JSch: How to keep the session alive and up

Question

I'm writing Java GUI program for static route management using SSH. My code is as follows:

import com.jcraft.jsch.*;
import java.io.*;

public class Konsep {
    String status;
    static String username;
    static String hostname;
    String inputcommand;
    String output;
    static Session session;

    JSch jsch = new JSch();

    public String status(String stringstatus) {
        stringstatus = status;
        return stringstatus;
    }

    public String InputCommand(String inputcommandstatus) {
        inputcommandstatus = inputcommand;
        return inputcommandstatus;
    }

    public void connect(String usernamelokal, String hostnamelokal,
            String password, int port) {
        //        JSch jsch=new JSch();
        try {
            Session sessionlokal = jsch.getSession(usernamelokal,
                    hostnamelokal, port);
            sessionlokal.setPassword(password);
            UserInfo ui = new UserInfoku.Infoku();
            sessionlokal.setUserInfo(ui);
            sessionlokal.setTimeout(0);
            sessionlokal.connect();
            status = "tersambung \n";
            username = usernamelokal;
            hostname = hostnamelokal;
            session = sessionlokal;
            System.out.println(username + " " + hostname);
        } catch (Exception e) {
            System.out.println(e);
            status = "Exception = \n " + e + "\n";

        }
    }

    public void disconnect() {
        //        JSch jsch=new JSch();
        try {
            Session sessionlokal = jsch.getSession(username, hostname);
            //            System.out.println(username +" "+ hostname);
            sessionlokal.disconnect();
            status = "wes pedhoott \n";
        } catch (Exception e) {
            System.out.println(e);
            status = "Exception = \n " + e + "\n";
        }

    }

    public void addRoute() {
        //        JSch jsch=new JSch();
        System.out.println(username + " " + hostname);
        try {
            Session sessionlokal = session; // =jsch.getSession(username, hostname);
            Channel channel = sessionlokal.openChannel("exec");
            ((ChannelExec) channel).setCommand(inputcommand);
            channel.setInputStream(null);
            channel.connect();
            ((ChannelExec) channel).setErrStream(System.err);
            InputStream in = channel.getInputStream();
            channel.connect();

            byte[] tmp = new byte[1024];
            while (true) {
                while (in.available() > 0) {
                    int i = in.read(tmp, 0, 1024);
                    if (i < 0)
                        break;
                    System.out.print(new String(tmp, 0, i));
                }
                if (channel.isClosed()) {
                    System.out.println("exit-status: "
                            + channel.getExitStatus());
                    break;
                }
                try {
                    Thread.sleep(1000);
                } catch (Exception ee) {
                }
            }

            channel.disconnect();
        } catch (Exception e) {
            System.out.println(e);
        }
    }
}      

The problem is when I call the connect method and then calling the addroute, the program returns

root 192.168.50.2
root 192.168.50.2
com.jcraft.jsch.JSchException: session is down

I've been trying to get session status with either

Session sessionlokal=session; //returns com.jcraft.jsch.JSchException: ChannelExec

or

Session sessionlokal=jsch.getSession(username, hostname); //returns session is down

I've also tried to use keepalive, but its not working either.

My intention is to create a session to host (log in), while leaving the session up, execute a command or commands and maybe executing other commands later, and then closing the session when its not needed (log out). I've been searching on this forum and I found this question but the code is create a method to define a command to execute first, and then creating the session, call the command's method and close the session.

Any ideas about how to do as I mentioned above ?

Answer 1

After trying Session.sendKeepAliveMsg() without success, I came to the following solution which seems to be rather stable:

private Session getSession() throws Exception {
    try {
        if (!session.isConnected()) {
            logger.info("Session successfully tested, use it again.");
            session.connect();
        }
    } catch (Throwable t) {
        logger.info("Session terminated. Create a new one.");
        session = jsch.getSession(user, host, port);
        session.setConfig(config);
        session.connect();
    }
    return session;
}

Update: Some days later it failed.

I tried to test it by killing the open session on the server. All prior versions I tested this way showed the exact same behavior, regardless whether the problem popped up after waiting some days or killing the server process, so I thought this test - and its outcome for the above solution - to be meaningful. Unfortunately, it isn't.

I'm going to try some other ways to fix it and keep you up to date.

Update 2: Final solution, guaranteed inelegant and working:

private Session getSession() throws Exception {
    try {
        ChannelExec testChannel = (ChannelExec) session.openChannel("exec");
        testChannel.setCommand("true");
        testChannel.connect();
        if(logger.isDebugEnabled()) {
            logger.debug("Session successfully tested, use it again.");
        }
        testChannel.exit();
    } catch (Throwable t) {
        logger.info("Session terminated. Create a new one.");
        session = jsch.getSession(user, host, port);
        session.setConfig(config);
        session.connect();
    }
    return session;
}

This version runs several weeks in a productive environment. Once a day I have the info message logged.

The costs of opening a channel and performing some do-nothing-command are somewhat annoying, but I found no other way to be definitely sure about the state of the session.

Answer 2

You can try by invoking the following method before invoking Session#connect().

Session#setServerAliveInterval(int milliseconds)

Although I found one more function Session#sendKeepAliveMsg() which can be tried.