Android Bus

There are broadly two sections of development, one is Android OS development and other is Android application development. I will try to cover this article with intent to anatomize Android from a developer’s context and later on giving a head-on for development with help of tools and platform. Android app market is huge with approximately more than 20 million applications, as a result there are infinite opportunities in area of application development.

Let us revisit the Android architecture. Radically starting from the root let us get inside the neogenic design of it.

1.Kernel:

 As shown in Figure 1(Figure 1: Android Bus), the Android bus has wheels which represent Linux based kernel which is responsible for moving the Open source head of Android.
Android has a Linux heart. Its kernel is based on the Linux kernel release 2.6.X(X varying with new releases), based on the Android version releases. But it is not full fledged Linux, as Android was envisioned for high performance, optimized for minimum possible system resources consumption. Certain components have been removed from base Linux kernel and at the same time few new patches have been added also. The primary reason for this is that the Linux kernel, that Android has adopted, was for desktop version as compared to Android’s mobile platform(and Tabs). So, patches on basic Linux kernel drivers have been affixed. Some of the enhancements were necessary, like adding Power Management component. Since, the basic Linux kernel was designed for Desktops which are maximum times connected to direct power, so separate Power Management code was written to optimize power consumption; like wake locks are used to keep extracting power for activity. All these components sum-up for better Power Management.

Some of the additional components of Android kernel are:

Logger & Kernel Debugging:

Logging and debugging activity for better debug process and tracing.

Low Memory Killer:

To save active system memory, special code components have been written. For instance if an application which is not in use is consuming power, then kernel program for Power management will kill that program freeing Power and CPU resources.

Binder IPC program:

Since many applications can share system resources and usually interact with each other for process communication, binder IPC program facilitates IPC calls for this purpose. There are other components like Alarm etc but I won’t be discussing them here in this article.

People who are interested in Android OS development can find the code online as it is an Open Source.

2.Native Libraries:

Native Libraries

Surface Manager

3. Dalvic Virtual Machine:

Android processes are themselves executed as separate Virtual Machines. That means each application is executed as a separate process, which again means that a separate stack of execution is made in which a seprate libc component, and system resources are allocated. The reason for making each application an independent entity is that, Android has been designed to rely on minimum possible system resources and it is easier to manage them as VMs. It executes Dalvik Executables .dex files, which are zipped in .apk files. It has byte code converter especially designed to support different platforms depending on the manufacturers.

4. Core Libraries:

These are core group of libraries of Java made for application development platform.

5. Application Framework:

This layer is active behind your working Mobile’s screen, behind the screen or scene because applications do not access them directly. Hardware services like Telephony Manager also constitutes this. Hardware services provide access to lower level hardware APIs like Bluetooth, telephony, radio etc. Activity manager deals with application lifecycle. There are various other managing components too.

Switching on an Android…Behind the Scene!

Application Stack

Inside an Application:

There are four major components of applications:

Activity, Service, Content provider and Receivers

Activity:

An activity can be explained as one view of an application like login page of an application which can be called as Activity.
Following is a piece of demo for invoking activity in Java class:
…

Java methods like OnCreate(), OnStart(), OnResume(), OnPause(), OnStop() and OnDestroy() are involved in an Activity’s initialization.
In Figure 5(Figure 5: Switching between apps) shows you a scenario from switching from a music player and coming back; it can be applicable for removing and plugging in earphones also which enables and disables the music playing.

Switchin in App

Services:

Service is something which runs in background. Services contain all the services which are running in background to support what is projected in foreground. For e.g. running music in background is a service.
Service class must be extended for a new service.

Content Provider:

Content provider is shared set of data that can be utilized by an application. This shared data can live in SQLite, data store or XML.

Receiver:

Receiver is responsible for listening to alerts and broadcasts. Alert can be something like Less Battery or USB connected and broadcast message is like receiving a new message.

There is a wide variety of tools and services available for application developers.
If you want to go into application development for Android then you need to be educated about the following points and tools.
First of all we need to install SDK or Software Development Kit, Android Development Tools and then set up a platform for this. So let me give you an overview the process of development.
First you need to install SDK depending on the platform version you want to work on. Then you need to download eclipse plugin or any other available IDEs for Android development. Then one has to set up a virtual device (AVD) which is connected through ADB (Android Development Bridge) to an emulator to run the application. After developing a project, you can test it on emulator by running your application. Then comes the debugging part; DDMS (Dalvik Debug Monitor Server) which not only can be used to debug the program but also for checking various action points and allocation of system resources like memory.

