Your orientation to Raspberry Pi.

http://www.raspberrypi.org/

Status LED Indicator 
OK  (Green) - SDCard Access       (D5 via GPIO16)
PWR (Red)   - 3.3 V Power         (D6           )
FDX (Green) - Full Duplex   (LAN) (D7 Model B   )
LNK (Green) - Link/Activity (LAN) (D8 Model B   )
10M (Yellow)- 10/100Mbit    (LAN) (D9 Model B   )

Click here for Raspberry Pi Schematic

STEP 01:

Download this quick start up guide to help you install your Linux OS on your Raspberry Pi.

STEP 02:

Get yourself a 4GB SD card, which is enough for use in many application.


NOTE: Not all SD cards work with the Raspberry Pi. High speed cards can be too fast for the Raspberry Pi bus. Check out which SD card is suitable for your Raspberry Pi. It has a lists of cards that have and have not worked for Raspberry Pi users. http://elinux.org/RPi_SD_cards

You may also like to check out the various peripherals that are compatiable to Raspberry Pi.
http://elinux.org/RPi_VerifiedPeripherals

STEP 03:

Format your SD card with SD Formatter 4.0 for SD/SDHC/SDXC 
SDFormatter4exe.zip (5.99MB)

STEP 04:

You can download the image version New Out Of Box Software (NOOBS), extract all the files and copy into your SD card.

Insert this SD card into your Raspberry Pi, and power on it. Follow the instruction on your screen display to complete the installation process. 

STEP 05:

You will be ask to select an Linux OS to install on your Raspberry Pi.

Choose the recommended "Raspian", which is also the Raspbian "wheezy".

The installation process will proceed.

Proceed to step 10.

Installing Raspbian operating system onto my Raspberry Pi.

STEP 06:

As of 02 Nov 2013, Raspbian now supports and pre-installed with Java.

Note: For those who want to run Java SDK on Raspberry Pi.

Raspbian “wheezy” is the recommended Linux OS for Raspberry Pi. This version is optimized to be run by Raspberry Pi which is using RP‘s ARM processor supporting ‘hard-float‘. However Java SDK only support ‘soft-float‘ at this point in time (Jul 2013). 

This call for another Debian Linux version which is known asSoft-float Debian “wheezy” (It is same as Raspbian "wheezy", except that it will be slower. Use this version if you need to run Java JDK Linux ARM)

STEP 07:

Download and run the Win32DiskImager on your Windows Operating System.
 win32diskimager-v0.8-binary.zip (5.67MB)

You can download the latest version at this website,
http://sourceforge.net/projects/win32diskimager/

STEP 08:

Unzip the Debian Linux version Soft-float Debian “wheezy”, which is a "2013-05-29-wheezy-armel.img" file.

Run the program Win32 Disk Imager.
a) Select the Image File "2013-05-29-wheezy-armel.img"
b) Select the Device, which is your storage drive for your SD card.
c) Click on the <Write> button to write the raw image onto your SD card.

Note: You can also use Win32 Disk Imager software to backup (clone)your existing SD card image, by click on the <Read> button, and choosing a *.img file name.

STEP 09:

Insert the SD card into your Raspberry Pi and power it up.

STEP 10:

On the first boot, the "raspi-config" menu will pop up.

Note: If you are at the command shell prompt. You can key in"sudo raspi-config" to access to this menu.

"raspi-config" menu

Note: You may find yourself having problem when trying to key in the ‘#‘ char by pressing <Shift+‘3‘>. A ‘£‘ pound char may be generated instead.

This is because the Raspberry Pi‘s default locale code is set as UK. You will need to set the locale code to US, for a US keyboard layout.

Key in the following command,
"sudo dpkg-reconfigure keyboard-configuration"

Alternative method to configure you keyboard layout.
a) key in "sudo nano /etc/default/keyboard"
b) look for the line containing "XKBLAYOUT="gb"".
c) change "gb" to "us" for US keyboard layout.
d) save and exit.
e) reboot or key in the following "invoke-rc.d keyboard-setup start", to reload the keymap.

STEP 11:

Select <1> and press enter to Expand Filesystem.

If you are connected to the network, select <8 Advanced Options> and press enter.

<A2 Hostname> to change the hostname default "raspberrypi".

"raspi-config" menu 8-A

To change to the Standard US Keyboard mapping, select <4 Internationalisation Options>,

<I1 Change Locale>, with the following options,
Default Locale : None

<I2 Time Zone >, with the following options,
Geographic area: Asia
Time Zone      : Singapore

<I3>, with the following options, 
Keyboard model : "Generic 105-key (Intl) PC"
Keyboard layout: "Others" -> "English (US)"
AltGr as       : "The default for the keyboard layout"
Compose Key    : "No compose key"
Ctrl+Alt+Backsp: "No", (don‘t use it to terminate Xserver)

You can also configure to allow the system to boot directly straight into the GUI desktop, using this raspi-config. 

Select <Finish> then press enter to proceed to the system command shell. 

You can always come back to this raspi-config menu again by executing the command "sudo raspi-config" from the shell command.

"raspi-config" menu 4-I

Raspberry Pi revision 2, header pins out.

This is my Raspberry Pi. I have custom built a prototyping board that can be plugged on top of my Raspberry Pi. This prototyping board is soldered with 2.54mm housing connector (2 rows of 13 pins) so that I can easily access to the I/O pins of my Raspberry Pi.

My LED indicator wiring is as follows,
LED0 - GPIO_17 (Pin11)
LED1 - GPIO_18 (Pin12)
LED2 - GPIO_27 (Pin13)
LED3 - GPIO_22 (Pin15)
LED4 - GPIO_23 (Pin16)
LED5 - GPIO_24 (Pin18)
LED6 - GPIO_29 (Pin22)

UART (serial communication) wiring,
Gnd -         (Pin06) 
TXD - GPIO_14 (Pin08)
RXD - GPIO_15 (Pin10)

SPI (serial communication) wiring,
MOSI - GPIO_10 (Pin19)
MISO - GPIO_09 (Pin21)
SCLK - GPIO_11 (Pin23)
CE0  - GPIO_08 (Pin24)
CE1  - GPIO_07 (Pin26)

I2C (serial communication) wiring,
SDA0 - GPIO_02 (Pin03)
SCL0 - GPIO_03 (Pin05)

Information taken from
http://www.mosaic-industries.com/embedded-systems/

Learning to control Raspberry Pi general purpose I/O pin 11 (which is known as GPIO_0, or GPIO_17 if base on BCM2835 IC pin assignment)Power on my Raspberry, and the operating system will prompt for my raspberrypi login.Key in "pi" for the login, and "raspberry" for the password.

raspberrypi login: pi
Password: raspberry

pi@raspberrypi ~ $

Setup or initialise I/O port 17, by sending text "17" to the operating file system "/sys/class/gpio/export"

A directory folder will be created. "/sys/class/gpio/gpio17/"

Reference:
http://elinux.org/RPi_Low-level_peripherals#GPIO_Driving_Example_.28C.29

I am able to control the I/O pins on my Raspberry Pi, but I want to larn more into controlling the I/O pins using native C. Controlling I/O pins using the "file directory system" like method will be very slow.The speed achieved base on this benchmark website, I/O control through this shell (or file directory system) method, achieved a maximum process speed of about 6.8kHz (2x 3.4kHz).To achieve a higher speed, I will need to use native C programming, which can process from 9.4Mhz to 44Mhz (2x 4.7Mhz to 22Mhz).

