if err != nil {
		return nil, nil, err
	}

	if len(config.Dns) == 0 && len(runtime.config.Dns) == 0 && utils.CheckLocalDns(resolvConf) {
		//"WARNING: Docker detected local DNS server on resolv.conf. Using default external servers: %v", defaultDns
		runtime.config.Dns = defaultDns
	}

	// If custom dns exists, then create a resolv.conf for the container
	if len(config.Dns) > 0 || len(runtime.config.Dns) > 0 {
		var dns []string
		if len(config.Dns) > 0 {
			dns = config.Dns
		} else {
			dns = runtime.config.Dns
		}
		container.ResolvConfPath = path.Join(container.root, "resolv.conf")
		f, err := os.Create(container.ResolvConfPath)
		if err != nil {
			return nil, nil, err
		}
		defer f.Close()
		for _, dns := range dns {
			if _, err := f.Write([]byte("nameserver " + dns + "\n")); err != nil {
				return nil, nil, err
			}
		}
	} else {
		container.ResolvConfPath = "/etc/resolv.conf"
	}

	// Step 2: save the container json
	if err := container.ToDisk(); err != nil {
		return nil, nil, err
	}

	// Step 3: register the container
	if err := runtime.Register(container); err != nil {
		return nil, nil, err
	}
	return container, warnings, nil
}

// CreateBridgeIface creates a network bridge interface on the host system with the name `ifaceName`,
// and attempts to configure it with an address which doesn't conflict with any other interface on the host.
// If it can't find an address which doesn't conflict, it will return an error.
func CreateBridgeIface(config *DaemonConfig) error {
	addrs := []string{
		// Here we don't follow the convention of using the 1st IP of the range for the gateway.
		// This is to use the same gateway IPs as the /24 ranges, which predate the /16 ranges.
		// In theory this shouldn't matter - in practice there's bound to be a few scripts relying
		// on the internal addressing or other stupid things like that.
		// The shouldn't, but hey, let's not break them unless we really have to.
		"172.17.42.1/16", // Don't use 172.16.0.0/16, it conflicts with EC2 DNS 172.16.0.23
		"10.0.42.1/16",   // Don't even try using the entire /8, that's too intrusive
		"10.1.42.1/16",
		"10.42.42.1/16",
		"172.16.42.1/24",
		"172.16.43.1/24",
		"172.16.44.1/24",
		"10.0.42.1/24",
		"10.0.43.1/24",
		"192.168.42.1/24",
		"192.168.43.1/24",
		"192.168.44.1/24",
	}

	nameservers := []string{}
	resolvConf, _ := utils.GetResolvConf()
	// we don't check for an error here, because we don't really care
	// if we can't read /etc/resolv.conf. So instead we skip the append
	// if resolvConf is nil. It either doesn't exist, or we can't read it
	// for some reason.
	if resolvConf != nil {
		nameservers = append(nameservers, utils.GetNameserversAsCIDR(resolvConf)...)
	}

	var ifaceAddr string
	if len(config.BridgeIp) != 0 {
		_, _, err := net.ParseCIDR(config.BridgeIp)
		if err != nil {
			return err
		}
		ifaceAddr = config.BridgeIp
	} else {
		for _, addr := range addrs {
			_, dockerNetwork, err := net.ParseCIDR(addr)
			if err != nil {
				return err
			}
			routes, err := netlink.NetworkGetRoutes()
			if err != nil {
				return err
			}
			if err := checkRouteOverlaps(routes, dockerNetwork); err == nil {
				if err := checkNameserverOverlaps(nameservers, dockerNetwork); err == nil {
					ifaceAddr = addr
					break
				}
			} else {
				utils.Debugf("%s: %s", addr, err)
			}
		}
	}
	if ifaceAddr == "" {
		return fmt.Errorf("Could not find a free IP address range for interface '%s'. Please configure its address manually and run 'docker -b %s'", config.BridgeIface, config.BridgeIface)
	}
	utils.Debugf("Creating bridge %s with network %s", config.BridgeIface, ifaceAddr)

	if err := createBridgeIface(config.BridgeIface); err != nil {
		return err
	}
	iface, err := net.InterfaceByName(config.BridgeIface)
	if err != nil {
		return err
	}
	ipAddr, ipNet, err := net.ParseCIDR(ifaceAddr)
	if err != nil {
		return err
	}
	if netlink.NetworkLinkAddIp(iface, ipAddr, ipNet); err != nil {
		return fmt.Errorf("Unable to add private network: %s", err)
	}
	if err := netlink.NetworkLinkUp(iface); err != nil {
		return fmt.Errorf("Unable to start network bridge: %s", err)
	}

	return nil
}

// CreateBridgeIface creates a network bridge interface on the host system with the name `ifaceName`,
// and attempts to configure it with an address which doesn't conflict with any other interface on the host.
// If it can't find an address which doesn't conflict, it will return an error.
func createBridge(bridgeIP string) error {
	nameservers := []string{}
	resolvConf, _ := utils.GetResolvConf()
	// we don't check for an error here, because we don't really care
	// if we can't read /etc/resolv.conf. So instead we skip the append
	// if resolvConf is nil. It either doesn't exist, or we can't read it
	// for some reason.
	if resolvConf != nil {
		nameservers = append(nameservers, utils.GetNameserversAsCIDR(resolvConf)...)
	}

