Embedded Systems and Linux Overview

Embedded Systems

• Embedded systems are designed for a specific task, using hardware optimized for that purpose.
• Users are responsible for supporting the embedded system, not the businesses selling the associated hardware.
• Businesses cannot charge for software, only hardware.
• Companies must share modifications to the system.
• Embedded systems' software source code is often viewable.

Linux Operating Systems

• Linux initially ran on specialized processor chips.
• Linux's original support included Intel 386 PCs.
• Macintosh systems were not an original method of Linux support.

Raspberry Pi Computers

• Bundling utilities, management tools and application software with a Linux kernel is called a distribution of Linux.
• A distribution is not a trademark or a type of hardware or a text editor.

Software Release Cycle

• A software release cycle describes the frequency of implementation of security fixes, upgrades and reboots needed when new software is introduced.

Apple's OS X

• OS X is tightly integrated with Apple hardware.
• OS X has the capability of running Windows binaries.
• OS X's primary use in the computer world is the management of network services.
• OS X is a fully certified UNIX distribution.
• OS X is derived from Linux.
• OS X is partially based on code from the FreeBSD project.

Microsoft Windows

• Microsoft Windows is known for being backwards compatible with previous versions.
• Windows includes a Linux compatibility mode.
• Windows incorporates a script environment called PowerShell.
• Windows has a new desktop version released annually.
• Windows maintains a short maintenance cycle.
• Windows offers desktop and server products.
• Windows is an interpreted programming language.
• Windows enables more features than compiled languages.
• Windows is converted into machine-specific instructions as the program runs.
• Windows requires a linking step but no compilation step.
• Windows takes fewer resources to run than a compiled language.

Linux Shells

• The two primary families of Linux shells are Bourne Shell and C Shell (or Korn Shell).
• Emacs and Python Shell are not listed as the fundamental Linux shell types.

Virtualization

• In virtualization, the host machine runs the virtual machines, while a guest is the machine that runs virtual machines.
• The terms host and guest can, however, be used interchangeably in certain situations.

Cloud Computing

• Cloud computing is a system where resources are shared among many users, which results in fewer resource requirements for each individual user.
• Cloud computing allows users in various regions to work together in real time.
• Cloud computing is useful for both business and home users.
• Cloud computing is made possible by faster internet speeds.

Strong Passwords

• Strong passwords include a mixture of uppercase and lower case letters.
• Strong passwords should contain at least 10 characters.
• Strong passwords should include unique symbols for increased security.
• Strong passwords must be long enough to prevent reuse on multiple websites.

Closed Source Licensing

• Closed source licenses give businesses no access to the underlying code.
• The source code is concealed, making modification impossible by users without explicit access, or consent of the business.

Copyleft Provision

• Copyleft provisions in software licensing require the redistributor of software to distribute the underlying source code for modifications.
• Copyleft provisions also require the redistributor to provide support for modifications.
• Businesses and third parties may not link with closed source software.

Public Domain Works

• Public domain works are free from copyright restrictions.
• Such content is available without restriction, because of the author having given up copyright.
• Public domain works are also available to the public due to the author's death.
• Public domain works are also usable without restrictions for commercial or noncommercial purposes.

Command Line Editing and Execution

• The semicolon (;) is used in order to distinguish different commands that need to be executed in succession.
• The echo and print commands are different commands that can print to the screen.
• list is a command that compiles a list of previously executed commands showing their history.
• The eval and exec commands are used to execute different commands in the shell, respectively.

Environment Variables

• An environment variable is a special type of variable used by the program in computing settings.
• HOME is an example of an environment variable.

File Location

• The directory for software documentation is typically found within /usr/share/doc.

Searching Operating Systems

• Pressing the / key typically starts a man page search.
• info and man are two commands used when searching documentation regarding a program.

Find by Keyword

• The info -q command in operating systems can search for files, applications and documentation.
• The apropos command allows searching for file or program.names.
• whatis and whereis are used for finding the location for documentation.
• locate provides general locating and searching in operating systems, similar to whereis or which.
• Hidden files begin with a period (.).

Top-Level Directory

• The top-level directory on a Linux system is represented by /.

File Sorting

• The ls -S command sorts files by the number of symbolic links from largest to smallest count.

Copy Commands

• To use the cp command, source and destination files must be specified with the command.

Deleting Files

• The rm -i command, when used for deleting files, prompts the user before deleting any files. This is part of the operating system's security controls.

File Filtering

• The echo /etc/*[!TW] code allows for viewing files that do not start with a letter T or W.

Compression

• Lossless compression can be used for an mp3 audio file to preserve the highest quality audio possible.

Archive Handling

• The gz command attached to a file (such as .tar) efficiently compresses files to preserve space and allow for sharing.
• The command tar -tzf foo.tar.gz will show the contents of a compressed .tar file with the .gz extension.

Command Output

• Command outputs (by default) are sent to the console or STDOUT.

Filtering Lines

• The grep ^test file.txt command displays only the lines that specifically begin with "test".

Shell Scripts

• #!/bin/csh at the beginning of a script means a C Shell is enabled to run the script or a program.

Conditional Statements

• The exit code 0 is used in conditional programming statements to determine "true" or a successful conclusion.

User Groups

• The id bob command can display the group ID of the user, "bob".
• Traditionally, UNIX operating systems have allowed users to belong to multiple groups.

Password Aging

• A password aging field value of 0 usually indicates that the user cannot change their password.

sudo

• sudo privileges allow users to execute operations with different user permissions or account levels.

Command Execution Time

• The command getent shows how long the system has operated since the last reboot or start up.

Modifying User Groups

• The groupmod command, can add users to specific groups.

User IDs

• User IDs are stored in files such as /etc/passwd and /etc/group.

User Account Restrictions

• The usermod command can limit or prevent the ability for a user to log in, as an admin level operation.

User Home Directories

• User home directories are located in the /home directory.

User Groups (GIDs)

• User private groups (UPGs) are intended for user-specific private use and accounts.
• System accounts and system use accounts typically have GIDs lower than 1000.

File Deletion

• The user who created or owns a file is the only one who can delete it, although this is not a universal, hard and fast rule across all file systems.

Ownership Management

• The chown command, generally administered by the root user, can permit altering group ownership.

Hard Links

• Deleting a source file causes a link to be broken or invalidated.

Command to Create a Hard Link

• The ln -s command creates a symbolic or soft link for files.

This quiz covers the fundamentals of embedded systems, Linux operating systems, and Raspberry Pi computers. It delves into concepts such as software release cycles and the responsibilities of users regarding embedded systems. Test your knowledge on these topics and deepen your understanding of how they interact in technology.