More things to learn...

References:

Notes regarding digital I/O pins,https://www.kernel.org/doc/Documentation/gpio.txt

UART

The UART port is actually pin8 (TxD) and pin10 (RxD) on the Raspberry Pi connectors. The UART signal is 3.3V.You can use RS232/RS422/RS485 communication to talk to the UART, but a level shifter (for example MAX3232) required. RS232 uses about +/- 7 to 13V, while UART uses digital voltage (1.8V, 3.3V or 5V). For our Raspberry Pi UART, it is 3.3V. More information about making your own level shifter, you can visit this page. There are also standard USB to UART products for interfacing to your Raspberry Pi.The Raspberry Pi default operating system uses this UART port as its diagnostic port. This port has the following default UART settings,
- Baudrate   : 115200bps
- Data       : 8 bits
- Parity     : None
- Handshaking: NoneThis default port act as another Linux shell terminal screen, as you would have seen on the screen through the Raspberry Pi‘s HDMI or video output.

You can use a terminal program to access through this port.Using the Window‘s Hyperterminal program, setup the correct com port settings. And connect the terminal. You will see nothing on the terminal screen, but actually the Raspberry Pi is prompting you for your login ID. This ID is "pi" which is similar to how you log on to your typical terminal screen. You will see the terminal replying you with the prompt for password. Key in the default password "raspberry". You shall get a similar print out from the terminal program, as on the right. ->Looks very much like the typical terminal on your local display. This is mainly for troubleshooting, diagnostic or perhaps used for remote access of your Raspberry Pi.

raspberrypi login: pi
Password:
Last login: Wed Jun 19 15:36:44 UTC 2013 on tty1
Linux raspberrypi 3.6.11+ #474 PREEMPT Thu Jun 13 17:14:42 BST 2013 armv6lThe programs included with the Debian GNU/Linux system are free software;
the exact distribution terms for each program are described in the
individual files in /usr/share/doc/*/copyright.

Debian GNU/Linux comes with ABSOLUTELY NO WARRANTY, to the extent
permitted by applicable law.
pi@raspberrypi:~$

The UART on the Raspberry Pi is quite an useful peripheral. For me, I would like to use this UART as a serial communication to control my other circuit modular.

In order to use this UART, I need to disable the diagnostic features from the operating system‘s boot up. This means that I do not want the system to setup the UART pins as diagnotic port, when the system boots up.

The following command is key in to edit the system boot up script. vi is an text editor program, which is not very user friendly.Alternative, you can usenano editor instead of vi for the text file editing.
Or gedit editor. You can install then if they are not installed.
"sudo apt-get install nano" or
"sudo apt-get install gedit " To learn how to use the vi editor, click on the following link,http://www.unix-manuals.com/tutorials/vi/vi-in-10-1.html

A summary of the vi editor‘s command is summeries as follows,http://osr600doc.sco.com/en/FD_create/vi_summary.html

After the vi command, you should see the following screen display. This is the vi editor diaplaying the text in the "cmdline.txt file".The objective is to delete the text (in red color), which is relating to the UART setup. Press ‘l‘ on your keyboard to shift the cursor to the right, until it is at the position of the char that we want to delete. Move the cursor under the first char ‘c‘ (char as illustrated in red).Press ‘x‘ on your keyboard to delete the char one by one. You should observed the delete action.When all the text in red are deleted, press ‘:w‘ on your keyboard, follow by a enter key to save the text file.Press ‘:q‘ on your keyboard, follow by a enter key to exit the vi program.If at anytime you have edit wrongly, you can enter the command ‘:q!‘ on your keyboard, to exit the vi program without saving the text file.

dwc_otg.lpm_enable=0 console=ttyAMA0,115200 kgdboc=ttyAMA0,115200 console=tty1 root=/dev/mmcblk0p2 rootfstype=ext4 elevator=deadline rootwait
~
~
~
~
~
~

Find and comment away the line containing the following text (near the end of the file),
"T0:23:respawn:/sbin/getty -L ttyAMA0 115200 vt100",
by pressing the ‘j‘ on your keyboard to scroll down line by line.Issue an insert command by pressing ‘i‘ to insert some text before the cursor. Insert a char ‘#‘ at the beginning of the line to comment the whole line. The ‘#‘ mask off the whole line. The line that are masked off will not be intepreted by the system.After the ‘#‘ char is inserted, press <Esc> key on your keyboard to end the insert command that was issued.Press ‘:w‘ save the text file.

Press ‘:q‘ to exit the vi program.

The UART device name is /dev/ttyAMA0
Now the UART is not in use by the Linux Raspbian operating system, and is available for my own use.

To test the UART serial communication port, we can install a program call minicom. The use of minicom is similar to hyperterminal program that I use in Windows operating system (OS).

Enter the command "sudo apt-get install minicom"

There are also alternative GUI based serial communication program, cutecom.

To run the minicom terminal program. Key in the following command "sudo minicom -b 9600 -o -D /dev/ttyAMA0".

-o              (skip initialisation)
-D /dev/ttyAMA0 (specify the serial port)

Key in command "man minicom" to find out the other options that you can set with the minicom program.

Configuration Settings: 
Baudrate : 9600bps 
Data bit : 8    (default)
Stop bits: 1    (default)
Parity   : None (default)

Apply the configuration settings to serial port "ttyAMA0". The label tty (known as teletype) denotes all serial communication that the linux operating system is handling. In Raspberry Pi, ttyAMA0 refers to the pin8 (TxD) and pin10 (RxD).

When you type a char on your keyboard, an ascii char code is actually sent out of the Raspberry Pi ‘s pin8 (TxD). You will not be able to see it on the screen. What you will see on your screen will be those serial data that the Raspberry Pi received through pin10, which is the RxD.

In order to see what we have transmitted out from TxD, we can short the pin8 (TxD) and pin10 (RxD) together. This means that what you send will be receive and display on the display. The serial port configuration for the TxD and RxD is the same, so the serial data that is received will be exactly what you have transmitted.

The following text "Hello World!!! " were typed on the keyboard after shorting the RxD and Txd pin. The text will be displayed, indicating that the UART is working properly.

