Assignment given by the mentor to explain the given terms with minimum 2 lines.
1. touch : It is used to modify the 'access time' & 'modification time'. To modify only "access time" use "-a" option and to modify only "modification time" use "-m". If a file doesn't exist it creates a new file with that name. So, touch command can be used to create a new file.
touch filename #creates a new file, if doesn't exist
touch -a filename # modify only the access time
touch -m filename # modify only the modification time
touch -c filename # prevent creation of new file, if it doesn't exists2. mkdir : It is used to create a new "directory" (folder). you can pass in -p option to create whole path, if the parent folder doesn't exists.
mkdir foldername # creates a new folder/directory
mkdir -p parentfolder/childfolder # create folder 'parentfolder' if it doesn't exits.3. cd : cd (change directory ) is used to switch between directories. cd .. will take you to one directory up. cd - will take you previous directory that you came from. ~ represents home directory. So, **cd ~** will take you to home directory.
# consider structure ~/homework/math/, you are in ~(home)
cd homework # get into homework folder
cd math # get into math folder
cd .. # go one directory up i.e. homework
cd - # takes you to last directory you were in i.e. math4. rm : It is a command to remove file and folder. Once the file is deleted. you cannot easily recover the file. To remove folders you can -d option. To delete the write protected files it will ask for you prompt and to avoid prompt use -f option and to delete files recursively use -r option. Use option -i for prompt to appear before delete a file.
NOTE: NEVER use rm -rf in home directory with ROOT permissions.
# delete using rm command
rm homework.md # delete the file
rm file.txt file2.txt # delete multiple files.
rm -i fib.py # to ask before deleting. (prompt) hit 'y' to delete
rm -d folder # delete folders
rm -rf node_modules # delete files recursively and force fully5. mv : It is used to move files and rename files. You can move multiples files to directory. to move files/folders you have first specify source and then destination. you can take backup before overwriting a files using -b option.
mv source_folder destination_folder # move the folder to a new folder
mv oldname.txt newname.txt # rename using mv command
mv file1.txt file3.txt file2.txt dest_folder # move multiple files to a folder.
mv file1.txt another_folder/file1.txt # overwrite to a file.
mv -b file1.txt file2.txt # backup of file1.txt will created before overwriting(renaming) to file2.txt
mv -S .bak -b file1.txt file2.txt # -S to specify the extension of the backup file that you want.
6. ls : used to list the files and directories in the current directory. -a lists all the files and folder i.e. hidden files and folder too. -h lists file sizes in human readable format. -F appends / at the end of the directories. -R lists files recursively inside all sub-directories (returns a very long list). -ltr option will list latest files first. -S list files according to size in descending order.
ls # lists files and folders inside the current folder
ls -l # list files and folder with size, permission and other details
ls -a server_files # list all (including hidden ones) files and folder in the given folder
ls -lh # -h option will display size in human readable form.
ls -F # appends "/" at the end of folder names while listing
ls -R # -R list all the files and folders inside the "sub-directories" inside the current folder.
ls -ltr # lists all the files in reverse time order (latest first) -r option to display in reverse.
ls -lS # -S with l with display size in descending order(biggest first)7. cp: used to copy files and folder. Use -R option to copy directory to another directory. cp takes source and destination file/folder as arguments. use --preserve option lets you preserve the file attributes like permissions, groups and user ownerships. -v prints out the files being copied currently to the stdout. -b Option to create backups before overwriting. -i option to ask before overwrite.
cp -R source_folder destination_folder # copy the source folder to a destination folder
cp oldfile.txt anotherfile.txt # copy using cp command
cp -i file1.txt file3.txt # ask before overwrite a file, hit y to proceed .
cp -v file1.txt another_folder/file1.txt # display which file is being copied now.
cp -b file1.txt file2.txt # backup of file1.txt will created before overwriting(renaming) to file2.txt
cp -S .bak -b file1.txt file2.txt # -S to specify the extension of the backup file that you want.
8. pwd: displays the current working directory. -P option shows the physical links rather than symbolic links
pwd # display the (whole path) current working directory.
