Execute multiple ssh commands and get result for each command

Question

I have opened session with jsch on Android, this way:

SshObjects Connect(String username, String password, String hostname, int port)
    {
        JSch jsch=new JSch();
        try
        {
            sshObjects._session = jsch.getSession(username, hostname, port);
        }
        catch (JSchException e)
        {
            e.printStackTrace();
            return null;
        }
        sshObjects._session.setPassword(password);
        Properties config = new Properties();
        config.put("StrictHostKeyChecking", "no");
        sshObjects._session.setConfig(config);
        try
        {
            sshObjects._session.connect();
        }
        catch (JSchException e)
        {
            e.printStackTrace();
            return null;
        }

        try
        {
            sshObjects._channel = (ChannelExec) sshObjects._session.openChannel("exec");
        }
        catch (JSchException e)
        {
            e.printStackTrace();
            return null;
        }


        connected = true;

        return sshObjects;
}

And then, to execute some command on opened session and get result, I did this:

private String ExecuteCommand(SshCommandsEnum cmdType)
    {
        String result = "";

        switch (cmdType)
        {
            case SERVER_INFO:
                sshObjects._channel.setCommand("uname --all");
                break;
            .......
        }

        try
        {
            BufferedReader in=new BufferedReader(new InputStreamReader(sshObjects._channel.getInputStream()));
            //sshObjects._channel.disconnect();
            try
            {
                sshObjects._channel.connect();
            }
            catch (JSchException e)
            {
                e.printStackTrace();
            }

            String msg=null;
            try
            {
                while((msg=in.readLine())!=null)
                {
                    System.out.println(msg);
                    result += msg;
                }
                sshObjects._channel.disconnect();
            }
            catch (IOException e)
            {
                e.printStackTrace();
            }
        }

        catch (IOException e)
        {
            return "";
        }



        return result;
    }

So I want to open my session only once. And then execute commands as "exec" on it. It works for first command executed after connect - everything seems to be ok and I can get result succesfully. But when I call "Execute Command" again, it doesn't work anymore. My thread hangs on sshObjects._channel.connect(); and nothing works. When I try to disconnect (close channel and session) and connect again - the same. I can connect and disconnect without any problems only if I don't even try to execute command.

However, I don't experience this issue without this:

BufferedReader in=new BufferedReader(new InputStreamReader(sshObjects._channel.getInputStream()));

But, obviously I need it to get my command output. So what's the problem? Do you have any idea what am I doing wrong?

ymnk · Accepted Answer · 2014-05-22 04:35:28Z

1

The ChannelExec is not re-usable, so you need to instantiate it for each command.

answered May 22, 2014 at 4:35

ymnk

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2 Comments

user1209216 Over a year ago

I'll try this. But why can't I disconnect and connect again after I execute command? I don't try to reuse channel in this case. Only close session, close (already used) channel. And conncet again - it hangs.

Damienknight Over a year ago

The session owns the channel. Close the channel, then create a new channel with the same session instance. Also, consider using a 'shell' Channel, as it allows more than one command to be sent.

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