Now that you know that the UART on your Raspberry Pi is ready for use, you can use it to communicate with many other peripheral.

Press <Ctrl + ‘A‘>, followed by <‘X‘>, then key in enter for "Yes" to quit the minicom program.

pi@raspberrypi ~ $ sudo minicom -b 9600 -o -D /dev/ttyAMA0

-------------------------------------------
Welcome to minicom 2.6.1OPTIONS: I18n
Compiled on Apr 28 2012, 19:24:31.
Port /dev/ttyAMA0Press CTRL-A Z for help on special keysHello World!!!

CTRL-A Z for help | 9600 8N1 | NOR | Minicom 2.6.1 | VT102 | Offline
-------------------------------------------

Setting up the serial port with other settings,
Baudrate : 115200bps 
Data bit : 8    
Stop bits: 1    
Parity   : Even

SPI

The SPI port onboard the Raspberry is disable by default. The first thing to do is to enable the SPI port.

Edit the file "/etc/modprobe.d/raspi-blacklist.conf"

Comment off the line "blacklist spi-bcm2708" with a # in front.

Key in Ctrl+‘X‘ to exit, then ‘Y‘ yes to save the change to the file, and finally ‘Enter‘. This will brings you back to the command prompt.

pi@raspberrypi ~ $ sudo nano /etc/modprobe.d/raspi-blacklist.conf

GNU nano 2.2.6 File: /etc/modprobe.d/raspi-blacklist.conf Modified

# blacklist spi and i2c by default (many users don‘t need them)

#blacklist spi-bcm2708
blacklist i2c-bcm27088

Check to see if the SPI is successfully enable in the Raspberry Pi.

You should see "/dev/spidev0.0 /dev/spidev0.1" created.

0.0 means SPI0 CS0 (CS is the chip select)
0.1 means SPI0 CS1

pi@raspberrypi ~ $ ls /dev/spidev*
/dev/spidev0.0 /dev/spidev0.1
pi@raspberrypi ~ $

Testing the SPI port

download this SPI loopback test code written in ‘C‘ programming language.

spidev_test.c

Compile the *.c file using gcc command,then run the compiled program.

You should see the following hex dump data, indicating all 0x00.

This means that the SPI is receiving nothing, no data.

pi@raspberrypi ~ $ gcc spidev_test.c -o spidev_test 
pi@raspberrypi ~ $ sudo ./spidev_test -D /dev/spidev0.0
spi mode: 0
bits per word: 8
max speed: 500000 Hz (500 KHz)

00 00 00 00 00 00
00 00 00 00 00 00
00 00 00 00 00 00
00 00 00 00 00 00
00 00 00 00 00 00
00 00 00 00 00 00
00 00
pi@raspberrypi ~ $

Now we do a SPI data loopback test.
Short the pins MISO (GPIO 9, Pin21) and MOSI (GPIO 10, Pin19) on your Raspberry Pie. This will enables the SPI MISO to received whatever data that is sent out from the MOSI pins.

From this test, we will be able to know if SPI hardware for sending and receving is working ok. Whatever that is sent out, the data should be properly received.

Run the compiled program again.

You should see the following hex dump data. This means that your SPI peripheral is working fine.

spi mode: 0
bits per word: 8
max speed: 500000 Hz (500 KHz)

FF FF FF FF FF FF
40 00 00 00 00 95
FF FF FF FF FF FF
FF FF FF FF FF FF
FF FF FF FF FF FF
DE AD BE EF BA AD
F0 0D
pi@raspberrypi ~ $

I2C

The SPI port onboard the Raspberry is disable by default. The first thing to do is to enable the SPI port.

Edit the file "/etc/modprobe.d/raspi-blacklist.conf"

Comment off the line "blacklist i2c-bcm2708" with a # in front.

Key in Ctrl+‘X‘ to exit, then ‘Y‘ yes to save the change to the file, and finally ‘Enter‘. This will brings you back to the command prompt.

pi@raspberrypi ~ $ sudo nano /etc/modprobe.d/raspi-blacklist.conf

GNU nano 2.2.6 File: /etc/modprobe.d/raspi-blacklist.conf Modified

# blacklist spi and i2c by default (many users don‘t need them)

blacklist spi-bcm2708
#blacklist i2c-bcm27088

Edit the file "/etc/modules"

Add in "i2c-dev" to the end of the file.

Key in Ctrl+‘X‘ to exit, then ‘Y‘ yes to save the change to the file, and finally ‘Enter‘. This will brings you back to the command prompt.

pi@raspberrypi ~ $ sudo nano /etc/modules

# /etc/modules: kernel modules to load at boot time.
#
# This file contains the names of kernel modules that should be loaded
# at boot time, one per line. Lines beginning with "#" are ignored.
# Parameters can be specified after the module name.

snd-bcm2835
i2c-dev

Allow Pi User to Access I2C peripheral.

This allow configuration of the software.

Check to see if the SPI is successfully enable in the Raspberry Pi.

You should see "/dev/i2c-0 /dev/i2c-1" created.

pi@raspberrypi ~ $ ls /dev/i2c*
/dev/i2c-0 /dev/i2c-1
pi@raspberrypi ~ $

Running the test program.

You will see that there is a total of 0x77 or 119 blanks "--". This indicates that no I2C devices is detected on the bus. 

Other command:
- ifconfig eth0 (display the first ethernet adaptor) 
- ifconfig -a (show all network interface, active or inactive) 
- traceroute

Install Samba on the system so that my Raspberry Pi can be access from a Window operating system.

Ensure that the network cable (internet enabled) is plugged onto the Raspberry Pi before powering on the board. Enter the following command to install samba software. The process will fetch the installation from the internet.

Search for the section marked ##### Authentication #####,
Change the following text "# security = user" to "security = user".
To save the text file, Press "Ctrl+X", then ‘Y‘, then enter.

Use command "hostname -I" to check the IP address.

Alternate command "ifconfig" to check the IP address of my Raspberry Pi, which IP address is "192.168.1.99"

pi@raspberrypi ~ $ hostname -I
192.168.1.99

pi@raspberrypi ~ $  ifconfig
eth0  Link encap:Ethernet  HWaddr b8:27:eb:dc:ee:af
      inet addr:192.168.1.99  Bcast:192.168.1.255  Mask:255.255.255.0
      UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
      RX packets:337 errors:0 dropped:0 overruns:0 frame:0
      TX packets:198 errors:0 dropped:0 overruns:0 carrier:0
      collisions:0 txqueuelen:1000
      RX bytes:30734 (30.0 Kib)  TX bytes:20136 (19.6 Kib)

Go to window‘s to map a network drive. The network folder path is "//192.168.1.99". Check box for "Reconnect at logon" & "Connect using different credentials"

Check the network and port bind on the Raspberry Pi.

From the list, it can be seen that UDP port 6324 is currently being used by process ID PID 2361/java program.