/home/mohammed/.zsh # output
pwd -P # Shows the physical location rather symbolic link
/home/mohammed/dotfiles/zsh
9. cat: used to display the contents of the file, concatinate files and redirect the ouput of the file.
cat file1.txt # displays the content of the file stdout(terminal)
cat file1.txt file2.txt > file3.txt # moves the contents file1.txt & file2.txt to new file3.txt
cat file1.txt file3.txt >> file2.txt # concat the file1.txt file3.txt an "existing" file3.
cat file1.txt file1.txt | sort > file3.txt # combine both files and sort the content in alphabetically and store to file3.txt.
10. nano: It is a light-weight text editor. nano "filename" to open a file. ctrl + o to save and ctrl + x to exit.
nano file1.txt # open the file in the nano editor.1. clear: used to clear the terminal screen, you can access the previous content by scrolling up.
clear # clear the terminal screen2. sudo: stands for "SuperUser Do". Lets you run any command with Admin (super User) privileges. Think twice before, running rm -rf with sudo
sudo sh run_package.sh # run script with super user privileges.3. history: it gives you the list of previous 500 commands (number depends on your config) ran in your terminal.
history # list 500 previous commands
history 25 # list 25 previous commands
histroy | tail # list 25 previous commands4. tar: it is used to compress and uncompress files. It supports formats like tar, tar.gz and tar.bz2. -c lets you create compressed file. -x, for uncompressing the file. It requires a f paramater to pass the file.
tar -cvf source_file.tar /home/source_file # -c :create file, v-verbose, f- filename - create a source_file in current directory
tar -cvzf source_file.tar /home/source_file # create gz file using z option
tar -xvf file.tar # extract the file. notice -x to extract
tar -tvf test_file.tar.gz # list the files in zip.
5. uname: show the information about the system your Linux/unix distro is running. uname -a prints the information like kernel release date, version, processor type, etc.
uname # just the distribution name
uname -a # kernel release date, version, processor type, etc.6. chmod: chmod is used to change the permissions of the file. you can change using octal values and using ugo (user, group others) + permission( rx or just x). Octal values are 4 - read, 2 - write, 1 - execute. So, we take the combination for read, write and execute 7. We take the sum of the values for each group
chmod 754 run_package.sh # user = 7 (rwx), group= 5(rx) & others = read (r)
chmod + x run_package.sh # add executable permission to all i.e ugo
chmod u+x run_package.sh # add execution perm to only user.
chmod u=rwx, g=rx, o=r run_package.sh #another way of giving permissions.7. hostname: It display the hostname. hostname -f newhostname to change the hostname (sudo perm required.). Paramters differ for mac and linux
hostname # display hostname
sudo hostname -f newhostname
hostname -s # display shortname, if any
8. top: It displays all currently-running processes and their owners, memory usage, and lots of other details.
top # display process detail9. echo: echo command is used to display the contents of evironment variables and display the passed text. echo * will work as ls command. echo can be used to fill in the text into a file.
echo $PATH # display Path env
echo * # works as ls command
echo some random line # displays 'some random line'
echo insert your line > test.txt # write term 'insert your line' to test.txt10. head: shows the first 10 lines of the file. with option -n no-of-lines will display the required lines. you pass in multiples files too.
head test.txt # display first 10 lines
head -n 20 test.txt # display first 20 lines
head test.txt config.txt # display 10 lines each from these files with headers to specify.1. ping : sends ICMP (Internet Control Protocol) echo request packages to the destination IP (server). You can use it check if you internet is workign or the remote destination is working.
ping 8.8.8.8 # ping google dns to check if you internet is working
ping your-website.com # to check if your server is up or not.2. ping : sends ICMP (Internet Control Protocol) echo request packages to the destination IP (server). You can use it check if you internet is workign or the remote destination is working.
ping 8.8.8.8 # ping google dns to check if you internet is working
ping your-website.com # to check if your server is up or not.3. traceroute : It is used to trace the route taken to network host.
traceroute facebook.com # trace the route taken to reach the domain facebook.com4. nslookup : used to query the Internet domain name servers. nslookup domain-name.com, checks if given domain name exists or not.
nslookup i-made-thatup.com # checks if the domain exists or not
"** server can't find i-made-thatup.com: NXDOMAIN" # output5. netstat : allows you a simple way to review each of your network connections and open sockets. It is helpful while performing web server troubleshooting.
netstat # displays protocol, ports information6. scp : allows you to copy files to and from another host in the network. This is useful when you are deploying application to you webserver.. -c to enable compression and 6 forces scp to use IPv6. 4 forces to scp to use IPv4.
