JSch: sudo sometimes not working

Question

I have three machines and I need to ssh to them one by one, and then sudo a command.

I need the JSch to do the following things:

ssh <user>@<machine>
sudo <some command>

This is the code block how I use to run JSch:

String homeFolder = System.getProperty("user.home");
JSch jsch = new JSch();
jsch.addIdentity(homeFolder + "/.ssh/id_rsa.pub");
jsch.setKnowHosts(homeFolder + "/.ssh/known_hosts");

final Session session = jsch.getSession(user, machine);
session.connect();

StringBuilder response = new StringBuilder();
try {
    final Channel channel = session.openChannel("exec");
    ((ChannelExec) channel).setCommand("sudo /etc/init.d/eedir status")
    channel.connect();

    try {
        InputStream in = channel.getInputStream();
        OutputStream out = channel.getOutputStream();

        out.write((password + System.getProperty("line.separator")).getBytes());

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

My problem is that I can use this program successfully to get the status of the eedir service on two of the three machines I have, but not the last one.

I can ssh to the remote machine with the given user name and then run this command directly:

sudo /etc/init.d/eedir status

The username used in ssh is already configured in my /etc/sudoers.

So, my questions are:

1. Why JSch can run this program on two of the three machines while the rest one cannot? The sudoers' configuration is exactlly the same on these machines.

2. And another question is: why sudo on the real machine can run without typing the password again if I configured the current user in sudoers, while JSch sudo require the password in the program?

Any directions are really appreciated. If there are some potential errors that I might have under my current circumstances, welcome everybody to point them out.

Thanks.

Answer 1

1. what output do you get from the jsch sudo attempt on the failed machine? to get the error output you may need:

   (ChannelExec)commandChannel.getErrStream();
   

   the ssh server probably has different settings. on my server you need pty:

   (ChannelExec)commandChannel.setPty(true);
   (ChannelExec)commandChannel.setPtyType("VT100");
   

2. generally you only need to type your password once per session for sudo. Maybe on the real machine you had already done sudo once and had not logged out. The above code reconnects each time so it needs to send the password every time.

Answer 2

I had the same problem on CentOS. Solved it by
1) after you do the setCommand on the channel do this:

((ChannelExec) channel).setPty(true);

2) make sure you have finally block/s to close the input stream, channel and session

Note: if the user does not require a password you don't need to open the output stream (unlike what is shown in the above example)

Answer 3

The latest version to date has a sample java class using sudo commands on a remote host. Download both the project .zip file and the .jar for they are separated for a reason only GOD knows !!