Basics

Create

Create a new branch

$ git checkout -b {new_branch_name}

Commit

Add changes to staging

$ git status

$ git add —all

Commit changes

$ git commit -m ‘users can be added and removed from projects’

OR

$ git commit -am “Refs  #{ticket_number}  #{message}.”

Push changes to remote origin

$ git push origin {branch_name}

Check and pull changes down from master if these are available

Rebase

Rebase to master and squish commits

$ git rebase -i master

Vim Interactive reference:
	insert changes: i,
	write & quit: :wq
		
  If using a ticketing system, add a reference to the ticket:
	Refs #{ticket_number}

Switch to master branch

$ git checkout master

Rebase branch onto master

$ git rebase {branch_name}

Push to origin/master

$ git push

Delete

Delete local branch

$ git branch -D {branch_name}

Delete remote branch

$ git push origin –delete {branch_name}

Deploy

Deploy from master branch

If you’re using capistrano for deployment and it is configured correctly, you can simply run:

$ cap production deploy

This is a descriptive glossary of computer networking terms, explaining individual components and how they fit together, based on recent research and implementations.

Computer Networking

A computer network is a set of computers connected together for the purpose of sharing resources such as a connection to the Internet, a printer or a file server.

Networked computing devices exchange data with each other along network links. An example of networked devices could be a printer and computer which is configured to use the printing service within the same network. Computers which do not have authority to access the printer cannot use it.

Computer network programming involves writing computer programs that enable processes to communicate with each other across a network.

Network Application Programming Interfaces (API)

An Application Programming Interface is a set of routines that an application program uses to request and carry out lower-level services performed by the operating system. Web APIs are a software-to-software interfaces allowing applications to work together without user knowledge

Internet Protocol (IP)

An IP address is a numerical label assigned to each device (e.g., computer, printer) participating in a computer network that uses the Internet Protocol for communication.

Domain

A domain name is an identification string which can be bought via a registry. Domain names follow the rules and procedures of the Domain Name System (DNS). Any name registered in the DNS is a domain name.

Domain Name Servers (DNS)

Domain Name Servers maintain a directory of domain names and translate them to Internet Protocol (IP) addresses. This is necessary because, machines only access websites using IP addresses, whereas people prefer domain names.

DNS Zone

A DNS zone is the part of a domain for which an individual DNS server is responsible. Each zone contains a single SOA record.

DNS Records

DNS records are basically mapping files that tell the DNS server which IP address each domain is associated with, and how to handle requests sent to each domain.

A DNS (Domain NameServer) record (also known as a zone file) is a small set of instructions for resolving specified Internet domain names to the appropriate number form of an Internet Protocol address (an IP address).

A - IPv4 address

CNAME - Canonical Name

MX - Mail Exchanger which controls email routing

NAPTR - pointer?

TXT - Text like comments or untyped info.

AAAA - IPv6 Address

SRV - Services which gives locations of well-known services

Start of Authority (SOA)

Every domain must have an SOA record at the cutover point where the domain is delegated from its parent domain. For example if the domain mycompany.com is delegated to DNSimple’s DNS servers, we must include an SOA record for the name mycompany.com in our authoritative DNS records. We add this record automatically for every domain that is added to DNSimple and we show this record to you as a System Record in your domain’s Manage page.

The SOA record includes the following details:

The primary name server for the domain, which is ns1.dnsimple.com or the first name server in the vanity name server list for vanity name servers.

The responsible party for the domain, which is admin.dnsimple.com.

A timestamp that changes whenever you update your domain.

The number of seconds before the zone should be refreshed.

The number of seconds before a failed refresh should be retried.

The upper limit in seconds before a zone is considered no longer authoritative.

The negative result TTL (for example, how long a resolver should consider a negative result for a subdomain to be valid before retrying).

https://support.dnsimple.com/articles/soa-record/

Name Servers (NS)

A name server is a specialised server on the Internet that handles queries or questions from local and remote hosts, about the location of a domain name’s various services. It translates domain names into IP addresses (or vice versa), enabling you to enter the websites name into the search bar instead of trying to remember an IP address. Name servers also have other uses such as caching answers to queries so that it can answer faster next time and transfering data between your name servers to keep them synchronised.

Hostname

A hostname is a label that is assigned to a device connected to a computer network and that is used to identify the device in various forms of electronic communication.