There is one more development kit called IntelliJ IDEA from Netbeans.of Java.
There is a list of Emulators beside the basic SDK emulator, which can be used for the purpose of testing:
• Marvin ZX Spectrum
• Frodo C64
• Snes9x EX
• PC Engine
• FPSE ps1 emulator
• N64oid – N64.
• UAE4Droid
• SNesoid
• NESoid

Please note that many of them are used by game developers and highly enthusiastic gamers to test games. SDK tools itself contains a wide variety of tools which are responsible for different purposes altogether.
Some of them are:
Dmtracedump, Draw 9-patch(Graphical tool), Hierarchy Viewer (Debug and optimize an UI), mksdcard, monkeyrunner(API for writing programs), sqlite3(Access the SQLite data).

You are walking down a dark road suddenly someone jumps from the dark with a knife in his hand, force you and takes away all your money , Credit Card , DL and your Car keys. Around every corner lurks danger and with nowadays you definitely need a big, burly bodyguard down in that street with you. Firewall is a specially designed software to protect you from mean guys online. Without a Firewall you will be like a millionaire carrying all its wealth in a suitcase inviting anyone to come and take it all away.

For all those who are still dazed and confused about the analogy let me get real. Firewall is a system or group of systems that enforces an access control policy between two networks. Their two major mechanisms that exist in a firewall are for allowing and blocking of traffic based on the criteria specified. The third mechanism that has been added recently is keeping a log as this help for future predictions in case of future requests, because of the logging procedure we can now develop various tools to combat different kind of web attacks. Hence the three main fundaments of a firewall are Forwarding, Blocking, Logging/Accounting. A Firewall can be prepared to work either on your machine so that it can protect as you use the internet or it can made to run between your network and your connection to the internet . We will be looking at selection of these in this roundup.

The reason why Open Source Firewalls are better source to drench your curiosity about Firewall, is that these days Infrastructure tool is getting green with Open Source. You can see transitions in various organizations fully migrating to Open Source.

Some of the Top Firewalls Around:

Moving on with the topic lets remove the curtains from some of the big names in the firewall industry. Using a Linux kernel you there exists a humungous chance that u might have already been introduced to some of these rulers of the security world. Today we will be going through iptables, IPCop, Shorewall, UFW and OpenBSD. These are some of the most widely used firewalls in current scenario. As per an online survey where 160 users participated these were the results

Lets get them now one by one.

Iptables: Iptables is an user space application program that does packet filtering, network address translation (NAT), and port address translation (PAT). This is the basic firewall that comes preinstalled with various Linux kernels. Iptables became primary Firewall from kernel version 2.4x onwards. It replaced its predecessor called IpChains.

IpTables allows a System Administrator to configure the tables provided by the Linux kernel firewall (implemented as different Netfilter modules) and the chains and rules it stores. Different kernel modules and programs are currently used for different protocols; IpTables applies to IPv4, ip6tables to IPv6, arptables to ARP, and ebtables for Ethernet frames. IpTables requires elevated privileges to operate and must be executed by user root, otherwise it fails to function. On most Linux systems, IpTables is installed as /usr/sbin/IpTables.

You can use Iptables to achieve all the basic essentials of network security i.e. Blocking, Accounting and Forwarding.

To list the existing rules in your firewall type:

——CODE——

sudo iptables –L

—-CODE—–

For those of you using iptables for the first time will most probably see a Firewall with no rules in there, this is because though an iptables firewall is provided, its use can vary from user to user as per their need. So you need to set up various rules depending on the type of protection you need. If your version of the Linux does not have this basic tool just download it from Netfilter’s website.

Ipcop : This is a stateful firewall based on Linux netfilter .Some of IPCops impressive base install features include: secure https , DHCP Server security, Proxying, DNS Proxying, Timed Server, Dynamic DNS configurations, Traffic prioritization ,  Intrusion Detection using Snort, ISDN/ADSL device support functionality , VPN (IPSec/PPTP)functionality and  Traffic /Systems /Firewall /IDS graphing. Apart from the astounding base features there are dozens of add-ons which can further expand the security scope of your IPCop from Web Filtering to Anti virus scanning.