scp $configure.sh user@targethost:/$path7. w : prints the summary of the current activity on the sysmtem, which includes what each user is doing, and their process plus list all logged in users and system load for 1, 5 and 15 minutes
w # display information
22:06 up 4 days, 26 mins, 6 users, load averages: 1.87 1.67 1.62
USER TTY FROM LOGIN@ IDLE WHAT
mohammed console - Wed21 4days -
mohammed s000 - Fri14 1day -zsh
mohammed s001 - Wed22 27:36 node /Users/mohammed/Documents
mohammed s002 - Sat11 27:00 -zsh
mohammed s003 - Sat18 - w
mohammed s004 - 21:46 3 -zsh8. whois : displays whois information about the given domain-name like registrar, name servers and so on
whois google.com9. tcpdump : allows you to capture and analyze network traffic going through your system. Often used to help troubleshoot network issues, as well security tool.
sudo tcpdump -D # lists the interfaces available for capture.
sudo tcpdump -i any # start capturing packets10. wget : used to downloading files from internet. It supports downloading multiples files, download resume and limiting bandwidth used for downloads.
wget http://archlinux.mirrors.uk2.net/iso/2016.09.03/archlinux-2016.09.03-dual.iso # download the iso files
wget -c http://archlinux.mirrors.uk2.net/iso/2016.09.03/archlinux-2016.09.03-dual.iso # resumes download if started again at same directory.1. git init : creates an empty git reposistory or reinitializes an existing one. There is ".git" folder created in the initialized directory.
git init # initilize a git repo.
2. git add : add files to staging area before committing. git add filename to file staging area. -u option adds the change of the tracked files and not the changes of new file (unstaged). -A option adds all changes to staging area (including new files i.e. unstaged).
git add server.py # add server.py to staging area.
git add -u # add changes of staged files only, ignore new files
git add -A # add all changes including new files and deletion of files.3. git status : shows the status of the tree like files in staging area, unstaged files, untracked files and also commits behind or forward by remote origin. -s shows the status in short form.
git status # shows the status of working tree
git status -s # show in short form
git status --show-stash # show status of stash as well.4. git push : push the files to remote repository. -u option to set upstream. -f push the files by force i.e by overwriting the refs.
git push # push the files remote repo
git push -u origin master # set the upstream to master branch of origin
git push -f # push files to remote repo by force i.e. overwriting refs5. git reset : remove the files from staging area. if you specify filename or multiple files then, it removes those files from staging area. --hard option removes files from staging area and discards the changes made after the last commit.
git reset # removes files from staging area.
git reset server.py # remove server.py from staging area.
git reset --hard server.py # remove server.py from staging area and discard all changes after prevous commit.6. git commit : commit the changes in the staging area. it takes -m takes a commit message. It opens a nano/vi editor to add a commit message.
git commit -m 'commit message' # commit
git commit # opens your default git text editor to add msg7. git stash : adds your changes (staged and unstaged) to stash and gives you clean working directory. --save option takes a name to save with. apply option applies the changes from the stash stack i.e. on the top of stack. list options lists all the stash in the stack.
git stash # stash all the changes to stash 'stack'
git stash --save 'fix: incorrect followr count' # save to stash with a name
git stash list # list all the stash saved in the stack
git stash apply # apply the changes from the stash to the working directory (a stash from top of the stack) when no stash-name is given.8. git pull : pull the changes from remote repo to local repo. It is required to pull before pushing to remote repo.
git pull # pull from remote repo.9. git cherry-pick : choose a commit from another branch and add it your branch and commit. It takes commit hash i.e atleast 4 characters.
git cherry-pick 1cb2fG # cherry-pick commit with given hash10. git merge : used to merge a given branch name to current branch. i.e all the changes (commits) from merged branch. This creates a new merge commit.
git merge another-branch # cherry-pick commit with given hashDatabase - It is an organized collection of data. Complex databases are developed using 'design and modelling' techniques.
SQL Database - SQL stands for Structured Query language, used for query, manipulate and define data. It is a relational database - a type of database that stores and datapoints access that are related to one another.
NoSQL Database - It is a non-relational database that does not require fixed schema, avoid joins and is easy to scale. Read is faster in case of NoSQL database. One such example would be MongoDB.