Sometimes you may like to access to your Raspberry Pi without connecting your display monitor and your keyboard. This section provide a guide to allow access to your Raspberry Pi remotely through network connection.

How to locate your Raspberry Pi IP address from a remote computer?

The method above requires you to plugged a monitor display to your Raspberry Pi in order to obtain its IP address. The following method allows you to obtain raspberry pi address through thr

You can also check the IP address of your Raspberry Pi that is plugged into a dynamic network through the router webserver. Typical router‘s IP address for a local network is 192.168.1.1. You will need your user name and password to log into the router‘s webserver. From the webserver, you should be able to locate the device name "raspberrypi" (or known as hostname) and its allocated dynamic IP address and its MAC address.

Alternative, you can use this software "Advance Port Scanner" to scan for your Raspberry Device on the network.

pi@raspberrypi ~ $ hostname
raspberrypi

Note: To change the Raspberry Pi‘s hostname "raspberrypi", use nano text editor to edit the following file "/etc/hostname" and "/etc/hosts". Replace the old hostname "raspberrypi" to your new hostname. Your new hostname can only contains lower/upper case character, numbers, and ‘-‘.

Your new hostname will appear on the raspberry prompt, after the device reboot.

pi@raspberrypi ~ $ sudo nano /etc/hostname

pi@raspberrypi ~ $ sudo nano /etc/hosts

pi@raspberrypi ~ $ sudo reboot

pi@newHostname ~ $

Download this program MobaXterm, and install in your Window operating system. You can download fromhttp://mobaxterm.mobatek.net/


Alternative, you can also use this program call Putty.
http://www.chiark.greenend.org.uk/~sgtatham/putty/download.html

Alternative, you can also use this program call Filezilla
https://filezilla-project.org/ (for Microsoft Windows OS).
or (for Linux OS) "sudo apt-get install filezilla"

These program allow SSH connection logging in to your Raspberry Pi. You will be able to see what you would see with the display monitor and keyboard connected to your Raspberry Pi

Run the installed MobaXterm program.
Click on "Session"->"Open New Session".
Choose "SSH" as the session type.
Key in the IP address of your Raspberry Pi.
The standard port number for SSH Remote Login Protocol is 22.

Click "OK" to connect to your Raspberry Pi.

Key in the Login user name "pi", then press enter, and 
standard password "raspberry" then press enter key.

You will see the following display as on the right. 

Login: pi
Permanently added ‘192.168.1.95‘ (ECDSA) to the list of known hosts.
rasppi@192.168.1.95‘s password:
Linux raspberrypi 3.6.11+ #474 PREEMPT Thu Jun 13 17:14:42 BST 2013 armv6lThe programs included with the Debian GNU/Linux system are free software;
the exact distribution terms for each program are described in the
individual files in /usr/share/doc/*/copyright.

Debian GNU/Linux comes with ABSOLUTELY NO WARRANTY, to the extent
permitted by applicable law.
Last login: Mon Jul 22 13:47:57 2013
pi@raspberrypi ~ $

You may encounter the following error on the right.
If not, you can skip this section.
This happens when you login successfully for the first time, but then you reinstall the server. The key becomes different, and you get prompt for this security message.Access into your Raspberry Pi and key in the following command, 
"rm -f ~/.ssh/known_hosts"
Delete from your client computer. 
C:\Users\LSB\Documents\MobaXterm\home\.ssh\known_hosts.

You may need to reboot the Linux in order for the change to take effect "sudo reboot". 

It should solve the problem. For more information regarding this issue, you can visit the following website,
http://www.geekride.com/ssh-warning-remote-host-identification-has-changed/

@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @ @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY! Someone could be eavesdropping on you right now (man-in-the-middle attack)! It is also possible that a host key has just been changed. The fingerprint for the RSA key sent by the remote host is xx:xx:xx:xx:b1:66:fd:05:0c:43: .... ... .. .

pi@raspberrypi ~ $ leadpad&

pi@raspberrypi ~ $ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO...
...
...
Thread model: posix
gcc version 4.6.3 (Debian 4.6.3-14+rpi1)

Key in the following hello world source code into the nano editor.

When finish typing in the source code text, press CTRL+X to save this file "main.c", press ‘Y‘ to confirm. Press enter key to finish the process.

#include <stdio.h>

int main()
{
   printf("Hello World!!!");
   return(0);
}

For compiling C++ language (*.cpp file), use g++ compiler.

pi@raspberrypi ~ $ python -V 
Python 2.7.3

Key in the following hello world source code into the nano editor.

When finish typing in the source code text, press CTRL+X to save this file "hello.py", press ‘Y‘ to confirm. Press enter key to finish the process.

#!/usr/bin/python

print "Hello World!!!"nt "Boon, you‘re awesome"
else : 
print "Hello", name

Using Python to control the digital I/O port.
Before starting to program your I/O on Raspberry Pi, we will need to download and setup the library.

pi@raspberrypi ~ $ wget http://pypi.python.org/packages/source/R/RPi.GPIO/RPi.GPIO-0.1.0.tar.gz
pi@raspberrypi ~ $ tar zxf RPi.GPIO-0.1.0.tar.gz
pi@raspberrypi ~ $ cd RPi.GPIO-0.1.0
pi@raspberrypi ~ $ sudo python setup.py install

Try controlling the Raspberry Pi‘s digital I/O GPIO1 (pin12 of the header, GPIO18) as output port, using Python script.

1) import RPi.GPIO
2) setup I/O direction, as output port. 
3) set digital I/O port to logic ‘1‘, high
4) set digital I/O port to logic ‘0‘, low

You should see the LED lights up and switched off, if wired an indicator to pin 12.

pi@raspberrypi ~ $ sudo Python
>>> import RPi.GPIO as GPIO
>>> GPIO.setup(18, GPIO.OUT)
>>> GPIO.output(18, True)
>>> GPIO.output(18, False)

#!/usr/bin/python 

import sys
import time
import serial

#print title 
print("start python program.")#print out the arg passed from command line 
for arg in sys.argv:
  print arg#delay 0.1sec 
time.sleep(0.1)
#delay 1.0sec 
time.sleep(1) #setup serial port 
port = serial.Serial("/dev/ttyAMA0", baudrate=115200, timeout=3.0)#get user input
name = raw_input(‘what is your name? ‘)#conditional statement
if name == ‘Boon‘ :
  print "Boon, you‘re awesome"
else : 
  print "Hello", name

#while loop
while True: 
  port.write("\r\nSay something:")
  rcv = port.read(10)
  port.write("\r\nYou sent:" + repr(rcv))

#!/usr/bin/python

import time
import RPi.GPIO as GPIO

GPIO.setup(11, GPIO.IN)
while True:
  mybutton = GPIO.input(11)
  if mybutton == False:
    print "giggle"
  time.sleep(.2)

Note: As of Nov 2013, the official operating system for Raspberry Pi "Raspian" is installed with Java by default. Proceed to the step for installing Pi4J.

