Chapter 3: Exploring Embedded Linux Systems

[fusion_builder_container backgroundcolor=”no” backgroundimage=”” backgroundrepeat=”no-repeat” backgroundposition=”left top” backgroundattachment=”scroll” video_webm=”” video_mp4=”” video_ogv=”” video_preview_image=”” overlay_color=”” video_mute=”yes” video_loop=”yes” fade=”no” bordersize=”0px” bordercolor=”” borderstyle=”” paddingtop=”0px” paddingbottom=”0px” paddingleft=”0px” paddingright=”0px” menu_anchor=”” equal_height_columns=”no” hundred_percent=”no” class=”” id=””][fusion_builder_row][fusion_builder_column type=”1_1″ layout=”1_1″ background_position=”left top” background_color=”” border_size=”” border_color=”” border_style=”solid” spacing=”yes” background_image=”” background_repeat=”no-repeat” padding_top=”” padding_right=”” padding_bottom=”” padding_left=”” margin_top=”0px” margin_bottom=”0px” class=”” id=”” animation_type=”” animation_speed=”0.3″ animation_direction=”left” hide_on_mobile=”no” center_content=”no” min_height=”none” last=”no” hover_type=”none” link=”” border_position=”all”][fusion_title size=”1″ content_align=”left” style_type=”single solid” sep_color=”” class=”” id=””]Introduction[/fusion_title][fusion_text columns=”” column_min_width=”” column_spacing=”” rule_style=”default” rule_size=”” rule_color=”” hide_on_mobile=”small-visibility,medium-visibility,large-visibility” class=”” id=””]

This is the chapter web page to support the content in Chapter 3 of the book: Exploring BeagleBone – Tools and Techniques for Building with Embedded Linux. The summary introduction to the chapter is as follows:

This chapter exposes you to the core concepts, commands, and tools required to effectively manage the Beagle-based embedded Linux system. The first part of the chapter is descriptive; it explains the basics of embedded Linux and the Linux boot process. After that, you learn step by step how to manage Linux systems. For this exercise, you are strongly encouraged to open a terminal connection to your board and follow along. Next, the chapter describes the Git source code management system. This topic is an important one because the source code examples in this book are distributed via GitHub. Desktop virtualization is also described; it is useful for cross-platform development in later chapters. The chapter finishes by describing how you can download the source code examples for this book.

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Learning Outcomes

After completing this chapter, you should be able to:

• Describe the basic concept of an embedded Linux system.
• Describe how embedded Linux devices, such as the Beagle boards, boot the Linux OS.
• Describe important Linux concepts, such as kernel space, user space, and system initialization using systemd.
• Perform Linux system administration tasks on the Beagle boards.
• Use the Linux file system effectively.
• Use a range of Linux commands for file and process management.
• Manage your own software development projects using Git.
• Install a Linux distribution on your desktop computer host OS using desktop virtualization tools, such as VirtualBox.
• Download the source code for this book using Git.

