Notes: Java module to convert PDF document to Image_Files

 import java.awt.image.BufferedImage;

import java.io.File;

import java.util.Arrays;

import javax.imageio.ImageIO;

import org.apache.commons.lang3.StringUtils;

import org.apache.pdfbox.pdmodel.PDDocument;

import org.apache.pdfbox.rendering.ImageType;

import org.apache.pdfbox.rendering.PDFRenderer;

private static void convertPdfToImage(String pdfFilePath, String imageFolderPath) throws Exception {

        File file = new File(pdfFilePath);

        String fileExtension = ".jpg";

        int dpi=300;

        try (PDDocument doc = PDDocument.load(file)) {

            PDFRenderer pdfRenderer = new PDFRenderer(doc);

            for (int i = 0; i < doc.getPages().getCount(); i++) {

                BufferedImage img = pdfRenderer.renderImageWithDPI(i, dpi, ImageType.RGB);

                File outputFile = new File(imageFolderPath + StringUtils.removeEnd(file.getName(),".pdf") + "_pgNo" + i + fileExtension);

                outputFile.delete();

                System.out.println(outputFile.getAbsolutePath());

                System.out.println(Arrays.toString(ImageIO.getWriterFormatNames()));

                boolean flg=ImageIO.write(img, "jpg", outputFile);

                System.out.println(flg);

            }

        }

    }

C++ code to connect Postgres Database

/* At first install libpqxx in linux*/

#include <pqxx/pqxx>

using namespace std;
using namespace pqxx;

class GetDbConn
{
public:
    static connection *getPostgresDbConnection(const std::string& conStr)
    {
        pqxx::connection *c=new connection(conStr);
        return c;
    }
};

----------------

/*Code to call this connection is as follows

#include <pqxx/pqxx>
#include "getDbConn.h"

using namespace std;
using namespace pqxx;

class MyDb
{
public:
    static connection * getTradingNseConnection()
    {
        char const *conStr="dbname = <database_name> user = <user_name> password = <db_password> hostaddr = 127.0.0.1 port = 5432";
        pqxx::connection *con=GetDbConn::getPostgresDbConnection(conStr);
        if ((*con).is_open())
        {
            cout << "Opened database successfully: " << (*con).dbname() << endl;
            return con;
        }
        else
        {
            cout << "Can't open database" << endl;
            return NULL;
        }
    }
};

Ubuntu Notes: Set up autossh as systemd useful-reminder commands

 sudo vim /etc/systemd/system/permanentAutossh.service

========================================

[Unit]

Description=Keeps a tunnel to myOciFreeNat open

After=network-online.target

[Service]

User=<username>

Environment="AUTOSSH_GATETIME=0"

ExecStart=/usr/bin/autossh -M 0 -q -N -o "ServerAliveInterval 60" -o "ServerAliveCountMax 3" -L 4322:127.0.0.1:5432 -i /<ssh_private_key_file_absolute_path> <username>@<ip_address> -p 22

[Install]

WantedBy=multi-user.target

========================================

sudo systemctl daemon-reload

sudo systemctl enable permanentAutossh

sudo systemctl start permanentAutossh

==================

sudo systemctl daemon-reload

sudo systemctl restart permanentAutossh

sudo systemctl status permanentAutossh

======================

sudo systemctl stop permanentAutossh

sudo systemctl disable permanentAutossh

sudo rm /etc/systemd/system/permanentAutossh.service

Reinstall Network-Manager in Ubuntu

 Assumptions: Network-Manager is somehow lost (or currepted) while updating/deleting some software and Internet access is lost. Internet access was there using data-cable usb port using mobile-internet connection.

Get Logical Name of the port: Type in terminal 
<sudo lshw -C network>

you will get list of ports with there logical name

Connect to internet using command:
<sudo dhclient <your_port_name>> e.g. in my case it was <sudo dhclient usb0>

Then reinstall Network-Manager using command:
<sudo apt-get install network-manager>

Done!

Ubuntu Notes: Using 7z in terminal

 I> Compress file using 7z

7z a <compressed_file_name.7z> file1 file2 

II> Decompress file using 7z

7z e <compressed_file_name>.7z

Ubuntu Notes: Commands to Shutdown, Restart

 1> to shutdown computer

sudo poweroff;

sudo shutdown -h now;

2> to restart computer

sudo reboot;

Ubuntu Notes: Set Password for a user in ubuntu

 Type:
sudo passwd <username>

Then type new password and repeat type new password as prompted

DONE!