1. MySQL server - It is a relational database. Most popular for web applications. It's a freeware, with frequent security and feature updates.
2. PostGresSQL - Relational Database, frequently used for web databases. Allows user to manage both structured and unstructured data. Can be hosted at number of enivronments.
3. Microsoft SQL Server - SQL database engine built by Microsoft. Works on both cloud-based servers and local servers. Provides features like dynamic data masking (only authorized users can see sensitive info). Ideal for organizations that use microsoft products. pricing wise only few organizations can afford.
4. MongoDB - non relational Database that supports JSON. Data of any structure can be stored and accessed quickly and easily. schema can be written without downtime.
5. MariaDB - originally forked from Mysql. It is highly compatible with MySql. gives variety of storage engines to choose from. Fairley new compared to Mysql DB.
6. SAP HANA - database engine by SAP that is column-oriented and can handle SAP and non SAP data. Supports SQL. Pricing is high.
7. Oracle Database - very first database engine to be developed and is relational. Oracle tends to set the bar for other databases. requires resources once installed. Pricing let's only few orgs use it.
8. DB2 - database developed by IBM, has NoSQL capabalities. It can read JSON and XML Files. Ideal for Large organizations.
9. Cassandra - NoSQL database engine by Apache, which is distributed, column wide store, with no single point of failure and high availability.
10. Redis - it is an open source database, with im-memory data structure store. Can be used database, cache and message broker.
ACID refers to the four key properties of a transaction: atomicity, consistency, isolation, and durability.
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Atomicity : All changes to data are performed as if they are a single operation. For example, in an application that transfers funds from one account to another, the atomicity property ensures that, if a debit is made successfully from one account, the corresponding credit is made to the other account.
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Consistency : Data is in consistent state when a transaction starts and when it ends.
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Isolation : the intermediate state of a transaction is invisible to other transations. As a result, transaction that run concurrently appear to be serialized.
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Durability : After a transaction successfully completes, changes to data persist and are not undone, even in the event of a system failure.
Aggregations is a process in which a single entity alone is not able to make sense in relationship so the relationship of two entities acts as one entity.
for Example, Manager manages Project or Employees doesn't makes sense. He has to manage both employees and work on project too. so both, enties - project and employees defin the relationship with manager.
Joins is a clause in SQL that lets combine columns while querying the data. Joins correspond to operation in relational algebra. inner join, outer join, cross join are the types of joins.
CAP theorem is a tool used to makes system designers aware of the trade-offs while designing networked shared-data systems.
The theorem states that networked shared-data systems can only guarantee two of the following three properties:
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Consistency - A guarantee that every node in a distributed cluster returns the same, most recent, successful write. Consistency refers to every client having the same view of data.
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Availabilty - Every non-failing node returns a response for all read and write request in a resonable amount of time.
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Partition Tolerant - The system continues to function and upholds its consistency guarantees in spite of network partitions.
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So, it possible to have two at a time i.e. CP (Consistent and Partition Tolerant) or CA Consistent and Available) or AP (Available and Partition Tolerant)
It is the process of reducing the redundancy of data in the table and also improving the data integrity. There are various database normalization rules like 1NF, 2NF and so on.
Sharding is a database Architechture pattern related to horizontal partitioning -- the practice of separating one table’s rows into multiple different tables, known as partitions.
Each partition has the same schema and columns, but also entirely different rows.
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Physical (Layer 1): responsible for transmission and reception of unstructured raw data between device and physical trasmission medium. Layers converts digital bits into electrical, radio or optical signals.
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Data Link (Layer 2) : The data link layer provides node-to-node data transfer - a link between two directly connected nodes. It detects and possibly corrects errors that may occur in the physical layer.
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Network (Layer 3): layer provides the functional and procedural means of transferring variable length of data sequences (called packets) from one node to another connected in different networks.
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Transport (Layer 4) - layer provides the functional and procedural means of transferring variable-length data sequences from a source to a destination host, while maintaining the quality of service functions.
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Session (Layer 5) - layer controls the connections between computers. It establishes, manages and terminates the connections between local and remote application.
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Presentation (Layer 6) - layer provides independence from data representation by translating between application and network formats. The presentation layer transforms data into the form that the application accepts.