[/fusion_text][/fusion_builder_column][fusion_builder_column type=”2_5″ layout=”2_5″ last=”yes” spacing=”yes” background_color=”” background_image=”” background_repeat=”no-repeat” background_position=”left top” border_size=”0px” border_color=”” border_style=”” padding_top=”” padding_right=”” padding_bottom=”” padding_left=”” class=”” id=”” min_height=”” hover_type=”none” link=”” border_position=”all”][fusion_text][toc][/fusion_text][fusion_sharing tagline=”Share this page:” tagline_color=”” title=”Exploring BeagleBone: Chapter 1″ link=”http://exploringbeaglebone.com/chapter1/” description=”” pinterest_image=”” icons_boxed=”” icons_boxed_radius=”4px” box_colors=”” icon_colors=”” tooltip_placement=”” backgroundcolor=”” class=”” id=”” /][/fusion_builder_column][/fusion_builder_row][/fusion_builder_container][fusion_builder_container backgroundcolor=”no” backgroundimage=”” backgroundrepeat=”no-repeat” backgroundposition=”left top” backgroundattachment=”scroll” video_webm=”” video_mp4=”” video_ogv=”” video_preview_image=”” overlay_color=”” video_mute=”yes” video_loop=”yes” fade=”no” bordersize=”0px” bordercolor=”” borderstyle=”” paddingtop=”0px” paddingbottom=”0px” paddingleft=”0px” paddingright=”0px” menu_anchor=”” equal_height_columns=”no” hundred_percent=”no” class=”” id=””][fusion_builder_row][fusion_builder_column type=”1_1″ layout=”1_1″ background_position=”left top” background_color=”” border_size=”” border_color=”” border_style=”solid” spacing=”yes” background_image=”” background_repeat=”no-repeat” padding_top=”” padding_right=”” padding_bottom=”” padding_left=”” margin_top=”0px” margin_bottom=”0px” class=”” id=”” animation_type=”” animation_speed=”0.3″ animation_direction=”left” hide_on_mobile=”no” center_content=”no” min_height=”none” last=”no” hover_type=”none” link=”” border_position=”all”][fusion_title size=”1″ content_align=”left” style_type=”single solid” sep_color=”” class=”” id=””]Further Materials[/fusion_title][/fusion_builder_column][fusion_builder_column type=”1_1″ layout=”1_1″ background_position=”left top” background_color=”” border_size=”” border_color=”” border_style=”solid” spacing=”yes” background_image=”” background_repeat=”no-repeat” padding_top=”” padding_right=”” padding_bottom=”” padding_left=”” margin_top=”0px” margin_bottom=”0px” class=”” id=”” animation_type=”” animation_speed=”0.3″ animation_direction=”left” hide_on_mobile=”no” center_content=”no” min_height=”none” last=”no” hover_type=”none” link=”” border_position=”all”][fusion_title size=”2″ content_align=”left” style_type=”single solid” sep_color=”” class=”” id=””]The tree utility[/fusion_title][fusion_text]

An additional utility that is not described in Chapter 3 is the tree program. It allows you to obtain a visual display of the directory tree using only the Linux terminal. The command is not installed by default, so begin with:

molloyd@beaglebone:~/$ sudo apt-get install tree

Once the tree program is installed, you can test it on a directory of your choice, for example:

molloyd@beaglebone:~$ cd exploringBB/
molloyd@beaglebone:~/exploringBB$ ls
License.txt chp02 chp05 chp08 chp10 chp12 extras
README.md chp03 chp06 chp09 chp11 chp13 library
molloyd@beaglebone:~/exploringBB$ tree library
library
|-- EBBGPIO.cpp
|-- ExploringBB.Doxyfile
|-- bus
| |-- BusDevice.cpp
| |-- BusDevice.h
| |-- I2CDevice.cpp
| |-- I2CDevice.h
| |-- SPIDevice.cpp
| `-- SPIDevice.h
|-- display
| |-- LCDCharacterDisplay.cpp
| |-- LCDCharacterDisplay.h
| |-- SevenSegmentDisplay.cpp
| `-- SevenSegmentDisplay.h
|-- gpio
| |-- GPIO.cpp
| |-- GPIO.h
| |-- PWM.cpp
| |-- PWM.h
| |-- util.cpp
| `-- util.h
|-- libEBBLibrary.so
|-- motor
| |-- DCMotor.cpp
| |-- DCMotor.h
| |-- Servo.cpp
| |-- Servo.h
| |-- StepperMotor.cpp
| `-- StepperMotor.h
|-- network
| |-- SocketClient.cpp
| |-- SocketClient.h
| |-- SocketServer.cpp
| `-- SocketServer.h
`-- sensor
|-- ADXL345.cpp
|-- ADXL345.h
|-- BMA180.cpp
|-- BMA180.h
|-- ITG3200.cpp
`-- ITG3200.h
6 directories, 35 files

