programmatic way for SSH

[Arjun Shastry]

Hi
We use Putty(SSH) to connect to one intermediate UNIX server.From this server we use Telnet to connect to production UNIX server to see the logs.Is there any better programmatic way to pass these credentials ? Basically checking the logs in browser is better than seeing unformatted logs on black UNIX screen!!

[Travis Hein]

yea, a simple servlet to do a tail operation on a log file, such that refreshing the page would re-run the tail.
but that would mean deploying a servlet container, or other script engine, on the machine where the logs are, and woud require the URL to this log viewer probably be secure, and assume the machine with the logs is even on the network in a way that http requests on some off beaten path port to view logs on is possible. and another problem if the log file (e.g. apache) is used for the application and this log viewer applet, then requests to view the logs will show up in the logs (what I call the 'fridge light problem').

but basically , in theory a general fie tailer might look like

  /**
   * @param fileName  the file we want tailed.
   * @param outputWriter the writer thing to write the last bits of this file out to, such as the servlet writer
   * @param lineTerminator the thing to end each file line with, such as \n for console, or possibly <br/> for HTML view
   */
  public void tailSomeFile(String fileName, Writer outputWriter, String lineTerminator) {
    InputStream instream = null;
    BufferedReader reader = null;
    File file = new File(fileName);

    try {
      if (!file.exists()) {
        return;
      } // file doesn't exist

      instream = new FileInputStream(file);

      int showSize=8192; // just show the last 8k of the file
      int skipAmount = Math.min(0, instream.available() - showSize); // skip ahead 0 or more bytes into the file.
      // note this is not really line oriented, but byte oriented, we could end up capturing part way through the first line.
      // but we assume sufficiently large showSize and don't care here.
      
      instream.skip(skipAmount);
      reader = new BufferedReader(new InputStreamReader(instream));

      // now read all that's left in this file.
      String line = null;
      while ( (line = reader.readLine()) != null) {
        outputWriter.write(line + lineTerminator);
      }
    }
    catch (IOException ex) {
      // handle error 
    }
    finally {
      if (reader != null) {
        try {
          reader.close();
        } catch (IOException ex) {}
      }
    }

and this could even be invoked from a JSP page, or a servlet

  @Override
  protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    tailSomeFile("/var/log/tomcat5/catalina.out", resp.getWriter(), "<br/>");  
  }

it would be really cool to extend this into an ajax driven auto refresh mechanism.

[Arjun Shastry]

Thanks for the help.

[Arjun Shastry]

Is there any API to pass SSH/Telnet parameters programmatically?So that servlet can connect to production server?
In Putty, i don't see any java api.

[Travis Hein]

Here are a couple projects I know of that might help for this.

for ssh, the "jsch" project
http://sourceforge.net/projects/jsch/

and for telnet the commons-net project
http://commons.apache.org/net/