Efficiently execute multiple commands that depend on another long running command on Unix host with JSch

Question

I need to execute commands on remote SSH server in Java. I'm using JSch for that.

A Command 1 is a command to setup an environment on Linux machine and which requires some time to execute (about 20 minutes). Command 1 is a one time operation. If I open a PuTTY session I need to execute the Command 1 only once.

A Command 2 dependents on the Command 1. It does not execute without the Command 1.

Once the Command 1 is executed (one time operation), the Command 2 (requires 2-3 seconds to execute) can be executed for different entities without the Command 1 being executed again.

I know I can do it with commands separated by &&, but in that way the Command 1 will execute unnecessarily degrading overall performance.

Code:

String host = "1.1.1.1";
String user = "parag";
String password = "abcdf";
String command1 = "command1";
String command2 = "command2";
try {

    java.util.Properties config = new java.util.Properties();
    config.put("StrictHostKeyChecking", "no");
    JSch jsch = new JSch();
    Session session = jsch.getSession(user, host, 22);
    session.setConfig(config);
    session.setPassword(password);
    session.connect();
    System.out.println("Connected");

    Channel channel = session.openChannel("exec");
    ((ChannelExec) channel).setCommand(command1 + " && " + command2);
    channel.setInputStream(null);
    ((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();
    session.disconnect();
    System.out.println("DONE");
} catch (Exception e) {
    e.printStackTrace();
}

Please let me know if this is possible. Also suggest an alternative if any, in case this is not possible with JSch.

Martin Prikryl · Accepted Answer · 2021-02-04T07:47:12.920

What you have now is the correct way.

If you really really need to optimize it, you have to feed the commands to a remote shell session. Either start a shell explicitly using the "exec" channel. Or use "shell" channel directly. And then write the individual commands to the shell input.

Efficiently execute multiple commands that depend on another long running command on Unix host with JSch

1 Answers1