Create .tar file in Linux

Following command can be used to create .tar file in Linux.

tar -cvf all.tar *.txt

Above command ceate tar files for all .txt files in the directory.

Find port usage

Following command can be used to check port usage.
In windows command prompt type following command.

netstat -aon |find /i "listening" |find "port"

This will return port usage.

SSH vfs2 Change FTP Directory

Following configuration can be used to change logged user directory. In normally, FTP directory is set to logging user home. Sometimes, you have to access directories outside of the logging SFTP user home.

SftpFileSystemConfigBuilder.getInstance().setUserDirIsRoot(opts, false);

This code snip can be used, when you are using vfs2 SFTP client.

Now, you can FTP files in any location using following SFTP URI.

"sftp://" + userID + ":" + password + "@" + sftpHost + "/" + remoteDirectory + fileName

Change remote directory as you preferred.

Ubuntu Graphical Desktop

In Ubuntu VM installations, you can't get graphical desktop. It only prompt for terminal view. You can use following command to start Ubuntu in graphical view.

startx

If this command not found, hen you have to update Ubuntu desktop using following command.

sudo apt-get install ubuntu-desktop

Then use startx command.

SFTP in JAVA

Following JAVA functions can be used to execute SFTP(Secure FTP).

    public boolean putSFTPFile(String sftpHost, String userID, String password, String remoteDirectory, String localDirectory, String fileName) throws FileSystemException {

        boolean put = false;
        StandardFileSystemManager manager = new StandardFileSystemManager();

        try {

            String filepath = localDirectory + fileName;
            File file = new File(filepath);
            if (!file.exists()) {
                throw new RuntimeException("Error. Local file not found.");
            }
            manager.init();

            FileSystemOptions opts = new FileSystemOptions();
            SftpFileSystemConfigBuilder.getInstance().setStrictHostKeyChecking(
                    opts, "no");
            SftpFileSystemConfigBuilder.getInstance().setUserDirIsRoot(opts, true);
            SftpFileSystemConfigBuilder.getInstance().setTimeout(opts, 10000);

            String sftpUri = "sftp://" + userID + ":" + password + "@" + sftpHost + "/" + remoteDirectory + fileName;

            FileObject localFile = manager.resolveFile(file.getAbsolutePath());
            System.out.println(file.getAbsolutePath());

            FileObject remoteFile = manager.resolveFile(sftpUri, opts);

            remoteFile.copyFrom(localFile, Selectors.SELECT_SELF);
            put = true;

        } catch (Exception ex) {
            ex.printStackTrace();
        } finally {
            manager.close();
        }
        return put;
    }

    public boolean getSFTPFile(String sftpHost, String userID, String password, String remoteDirectory, String localDirectory, String fileName) {

        boolean get = false;
        StandardFileSystemManager manager = new StandardFileSystemManager();

        try {

            manager.init();

            FileSystemOptions opts = new FileSystemOptions();
            SftpFileSystemConfigBuilder.getInstance().setStrictHostKeyChecking(
                    opts, "no");
            SftpFileSystemConfigBuilder.getInstance().setUserDirIsRoot(opts, true);
            SftpFileSystemConfigBuilder.getInstance().setTimeout(opts, 10000);

            String sftpUri = "sftp://" + userID + ":" + password + "@" + sftpHost + "/"
                    + remoteDirectory + fileName;

            String filepath = localDirectory + fileName;
            File file = new File(filepath);
            FileObject localFile = manager.resolveFile(file.getAbsolutePath());

            FileObject remoteFile = manager.resolveFile(sftpUri, opts);

            localFile.copyFrom(remoteFile, Selectors.SELECT_SELF);
            get = true;
        } catch (Exception ex) {
            ex.printStackTrace();
        } finally {
            manager.close();
        }
        return get;
    }

    public boolean deleteSFTFile(String sftpHost, String userID, String password, String remoteDirectory, String fileName) {

        boolean delete = false;
        StandardFileSystemManager manager = new StandardFileSystemManager();

        try {

            manager.init();

