直接从/dev/log读取数据 Unix Domain Socket

Question

My project aims at reading log messages directly from /dev/log UNIX domain socket in Java. Currently I am using junixsocket . Below is a sample code of client that reads from a unix socket.

import java.io.File;
import java.io.IOException;
import java.io.InputStream;

import org.newsclub.net.unix.AFUNIXSocket;
import org.newsclub.net.unix.AFUNIXSocketAddress;
import org.newsclub.net.unix.AFUNIXSocketException;

public class SimpleTestClient {
    public static void main(String[] args) throws IOException {
        final File socketFile = new File("/dev/log");

        AFUNIXSocket sock = AFUNIXSocket.newInstance();
        try {
            sock.connect(new AFUNIXSocketAddress(socketFile));
        } catch (AFUNIXSocketException e) {
            System.out.println("Cannot connect to server. Have you started it?\n");
            System.out.flush();
            throw e;
        }
        System.out.println("Connected");

        InputStream is = sock.getInputStream();

        byte[] buf = new byte[8192];

        int read = is.read(buf);
        System.out.println("Server says: " + new String(buf, 0, read));
    
        is.close();

        sock.close();

        System.out.println("End of communication.");
    }
}

The above mentioned code is unable to connect to /dev/log . It throws an exception:

Cannot connect to server. Have you started it?
Exception in thread "main" org.newsclub.net.unix.AFUNIXSocketException: Protocol wrong type for socket (socket: /dev/log)
        at org.newsclub.net.unix.NativeUnixSocket.connect(Native Method)
        at org.newsclub.net.unix.AFUNIXSocketImpl.connect(AFUNIXSocketImpl.java:125)
        at org.newsclub.net.unix.AFUNIXSocket.connect(AFUNIXSocket.java:97)
        at org.newsclub.net.unix.AFUNIXSocket.connect(AFUNIXSocket.java:87)
        at SimpleTestClient.main(SimpleTestClient.java:40)

I am unable to figure out how to solve this problem. Any help would be appreciable.

Answer 1

Since you cannot connect to an existing server socket as mentioned in the log traces, then you haven't bound one one the mentioned file, so try creating an AF_UNIX server socket then connect to it.

It could be done in a separate class:

public class DevLogServer {

  public static void main(String[] args) throws IOException {

    final File socketFile = new File("/dev/log");
    AFUNIXServerSocket server = AFUNIXServerSocket.newInstance();
    try {
      server.bind(new AFUNIXSocketAddress(socketFile));
    } catch (Exception e) {
      throw e;
    }

  }

}

Edit as per @Ankit comment:

You may also need to make sure the syslod daemon is stopped by runnig below command in a terminal window:

sudo service syslog stop

You may alternatively need to grand write permission to the /dev directory.

Answer 2

您是否以root特权启动应用程序？