Execution of SSH command from Java sends status code 255, but in the terminal if it works

Question

I am trying to develop a small application that allows me to send certain commands by SSH to a remote server. If I try it from the Linux terminal or from the Windows Command Prompt it works without problems, but when I do it from my Java application it always responds with a status code of 255.

I have disabled the firewall and I have changed the port where I have listening SSH on the server to 22, because I use another, but nothing works. It does not throw me exceptions or anything and if it connects without problems. Any ideas?

I have tried with the sshj and JSch libraries and with both I have the same problem.

ForwardAgent is turn off

sshj example

private void sshj() throws Exception {
    SSHClient ssh = new SSHClient();
    ssh.addHostKeyVerifier((s, i, publicKey) -> true);
    ssh.connect("host", 22);
    Session session = null;
    try {
        ssh.authPassword("username", "password");
        session = ssh.startSession();
        Session.Command cmd = session.exec("command");
        System.out.println(IOUtils.readFully(cmd.getInputStream()).toString());
        cmd.join(5, TimeUnit.SECONDS);
        System.out.println("Exit status: " + cmd.getExitStatus());
    } catch (Exception e) {
        e.printStackTrace();
    } finally {
        if (session != null) {
            session.close();
        }

        ssh.disconnect();
    }
}

JSch example

private static void jsch() throws Exception {
    JSch js = new JSch();
    Session s = js.getSession("username", "host", 22);
    s.setPassword("password");
    Properties config = new Properties();
    config.put("StrictHostKeyChecking", "no");
    s.setConfig(config);
    s.connect();

    Channel c = s.openChannel("exec");
    ChannelExec ce = (ChannelExec) c;
    ce.setCommand("command");
    ce.connect();

    BufferedReader reader = new BufferedReader(new InputStreamReader(ce.getInputStream()));
    String line;
    while ((line = reader.readLine()) != null) {
        System.out.println(line);
    }

    ce.disconnect();
    s.disconnect();

    System.out.println("Exit status: " + ce.getExitStatus());
}

Answer 1

change to code so that you get the inputStream before doing connect

InputStream in = ce.getInputStream();
ce.connect();
BufferedReader reader = new BufferedReader(new InputStreamReader(in));

Also, the getSession is wrong as it should be

public Session getSession(String username,
                      String host,
                      int port)

edit

The below code works for me

JSch js = new JSch();
Session s = js.getSession("username", "127.0.0.1", 22);
s.setPassword("password");
Properties config = new Properties();
config.put("StrictHostKeyChecking", "no");
s.setConfig(config);
s.connect();

Channel c = s.openChannel("exec");
ChannelExec ce = (ChannelExec) c;
ce.setCommand("uptime");

InputStream in = ce.getInputStream();
ce.connect();

BufferedReader reader = new BufferedReader(new InputStreamReader(in));
String line;
while ((line = reader.readLine()) != null) {
      System.out.println(line);
}

ce.disconnect();
s.disconnect();

System.out.println("Exit status: " + ce.getExitStatus());

output

 10:26:08 up 149 days, 58 min,  3 users,  load average: 0.61, 0.68, 0.68
Exit status: 0