Calculate mid value in indexes/number

If value of start and end are max. range of integer. 

So, by adding these 2 it will give Exception: java: integer number too large.

Hence, using 2nd approach this problem will not come.

// avoid using below thing
int mid = (start + end) / 2;

// correct approach
int mid = start + ((end - start) / 2);

Calculate length/number of digits in a Number

int n=12345;

int number_of_digits = (int)Math.log10(n)+1;

GCD/HCF and LCM

 Euclidean Theorm: gcd (a, b) = gcd (b, a % b)

HCF * LCM = a * b

public class GCD_LCM {
    public static void main(String[] args) {
        int a = 36;
        int b = 24;

        int original_a = a, original_b = b;
        while (b > 0) {
            int rem = a % b;
            a = b;
            b = rem;
        }

        System.out.println("HCF: " + a);

        System.out.println("LCM: " + original_a * original_b / a);


    }
}

Run Executable JAR in background on Linux

Nohup means, no hang up. 

The nohup utility makes the command passed as an argument run in the background even after you log out.

After the command is run, it is the foreground process

• nohup java -jar xxx.jar

& Let the program run in the background

• java -jar xxx.jar &

 

Processing of log files

The command will generate one by default nohup.out, file to log, standard output and error output will be in this file.

nohup.out file can be accessed using the below-mentioned command:

• tail –f nohup.out

 

 

Resources:

·        https://developpaper.com/nohup-and-let-the-program-run-in-the-background/#:~:text=use%20nohup%20java%20%2Djar%20xxx,you%20specify%20%3E%20Specify%20your%20file.

Docker: Copy file from Server to Docker Container and vice versa

The docker cp utility copies the contents of SRC_PATH to the DEST_PATH. You can copy from the container’s file system to the local machine or the reverse, from the local filesystem to the container. 

The docker cp command assumes container paths are relative to the container’s / (root) directory. This means supplying the initial forward slash is optional;

Below mentioned commands are treated as identical:

• myContainer:/tmp/myFile.txt
• myContainer:tmp/myFile.txt

Local machine paths can be an absolute or relative value.

The command interprets a local machine’s relative paths as relative to the current working directory where docker cp is run.

 

Copying Remote Server File to Docker Container:

docker cp [source_pathOfFile_RemoteServer] [docker_containerName]:[destination_path_dockerContainer] 

docker cp /tmp/myFile.xls myContainer:/tmp/

 

Copying Docker Container File to Remote Server:

docker cp [docker_containerName]:[sourcepathOfFile_dockerContainer] [destination_pathOfFile_RemoteServer] 

docker cp myContainer:/tmp/myFile.xls  /tmp/myFile.xls 

 

Note: These commands need to be executed from Remote Server on which docker is installed and any docker container is up and running.

          

 

Resources:

·         https://docs.docker.com/engine/reference/commandline/cp/ 

 

 

Linux: SCP Command to Securely Transfer Files

SCP (secure copy) is a command-line utility that allows you to securely copy files and directories between two locations.

With scp, you can copy a file or directory:

• From your local system to a remote system.
• From a remote system to your local system.
• Between two remote systems from your local system.

It uses the same authentication and security as it is used in the Secure Shell (SSH) protocol

 

Before you Begin

The scp command relies on ssh for data transfer, so it requires an ssh key or password to authenticate on the remote systems.

The colon (:) is how scp distinguish between local and remote locations.

To be able to copy files, you must have at least read permissions on the source file and write permission on the target system.

Be careful when copying files that share the same name and location on both systems, scp will overwrite files without warning.

 

Copying Local File to Remote System:

scp [source_file_path_LOCAL] [user]@[Destination_Host_IP]:[destination_file_path_REMOTE]

scp C:\Prabhat\fileName.xls prabhatk@10.10.0.2:/tmp/

 

Copying Remote File to Local System: 

scp [user]@[Destination_Host_IP]:[source_file_path_REMOTE] [destination_file_path_LOCAL]

scp prabhatk@10.10.0.2:/tmp/ fileName.xls C:\Prabhat\

 

Note: These commands need to be executed from Local System to perform above operation.

 

 

 

Resources:

·         https://linuxize.com/post/how-to-use-scp-command-to-securely-transfer-files/ 

·         https://www.geeksforgeeks.org/scp-command-in-linux-with-examples/