NetworkInterface.getNetworkInterfaces()未列出所有接口

Question

(eth0,Loopback,wlan0)我的机器上有三个接口,我想使用Java-API来获取mac地址.

• 我用这个代码.

  Enumeration<NetworkInterface> nets = NetworkInterface.getNetworkInterfaces();
      for (NetworkInterface netint : Collections.list(nets))
          displayInterfaceInformation(netint);
  }
  
  static void displayInterfaceInformation(NetworkInterface netint) 
    throws SocketException 
  {
      System.out.println("Display name: " 
         + netint.getDisplayName());
      System.out.println("Hardware address: " 
         + Arrays.toString(netint.getHardwareAddress()));
  }
  

• 但那个代码打印wlan0,loopback,但错过了eth0.

• 我的操作系统Ubuntu,任何帮助.

更新

• o/p(strace -f java Networks 2>&1| grep ioctl).. 空白(空).

• java -version

java版"1.7.0_21"Java(TM)SE运行时环境(版本1.7.0_21-b11)Java HotSpot(TM)64位服务器VM(版本23.21-b01,混合模式)

• strace ifconfig 2>&1 | grep ioctl

ioctl(4, SIOCGIFCONF, {80, {{"lo", {AF_INET, inet_addr("127.0.0.1")}}, {"wlan0", {AF_INET, inet_addr("192.168.1.101")}}}}) = 0
ioctl(5, SIOCGIFFLAGS, {ifr_name="eth0", ifr_flags=IFF_UP|IFF_BROADCAST|IFF_MULTICAST}) = 0
ioctl(5, SIOCGIFHWADDR, {ifr_name="eth0", ifr_hwaddr=-----------------}) = 0
ioctl(5, SIOCGIFMETRIC, {ifr_name="eth0", ifr_metric=0}) = 0
ioctl(5, SIOCGIFMTU, {ifr_name="eth0", ifr_mtu=1500}) = 0
ioctl(5, SIOCGIFMAP, {ifr_name="eth0", ifr_map={mem_start=0, mem_end=0, base_addr=0, irq=0, dma=0, port=0}}) = 0
ioctl(5, SIOCGIFMAP, {ifr_name="eth0", ifr_map={mem_start=0, mem_end=0, base_addr=0, irq=0, dma=0, port=0}}) = 0
ioctl(5, SIOCGIFTXQLEN, {ifr_name="eth0", ifr_qlen=1000}) = 0
ioctl(4, SIOCGIFADDR, {ifr_name="eth0", ???}) = -1 EADDRNOTAVAIL (Cannot assign requested address)
ioctl(5, SIOCGIFFLAGS, {ifr_name="lo", ifr_flags=IFF_UP|IFF_LOOPBACK|IFF_RUNNING}) = 0
ioctl(5, SIOCGIFHWADDR, {ifr_name="lo", ifr_hwaddr=00:00:00:00:00:00}) = 0
ioctl(5, SIOCGIFMETRIC, {ifr_name="lo", ifr_metric=0}) = 0
ioctl(5, SIOCGIFMTU, {ifr_name="lo", ifr_mtu=16436}) = 0
ioctl(5, SIOCGIFMAP, {ifr_name="lo", ifr_map={mem_start=0, mem_end=0, base_addr=0, irq=0, dma=0, port=0}}) = 0
ioctl(5, SIOCGIFMAP, {ifr_name="lo", ifr_map={mem_start=0, mem_end=0, base_addr=0, irq=0, dma=0, port=0}}) = 0
ioctl(5, SIOCGIFTXQLEN, {ifr_name="lo", ifr_qlen=0}) = 0
ioctl(4, SIOCGIFADDR, {ifr_name="lo", ifr_addr={AF_INET, inet_addr("127.0.0.1")}}) = 0
ioctl(4, SIOCGIFDSTADDR, {ifr_name="lo", ifr_dstaddr={AF_INET, inet_addr("127.0.0.1")}}) = 0
ioctl(4, SIOCGIFBRDADDR, {ifr_name="lo", ifr_broadaddr={AF_INET, inet_addr("0.0.0.0")}}) = 0
ioctl(4, SIOCGIFNETMASK, {ifr_name="lo", ifr_netmask={AF_INET, inet_addr("255.0.0.0")}}) = 0
ioctl(5, SIOCGIFFLAGS, {ifr_name="wlan0", ifr_flags=IFF_UP|IFF_BROADCAST|IFF_RUNNING|IFF_MULTICAST}) = 0
ioctl(5, SIOCGIFHWADDR, {ifr_name="wlan0", ifr_hwaddr=---------------}) = 0
ioctl(5, SIOCGIFMETRIC, {ifr_name="wlan0", ifr_metric=0}) = 0
ioctl(5, SIOCGIFMTU, {ifr_name="wlan0", ifr_mtu=1500}) = 0
ioctl(5, SIOCGIFMAP, {ifr_name="wlan0", ifr_map={mem_start=0, mem_end=0, base_addr=0, irq=0, dma=0, port=0}}) = 0
ioctl(5, SIOCGIFMAP, {ifr_name="wlan0", ifr_map={mem_start=0, mem_end=0, base_addr=0, irq=0, dma=0, port=0}}) = 0
ioctl(5, SIOCGIFTXQLEN, {ifr_name="wlan0", ifr_qlen=1000}) = 0
ioctl(4, SIOCGIFADDR, {ifr_name="wlan0", ifr_addr={AF_INET, inet_addr("192.168.1.101")}}) = 0
ioctl(4, SIOCGIFDSTADDR, {ifr_name="wlan0", ifr_dstaddr={AF_INET, inet_addr("192.168.1.101")}}) = 0
ioctl(4, SIOCGIFBRDADDR, {ifr_name="wlan0", ifr_broadaddr={AF_INET, inet_addr("192.168.1.255")}}) = 0
ioctl(4, SIOCGIFNETMASK, {ifr_name="wlan0", ifr_netmask={AF_INET, inet_addr("255.255.255.0")}}) = 0