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Application (Layer 7) - layer closest to the end user, which means both OSI application layer and user interact directly with software application. This layer interacts with software applications that implement a communicating component.
Request-response protocal is basic method that computers use to communicate, in which the sender(client computer) requests for data and the second (server) responds to the request.
API - kind of interface which has set of functions that allow programmers to access specific features or data of an application or other services.
Web API is an API that on Web and uses HTTP protocol.
API that follows the following rules:
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Client Server Architecture - separating client and server constraints, which allows them to evolve independently.
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Statelessness - NO client context being stored on the server between requests. Each request from any client contains all the information necessary to service the request, and the session state is held in the client.
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Cacheability - clients and intermediaries can cache responses. Response must specify (explicitly or implicitly) that if it is cacheable or not, to prevent client from getting stale response. Well-managed caching partially or completely eliminates some client-server interactions, further improving scalability and performance.
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Layered system - A client cannot ordinarily tell whether it is connected directly to the end server, or to an intermediary along the way. This means that the client doesn't know if it's talking with an intermediate or the actual server.
HTTP status codes are issued by server in respose to client's request and they have a meaning for each status code like 200 for success, 404 for resource not found.
Hypertext Markup Language (HTML) is the standard markup language for documents designed to be displayed in a web browser.
The term Box Model refers to a box that wrap around every html element. It consists of margin, borders, padding and the actual content
Area outside the border of an HTML element. It is transparent. You can specify for four corners i.e. top, bottom, right and left.
Area between border and actaul content of an HTML element. It is transparent. You can specify for four corners i.e. top, bottom, right and left.
Used to select the content you want to style. Selectors are the part of CSS rule set. CSS selectors select HTML elements according to its id, class, type, attribute etc.
CSS Specificity is the set of the rules applied to CSS selectors in order to determine which style is applied to an element.
Highest specificity to Lowest sepcificity
Style attribute > ID > class, pseduo-class, attribute > Elements
Flexbox is layout model in css that let's you arrange (style) elements in easier way. It is one-dimensional
The CSS Grid Layout Module offers a grid-based layout system, with rows and columns, making it easier to design web pages without having to use floats and positioning.
Git is a distributed version-control system for tracking changes in source code during software development.
HTTP stands for Hyper Text Transfer Protocol, used for communicating between computers over web.
Communication between client computers and web servers is done by sending HTTP Requests and receiving HTTP Responses
TCP (Transmission Control Protocol) is a standard that defines how to establish and maintain a network conversation through which application programs can exchange data.
UDP is a communication protocol used across the Internet for especially time-sensitive transmissions such as video playback or DNS lookups.
Web sever can be reffered to both software or hardware that satisfies the criteria of (serve clients) World Wide web client requests.
A static web server, consists of a computer (hardware) with an HTTP server(software) that sends its hosted files as-is to the web browser.
A static server with some extra software. Application server updates the hosted files before sending them over to the browser.
Domain name system maps the "name" of the domain to the corresponding ip address of the server. DNS sever is the server that hosts this DNS system.
A database server is a server which uses a database application that provides database services to other computer programs.
Computer programs that can work offline, i.e. does not necessarily require network connection to function
Model View Controller is a software design pattern commonly used for developing user interfaces which divides the related program logic into three interconnected components.
Operating System is a system software that manages computer hardware, software resources and provides common services for computer programs. It is an interface between user and computer hardware.
Kernel is a computer program that is the core part of an operating system. It has complete control over the system.
Process is an instance of computer program that is being executed by one or more threads.
Thread (of execution) is way for program to split themselves in two or more simultaneously running tasks. You can say, thread is a light weight version of process. one or threads are present in a process.
SOLID is an Acronym for Five Object-oriented Design Principles by Robert C Martin.
- S - Single-responsiblity principle
- O - Open-closed Principle
- L - Liskov Substitution Principle
- I - Interface Segregation Principle
- D - Dependency Inversion Principle
Apache is most widely used web server software. a Server that run this software is called Apache web server.
Nginx is web server software, which known for its high perfomance and scalibilty. It is opensource, comes bundled many other things like reverse proxy etc.
Messaging Queue allows application to communicate by sending messages to each other. The message queue stores messages when the destination program is busy or not connected.
a communication system between mutually interacting software applications in service-oriented architecture.
RabbitMQ is a message-queueing software also known as a message broker or queue manager. It is a software where queues are defined, to which applications connect in order to transfer a message or messages.