You can also use options (use man tree to see the full list) such as: -a display all files including hidden files, -l follows symbolic links, -u displays the owner, -C turns on colorization, -L 2 displays only the first two levels, and -d displays only directories. So, for example:

molloyd@beaglebone:~$ tree -dL 1 ~/exploringBB/
/home/molloyd/exploringBB/
|-- chp02
|-- chp03
|-- chp05
|-- chp06
|-- chp08
|-- chp09
|-- chp10
|-- chp11
|-- chp12
|-- chp13
|-- extras
`-- library
12 directories

displays only the first level of directories in the exploringBB directory.[/fusion_text][fusion_separator style_type=”shadow” top_margin=”10″ bottom_margin=”10″ sep_color=”” icon=”fa-linux” width=”” class=”” id=”” /][/fusion_builder_column][fusion_builder_column type=”1_1″ layout=”1_1″ background_position=”left top” background_color=”” border_size=”” border_color=”” border_style=”solid” spacing=”yes” background_image=”” background_repeat=”no-repeat” padding_top=”” padding_right=”” padding_bottom=”” padding_left=”” margin_top=”0px” margin_bottom=”0px” class=”” id=”” animation_type=”” animation_speed=”0.3″ animation_direction=”left” hide_on_mobile=”no” center_content=”no” min_height=”none” last=”no” hover_type=”none” link=”” border_position=”all”][fusion_title size=”2″ content_align=”left” style_type=”single solid” sep_color=”” class=”” id=””]VirtualBox: Installing a Linux Guest Under a Windows Host[/fusion_title][fusion_text]Here are some tips on installing a Linux guest VirtualBox VM under a Windows host:

• Enable VT-x/AMD-V in the system BIOS settings of your physical computer in order to run a 64-bit guest OS.
• Install VirtualBox (virtualbox.org) on your host OS.
• Download your favourite Linux distribution as an ISO file. In this book 64-bit Debian is used. Download the Net debian-jessie-DI-rc1-amd64-netinst.iso or equivalent from the page www.debian.org/releases/. Do not use the ia64 branch unless you are using a high-end Itanium-based server. Important: see note at the top of the page about Debian Wheezy.
• Start Oracle VM VirtualBox Manager and choose New. If available, give the installation 2GB+ memory. Create a virtual hard drive (VDI format, dynamic allocated) and make the size much greater than the 8GB it recommends. Choose the location on your computer to store the disk and use a minimum of 25–30GB! It is difficult to resize a disk after the fact. If you choose “dynamically allocated”, it will only occupy real disk space when you fill the Linux disk, so feel free to choose a large disk size.
• You now have a new VM that is powered off. Select it and click on settings. Under storage you should see your VDI (under SATA) and an “Empty” entry (under IDE). Select the “Empty” entry and click the disk icon under Attributes. Find and select the Linux ISO file that you downloaded, as shown in the figure below.

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Figure 2-A1: The VirtualBox VM configuration pane

• Start your VM and install Linux by booting off the virtual drive. If you see a message “No Boot Device,” go to Settings System and disable the floppy drive.
• Once your guest OS is running, choose Devices Install Guest Additions from the menu bar of your VirtualBox window. If all goes well, you will now be able to resize the window and cut-and-paste text between the host and guest OSs (by enabling Devices ⇒ Shared ⇒ Clipboard Bidirectional).
• Choose “Devices”->”Insert Guest Additions CD image…”
• If the guest additions do not install automatically, follow these steps (for Debian desktop — tested on Wheezy and Jessie images) in a terminal window:

molloyd@debian:~$ su -
root@debian:~# apt-get update
root@debian:~# apt-get install build-essential module-assistant
root@debian:~# m-a prepare
root@debian:~# cd /media/cdrom
root@debian:~# sh ./VBoxLinuxAdditions.run
root@debian:~# reboot

•  With your network settings set as NAT on Adapter 1 (default setting) you should now be able to ping 192.168.7.2 (your BBB when using Internet-over-USB), or its equivalent network IP address (if connected by regular Ethernet).

 If you go to the VirtualBox System ⇒ Processor settings, you will see the number of cores that can be allocated to the guest OS. On an Intel i7 processor you will see either 16 or 24 as the upper limit, depending on your exact processor. On a 4-core processor, you will see one core per thread, so 8 “real” cores, and you will also see that number again in “virtual” cores. Do not use virtual cores, as they will be provided through time slicing and your machine may slow down considerably. The maximum number of cores you should allocate to your guest OS is the total number of real cores minus one.