Installing Java to your Raspberry Pi

First, we will need to download and instal the Java JDK onto the Raspberry Pi.Do take note that the JDK version that we will be downloading is meant for Linux ARM processor "Linux ARM v6/v7 Soft Float ABI".
(28 July 2013)
JDK for Linux ARM, "jdk-21-linux-arm-sfp.tar.gz (65.12MB)"

You can download the lastest version of this file from thisJava website,
http://www.oracle.com/technetwork/java/javase/downloads/jdk7-downloads-1880260.html

Remember to accept the Oracle Binary Code License Agreement for Java SE.

Check that the Java environment variable is setup correctly.

Note: If the following error is encountered when the command "java -version" is executed. 
java: error while load­ing shared libraries: libjli.so: can­not open shared object file: No such file or directory

It is propably that you have installed the incorrect version of Debian Linux. At this point in time, Java SDK for Linux ARM has yet to support.

Please refer to the previous section, for the installtion of the correct Debian Linux version for use with Java SDK Linux ARM. 

Check if PI4J is installed correctly.
Go to PI4J directory.
Compile the example "WiringPiGpioExample.java".
Run the compile java program "WiringPiGpioExample".

I am able to see my rows of LED lighting up in a wave sequence, up and down non-stop.

pi@raspberrypi ~ $ cd /opt/pi4j/examples/
pi@raspberrypi /opt/pi4j/examples $ sudo javac -classpath .:classes:/opt/pi4j/lib/‘*‘ -d . WiringPiGpioExample.java
pi@raspberrypi /opt/pi4j/examples $ sudo java -classpath .:classes:/opt/pi4j/lib/‘*‘WiringPiGpioExample

Testing out with a simple Java program.
Let us do a hello world example.

Key in "nano hello.java".
This will open a text editor for us to key in the java source code for our hello world example.

Key in the following java source code.

Press ‘Ctrl+X‘ to exit, then ‘Y‘ to save, then press ‘Enter‘.

pi@raspberrypi ~ $ nano hello.java

class hello
{
   public static void main(String args[])
   {
      System.out.println("Hello World!");
   }
}

Compile the java source code "hello.java", a java compiled file "hello.class" will be generated.

pi@raspberrypi ~ $ javac hello.java

To run the program, key in "java hello".

You should be able to see the printed text "Hello World!" after execution.

pi@raspberrypi ~ $ java hello
Hello World!

Looking back to the wiringPi, which is the library for java to access to the native hardware I/O on the Raspberry Pi.

Taking a look at the java code using pi4j wiringPi.

- WiringPiGpioExample.java

Run the java program.

You may notice "wiringPiSetup: Unable to open /dev/mem". This means that you do not have access to the hardware.

Run the java program with the "sudo" in front as follows.

You should see the LED light running from left to right. 

pi@raspberrypi ~ $ java -classpath .:classes:/opt/pi4j/lib/‘*‘ WiringPiGpioExample

<--Pi4J--> GPIO test program
wiringPiSetup: Unable to open /dev/mem: Permission denied
==>> GPIO SETUP FAILED

pi@raspberrypi ~ $ sudo java -classpath .:classes:/opt/pi4j/lib/‘*‘ WiringPiGpioExample

<--Pi4J--> GPIO test program

Serial Java Programming with pi4j on Raspberry Pi

- SerialExample.java

Run the "SerialExample.java"

If you encounter error when opening the serial port, do check out the eariler posting to ensure that the serial port is properly configured.

CURRENT TIME: Mon Nov 04 12:23:23 SGT 2013
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CURRENT TIME: Mon Nov 04 12:23:24 SGT 2013
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CURRENT TIME: Mon Nov 04 12:23:25 SGT 2013
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Java examples (taken from www.pi4j.com)

- WiringPiGpioExample.java
- ControlGpioExample.java
- ListenGpioExample.java
- ShutdownGpioExample.java
- TriggerGpioExample.java
- SerialExample.java
- SystemInfoExample.java

Linux bash script for launching/starting Java program. The command to launch Java is similar to those in WinOs, except for some notation changes. Note the use of char ‘:‘ as the seperator and the slash ‘/‘ for its file path. WinOS uses ‘;‘ and the backslash ‘\‘. 
The script is similar to the batch file used in WinOS.

The following is an example of the script,
"run.sh"

Key in ". run.sh" to run the script in Linux command prompt.
Note: remember to make this file "run.sh" executable. (see examples in this website.)

inside file "run.sh"
#!/bin/bash
echo "Running SmartHomeSensors Java Program..."
java -classpath .:bin:lib/log4j-1.2.14.jar:lib/commons-logging-1.1.jar:classes:/opt/pi4j/lib/‘*‘:lib/json-simple-1.1.1.jar:lib/org.apache.httpcomponents.httpclient_4.3.1.jar:lib/utilities.jar:resource com.picControl.smartHomeSensors.MyMain

pi@raspberrypi ~ $ . run.sh

To auto run the script which launch the java program upon Raspberry Pi boot up (startup), edit the file "rc.local".

Add in the following to the file,

cd /home/pi/smartHomeSensor
echo "Run script for SmartHomeSensor Java program"
SCRIPT="/home/pi/smartHomeSensor/run.sh"
echo "run script \"-> $SCRIPT\""
sudo $SCRIPT &

The add command set the current directory to the project folder. During the boot process, it cannot be assume that you are in the user directory. Reference to the root directory to be safe.

Use sudo to run the script, and make the script run in the background.

#!/bin/sh -e
#
# rc.local
#
# This script is executed at the end of each multiuser runlevel.
# Make sure that the script will "exit 0" on success or any other
# value on error.
#
# In order to enable or disable this script just change the execution
# bits.
#
# By default this script does nothing.

# Print the IP address
_IP=$(hostname -I) || true
if [ "$_IP" ]; then
   printf "My IP address is %s\n" "$_IP"
fi

cd /home/pi/smartHomeSensor
echo "Run script for SmartHomeSensor Java program"ensor Java program"
SCRIPT="/home/pi/smartHomeSensor/run.sh"
echo "run script \"-> $SCRIPT\""
sudo $SCRIPT &

exit 0

pi@raspberrypi ~ $ sudo nano /etc/rc.local

Login to check if the java process is running.
command "ps ax" print out the list of processes (thread) currently running in Raspberry Pi. "| grep java" pipe the output result and print out only those result that have the word "java" in it.

