## Posts

### A New Era of Spaceflight is Set to Begin | NASA

On May 27, NASA will launch their first flight with astronauts to the International Space Station from U.S. soil in nearly 10 years. This mission is the first launch of American astronauts aboard an American rocket and spacecraft as part of their Commercial Crew Program.
NASA astronauts Bob Behnken and Doug Hurley will fly on SpaceX’s Crew Dragon spacecraft, lifting off on a Falcon 9 rocket from Kennedy Space Center in Florida, for an extended stay at the space station for the Demo-2 mission. The specific duration of the mission is to be determined.
As the final flight test for SpaceX, this mission will validate the company’s crew transportation system, including the launch pad, rocket, spacecraft, and operational capabilities. This also will be the first time NASA astronauts will test the spacecraft systems in orbit.
Behnken and Hurley were among the first astronauts to begin working and training on SpaceX’s next-generation human space vehicle and were selected for their extensive test …
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### Mathematics for Computer Scientists | Integers

NumbersDefendit numerus: There is safety in numbers
We begin by talking about numbers. This may seen rather elementary but is does set the scene and introduce a lot of notation. In addition much of what follows is important in computing. Integers I will assume you are familiar with the integers. 1,2,3,4,. . .,101,102, . . . , n, . . . , 2^32582657 − 1, . . . sometime called the whole numbers. These are just the numbers we use for count- ing. To these integers we add the zero, 0, defined as: 0 + any integer n = 0 + n = n + 0 = n Once we have the integers and zero mathematicians create negative integers by defining (−n) as: the number which when added to n gives zero, so n + (−n) = (−n) + n = 0. Eventually we get fed up with writing n+(−n) = 0 and write this as n−n = 0. We have now got the positive and negative integers {. . . , −3, −2, −1, 0, 1, 2, 3, 4, . . .} You are probably used to arithmetic with integers which follows simple rules. To be on the safe side we itemize them, so for i…

### BASH | VARIABLES | LINUX SERIES

Create a new file called hello.sh with the following content and give it executable permissions with chmod +x hello.sh

Execute/Run via: ./hello.sh

#!/usr/bin/env bash
# Note that spaces cannot be used around the `=` assignment operator
whom_variable="World"
# Use printf to safely output the data
printf "Hello, %s\n" "\$whom_variable"

#> Hello, World

This will print Hello, World to standard output when executed.
To tell bash where the script is you need to be very specific, by pointing it to the containing directory, normally with ./ if it is your working directory, where . is an alias to the current directory. If you do not specify the directory, bash tries to locate the script in one of the directories contained in the \$PATH environment variable.

The following code accepts an argument \$1 , which is the first command line argument, and outputs it in a formatted string, following Hello, .
Execute/Run via: ./hello.sh World

#!/usr/bin/env bash
printf "Hello, %s\n…

### BASH | INTRO | LINUX SERIES

GNU Bash or simply Bash is a Unix shell and command language written by Brian Fox for the GNU Project as a free software replacement for the Bourne shell. First released in 1989, it has been used widely as the default login shell for most Linux distributions and Apple's macOS Mojave and earlier versionsInteractive ShellThe Bash shell is commonly used interactively:
It lets you enter and edit commands, then executes them when you press the Return key. Many Unix-based and Unix-like operating systems use Bash as their default shell (notably Linux and macOS). The terminal automatically enters an interactive Bash shell process on startup.
Output Hello World by typing the following:

echo "Hello World"
#> Hello World # Output Example

Non-Interactive ShellThe Bash shell can also be run non-interactively from a script, making the shell require no human interaction. Interactive behavior and scripted behavior should be identical – an important design consideration of Unix V7 Bourne s…

### FILE COMPRESSION WITH 'tar' COMMAND | LINUX SERIES

File Compression with 'tar' command:Common Options -c --create
Create a new archive.

-x --extract
Extract files from an archive.

-t --list
List the contents of an archive.

-f --file=ARCHIVE
Use archive file or dir ARCHIVE.

-v --verbose
Verbosely list files processed.
Compression Options - -a --auto-compress
Use archive suffix to determine the compression program.

-j --bzip2
Filter the archive through bzip2.

-J --xz --lzma
Filter the archive through xz.

-z --gzip
Filter the archive through gzip.
Compress a folderThis creates a simple archive of a folder : tar -cf ./my-archive.tar ./my-folder/
Verbose output shows which files and directories are added to the archive, use the -v option: tar -cvf ./my-archive.tar ./my-folder/
For archiving a folder compressed 'gzip', you have to use the -z option : tar -czf ./my-archive.tar.gz ./my-folder/
You can instead compress the archive with 'bzip2', by using the -j option: tar -cjf ./my-archive.tar.bz2 ./my-folder/
Or compress with 'xz&…

### INSTALLING DATABASE SERVERS ON UBUNTU ® | LINUX SERIES

Database servers are used mainly to store databases and keep data into it in collaboration
with application or web application servers.

The most famous database servers are:
MySQL and Oracle DB 12c

INSTALLING AND CONFIGURING MYSQL SERVER
To install MySQL server, you will need to run the following command: sudo apt-get install mysql-server

Some other people install maria db package and this will be done using the following command: sudo apt-get install maria-db
Then for security reasons, you may run the following command to get your server up and running securely: mysql_secure_install
The last thing, we need to install is oracle 12c database server express edition. INSTALLING AND CONFIGURING ORACLE DATABASE SERVER12C EXPRESS EDITION
Oracle Database Server 12c Express Edition is one of the mostly highly ranked database server in 2017 and it acts exactly as the data container that holds applications or web applications data.

### INSTALLING WEB SERVERS ON UBUNTU® | LINUX SERIES

Web server is a kind of a container that contains a web application programmed by software
and web application programmer and the web application performs all of its functionality
using the web server.
INSTALLING GLASSFISH SERVER ON UBUNTU ®
First, let us get to install glassfish server as one of the most popular web application servers for java programming language as follows:
sudo apt-get update
sudo apt-get install default-jdk