[/fusion_text][fusion_separator style_type=”shadow” top_margin=”” bottom_margin=”20″ sep_color=”#9b9b9b” icon=”” width=”” class=”” id=”” /][/fusion_builder_column][fusion_builder_column type=”1_1″ layout=”1_1″ background_position=”left top” background_color=”” border_size=”” border_color=”” border_style=”solid” spacing=”yes” background_image=”” background_repeat=”no-repeat” padding_top=”” padding_right=”” padding_bottom=”” padding_left=”” margin_top=”0px” margin_bottom=”0px” class=”” id=”” animation_type=”” animation_speed=”0.3″ animation_direction=”left” hide_on_mobile=”no” center_content=”no” min_height=”none” last=”no” hover_type=”none” link=”” border_position=”all”][fusion_title size=”2″ content_align=”left” style_type=”single solid” sep_color=”” class=”” id=””]Useful tools – Cairo Dock [/fusion_title][fusion_text]The latest windowing interface for Debian Jessie contains some very nice features, but it is quite lean. One tool that is useful and will be familiar to Mac OS X users is the Cairo Dock. It is illustrated in Figure 2-A2 below. You can install it using the following step:

molloyd@DebianJessieVM:~$ sudo apt-get install cairo-dock

Figure 2-A2: The Cairo Dock in action under Debian 8 (Jessie)

Debian 8 Jessie uses Gnome 3. To start up this dock automatically on boot you can perform the following steps:

molloyd@DebianJessieVM:~$ gnome-tweak-tool

And then click “Startup Applications” on the left-hand menu. On the right-hand pane click on the “+” icon and add Cairo-Dock to the list.[/fusion_text][/fusion_builder_column][/fusion_builder_row][/fusion_builder_container][fusion_builder_container backgroundcolor=”no” backgroundimage=”” backgroundrepeat=”no-repeat” backgroundposition=”left top” backgroundattachment=”scroll” video_webm=”” video_mp4=”” video_ogv=”” video_preview_image=”” overlay_color=”” video_mute=”yes” video_loop=”yes” fade=”no” bordersize=”0px” bordercolor=”” borderstyle=”” paddingtop=”0px” paddingbottom=”0px” paddingleft=”0px” paddingright=”0px” menu_anchor=”” equal_height_columns=”no” hundred_percent=”no” class=”” id=””][fusion_builder_row][fusion_builder_column type=”1_1″ layout=”1_1″ background_position=”left top” background_color=”” border_size=”” border_color=”” border_style=”solid” spacing=”yes” background_image=”” background_repeat=”no-repeat” padding_top=”” padding_right=”” padding_bottom=”” padding_left=”” margin_top=”0px” margin_bottom=”0px” class=”” id=”” animation_type=”” animation_speed=”0.3″ animation_direction=”left” hide_on_mobile=”no” center_content=”no” min_height=”none” last=”no” hover_type=”none” link=”” border_position=”all”][fusion_separator style_type=”shadow” top_margin=”” bottom_margin=”20″ sep_color=”#9b9b9b” icon=”” width=”” class=”” id=”” /][/fusion_builder_column][fusion_builder_column type=”1_1″ layout=”1_1″ background_position=”left top” background_color=”” border_size=”” border_color=”” border_style=”solid” spacing=”yes” background_image=”” background_repeat=”no-repeat” padding_top=”” padding_right=”” padding_bottom=”” padding_left=”” margin_top=”0px” margin_bottom=”0px” class=”” id=”” animation_type=”” animation_speed=”0.3″ animation_direction=”left” hide_on_mobile=”no” center_content=”no” min_height=”none” last=”no” hover_type=”none” link=”” border_position=”all”][fusion_title size=”1″ content_align=”left” style_type=”single solid” sep_color=”” class=”” id=””]External Resources[/fusion_title][/fusion_builder_column][/fusion_builder_row][/fusion_builder_container][fusion_builder_container hundred_percent=”yes” overflow=”visible”][fusion_builder_row][fusion_builder_column type=”1_2″ layout=”1_2″ last=”no” spacing=”yes” background_color=”” background_image=”” background_repeat=”no-repeat” background_position=”left top” border_size=”0px” border_color=”” border_style=”” padding_top=”” padding_right=”” padding_bottom=”” padding_left=”” class=”” id=”” min_height=”” hover_type=”none” link=”” border_position=”all”][fusion_title size=”2″ content_align=”left” style_type=”single solid” sep_color=”” class=”” id=””]Important Documents[/fusion_title][/fusion_builder_column][fusion_builder_column type=”1_2″ layout=”1_2″ last=”yes” spacing=”yes” background_color=”” background_image=”” background_repeat=”no-repeat” background_position=”left top” border_size=”0px” border_color=”” border_style=”” padding_top=”” padding_right=”” padding_bottom=”” padding_left=”” class=”” id=”” min_height=”” hover_type=”none” link=”” border_position=”all”][fusion_title size=”2″ content_align=”left” style_type=”single solid” sep_color=”” class=”” id=””]External Web Sites[/fusion_title][/fusion_builder_column][fusion_builder_column type=”1_4″ layout=”1_4″ last=”no” spacing=”yes” background_color=”” background_image=”” background_repeat=”no-repeat” background_position=”left top” border_size=”0px” border_color=”” border_style=”” padding_top=”” padding_right=”” padding_bottom=”” padding_left=”” class=”” id=”” min_height=”” hover_type=”none” link=”” border_position=”all”][fusion_imageframe lightbox=”no” style_type=”dropshadow” bordercolor=”” bordersize=”0px” borderradius=”0″ stylecolor=”” align=”center” link=”http://git-scm.com/book/en/v2″ linktarget=”_blank” animation_type=”0″ animation_direction=”down” animation_speed=”0.1″ class=”” id=””] [/fusion_imageframe][fusion_text]