TTL

Time to live (TTL) is a mechanism that limits the lifespan or lifetime of data in a computer or network. When you change a domain records to point at a different server, the change does not take effect immediately. Instead, it has to propagate throughout the Internet. How long this takes can depend on the current TTL, or Time to Live setting. This is typically measured in seconds, so a TTL of 3600, for example, means it might take up to an hour for the changed to propagate.

*Ref

• https://en.wikipedia.org/wiki/Computer_network
• http://www.networksolutions.com/support/what-is-a-domain-name-server-dns-and-how-does-it-work/
• http://searchnetworking.techtarget.com/definition/time-to-live

What is a Server? This article is going to describe a broad overview of the term ‘server’. There is a range of server types, which do things slightly different to one another but before looking into specialist types, it is vital to understand what a server essentially is and does in the first place.

The term server is used quite broadly in information technology. In theory, any computerised process that shares a resource to one or more client processes is a server.

A server essentially serves up data. What that means is that data (individual pieces of information) is measured, collected and analysed in order for it to be visualised using graphs or images. An example of this is a web server, which serves up scripted HTML, CSS, and Javascript into the web browser in a visual format so that people can view and read it.

There are many other types of server including database server, file server, mail server, print server, game server and application server.

A server can refer to a single mechanism which connects to multiple clients over a network. A small scale example of this is a restaurant who uses a POS or till operating system over a secure network. An individual restaurant might have its own server housing all the information for that particular restaurants transactions. The restaurant might then have 2 or 3 tills (clients) which staff use to run transactions throughout service. The reason that the server and client wouldn’t be run on the same machine is that if a server crashes, everything is lost but if a client crashes, it can be easily replaced and the information remains available on the server.

Generally speaking, a computer primarily designed as a server is specialised in some way for its task and would not be used as a desktop computer. Also, as servers are generally accessed over a network, they often don’t have a monitor, mouse or keyboard anyway.

Massive companies like Google have their own infrastructure and maintain their own servers. Google’s server infrastructure is actually divided into several types. One example is Google’s web server, which runs Google Search Engine, the biggest search engine in the world. When running searches, your personal (client) computer connects to Google (server) via www.google.com (Network). You can see how multiple clients have the ability to connect to the these servers at the same time, each being served only the information they have searched. This particular web servers job is to execute the clients search query and then format the results into an HTML page. This complex example involves querying index servers (a different type of server), merging the result, applying google’s search ranking algorithms, spell checking searches and a range of other processes to complete its task and give each client their individual search results.

Google is a linux based web server. Linux is an open-source operating system modelled on the UNIX system which was originally developed as a free os for personal computers, based on the intel x86 architecture. The Linux Kernel was first released on 5 October 1991 by Linus Torvalds. Linux has since become useable in more hardware platforms than any other operating system out there.

Now days we have a thing called the cloud. The cloud is a network of servers and are not physical machines, they are virtual space. Some cloud servers allow you to store and access data, examples of this can be found in social media applications which make the data you upload available from any device with the correct credentials. While other cloud servers provide an online service, such as Rackspace, Oracle, AWS where you pay a subscription fee for the use of their services. The benefits of cloud storage are predominantly cost driven as you no longer have to pay for hardware, hardware maintenance and upgrades, and you only pay for the space that you actually use.

References:

• https://en.wikipedia.org/wiki/Google_platform
• http://techterms.com/definition/server
• http://www.teach-ict.com/technology_explained/server/server.html
• http://computer.howstuffworks.com/web-server.htm
• http://www.interoute.com/what-are-cloud-servers
• http://mashable.com/2013/08/26/what-is-the-cloud/#VCRrl7Q2wkqc
• http://www.explainthatstuff.com/cloud-computing-introduction.html

Not that I’m not a windows fan but I am interested to understand how operating systems differ and see them in action so I have written this simple tutorial to create, move and destroy directories with command line for windows..

This article describes how to use command line with windows to create a new dir with a new .txt file, rename the file,  edit and display file contents. Remove the file and remove the dir open  your cmd.

1. Press the following keys on your keyboard to open the command line prompt:

window key & R

2. Create a new dir

$ mkdir WindowsLearn

Your new directory already contains 2x files

3. Create a new empty text file

$ echo. 2>EmptyFile.txt

4. ren  or rename = Rename your file

$ ren EmptyFile.txt SelenasFile.txt

Follow the dir path to find your new file and edit it

5. Display the content of you .txt file in terminal

$ SelenasFile

6. Delete your file

$ erase SelenasFile.txt

7. Delete your dir

$ cd .. (to go back one dir)

$ rd WindowsLearn

The following article, assisted with representational diagrams, describes in simple terms what a linked list is and the data structures which create them.