	var ifaceAddr string
	if len(bridgeIP) != 0 {
		_, _, err := net.ParseCIDR(bridgeIP)
		if err != nil {
			return err
		}
		ifaceAddr = bridgeIP
	} else {
		for _, addr := range addrs {
			_, dockerNetwork, err := net.ParseCIDR(addr)
			if err != nil {
				return err
			}
			if err := networkdriver.CheckNameserverOverlaps(nameservers, dockerNetwork); err == nil {
				if err := networkdriver.CheckRouteOverlaps(dockerNetwork); err == nil {
					ifaceAddr = addr
					break
				} else {
					utils.Debugf("%s %s", addr, err)
				}
			}
		}
	}

	if ifaceAddr == "" {
		return fmt.Errorf("Could not find a free IP address range for interface '%s'. Please configure its address manually and run 'docker -b %s'", bridgeIface, bridgeIface)
	}
	utils.Debugf("Creating bridge %s with network %s", bridgeIface, ifaceAddr)

	if err := createBridgeIface(bridgeIface); err != nil {
		return err
	}

	iface, err := net.InterfaceByName(bridgeIface)
	if err != nil {
		return err
	}

	ipAddr, ipNet, err := net.ParseCIDR(ifaceAddr)
	if err != nil {
		return err
	}

	if netlink.NetworkLinkAddIp(iface, ipAddr, ipNet); err != nil {
		return fmt.Errorf("Unable to add private network: %s", err)
	}
	if err := netlink.NetworkLinkUp(iface); err != nil {
		return fmt.Errorf("Unable to start network bridge: %s", err)
	}
	return nil
}

// Create creates a new container from the given configuration.
func (runtime *Runtime) Create(config *Config) (*Container, error) {
	// Lookup image
	img, err := runtime.repositories.LookupImage(config.Image)
	if err != nil {
		return nil, err
	}

	if img.Config != nil {
		MergeConfig(config, img.Config)
	}

	if len(config.Entrypoint) != 0 && config.Cmd == nil {
		config.Cmd = []string{}
	} else if config.Cmd == nil || len(config.Cmd) == 0 {
		return nil, fmt.Errorf("No command specified")
	}

	// Generate id
	id := GenerateID()
	// Generate default hostname
	// FIXME: the lxc template no longer needs to set a default hostname
	if config.Hostname == "" {
		config.Hostname = id[:12]
	}

	var args []string
	var entrypoint string

	if len(config.Entrypoint) != 0 {
		entrypoint = config.Entrypoint[0]
		args = append(config.Entrypoint[1:], config.Cmd...)
	} else {
		entrypoint = config.Cmd[0]
		args = config.Cmd[1:]
	}

	container := &Container{
		// FIXME: we should generate the ID here instead of receiving it as an argument
		ID:              id,
		Created:         time.Now(),
		Path:            entrypoint,
		Args:            args, //FIXME: de-duplicate from config
		Config:          config,
		Image:           img.ID, // Always use the resolved image id
		NetworkSettings: &NetworkSettings{},
		// FIXME: do we need to store this in the container?
		SysInitPath: sysInitPath,
	}
	container.root = runtime.containerRoot(container.ID)
	// Step 1: create the container directory.
	// This doubles as a barrier to avoid race conditions.
	if err := os.Mkdir(container.root, 0700); err != nil {
		return nil, err
	}

	resolvConf, err := utils.GetResolvConf()
	if err != nil {
		return nil, err
	}

	if len(config.Dns) == 0 && len(runtime.Dns) == 0 && utils.CheckLocalDns(resolvConf) {
		//"WARNING: Docker detected local DNS server on resolv.conf. Using default external servers: %v", defaultDns
		runtime.Dns = defaultDns
	}

	// If custom dns exists, then create a resolv.conf for the container
	if len(config.Dns) > 0 || len(runtime.Dns) > 0 {
		var dns []string
		if len(config.Dns) > 0 {
			dns = config.Dns
		} else {
			dns = runtime.Dns
		}
		container.ResolvConfPath = path.Join(container.root, "resolv.conf")
		f, err := os.Create(container.ResolvConfPath)
		if err != nil {
			return nil, err
		}
		defer f.Close()
		for _, dns := range dns {
			if _, err := f.Write([]byte("nameserver " + dns + "\n")); err != nil {
				return nil, err
			}
		}
	} else {
		container.ResolvConfPath = "/etc/resolv.conf"
	}

	// Step 2: save the container json
	if err := container.ToDisk(); err != nil {
		return nil, err
	}

	// Step 3: if hostname, build hostname and hosts files
	container.HostnamePath = path.Join(container.root, "hostname")
	ioutil.WriteFile(container.HostnamePath, []byte(container.Config.Hostname+"\n"), 0644)

	hostsContent := []byte(`
127.0.0.1	localhost
//.........這裏部分代碼省略.........