Executing sudo using SSH “exec” channel in JSch

Question

I am using file in which I passed below commands:

1. hostname
2. pwd
3. pbrun su - fclaim
4. whoami
5. cd ..
6. pwd

Ad the Java code below:

for (String command1 : commands) {

    Channel channel=session.openChannel("exec");
    ((ChannelExec)channel).setCommand(command1);

    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.println(new String(tmp, 0, i));
      }
      if(channel.isClosed()){
        break;
      }
    }
    channel.setInputStream(null);
    channel.disconnect();
}

But I'm getting this output:

1. some hostname
2. /home/imam
3. missing output
4. imam
5. missing output
6. /home/imam

Answer 1

I had a similar issue and got it resolved with some help from @Martin, lot of R&D and scanning through SO links. Here is the program that worked for me.

public class SSHConn {

    static Session session;
    static String suCmds = "su - simba -c \"whoami ; pwd\"";
    static String[] commands = {"whoami", suCmds};

    public static void main(String[] args) throws Exception {
        open();
        runCmd(commands);
        close();
    }

    public static void runCmd(String[] commands) throws JSchException, IOException {
        for (String cmd : commands) {
            System.out.println("\nExecuting command: " + cmd);
            Channel channel = session.openChannel("exec");
            ((ChannelExec) channel).setCommand(cmd);
            InputStream in = channel.getInputStream();
            OutputStream out = channel.getOutputStream();
            channel.connect();
            //passing creds only when you switch user
            if (cmd.startsWith("su -")) {
                System.out.println("Setting suPasswd now....");
                out.write((Constants.suPasswd + "\n").getBytes());
                out.flush();
                System.out.println("Flushed suPasswd to cli...");
            }
            captureCmdOutput(in, channel);
            channel.setInputStream(null);
            channel.disconnect();
        }
    }

    public static void captureCmdOutput(InputStream in, Channel channel) throws IOException {
        System.out.println("Capturing cmdOutput now...");
        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()) {
                break;
            }
            try {
                Thread.sleep(1000);
            } catch (Exception ee) {
                System.out.println(ee.getMessage());
            }
        }
    }

    public static void open() throws JSchException {
        JSch jSch = new JSch();
        session = jSch.getSession(Constants.userId, Constants.host, 22);
        Properties config = new Properties();
        config.put("StrictHostKeyChecking", "no");
        session.setConfig(config);
        session.setPassword(Constants.userPasswd);
        System.out.println("Connecting SSH to " + Constants.host + " - Please wait for few seconds... ");
        session.connect();
        System.out.println("Connected!\n");
    }

    public static void close() {
        session.disconnect();
        System.out.println("\nDisconnected channel and session");
    }

}

Output:

Connecting SSH to my-unix-box.net - Please wait for few seconds... 
Connected!

Executing command: whoami
Capturing cmdOutput now...
john

Executing command: su - simba -c "whoami ; pwd"
Setting suPasswd now....
Flushed suPasswd to cli...
Capturing cmdOutput now...
simba
/home/simba

Disconnected channel and session

Answer 2

Your code executes each command in an isolated environment. So your second whoami does not run within pbrun su, as you probably hoped for.

The pbrun su executes a new shell.

To provide a command to the shell you either:

• specify the command on su command-line, like the official JSch Sudo.java example shows:

  ((ChannelExec)channel).setCommand("pbrun su - fclaim -c whoami");
  

• or feed the command to the shell using its standard input:

  OutputStream out = channel.getOutputStream();
  out.write(("whoami\n").getBytes());
  

  See also:
  Executing multiple bash commands using a Java JSch program after sudo login and
  Running command after sudo login.

In general, I recommend the first approach as it uses a better defined API (command-line argument).