[Figure 4:Ipcop’s URL Filter]

If you work on a SOHO network, then you can just use any old PC and convert it into an protector for your network interface. Just run this firewall on a low power PC and it will be the thing you always needed. You just need to establish the ground rules using simple GUI’s and leave the rest to this tool. Feel free now and use the internet with your networks personalized bodyguard. In addition to the Firewall effect it also increases your net experience by just storing the frequently used information.

Shorewall :

Also known as Shoreline Firewall is one of the advanced tools available when you want to stick with iptables. As the logo says “iptables made easy”.

If you have hard time understanding iptables rules you should really try Shorewall as it provides a high level abstraction of iptables rules in text files.

http://www.shorewall.net/Introduction.html

You have to describe all of the firewall requirements using entries among a group of configuration files.  then analyses these files and using the iptables and its utilities , Shirewall then configures Ntefilter and the networking components of your Linux to match the specified requirements. Shorewall can be used on a dedicated system , a muti functional gateway or a standalone Linux PC .

Shorewall does not use Netfilter’s ipchains compatibility mode and can thus take advantage of Netfilter’s connection state tracking capabilities.

UFW-Uncomplicated Firewall :

Ufw is another tool to manage the netfilter iptables firewall. It is the default Ubuntu firewall configuration .

UFW provides for an easy and interactive tool to create an IPv4 or IPv6 host-based firewall.  It uses a iptables for configuration  and a command prompt interface consisting of a small number of  simple instructions . Its graphical interface is Gufw. It is very simple and intuitive to maintain your iptables using Gufw .It can be used on any Linux system that has python, GTK and ufw. UFW can be installed by just 1 simple command on your command prompt “sudo apt-get install ufw”. By default UFW is disabled. To enable UFW just type “sudo ufw enable “on your command prompt. UFW can now be used to perform all the stuff you can do with the help of iptables.

OpenBSD and PF :

The OpenBSD project produces a FREE, multi-platform 4.4BSD-based UNIX-like operating system. PF implies Packet filter. PF is licensed for BSD and is developed on OpenBSD platform . PF firewall  is preinstalled  on OpenBSD, FreeBSD, NetBSD. PF can be used to perform Packet Filtering , Port scanning , Port forwarding , IP filtering, Prioritization of packets , Log data , and other firewall basic operations .

Conclusions :

Iptables : This is basically for explorers , thinkers or in short developers. The limits are up to what you can think .You can create scripts to create whatever kind of protection you need. Iptables is the most common backend for most successful firewalls around.

Ipcop: This Firewall can do all types of tasks but is more suggested for the SOHO networks. Easy to use, Interactive GUIs, Free license, Open source,etc. Makes it one of the most widely used firewalls around the Linux world.

Shorewall Firewall: ‘Iptables made easy’, well if you need to work with iptables but you are having a hard time understanding or learning its commands, what you need is a shorewall firewall i.e. Shoreline. It provides with functions that read what u need from text files and give you a firewall based on iptables that will suit your needs. In short this can be called as iptables simplified

UFW: This is again a configuration tool for iptables. It is the default firewall configuration system which comes already installed on many Linux kernals. Gufw is the part that controls the GUI’s for this firewall configuration system.

The GUI’s are quit interactive and make it easier to manage a firewall of your own.

OpenBSD and PF: PF as the name goes Packet Filter is the component that handles the network interface on OpenBSD. It comes preinstalled on major BSD kernels . It can supply for all the needs of a firewall for the BSD systems.

Before all that fun and learn I want to explain the concept of mail and general email-flow concept.

What is MUTT?

We  all know various mail services and we are using them like our organ.  Now can’t live without them literally. That is why we are extending them to our life. That is the reason Blackberry got famous because of their exclusive mail service blended in it; more providers came into play, they also tried to extend it to mobiles not exactly like Blackberry but in their own ways. Now every smart phone has Mail app. Mails are  an essential component of our life now.  Most prominent of them  Gmail/Yahoo/Hotmail etc are all available across  the  cloud.

