D281 - Linux Foundations

Linux Foundations prepares learners for the LPI Linux Essentials certification, and is an introduction to Linux as an operating system as well as an introduction to open-source concepts and the basics of the Linux command line. Learners will gain skills in identifying the fundamentals of open-source software and to develop resources for data access and security.

Resources

What is Linux?

Usually when people say "Linux" they mean GNU/Linux
- Combination of software
- Defines the operating system

FLOSS and FOSS

FLOSS
- Free/Libre/Open Source Software
- Libre is all about freedom; do what you want
FOSS
- Free and Open Source Software
Open source
FSF
- GNU came from this
Licenses range from permissive to more restrictive (copyleft)

Operating systems

Linux distributions
- Bundling of software (web browser, email client, package manager, etc.) to make a useful system
- Run the Linux kernel
  - Kernel is like an air traffic controller, applications are the airplanes
  - Kernel decides which program gets which block of memory, starts/stops applications, handles displaying text, etc.
  - Abstracts things away for applications to access them (eg. writing to storage)
- Debian based
  - More community focused than some other distros
  - Ubuntu + Ubuntu variants
    - Most popular Debian distro
  - Any .deb based systems
- Red Hat based
  - RHEL
    - Red Hat Enterprise Linux
  - Fedora
    - Shorter release cycles than RHEL
  - CentOS
    - Recompiles RHEL and gives them away for free
    - No paid support like RHEL
  - RPM (Red Hat Package Manager) based systems
- Other
  - Arch
  - Slackware
  - SUSE
    - Derived from Slackware
  - Android
    - Most popular Linux distro
    - Uses Dalvik virtual machine
      - Provides a good platform for mobile devices
    - Lacks typical packages like GNU so incompatible with desktop Linux distros
  - Embedded systems
  - Linux From Scratch
    - Teaches you to build a distro from the ground up

Decision points

Role
- Desktop vs server
Function
Life cycle
Stability
Compatibility
Cost
Interface

Linux

Life cycle
- Distros are broadly enthusiast or enterprise
- Enterprise distros are stable, have good support, regular releases, etc.

Working in Linux

Major applications

Typically three categories of software
- Server applications
  - No interaction with I/O (monitor, keyboard)
  - Interacts with other computers
- Desktop applications
  - Users directly interact with them
- Tools
  - Make it easier to manage computer systems

Server applications

Email servers

Mail Transfer Agent (MTA)
- User to transfer messages to other systems
Mail Delivery Agent (MDA)
- Sorts the email in a user's mailbox
- Invoked from the final MTA in the chain
POP/IMAP server
- Post Office Protocol (POP) and Internet Message Access Protocol (IMAP) allow email clients to get emails from email servers

Samba
- Windows-centric
- Allows a Linux machine to share files and work on a Windows domain
Netatalk
- Allows a Linux machine to perform as an Apple Macintosh file server
- Network File System (NFS)

Desktop applications

Email
- Thunderbird
- Evolution
- KMail
Creative
- Blender
- GIMP (GNU Image Manipulation Program)
- Audacity
Productivity
- LibreOffice

Console tools

Shells

Accepts commands from a user and passes them to the Linux kernel to execute
Provides a language for interacting with the environment
Two main shell families:
- Bourne shell
- C shell
More modern shells:
- Bourne Again Shell (bash)
  - Default on most systems
- tsch

Text editors

Fully featured:
- vi/vim
- emacs
Simpler:
- pico
- nano

Package managers

Adding, updating, or removing packages usually requires administrative access

Debian

.deb extension
dpkg
- Lower level tool for managing Debian packages
apt-get
- Advanced Package Tool
- Frontend for dpkg
- Makes management of packages easier

RPM

Standard package management system according to Linux Standards Base
.rpm extension
rpm
- Backend to the package management system
- Install, update, query, or remove packages
yum and up2date
- Frontends for RPM
- Automate resolving dependency issues

Linux in the cloud

Powers 90% of the public cloud workload
Most virtual servers are based on some version of the Linux kernel
Why is Linux uniquely suited for the cloud?
- Flexibility
  - Modular design
  - Huge ecosystem
- Accessibility
- Cost-effective
  - Power efficient operating system
  - Kernel is completely free (as are many applications)
- Manageability
  - Very widespread, lots of talent in the industry know how to use Linux
  - Can be managed by automated programs
- Security
  - One of the most secure and reliable operating systems
  - Open source lends itself to security vulnerabilities being discovered and fixed quickly
- Virtualization