使用ifconfig

$ ifconfig
eth0      Link encap:Ethernet  HWaddr -------------  
          UP BROADCAST MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:1695 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1695 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:129949 (129.9 KB)  TX bytes:129949 (129.9 KB)

wlan0     Link encap:Ethernet  HWaddr -------------------  
          inet addr:192.168.1.101  Bcast:192.168.1.255  Mask:255.255.255.0
          inet6 addr: fe80::-------------- Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:8396 errors:0 dropped:0 overruns:0 frame:0
          TX packets:5524 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:3959941 (3.9 MB)  TX bytes:1513934 (1.5 MB)

Answer 1

显然,我首先错了:即使两者ifconfig和Java API都使用相同的ioctl()系统调用,它们的行为也不同.

首先,SIOCGIFCONF ioctl()记录如下(参见http://linux.die.net/man/7/netdevice):

SIOCGIFCONF
    Return a list of interface (transport layer) addresses.
    ...
    The kernel fills the ifreqs with all current L3 interface 
    addresses that are running.

因此,SIOCGIFCONF ioctl()两者ifconfig和JAVA API使用的只返回正在运行的接口.这也可以在看到strace ifconfig ...的第一个-从问题的输出ioctl只有收益lo和wlan0,但不为eth0.

然后,从哪里ifconfig获取eth0来自？检查ifconfig源代码(来自net-toolsDebian/Ubuntu上的软件包),我们看到ifconfig没有使用ioctl()作为网络设备枚举基础的结果,但首先读取/proc文件系统以确定所有网络接口.然后,它使用ioctl()系统调用来确定有关每个接口的更多信息.

不幸的是,java.net.NetworkInterface.getByName()如果我们明确地传递名称,该方法甚至不会为未配置的接口返回网络接口对象eth0.

从本质上讲,还有三种不同的方法可以获取Linux 上所有设备的硬件地址:

• 调用ifconfig并解析输出(应该是最后的手段)
• 实现JNI库以执行相同的ifconfig操作(需要依赖于体系结构的共享库)
• 直接从读取数据/proc和/sys文件系统.

所有这些方法都依赖于系统而不是便携式的.第三种方法的好处是它可以用纯Java实现.以下是在我的环境中运行良好的第三种方法的示例实现:

static void printHardwareAddresses() throws SocketException {
    if (System.getProperty("os.name").equals("Linux")) {

        // Read all available device names
        List<String> devices = new ArrayList<>();
        Pattern pattern = Pattern.compile("^ *(.*):");
        try (FileReader reader = new FileReader("/proc/net/dev")) {
            BufferedReader in = new BufferedReader(reader);
            String line = null;
            while( (line = in.readLine()) != null) {
                Matcher m = pattern.matcher(line);
                if (m.find()) {
                    devices.add(m.group(1));
                }
            }
        } catch (IOException e) {
            e.printStackTrace();
        }

        // read the hardware address for each device
        for (String device : devices) {
            try (FileReader reader = new FileReader("/sys/class/net/" + device + "/address")) {
                BufferedReader in = new BufferedReader(reader);
                String addr = in.readLine();

                System.out.println(String.format("%5s: %s", device, addr));
            } catch (IOException e) {
                e.printStackTrace();
            }
        }

    } else {
        // use standard API for Windows & Others (need to test on each platform, though!!)
        ...
    }
}