Now when we say mailclient, they are the  one which organize  those  mails and let you arrange /store  and read them according to your own preferences. You use them, some  of the popular ones  are: Mozilla Thunderbird, Microsoft office Outlook and Outlook Express and the  one which is topic of this  article  MUTT.  So now it is clear that mutt is an email client or what we say MUA(Mail User Agent).

These are following protocols used for mail  purpose:

• IMAP4(Most recent one in the list)
• SMTP
• POP3
• HTTP

IMAP4 replaced POP3 in business. IMAP4 is better/faster/lighter and more proper than POP3 so it got over POP3 in maximum mail services. IMPA4 and POP3 is for incoming. Ports defined for IMAP4 is 993, where it is  995 for POP3. SMTP is used for outgoing and port for it is 465. HTTP is not only dedicated to email services but it is used for accessing mailboxes. Secured version is used, so port is 443.

MAIL Components Explained:

MUA,MTA, MDA and MRA are involved in a ideal mailflow process. Now what are they I just give them here a brief intro and explain them by the process of email flow.

MUA(Mail User Agent): It is the client program in which the user sends and receives mail. It may use scripts to complete its actions. It can be highly configurable like we do have MUTT. For instance for explaining one can configure text editors or word processors of its own choice for writing the email. Various other Linux MUAs are kmail, evolution, sylpheed, mulberry, pegasus, pine and elm.

MTA(Mail Transfer Agent): They are the one which receive envelopes from MUA and send, receive and route them accordingly. MTA don’t read headers they just see if the envelopes can be delivered to mailboxes. MTAs are vital components they don’t just send it ahead. But they decide whether emails are valid and can be moved ahead or not, if it contains error mail is sent back to user. It also acts SPAM FILTER for mail services. MTAs test the emails against a certain blacklist which they have. So they are not just transfer agent, they are smart agent. MTA uses SMTP for talking. Some of the popular MTAs for the job are sendmail, qmail, exim and postfix.

MDA(Mail Delivery Agent): They take mail from MTA and do the actual delivery plus filtering which may actually include many functions like virus detection, sorting and automatic answering.

Maildrop and procmail are MDAs.

MRA(Mail Retrieval Agent): MDA transfer mail to Mailbox. MRA fetch them from mailbox and then delivers to MUA. Some of them are fetchmail, getmail and retchmail.

Now I chain up them in a flow how they act in a mailflow process:

Mailflow Process

Email starts form a user who write it at MUA. MUA provides various  options  through programs and scripts. It may also contain security and encryption options . The finished mail in form of Envelope  transfers to MTA.  MTA receives  envelope and irrespective of message inside validates it. If message is proper, routes it ahead in internet cloud and if it is invalid, then it is reflected back to user with error message. Mail is checked against SPAM blacklist and validated and is forwarded to MTA. Please note if it is special mail service or dedicated mail service MUA can directly send it to receiving MTA bypassing internet. MTAs uses SMTP.

MDA receives mail from MTA and they do filtering process which include sorting according to various parameters and virus protection or may include auto-answering options. MDA delivers them to mailboxes. Then MRA fetches these mails from mailboxes using IMAP4 or POP3 and transfers them to MUA.

Now coming over to our very own MUTT, we know MUTT is MUA. It uses sendmail as MTA in our case.

Some of the key features of MUTT which makes it special are:

• Its  own configurable color setting. For messages, mailboxes and all.
• MIME support / PGP Support(Encryption/Signature)
• Support for multiple mailbox formats
• Keybindings and macros( They are superb. Easily they are one of the best feature of MUTT. You say the action and give and do any key binding for it.)
• Searches using regular expressions, including an internal pattern matching language
• It has .****rc configuration files for various setups of it, which are easy to edit and maintain.

Despite of them all it have all other regular features.

MUTT is text based because its developers think this is where it should be because if it is terminal based , it makes it more powerful.

I used MUTT version 1.4.2.3 which with sendmail as its MTA on my Ubuntu 10.10. As common user like me, you do not use our own domain services and our own mailboxes like those organizations where MUTT is highly used. I tried to configure my Gmail accounts to play with MUTT. Yes you may also configure any mail accounts using SMTP and IMAP protocols. For this you may refer MUTT manuals.

Installing MUTT is stunningly easy.

