Log into a Linux machine and execute multiple commands

问题

I am trying to login and execute a set of commands through java from my remote computer (windows 7) into linux machine,

(Distributor ID: RedHatEnterpriseServer
Description: Red Hat Enterprise Linux Server release 5.10
Release: 5.10 )

Please look into the Perl script , which is working perfectly, same functionality needs to be achieved.

use strict;  
use warnings; 

use Net::SSH::Expect; 

my $ssh = Net::SSH::Expect->new(   
    host     => "host123",  
    password => "passwd",  
    user     => "username",  
    raw_pty  => 1,  
    timeout  => 1, 
);
$ssh->login();

$ssh->exec("su - root");  
$ssh->exec("passwd");  
$ssh->exec("su - user");  
$ssh->exec("command1");  
$ssh->exec("subcommand"); 

my $output = $ssh->exec("subcommand 2");  
warn "$output\n";  
$ssh->exec("\n");

my $output2 = $ssh->exec("subcommand 3");  
warn "$output2\n";  
$ssh->exec("\n")

similar function need to be executed with the help of java.. currently i have written the following java code

import java.io.InputStreamReader;
import ch.ethz.ssh2.Connection;
import ch.ethz.ssh2.SCPClient;
import ch.ethz.ssh2.Session;
import ch.ethz.ssh2.StreamGobbler;
import java.util.concurrent.TimeUnit;
import java.util.logging.Level;
import java.util.logging.Logger;

public void sshExecute() throws Exception {

    String username = "username";
    String password = "passwd";
    String hostname = "host123";
    logger.setLevel(Level.INFO);

    Object lastCommandOutput = null;
    logger.info("starting connection with " + hostname);

    Connection connection = new Connection(hostname);
    logger.info("connection object created..");

    connection.connect();
    connection.authenticateWithPassword(username, password);

    Session session = connection.openSession();
    InputStream stdout = new StreamGobbler(session.getStdout());
    BufferedReader stdoutReader = new BufferedReader(new InputStreamReader(stdout));
    logger.info("connected");

    String tempCommand = "su - root";
    String Pswd = "passwd";
    logger.info("sending command: " + tempCommand);

    session.execCommand(tempCommand + Pswd);
    TimeUnit.SECONDS.sleep(5);

    session.execCommand("su - user");

    // Get output
    StringBuffer sb = new StringBuffer();

    while (true) {
        String line = stdoutReader.readLine();
        if (line == null)
            break;
        sb.append(line + "\n");
    }

    String output = sb.toString();
    lastCommandOutput = output;
    logger.info("got output: " + output);

    stdoutReader.close();
}

This is working fine till line session.execCommand("su - user");. There, it gives an error as :

java.io.IOException: A remote execution has already started.  java.lang.Error: java.io.IOException: A remote execution has already started at com.user1.test.Assert.fail(Assert.java:35)

How to login twice, i.e su -root and then su - user, and also why can't we use execCommand more than once for a session? Is there any other way to achieve this instead of execCommand, to achieve the above functionality?

来源：https://stackoverflow.com/questions/47509180/log-into-a-linux-machine-and-execute-multiple-commands