Question

I want to run a command on a remote machine using the RExecClient Apache Commons-Net class.

My code is:

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

import org.apache.commons.io.IOUtils;
import org.apache.commons.net.bsd.RExecClient;

public class TestRlogin {

    static final int PORT_NUMBER = 512;
    private RExecClient client;
    private final String url = "test.corp";
    private final String login = "bob";
    private final String password = "bob";

    public TestRlogin() {
        client = new RExecClient();
    }
    public String run(String cmd) throws IOException {
        String res = null;
        InputStream is = null;
        if (client != null) {
            try {
                if (!client.isConnected()) {
                    client.connect(url, PORT_NUMBER);
                }
                client.rexec(login, password, cmd);
                is = client.getInputStream();
                if (is != null && is.available() > 0) {
                    res = IOUtils.toString(is);
                } else {
                    System.err.println("InputStream is not available!");
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
            finally {
                IOUtils.closeQuietly(is);
                client.disconnect();
            }
        } else {
            System.err.println("The RLogin client is not connected to "+url);
        }
        return res;
    }
    public void main(String[] args) {
        TestRlogin trl = new TestRlogin();
        try {
            System.out.println(trl.run("ls -lrt /tmp;"));
            System.out.println(trl.run("tar -xf /tmp/archive.tar;"));
            System.out.println(trl.run("ls -lrt /tmp;"));
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

The ls command works fine but the tar command does not extract the archive and returns nothing. The message I get is InputStream is not available!.

I checked twice the tar archive exists on the server. When I rlogin manually and run the command, nothing is returned but the tar archive is extracted.

I am out of ideas.

Answer 1

I finally solved this problem. It is not necessary to specify the port when connecting.

Also, if you are logged as root, check the $HOME/.rhosts file. When logged as non root, configure both $HOME/.rhosts and /etc/hosts.equiv.

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

import org.apache.commons.io.IOUtils;
import org.apache.commons.net.bsd.RExecClient;

public class TestRlogin {

    private RExecClient client;
    private final String url = "test.corp";
    private final String login = "bob";
    private final String password = "bob";

    public TestRlogin() {
        client = new RExecClient();
    }
    public String run(String cmd) throws IOException {
        String res = null;
        InputStream is = null;
        if (client != null) {
            try {
                if (!client.isConnected()) {
                    client.connect(url);
                }
                client.rexec(login, password, cmd);
                is = client.getInputStream();
                if (is != null && is.available() > 0) {
                    res = IOUtils.toString(is);
                } else {
                    System.err.println("InputStream is not available!");
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
            finally {
                IOUtils.closeQuietly(is);
                client.disconnect();
            }
        } else {
            System.err.println("The RLogin client is not connected to "+url);
        }
        return res;
    }
    public void main(String[] args) {
        TestRlogin trl = new TestRlogin();
        try {
            System.out.println(trl.run("ls -lrt /tmp;"));
            System.out.println(trl.run("tar -xf /tmp/archive.tar;"));
            System.out.println(trl.run("ls -lrt /tmp;"));
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

But I still have a question. How to check the command terminated correctly (I posted the question here)? Maybe it is possible to use the method addProtocolCommandListener from the SocketClient class. I saw there is a protected method fireReplyReceived.

Thanks for the help.