On Debians(For others too you may find tutorials) just write:

#> apt-get install mutt

Reading package lists… Done

……………

……………..

You may require the root login to install it and use it. It installs it in root directory. So if you want to access its files change to root directory after super user login where ~ indicates root home directory which is generally locked when accessing through GUI. Type:

#>cd ~

Please remember that it creates a lot of hidden directories after installation starting with . In case you don’t know.

To see all directories and files you may see all of them by pressing:

#>ls –a

MUTT directory content look like one below:

MUTT directory content

The most basic configuration file for MUTT is called .muttrc where . signifies it as hidden file. It is one power script which controls whole MUTT configuration. You may open it with any editor you want and add/remove and manipulate the stuff.

You may prepare your .muttrc file by having look on to sample .muttrc files. To give a glance I show my .muttrc file here( I am afraid of it though)

.muttrc file

Please note that this is just a stub of .muttrc file. Whole content can’t be shown here.

To start MUTT you should have super user access or user with adequate privileges. Just type mutt from any space and it will be fire up.

Now configure your gmail account you may have to add following lines to your .muttrc file :

set imap_user = “yourgmailid1@gmail.com”

set imap_pass = “”

set folder = “imaps://imap.gmail.com:993″

set spoolfile=”+INBOX”

set postponed=”+[Gmail]/Drafts”

set record=+[Gmail]/”Sent Mail”

set from = “abc@abc.com”

set realname = “yourname”

set smtp_url = “smtp://gmailuserid2@smtp.gmail.com:587/”

set smtp_pass=”"

set from=”gmailuserid2@gmail.com”

set realname=”anythingyouwant”

Please note you may use multiple accounts for incoming and outgoing mails and use Account-hook for that. If you just write down the multiple IDs in suppose incoming mails automatically the later in the queue will be opened by MUTT. I have used different incoming and outgoing IDs in my configuration. Please note I have kept the password blank because of security reason. If you don’t enter the corresponding password here you will  be asked for it while you use it in MUTT.

Note that SMTP URL and IMAP URL are the corresponding address mailboxes of Google for incoming and outgoing.

But it’s not just that you want for activating Gmail in MUTT. You need various SSL security certificates for that. They can be added right from command line using apt-get just like other packages. Every time after initializing MUTT it installs these certificates and try to access the Gmail mailbox.

Following is the accessing a mailbox in progress

Below figure shows some functions for which generic binding can be done. Above shows the above in figure shows some the keys which have been keybounded.

Generic Binding

Aliases can also be used in MUTT

An alias file needs to be created for the purpose where all the aliases are defined with their extensions. I use in this example s for sariskka@gmail.com which I have defined in my aliases file.

Aliases file format is like:

alias b namby147@gmail.com

alias s sariskka@gmail.com

alias sa sanskriver@gmail.com

Following in figure was the sa alias which was auto filled with EmaiID later.

The source for alias file need to be defined in .muttrc like :

set alias_file=~/.mutt/aliases

source ~/.mutt/aliases

Install Abook for simpler alias setting.

Just hit Ctrl A and if you have selected some mail it will let you to store alias for current email address. Or you can add more emails by accessing it through terminal. Abook is best phonebook integration for MUTT.

Following is an alias making in progress of LFY editor Aditya:

For integration of Abook you need to add following text in .muttrc file:

set query_command=”abook –mutt-query ‘%s’”

macro index,pager A “abook –add-email” “add the sender address to abook”

macro generic,index,pager \ca “abook” “launch abook”

We can use signatures in for which separate .signature file is needed.

Source for signature is defined like:

set signature=”~/.signature”

My signature looks like in light green in Gmail to which I have sent this mail. You may make it much beautiful than me.:

Signature

Please note that editor for writing mail is Nano. You may use any other editor for the purpose for this you just have to set another editor in .muttrc file like:

set editor=”emacs -nw”

Any file can be attached by simply attaching few options and giving path that too before even starting mutt.

root@tuxxxy:~# mutt -s “HI” -a “/home/tuxxxy/Desktop/jkhk”

-s is for subject

-a is for attachment file

Below in green is the attachment in mutt along with main message body attachment:

Beside these they are million options to configure MUTT.

