平臺

RK3288 + Android 7.1

問題

android 應用無法繫結 < 1024 的埠號.

    void tryBind80Port(){
        new Thread(){
            @Override
            public void run() {
                try {
                    InetSocketAddress addr = new InetSocketAddress(80);//以80測試
                    ServerSocket ss =
 
 new ServerSocket();
                    ss.bind(addr);
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }.start();
    }

報錯LOG

2017-01-01 20:03:11.998 2762-2778/com.ansondroider.appshortcut W/System.err: java.net.BindException: Permission denied
2017-01-01 20:03:11.998 2762-2778/com.ansondroider.appshortcut W/System.err:     at java.net.PlainSocketImpl.socketBind(Native Method)
2017-01-01 20:03:11.998 2762-2778/com.ansondroider.appshortcut W/System.err:     at java.net.AbstractPlainSocketImpl.bind(AbstractPlainSocketImpl.java:368)
2017-01-01 20:03:11.998 2762-2778/com.ansondroider.appshortcut W/System.err:     at java.net.ServerSocket.bind(ServerSocket.java:377)
2017-01-01 20:03:11.998 2762-2778/com.ansondroider.appshortcut W/System.err:     at java.net.ServerSocket.bind(ServerSocket.java:331)
2017-01-01 20:03:11.998 2762-2778/com.ansondroider.appshortcut W/System.err:     at com.ansondroider.appshortcut.MainActivity$1.run(MainActivity.java:39)
 

解決

參考:https://www.linuxquestions.org/questions/linux-networking-3/allowing-non-root-to-bind-to-ports-1024-a-350437/

        //kernel/include/net/sock.h
        /* Sockets 0-1023 can't be bound to unless you are superuser */
          #define PROT_SOCK	1024

    檔案中已宣告, 0 - 1023 端僅 SU使用者能使用.
    所以, 修改的方法只是也是把限制的埠號改低或直接改為0.
 

PS: 個人並不建議去修改這個埠號, 最好還是APP能夠申請其它埠, 這樣也會少一些衝突