Pro Git book (free online)

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The BeagleBone Black System Reference Manual (SRM)

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• The Debian Policy Manual: tiny.cc/ebb303

[/fusion_text][/fusion_builder_column][/fusion_builder_row][/fusion_builder_container][fusion_builder_container backgroundcolor=”no” backgroundimage=”” backgroundrepeat=”no-repeat” backgroundposition=”left top” backgroundattachment=”scroll” video_webm=”” video_mp4=”” video_ogv=”” video_preview_image=”” overlay_color=”” video_mute=”yes” video_loop=”yes” fade=”no” bordersize=”0px” bordercolor=”” borderstyle=”” paddingtop=”0px” paddingbottom=”0px” paddingleft=”0px” paddingright=”0px” menu_anchor=”” equal_height_columns=”no” hundred_percent=”no” class=”” id=””][fusion_builder_row][fusion_builder_column type=”1_1″ layout=”1_1″ background_position=”left top” background_color=”” border_size=”” border_color=”” border_style=”solid” spacing=”yes” background_image=”” background_repeat=”no-repeat” padding_top=”” padding_right=”” padding_bottom=”” padding_left=”” margin_top=”0px” margin_bottom=”0px” class=”” id=”” animation_type=”” animation_speed=”0.3″ animation_direction=”left” hide_on_mobile=”no” center_content=”no” min_height=”none” last=”no” hover_type=”none” link=”” border_position=”all”][fusion_title size=”2″ content_align=”left” style_type=”single solid” sep_color=”” class=”” id=””]Recommended Books on the Content in this Chapter[/fusion_title][fusion_text][amazon asin=1593273894&template=Iframe Image] [amazon asin=1593275676&template=Iframe Image] [amazon asin=111821854X&template=Iframe Image] [amazon asin=0131480057&template=Iframe Image] [amazon asin=1484200772&template=Iframe Image] [amazon asin=1449316387&template=Iframe Image][/fusion_text][/fusion_builder_column][fusion_builder_column type=”1_1″ layout=”1_1″ background_position=”left top” background_color=”” border_size=”” border_color=”” border_style=”solid” spacing=”yes” background_image=”” background_repeat=”no-repeat” padding_top=”” padding_right=”” padding_bottom=”” padding_left=”” margin_top=”0px” margin_bottom=”0px” class=”” id=”” animation_type=”” animation_speed=”0.3″ animation_direction=”left” hide_on_mobile=”no” center_content=”no” min_height=”none” last=”no” hover_type=”none” link=”” border_position=”all”][fusion_title size=”1″ content_align=”left” style_type=”single solid” sep_color=”” class=”” id=””]Errata[/fusion_title][fusion_text columns=”” column_min_width=”” column_spacing=”” rule_style=”default” rule_size=”” rule_color=”” hide_on_mobile=”small-visibility,medium-visibility,large-visibility” class=”” id=””]

• None as yet in Revision 2

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