Like below we can configure it supernumerary ways:

set timeout=60  #Check for mail every minute

set mail_check=5

That’s  why it is known as the one of the most flexible MUA ever. To switch between various mailboxes you need to just press y.

The security and encryption are one of the most important aspects in today’s time. Security is to prevent your emails from intruders. There are various security techniques like public key , and asymmetric keys and various other you must be knowing. But the strongest out of them is PGP.  PGP stands for Pretty Good Privacy. MUTT supports PGP for its mail services. I have used GPG here which is GnuPG.

Following is the  key making in progress:

Key making in progress

It is very hybrid  approach to secure your mails. It uses symmetric-key cryptography for speed, and public-key cryptography with a session key to ensure maximum performance.

While mailing at the last step just before sending just press p and and it asks you what do you want to mail to be encrypted or signature or both.

Please note signature is necessary for the reason because it ensures that your mail is not manipulated in-between. By decrypting the sent signature which is sent along mail file it can be decrypted to the date and email id attached to it. For that you have to use the signature file as input in format .asc or .sig.

As I show you the mail in which I used signature. Signature file comes along with mail in a file signature.asc which user can use to verify mail.

signature.asc

Similarly press E for encryption and you will be asked for the keyID which you had generated after entering your mail will be encrypted.

Use gpg  –list-keys to list your all of keys which you have made.

These were the few of things which you can do while playing with MUTT, but please note that this is not the end to possibilities for MUTT. MUTT gives you that much space to play that neither I can cover all of them here, nor I have learnt all of them. Try using it and you will explore yourself and you may share with us all so that we can also learn.

So give wings to your excellence and let them flutter in the sky of LINUX.

GRUB Logo

This is what you get an interactive scene giving you pseudo programming language options in multiple lines. If you have Windows thing installed in your system you get a little relax after seeing Window something something.
Bootloading is the term which reminds core OS classes if you are any how related to architecture of Operating System. Boot loading is like a lift board which tells you to which floor you want to get on. The people who have heard it for first time and are of confused and making pictures of your flashy boots in your mind, Bootloader ,also called a boot manager is term for a small program that places the operating system (OS) of a computer into memory. When a computer is powered-up or restarted, the basic input/output system (BIOS) performs some initial tests, and then transfers control to the Master Boot Record (MBR) where the bootloader resides. Bootloader is the door where you bell to enter into the system. It gives you complete list of OS that too with other advance options.
The modern GRUB is called GRUB 2 and it is indeed GRUB version number 2 as there are a lot of things absent inside the new GRUB and other vital changes too.
GRUB 2′s major improvements over the original GRUB include:

GRUB 2 Config file.

• Scripting support including conditional statements and functions

• Dynamic module loading

• Rescue mode

• Custom Menus

• Graphical boot menu support and improved splash capability

• Boot LiveCD ISO images directly from hard drive

• New configuration file structure

• Non-x86 platform support (such as PowerPC)

• Universal support for UUIDs

(from: Ubuntu forums)

Before stepping up one level in the conversation let me tell you the concept of chainloading. Chainloading is skipping first default assigned kernel to boot and getting booted on present kernel.
This is an useful technique in cases where Linux do not recognize the kernel and its boot data so what usually is done is that just partition corresponding to that kernel is named and chainloder +n is set where n is the nth kernel configuration after the first. This is generally done for making Windows and other proprietary OS as default boot option.
Let me first introduce you with the some of the important of files that are critical for GRUB 2.
/boot/grub/grub.cfg
This is like the file GRUB’s /boot/grub/menu.lst. This file contains the GRUB 2 menu information but unlike GRUB’s menu.lst the grub.cfg file is not meant to be edited.

/etc/default/grub
This configuration file contains information formerly contained in the upper section of GRUB‘s menu.lst and items contained on the end of the kernel line. The entries in this file can be edited by a user with administrator (root) privileges and are incorporated into grub.cfg when it is updated. Specific configuration settings are detailed in the Configuring GRUB 2 later in this section.