The result shows that the java program is running with PID 2242 (process ID). Remember this number, for you may need to use it to kill the process.

pi@raspberrypi ~ $ ps ax | grep java
2242 ? Sl 0:44 java -classpath .:bin:lib/log4j-1.2.14.jar:lib/commons-logging-1.1.jar:classes:/opt/pi4j/lib/*:lib/json-simple-1.1.1.jar:lib/org.apache.httpcomponents.httpclient_4.3.1.jar:lib/utilities.jar:resource com.picControl.smartHomeSensors.MyMain
2461 pts/0 S+ 0:00 grep --color=auto java

Now grep "run.sh". Notice the PID 2241.

This is generated before the Java program is launch. Remember this PID no. You may need this number to kill the same java program.

pi@raspberrypi ~ $ ps ax | grep run.sh

2233 ? S 0:00 sudo /home/pi/smartHomeSensor/run.sh
2241 ? S 0:00 /bin/bash /home/pi/smartHomeSensor/run.sh
2481 pts/0 S+ 0:00 grep --color=auto run.sh

pi@raspberrypi ~ $ sudo kill -9 2242
pi@raspberrypi ~ $ ps ax | grep run.sh
2487 pts/0 S+ 0:00 grep --color=auto run.sh 
pi@raspberrypi ~ $ ps ax | grep java
2489 pts/0 S+ 0:00 grep --color=auto java

Commands Illustration

Access to /sys directory which is hidden.
Containing system peripherals directory/information, for example GPIO, I2C, tty (UART, teletype).
http://www.linusakesson.net/programming/tty/index.php

To get help or further details for any linux command, use the "man" command. 
Help manual for any command or program, where ???? is the command/program name.

Display the content of the file "XXXX".
Example to display Raspberry Pi hardware revision, key in "cat /proc/cpuinfo"

Example to display Linux OS information, key in "cat /etc/lsb-release"

Hardware : BCM2708
Revision : 000e
Serial : 000000005fdceeaf

Command "PS" List the program or threads running in the background of the Linux operating system (for the current user session only).
Where PID is the process ID number.

Command "ps" is a useful troubleshooting tools. Other related command is "top".

Other useful troubleshooting commands are,
- "strace", "ltrace"
- "mtrace"

pi@raspberrypi ~ $ ps
PID TTY TIME CMD
2803 pts/1 00:00:02 bash
2948 pts/1 00:00:00 ps

To list all the process running in the Raspberry Pi device, use command "PS AX".
You can see the process created by other user session and you can kill it as well.

These are the bash session started by various user session 0, 1, 2, etc... ,

3477 pts/0 T 0:00 -bash
347? pts/1 T 0:00 -bash
347? pts/2 T 0:00 -bash

This is a bash session started for the main hardware,

2121 tty1 S+ 0:01 -bash

To list only the PID for a particular program, you can use with grep.

pi@raspberrypi ~ $ ps ax 
PID TTY STAT TIME COMMAND
1 ? Ss 0:01 init [2]
2 ? S 0:00 [kthreadd]
3 ? S 0:00 [ksoftirqd/0]
5 ? S< 0:00 [kworker/0:0H]
6 ? S 0:01 [kworker/u:0]
7 ? S< 0:00 [kworker/u:0H]
8 ? S< 0:00 [khelper]
9 ? S 0:00 [kdevtmpfs]
10 ? S< 0:00 [netns]
12 ? S 0:00 [bdi-default]
13 ? S< 0:00 [kblockd]
14 ? S 0:00 [khubd]
15 ? S< 0:00 [rpciod]
16 ? S 0:00 [khungtaskd]
17 ? S 0:00 [kswapd0]
18 ? S 0:00 [fsnotify_mark]
19 ? S< 0:00 [nfsiod]
20 ? S< 0:00 [crypto]
27 ? S< 0:00 [kthrotld]
28 ? S< 0:00 [VCHIQ-0]
29 ? S< 0:00 [VCHIQr-0]
30 ? S< 0:00 [VCHIQs-0]
31 ? S< 0:00 [iscsi_eh]
32 ? S< 0:00 [dwc_otg]
33 ? S< 0:00 [DWC Notificatio]
35 ? S< 0:00 [deferwq]
36 ? S 0:00 [kworker/u:2]
37 ? S 0:08 [mmcqd/0]
38 ? S 0:00 [jbd2/mmcblk0p6-]
39 ? S< 0:00 [ext4-dio-unwrit]
154 ? Ss 0:00 udevd --daemon
1503 ? S 0:01 /usr/sbin/ifplugd -i lo -q -f -u0 -d10 -w -I
1592 ? S 0:07 /usr/sbin/ifplugd -i eth0 -q -f -u0 -d10 -w -I
1778 ? Sl 0:00 /usr/sbin/rsyslogd -c5
1863 ? Ss 0:00 /usr/sbin/cron
1888 ? Ss 0:00 dhclient -v -pf /run/dhclient.eth0.pid -lf /var/lib/dhcp/dhcli
1918 ? Ss 0:00 /usr/bin/dbus-daemon --system
1964 ? Ss 0:02 /usr/sbin/ntpd -p /var/run/ntpd.pid -g -u 102:104
2003 ? Ss 0:00 /usr/sbin/thd --daemon --triggers /etc/triggerhappy/triggers.d
2008 ? Ss 0:00 /usr/sbin/sshd
2037 tty1 Ss 0:00 /bin/login -f tty1
2038 tty2 Ss+ 0:00 /sbin/getty 38400 tty2
2039 tty3 Ss+ 0:00 /sbin/getty 38400 tty3
2040 tty4 Ss+ 0:00 /sbin/getty 38400 tty4
2041 tty5 Ss+ 0:00 /sbin/getty 38400 tty5
2042 tty6 Ss+ 0:00 /sbin/getty 38400 tty6
2044 ? Sl 0:01 /usr/sbin/console-kit-daemon --no-daemon
2111 ? Sl 0:00 /usr/lib/policykit-1/polkitd --no-debug
2121 tty1 S+ 0:01 -bash
2151 ? S 0:00 [kworker/0:0]
2249 ? Ss 0:00 sshd: pi [priv]
2256 ? S 0:00 sshd: pi@notty
2257 ? Ss 0:00 /usr/lib/openssh/sftp-server
2258 ? Ss 0:00 /usr/lib/openssh/sftp-server
2662 ? S 0:00 [flush-179:0]
2663 ? Ss 0:00 sshd: pi [priv]
2667 ? Ss 0:00 sshd: pi [priv]
2674 ? S 0:01 sshd: pi@pts/0
2678 ? S 0:00 sshd: pi@notty
2679 ? Ss 0:00 /usr/lib/openssh/sftp-server
2684 pts/0 Ss 0:03 -bash
3127 ? S 0:00 udevd --daemon
3130 ? S 0:00 udevd --daemon
3338 ? S 0:00 [kworker/0:1]
3393 ? Ss 0:00 sshd: pi [priv]
3397 ? Ss 0:00 sshd: pi [priv]
3404 ? S 0:00 sshd: pi@pts/1
3408 ? S 0:00 sshd: pi@notty
3409 ? Ss 0:00 /usr/lib/openssh/sftp-server
3416 pts/1 Ss+ 0:01 -bash
3469 ? S 0:00 [kworker/0:2]
3476 pts/0 R+ 0:00 ps ax
3477 pts/0 T 0:00 -bash
3478 pts/0 Tl 0:03 java -classpath .:bin:lib/log4j-1.2.14.jar:lib/commons-logging

pi@raspberrypi ~ $ ps ax | grep java
3478 pts/0 Tl 0:03 java -classpath .:bin:lib/log4j-1.2.14.jar:lib/commons-logging

To terminate the program running in the background thread, use the kill command. Where "####" is the process ID (PID)

Putting an option -9 will force the process to be killed.