It is sofware used to process the streaming data. It is developed LinkedIn and donated to Apache. It has high-throughput and low latency for handling real-time data feeds.
Apache Zookeeper is distributed coordination service that lets you manage a large sets of hosts like maintaining configuration of all systems at one place.
a style of software design where services are provided to other components by application components, through a communication protocol over a network.
an architectural style that structures an application as a collection of small autonomous services, modeled around a business domain.
Redis is an in-memory data structure store, used as a database, cache and message broker.
Why?
Because, It is NoSQL database, which is fast to read. Caching mechanism makes it much more faster.
Solr is an enterprise-search platform. Features include full-text search, hit highlighting etc.
Why?Elasticsearch is a highly scalable open-source full-text search and analytics engine. It allows you to store, search, and analyze big volumes of data quickly and in near real time.
because, database does't usually have wildcard based search system. Solr provides full text search and it is very fast.
Elasticsearch is a highly scalable full-text search and analytics engine. It allows you to store, search, and analyze big volumes of data quickly, which is near to real time.
Why? Elasticsearch speaks JSON, if you use JSON all around then it is a good choice.
Celery is Python task Queue system that handles distrubution of task across workers or a network. It makes handling of Asynchronous task easier.
Why? If you are using django, then use celery. It goes well with it and it is written in python.
Node.js is cross-platform, JavaScript runtime environment that executes JavaScript code outside of a browser. It is famous for it's asynchronous nature of execution
A Progressive Web App (PWA) is a web app that uses modern web capabilities to deliver an app-like experience to users. It should meet certain criteria like Progresssive - give same experience to every user regardless of browser, it should be resposive and so on ..
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Session based authentication is one in which the user state is stored on the server’s memory.
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the server creates and stores the session data in the server memory when the user logs in and then stores the session Id in a cookie on the user browser.
- Token based authentication is one in which the user state is stored on the client. Preferred mode of authentication for RESTful APIs.
Authorization is the process of giving someone permission to do or have something.
Docker is a computer program that performs operating-system-level virtualization also known as containerization. These containers are isolated from one another and bundle their own software, libraries and configuration files;
Infrastructure as a service (IaaS) is an instant computing infrastructure, provisioned and managed over the internet.
Amazon Web Services (AWS) is amazon cloud computing platform, where you can rent computing instances to deploy your apps.
Platform as a service (Paas) is a complete development and deployment environment in the cloud. It is designed to support the complete web application lifecycle: building, testing, deploying, managing and updating.
It is a PaaS that let's you deploy applications easily, without much effort.
Hoisting is JavaScript's default behavior of moving declarations to the top.
Closure is the combination of a function bundled together (enclosed) with references to its surrounding state. In other words, two functions clubbed together i.e one function inside other one. Closure gives you access to an outer function’s scope from an inner function.
function makeFunc() {
var name = 'Ayaz';
function displayName() {
alert(name);
}
return displayName;
}
var myFunc = makeFunc();
myFunc();
React is a javascript library created by Facebook. React is used to build user interface components. It has support for JSX, that let's you put in HTML code in javascript.
Why? React let's you create large web applications that change the data without reloading the page. You can create single page websites using react.
state is an object that represents part of the app that can change. Each component can have their own state or you can store all the states in parent component and access it using this.props.state
Props is a special keyword in React, which stands for Properties. It is like function argument passed in components. It can be passed in uni-directional flow i.e only one way parent to child.
Redux is a predictable state container for JavaScript apps. It makes it easy to manage the state of your application. It is like a place to store states at one place and change it using functions.
Why? Having multiples states at different components is difficult to manage. Redux makes it easier to manage the states at one place and only special function can make changes to a state.
Mutable methods are those methods that change the state of the original objects that are passed in like slice, push, splice
Immutable Methods are those methods do not change the state of original objects that are passed in, instead they return a new object with the changes. like concat or spread operator.
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Inheritance is not same as other object oriented languages like C++ or Java.
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In javascript, everything is an Object and every object has a prototype of it's parent object.
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Any methods that are there in parent object are accessible by the child object. In other words, methods of parent object are inherited by the child object.
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If a method is not found on the current object then it's looks in prototype of the parent object. this is called method chaining.
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In javascript, everything function is constructor.