/etc/grub.d/

Changes to be done here

The files in this directory are read during execution of the update-grub command and their instructions are incorporated into /boot/grub/grub.cfg.
GRUB2 has lesser editing options comparing to GRUB or we can say they have made changes making more complex.
/etc/default/grub gives few basic options to change you configuration.
Use sudo gedit /etc/default/grub for editing.
Like you can change the order of booting.
I have shown you to how to make Windows as default menu just by changing the parameter to 4 as it appears on 4th on menu list in figure.
Further we can add another kernel entry this is the format saying name and its partition location in format

hd(harddisk),nth partitionname and other generic root location.
set root=(hdX,Y)
linux /vmlinuz root=/dev/sdXY ro
initrd /initrd.img
boot

GRUB 2 edit mode while booting.

GRUB menu at the booting time can be converted to command-line by pressing c and there are few grub commands which can be used right there. There are few commands which can be listed by using help command.
ls lists defaults.

I will also explain the settings how to change the splashimage for bootloader.
For this you need to have the png, jpeg 8bit or tga format image. By default its tga format for the splashimage. You need to install a package for that:grub2-splashimages
Changes are made in the grub.d directory in the file in 05_debian_theme where there is some path given to a default splashimage which needs to be edited for your own image.
I made one that is in pic.

This splashimage I managed to add.

Various file formats

Compression , archiving , zipping and encoding are some of the keywords which you might have listen when you deal with huge amount of data, or you deal with systematic data and where data storage is critical for example your organizational data.
Linux ensures best archiving, zipping and security methods for data by supporting never ending data storage packages. I have been able to concise the availability and I am today presenting the some of the most important techniques that is followed or must be followed in Linux terminals.

• tar:

One of the most common technique to archive data in Linux is tar (Tape Archive) and a tape archived file is called tarball.

tar -c foo

Creates tar

tar -x foo

tar -xvf firefox.tar

This will untar the tarball. Note c switch creates a archive and x extracts the archive, v is for verbose that means output the name of each file in extraction.

tar -xvvzf foo.tar.gz

Now using z switch will uncompress the .gz compressed tar archive, so above command will uncompress as well as untar the package.

tar -jxvf foo.tar.bz

Similar to above extracts and uncompress bzip tarball.

tar -cvf foo.tar foo/

This will create a tarball using c switch from foo to foo.tar.
Similarly using -cvzf will create a gunzip compressed tarball and -cvjf will create a bzip2 compressed tarball.

• zip:

Unzipping a file in progress

Similar to tar we have zip which compresses as well as archives the files, but compression is on low volume. Opposite of zip is unzip.

unzip filename -d “direcotry”

Extracts to directory path

unzip filename -p “directory”

Extract in pipe in binary format

unzip filename -q “directory”

Hides all messages while decrypting

• Gunzip(gzip)

gzip- A really good compression technique creates a file in .gz format.

• bzip2

A really good compression technique creates a file in .bz2 format.
.tgz and .tbz2 are short for tar.gz and tar.bz2 which are archived compressed files.

bunzip2 -c a.tar.bz2 | tar -xvf

This extracts a .tar.bz file

• Lzma:

It stands for Lempel-Ziv-Markov chain Algorithm. Lzma is a compression tool like bzip2 and gzip to compress and decompress files. It tends to be significantly faster and efficient than bzip compression. As we know, bzip2 compression ratio is worse than gzip.

lzma -d yeas.in.lzma

Decompresses file in .lzma format.

lzma -f yeas.in.lzma

Force compresses the file yeas.in to yeas.in.lzma.

• 

  Decompressing a p7zip file.

  7zip

7z a filename

It compresses up to 7 fold and uses LZMA and is known best compression technique.
p7zip is used to compress and decompress the 7z files.
But for backing up data a user must create a tar first and then 7zip compression.

• Rar

Password given for file.

Last but not the least because it is most widely used compression format across all platforms. It has wide support and own advantages of using it
ZIP uses LZW compression whereas RAR goes one step further using pattern compression, ideal for multimedia data. RAR incorporates some error checking, it also allows a recovery record which can be used to retrieve files even when an archive is damage. RAR offers solid archiving (files encoded in one go) which gains a bit of space. RAR archives have better password.
Both rar and unrar are there for Linux.

rar a file

Compressed a file to to make it a rar archive
d options used to delete from archive and using p we can ensure password security for file.

Please feel free to add your contributions and correct me if I have passed incorrect information.

Here are some tips for using VI or VIM editor:

* For opening vi editor first open terminal and write:

vi filename

Now hit i for insert.