The process PID can be kill from another user session, even if the PID is not listed in its session.

pi@raspberrypi ~ $ kill ####

or

pi@raspberrypi ~ $ kill -9 ####

To run the "bash_script.sh" without the command bash, set the file as executable and run the file. 

Note: You may encounter with the following 
./test.sh: /bin/bash^M: bad interpreter: No such file or directory.

There is a ‘^M‘ char detected at the end of the first line. Ensure that the script is not written on a Microsoft Window OS. Window‘s environment will append ‘^M‘ for enter key.

Use vi editor to view the file.
Type in command "vi bash_script.sh".
You will see the ‘^M‘ char in blue.
Delete those char. 

Press ‘:w‘ save the text file.
Press ‘:q‘ to exit the vi program.

Try again, it should work fine now.

To check the permission for the files in the current directory use "ls -l".

To check permission for a particular file, type out the file name behind "ls -l filname"

File permissiondrwxrwxrwx 2 pi pi

    d - represent the name as a directory.
    - - Regular file or program.
    l - file/dir is a symbolic link.
    s - setuid/setgid permissions. 
    t - sticky bit permissions.
    b - driver for storage medium.
    c - driver for communication hardware.


rwx - ‘r‘ refers to the read permission
      ‘w‘ refers to the write permission
      ‘x‘ refers to the permission to execute

1st "rwx" -> owner (‘u‘) 
2nd "rwx" -> group (‘g‘) 
3rd "rwx" -> all users (‘o‘ or ‘a‘) 
2 - referes to the number of hardlinks to the file.
pi pi -> Owner:Group

To change the file permission, use the following command,

"chmod a+x filename"
This will add all (‘a‘) with executable (‘x‘) permission.

"chmod a-x filename"
This will remove all (‘a‘) with executable (‘x‘) permission.You can also set file permission using binary references (set to _rwxr-----),
command "chmod 740 filename"To change file‘s owner and group,
command "chown newuser:newgroup filename" 

pi@raspberrypi ~ $ ls -l
drwxr-xr-x 2 pi pi 4096 May 30 04:07 Desktop
-rw-r--r-- 1 pi pi 5781 Feb  3  2013 ocr_pi.png
drwxrwxr-x 2 pi pi 4096 Mar 10 18:20 python_games

pi@raspberrypi ~ $ ls -l Desktop 
drwxr-xr-x 2 pi pi 4096 May 30 04:07 Desktop

pi@raspberrypi ~ $ chmod a+x ocr_pi.png
pi@raspberrypi ~ $ ls -l
drwxr-xr-x 2 pi pi 4096 May 30 04:07 Desktop
-rwxr-xr-x 1 pi pi 5781 Feb  3  2013 ocr_pi.png
drwxrwxr-x 2 pi pi 4096 Mar 10 18:20 python_games

pi@raspberrypi ~ $ chmod a-x ocr_pi.png
pi@raspberrypi ~ $ ls -l
drwxr-xr-x 2 pi pi 4096 May 30 04:07 Desktop
-rw-r--r-- 1 pi pi 5781 Feb  3  2013 ocr_pi.png
drwxrwxr-x 2 pi pi 4096 Mar 10 18:20 python_games

Auto Login (login without being prompt for password). Edit the file /etc/inittab.

Comment away the following line by inserting a ‘#‘ in front of the statement.
"#1:2345:respawn:/sbin/getty 115200 tty1"
and insert the following line below it.
"1:2345:respawn:/bin/login -f pi tty1 </dev/tty1 >/dev/tty1 2>&1"

Reboot the system and you should be able to power up and go striaght into the command prompt without being prompt for user ID and password. 

pi@raspberrypi ~ $ sudo nano /etc/inittab

#1:2345:respawn:/sbin/getty 38400 tty1
1:2345:respawn:/bin/login -f pi tty1 </dev/tty1 >/dev/tty1 2>&1

Run a script after login (user specific),
by adding the following line to the end of the file /etc/profile (similar to /home/pi/.bashrc) 
". /home/pi/script1.sh"

"script1.sh" will run after the user has been sucessfully login. Local or remote user will get to auto execute "script1.sh" after login.

NOTE!!!
Please ensure to set the file as executable and run the file.

Run a script after the booting process (or within the booting process), but before the login (using service method).

1) Create a script "script2.sh" in the folder /etc/init.d/script2.sh.
"sudo nano /etc/init.d/script2.sh"

2) Make the script executable.
"sudo chmod 755 /etc/init.d/script2.sh" 

3) Test the script (service start).
"sudo /etc/init.d/script2.sh start" 

4) Test the script (service stop).
"sudo /etc/init.d/script2.sh stop" 

5) Register the script to be run at start-up (with default priorities).
"sudo update-rc.d script2.sh defaults"

update-rc.d is a program which mananged the start-up and shutdown using the file /etc/rcX.d (where rcX.d means rc0.d to rc6.d, rcS.d)
You can key in the following command to view the link to your script. 
"ls -l /etc/rc?.d/"

6) To remove the script from start-up,
"sudo update-rc.d -f script2.sh remove"
‘-f‘ is to force the removal of the symlinks even if the script is still under the /etc/init.d folder. Remember to delete away your script away from the folder /etc/init.d 
Note: The command above will only disable the service until the next time the service is upgraded. To enable the service will not be re-enabled upon upgrade, type the following command, "update-rc.d script2.sh stop 80 0 1 2 3 4 5 6"

7) You can also register the services with custom priorities. (you can visit this website)

#! /bin/sh
# /etc/init.d/script2.sh### BEGIN INIT INFO
# Provides: --- 
# Required-Start: $remote_fs $syslog
# Required-Stop: $remote_fs $syslog
# Default-Start: 2 3 4 5
# Default-Stop: 0 1 6
# Short-Description: Simple script to start a program at boot
# Description: A simple script which will start / stop a program a boot / shutdown.
### END INIT INFO# If you want a command to always run, put it here# Carry out specific functions when asked to by the system
case "$1" in
  start)
    echo "--- script<2> start ---------"
    # run application you want to start
    # /usr/local/bin/noip2
    ;;
  stop)
    echo "--- script<2> stop ---------"
    # kill application you want to stop
    # killall noip2
    ;;
  *)
    echo "Usage: /etc/init.d/noip {start|stop}"
    exit 1
    ;;
esac

exit 0

After testing with various start-up scripts process, I have summarizes the sequence in which the scripts are call up.