A linked list is the simplest and most common form of data structure. It consists of a group of nodes which, together represent a sequence.

Fig 1: Single linked list

Each node is composed of 2 elements: data and a reference or link t o the next node in the sequence.

Fig 2: Data structure

This allows for efficient insertion and removal of elements from any position in the sequence. All that is required is a new node-link combo and a link redirection.

Fig 3: Representation of node insertion

Fig 4: Representation of node removal

Because data items don’t need to be stored in continuous memory, list insertion and removal does not require relocation or reorganisation of the entire structure.

Also, insertion and removal of elements can occur at any point on the list and a with a constant number of operations (if previous link is maintained)

A double linked list is slightly more complex and is made up of nodes, composed of 3 elements: data and two links which point to the next and previous node in the sequence.

Fig 5: Double linked list

This tutorial will explain how to use command line basics for beginners with mac os x, including examples of creating and destroying directories and files.

1. Hold down command and press space to get a spotlight search bar in the top right of your screen.

2. Type the word terminal to find your terminal and open a new window

A terminal window will tell you in the first line when your last login was and which directory you are in (dir). A terminal or unix shell is the default command line interpreter on linux and mac osx. Command line comprises of communications between the user and their computer. By executing commands (typing them out and pressing enter) you can create new folders and files, maintain your digital library and documents, and run programs.

3. To see what’s in the home dir, type ‘ls’ and press enter. This shows a list of all directories available

$ ls

4. To create a new dir (within the home dir), execute ‘mkdir TEST’

(make directory TEST, the directory name is case sensitive)

$ mkdir TEST

5. Execute ‘ls’. You should see the list of current dirs, including the new TEST dir you have just created.

$ ls

6. To move into the new dir, execute ‘cd TEST’. You will see that the bash shell dir has changed to ‘TEST’

$ cd TEST

7. To create a new text file in the TEST directory, execute ‘touch second_test.doc’.

$ touch second_test.doc

8. Execute ‘ls’ to see the contents of the TEST dir, including the new second_test.doc document file you have just created.

9. Now create a new dir called ‘ThirdTest’ (reference steps 4-5)

$ mkdir ThirdTest

10. Cd into the new dir by typing ‘cd Th’ and then pressing ‘tab’. Tab will auto complete dir and file names within your current location.

11. To iterate through previous commands, press the up arrow and execute (press enter) when you get to the one that you’re looking for. Try this method to view the contents of your current location. You’ll notice the dir is currently empty.

12. To move back to the previous dir, type ‘cd ..’

$ cd ..

13. Again, execute ‘ls’ to view the folders contents

14. To rename a file, you can type ‘mv oldfielname newfilename’. Change the name of the second_test.doc file to test2.doc by executing ‘mv second_test.doc test2.doc ‘. Execute ‘ls’ to see the file name has changed

$ mv second_test.doc test2.doc

15. To delete a file, you can type ‘rm filename’. Execute ‘rm test2’, and then ‘ls’ to see the current dir’s new contents

$ rm test2.doc

16. To delete a dir, you can type ‘rmdir dirname’. Execute ‘rmdir TestThree’, and execute ‘ls’ to see the current dir’s new contents. It should now be empty.

$ rmdir ThirdTest

A binary number is a sequence of bits. Bits can either be on or off (1 or 0). If one bit in a binary code is switched from ‘on’ to ‘off’, it can affect the overall result of whole the code. Learn how to represent numbers in binary and understand what that means.

Binary numbers can be worked out by adding the sum of what each bit represents. Each ‘1’ bit represents a power of 2, and each ‘0’ bit represents 0.

While 4 bits make up one nybble of data, 8 bits typically make up one byte and usually represent a letter.

One full byte of data is the sum of 255

Words are often represented with 16 – 32 bits. The word ‘hello’ can be represented as 01001000-01000101-01001100-01001100-0100111

Two’s compliment is the negative notation of the binary representation of an integer and is the way every computer chooses to represent it’s integers. If the left-most bit in a piece of binary is ‘1’ then the number represented will be negative, if the left-most bit is ‘0’ then the number will be positive.

Key Sources:

• https://en.wikipedia.org/wiki/Binary_number
• http://www.mycomputeraid.com/networking-support/general-networking-support/howto-read-binary-basics/