* For exiting writing mode hit escape.

* Write man vi any time for help pages for vi.

Shift+G will take you to the last line.

* If finished with your work you can save your work by hitting :w or Esc+Z+Z.

* If you don’t want to save the work and simply quit then

:q

* For quick save and exit:

:wq

* yy is used for copying and p for pasting.

* :n moves to nth line.

*This is the pattern for searching and replacing, the string s is for searching:

:s/search_string/replacement_string/

Line number can also be specified after colon for the replacement.
%s will do the same purpose.

* :g will search whatever specified and commit specified action

Pattern is:

:g/search pattern/command

* Contrary to above

:v/string/d

This will delete every line which does not contain specified string, d deletes the string.

*It deletes every empty line.

:g/^$/d

Ain’t it enough for a beginner!

For Vi, Vim or gVim click :

DOWNLOAD

01. APT- Advanced Package Tool

02. BSD – Berkeley Software Distribution

03. bash – Bourne again shell

04. cc - C compiler

05. csh – C shell

06. FOSS - Free and Open Source Software

07. GIMP – GNU Image Manipulation Program

08. GNU - GNU is Not UNIX

09. GNOME – Gnu Network Object Modeling Environment

10. GTK - GIMP Toolkit

11. GPL – GNU General Public License

12. grep - Global regular expression print

13. GCC - GNU C Compiler

14. Grub- Grand Unified Bootloader

15. ksh – Korn shell

17. KDE – K Desktop Environment

18. LILO - Linux Loader

19. LINUX – Linus Torvald’s UNIX  ;Linux Is Not Unix; Linus’s MINIX

20. LUG – Linux users group

21. LFS - Linux From Scratch

22. lex - Lexical analyser

23. MD5 – Message digest 5

24. man - Manual

25. POSIX – Portable operating system interface

26. pwd – Print working directory

27. RHCE - Red Hat Certified Engineer

28. RPM – Red Hat package manager

29. sed - Stream editor

30. SUSE – Software- und System-Entwicklung(Software and system development)

31. tar – Tape archive

32. telnet - Terminal over network

33. UNIX - UNIpleX information and computer services

34. VimVi - Improved

35. WINE - WINE is not an emulator

36. X – X Window System

37. YaST - Yet another Setup Tool

38. yacc – Yet another compiler compiler

(1) su
su stands for superuser. Linux has limited user access that is why it is considered and de facto is secure. It asks for administrative password at every gateway.
Switching user to administrator is a lot simple than windows.
Type su in terminal window and it’ll ask for password.

su

(2) mv
Its like cut and paste

cp ~$ mv /home/ashish/Desktop/1.png /home/ashish/Desktop/picsr/1.png

(3) rm

Its like delete in windows.

rm files

(4) gzip
Compresses the file and give it a extension .gzip or .gz. Winrar/Winzip do the same job over windows.

gzip filename

(5) cat
It displays the content of file right there.

cat [Options] [File]

(6) mount
It mounts the CD/DVD and other external devices.

mount | column -t

(7) pkill/pkillall
Its like pressing ctrl+alt+delete and forcefully terminating a humpy process. Actually its better than classic kill and killall which requires pid number.

pkill [-signal]

(8) passwd
Its for changing the password.

passwd [options...]

(9) halt
In case of emergency for avoiding loss of data forcefully shutting down.

halt [-d | -f | -h | -n | -i | -p | -w]

(10) reboot
Simply restart the system

reboot [-d | -f | -i | -n | -w]

(11) clear
It clears visible area of console.

clear

(12) vi
It is like notepad editor in Windows. It can be used inside terminal.

(13) man

It is used to read information, help and other details about command, information or process.

man commandname [options]

(14) gcc

It invokes C/C++ compiler.

(15) ifconfig
Its Linux counterpart for Windows’ ipconfig.

ifconfig [options]

(16) lock
It temporarily locks the terminal.

(17) pwd
It prints present working path.

pwd [options]

(18) cksum

Checksums and count the bytes in file specified. Prints CRC check-sum and byte counts of each FILE.

cksum filename

(19) gunzip

It un-compresses file.

gunzip [-Z]

(20) installpkg
It is used to install one of the packages from the program sets.

installpkg [options]