--- Booting process --------
    before user login

- Script registered with update-rc.d
- /etc/rc.local

--- User login prompt-------
    after user login

- /etc/profile
- /home/pi/.bashrc

--- End of start-up process -----
    command prompt 

Custom Splash screen
"apt-get install fbi"

Name your image file to "splash.png" and copy to the directory /etc

****encounter problem copying file to /etc directory.***
If the error above is encountered, copy the image file to the user directory instead. Then use "sudo mv" (move file command) to move it to the etc directory.

Edit a new text file "sudo nano".
Cut and paste the followings,

#! /bin/sh
### BEGIN INIT INFO
# Provides:          asplashscreen
# Required-Start:
# Required-Stop:
# Should-Start:
# Default-Start:     S
# Default-Stop:
# Short-Description: Show custom splashscreen
# Description:       Show custom splashscreen
### END INIT INFO      
do_start () {    
    /usr/bin/fbi -T 1 -noverbose -a /etc/splash.png      
    exit 0  
}    
case "$1" in  
  start|"")  
    do_start  
    ;;  
  restart|reload|force-reload)  
    echo "Error: argument ‘$1‘ not supported" >&2  
    exit 3  
    ;;  
  stop)  
    # No-op  
    ;;  
  status)  
    exit 0  
    ;;  
  *)  
    echo "Usage: asplashscreen [start|stop]" >&2  
    exit 3  
    ;;  
esac   
 
:

save the file as /etc/init.d/asplashscreen

make the script executable and install it for init mode:

"sudo chmod a+x /etc/init.d/asplashscreen"

"sudo insserv /etc/init.d/asplashscreen"

Reboot

"sudo reboot "

The custom logo is displayed near the end of the booting process, not at the beginning.

This is followed by a blank screen.
Press <Ctrl + Alt + F2> to return to the command prompt. 

pi@raspberrypi ~ $ sudo apt-get install fbi

pi@raspberrypi ~ $ sudo mv splash.png /etc

pi@raspberrypi ~ $ sudo nano

cut and paste, save file as

/etc/init.d/asplashscreen

pi@raspberrypi ~ $ sudo chmod a+x /etc/init.d/asplashscreen

pi@raspberrypi ~ $ sudo insserv /etc/init.d/asplashscreen

pi@raspberrypi ~ $ sudo reboot

Place your favourite wall paper on the desktop.
-> Login GUI Desktop
-> On the desktop, press right click , and -> Select "Desktop Preferences".
-> Select your favourite wallpaper.

enable sound
sudo modprobe snd_bcm2835
disable sound
rmmod snd_bcm2835

Root access

Some users believe that the root account has a password that they are not aware of. This is not the case. For security reasons, Raspbmc has been hardened by disabling the root account. There is no need to enable the root account in Raspbmc, and doing so increases the likelihood of you causing damage to the system. Instead, the following options are recommended:

• Prefixing the command requiring root privileges with sudowill allow you to run the command as root.
• Alternatively, you can temporarily have root privileges with the command sudo -s

If you truly wish to enable root access so that you can login as root. You can do so as follows:sudo passwd rootYou have now set a root password you can login with.To disable the root account again:

sudo passwd -l root

Changing Raspberry Pi user name ("newUserName") and password ("abc1234").

Follow the following procedure,

pi@raspberrypi ~ $ sudo adduser newUserName

Adding user `newUserName‘ ...
Adding new group `newUserName‘ (1004) ...
Adding new user `newUserName‘ (1001) with group `newUserName‘ ...
Creating home directory `/home/newUserName‘ ...
Copying files from `/etc/skel‘ ...
Enter new UNIX password:
Retype new UNIX password:
passwd: password updated successfully
Changing the user information for newUserName
Enter the new value, or press ENTER for the default
     Full Name []:
     Room Number []:
     Work Phone []:
     Home Phone []:
     Other []:
Is the information correct? [Y/n] y
 

Give the new user sudo privileges, by editing the sudoers file.
Copy the line with the default user name pi and copy below it. Change the name pi to your newUserName.

After you have finished, key in Ctrl+‘x‘ then ‘Y‘, followed by enter key.

pi@raspberrypi ~ $ sudo visudo

pi ALL=(ALL) NOPASSWD: ALL
newUserName ALL=(ALL) NOPASSWD: ALL

pi@raspberrypi ~ $ logout

pi@raspberrypi ~ $ login

Enter your newUserName and passsword.

Try to see if you can edit the sudoers file. The file can only be edited if it has sudo access privileges.

Delete the line containing the "pi" user, if it is no longer required.
After you have finished, key in Ctrl+‘x‘ then ‘Y‘, followed by enter key.

Delete the old user "pi" account,
or add in option flag "-remove-home" to remove the "/home/pi" directory as well.

The process of changing the Raspberry Pi user name and password is completed.
Reboot the Raspberry Pi for the new user name to take effect. Old user name can no longer be in use.

(method do not work so well. still able login using pi as the user name.)

newUserName@raspberrypi ~ $ sudo nano /etc/kbd/config

BLANK_TIME=0
BLANK_DPMS=off
POWERDOWN_TIME=0

Advance command
- "lsusb" List all the USB peripherals
- "df /" check disk space
- "free" check memory RAM 

Linux Files and Directory Structure Reference

Linux Command Reference
- linux_quickref.pdf
- linuxcard.pdf

Add Wifi to Raspberry Pi 
Add a Wifi to tap the internet access from your Wifi wireless network.

WiFi dongle keyword
- Edimax EW-7811Un 
- Dynamode WL-700N-RXS

Commands Illustration

In order to connect to the Wifi, the first thing you will need is a Wifi dongle for your Raspberry Pi. The following contains the list of Wifi adaptors available that can work with Raspberry Pi.

http://elinux.org/RPi_USB_Wi-Fi_Adapters

In this example, D-Link DWA-123, H/W Ver.: B1, P/N IWA123EU.....B1G

Original setup look like the following,
------------------------------------------------------
auto lo

iface lo inet loopback
iface eth0 inet dhcp

allow-hotplug wlan0
iface wlan0 inet manual
wpa-roam /etc/wpa_supplicant/wpa_supplicant.conf
iface default inet dhcp 

If you have a DHCP server, change to the following 
------------------------------------------------------
auto lo

iface lo inet loopback
iface eth0 inet dhcp

allow-hotplug wlan0
auto wlan0
iface wlan0 inet manualdhcp
wpa-roam /etc/wpa_supplicant/wpa_supplicant.conf
iface default inet dhcp