            FileSystemOptions opts = new FileSystemOptions();
            SftpFileSystemConfigBuilder.getInstance().setStrictHostKeyChecking(
                    opts, "no");
            SftpFileSystemConfigBuilder.getInstance().setUserDirIsRoot(opts, true);
            SftpFileSystemConfigBuilder.getInstance().setTimeout(opts, 10000);

            String sftpUri = "sftp://" + userID + ":" + password + "@" + sftpHost + "/"
                    + remoteDirectory + fileName;

            FileObject remoteFile = manager.resolveFile(sftpUri, opts);

            if (remoteFile.exists()) {
                if (remoteFile.delete()) {
                    delete = true;
                }
            }

        } catch (Exception ex) {
            ex.printStackTrace();
        } finally {
            manager.close();
        }
        return delete;
    }

    public Collection getSFTPFileList(String sftpHost, String userID, String password, String remoteDirectory) throws FileSystemException {

        Collection fileCollection = new ArrayList();
        StandardFileSystemManager manager = new StandardFileSystemManager();

        FileObject localFileObject = manager.resolveFile("sftp://" + userID + ":" + password + "@" + sftpHost + "/" + remoteDirectory);
        FileObject[] children = localFileObject.getChildren();

        for (int i = 0; i < children.length; i++) {
            fileCollection.add(children[ i].getName().getBaseName());
        }

        return fileCollection;
    }

    public boolean isRemoteFileExist(String sftpHost, String userID, String password, String remoteDirectory, String fileName) {
        StandardFileSystemManager manager = new StandardFileSystemManager();
        boolean isExist = false;

        try {
            manager.init();

            //Setup our SFTP configuration
            FileSystemOptions opts = new FileSystemOptions();
            SftpFileSystemConfigBuilder.getInstance().setStrictHostKeyChecking(
                    opts, "no");
            SftpFileSystemConfigBuilder.getInstance().setUserDirIsRoot(opts, true);
            SftpFileSystemConfigBuilder.getInstance().setTimeout(opts, 10000);

            String sftpUri = "sftp://" + userID + ":" + password + "@" + sftpHost + "/"
                    + remoteDirectory + fileName;

            FileObject remoteFile = manager.resolveFile(sftpUri, opts);

            isExist = remoteFile.exists();

        } catch (Exception e) {
            throw new RuntimeException(e);
        } finally {
            manager.close();
        }
        return isExist;
    }

Password Authenticate with SALT value

In password authentication, most developers use hash value generation. Hash value has a unique value for every word. If two users have same password, both has same hash value for their password. The solution is to generate salt value for password. Before proceeding hash generating, password is appended with salt value. The salt value is not a secret value. For validation, hash value and  salt value must be known from the developer.

Following article for user authentication described clearly with sources..

https://crackstation.net/hashing-security.htm#normalhashing

Cron to STOP/ START Program

In Linux, you can use crontab to stop/ start applications.

 Following shell script (stop.sh) can be used to grep your program & kill it.

#!/bin/bash

PGID=`ps -eaf | grep YourProgram | grep YourName | grep -v grep | awk '{print $2}'`

if [ -n $PGID ]

then 

/bin/kill -9 $PGID

else

echo "Not Running"

fi

After stopping, you can run the following program(start.sh) to restart the application. This will grep to check whether application runs or not. If runs, shell terminates with "Already Running" error. Else, it will run the application with nohup and send a mail to owner using mailx linux API.

#!/bin/bash

PRGHOME=/home/sujith/ReminderSMS

ps –eaf | grep YourProgram| grep YourName|grep -v grep | awk '{print $2}' > /home/ sujith/.tmp.ReminderAlert

if [ -s /home/ sujith/.tmp.ReminderAlert ]

then

echo "Already Running"

else

#. /home/ sujith/.bash_profile

cd $PRGHOME

echo 'program_alert_started' | mailx sujith@test1.lk

nohup java YourProgram &

rm /home/ sujith/.tmp.ReminderAlert

fi