Open source software and licensing

Open source users have a right to obtain the source code
Increases accountability for bugs, security vulnerabilities, and compatibility issues
- Becomes a shared responsibility

Licensing

Three components
- Ownership
- Money transfer
- Licensing
End User License Agreement (EULA)
- Legal document that must be accepted to install software
GNU General Public License v2 (GPLv2)
- Source code must be made available to those who ask
- Anyone can make changes to the code
  - If you distribute your changes, they must also be GPLv2 licensed
- No one can charge for distributing the code
Berkeley Software Distribution (BSD)
- Simpler than GPL
- Can redistribute source/binaries if you maintain copyright notices and don't imply original creator endorses your code
  - "Do what you want, don't take credit"

Creative Commons

Tries to carry the intentions of FOSS licenses to non-software things
Available conditions:
- Attribution (BY)
  - Creator must be given credit even if they don't endorse the use
- ShareAlike (SA)
  - Can copy, distribute, perform, and modify if they do so under the same terms
- NonCommercial (NC)
  - Can't do anything commercially with the work
- NoDerivatives (ND)
  - Creator must provide permission to modify
Licenses
- Attribution (CC BY)
  - Similar to BSD
  - Can use the content in any way but must give credit to the creator
- Attribution ShareAlike (CC BY-SA)
  - Copyleft version of Attribution
  - Derived works must have same license
- Attribution NoDerivs (CC BY-ND)
  - You can redistribute but cannot modify
- Attribution NonCmercial (CC BY-NC)
  - CC BY but can't use it for commercial purposes
- Attribution NonCommercial ShareAlike (CC BY-NC-SA)
  - CC BY-NC + changes must be shared under the same license
- Attribution NonCommercial NoDerivs (CC BY-NC-ND)
  - Sharing can be done for non-commercial purposes, no modifying
- No Rights Reserved (CC0)
  - Creative Commons version of public domain

Command line skills

Variables

Local variables
- Only exist in the current shell
  - When closing the shell, variables are lost
- Can't affect other commands/applications
Environment variables
- Also called global variables
- Examples: PATH, HOME, HISTSIZE
- env outputs environment variables
export turns a local variable into an environment variable
- Remove exported variables with unset
PATH variable
- Contains a list of directories that the shell will look in to find commands

Command types

type allows you to check a commands type
Internal commands
- Built-in to the shell
- Eg. cd, echo
External commands
- Binary executables stored in directories
- Eg. ls, cal
- Using the which command will tell you where the shell is running that command from
Aliases can be created with alias name=command
- Shorten commands you commonly run
- type will identify when a command is an alias

Quotes

Double quotes
- Prevent the shell from interpreting meta characters, including glob characters
- Allow for command substitution and variable substitution
Single quotes
- Prevents the shell interpreting meta characters, glob characters, variables, and command substitution
Backslash
- Can be used to stop the shell from interpreting a character
Backticks
- Used to specify a command within a command (command substitution)

Control statements

Semicolon ;
- Used to run multiple commands, one after another
- Each command runs regardless of the result of the previous command
Double ampersand &&
- Logical "and" operator
- Only if the previous command succeeds will the next command run
Double pipe ||
- Logical "or" operator
- Only if the previous command fails will the next command run

Helpful commands

uname
- Lists information about the current system
- -n/--nodename will give the node name
history
- View your command history
- Param is a number of how many history items you want to see (eg. history 5)

Getting help

Man pages

Use man -f <command> to search man pages by name
- Allows you to see when there are different man pages with the same name (eg. for passwd)
- whatis often does the same thing
Use man -k <command> to search man pages by name and description
- apropos often does the same thing
Sections
- Name
  - Name of the command and a brief description
- Synopsis
  - Examples and shows how to execute the command
  - Square brackets indicate something is optional
- Description
  - Detailed description of the command
- Options
  - All options for the command listed with descriptions
- Files
  - Lists files associated with the command
- Author
  - Name of the author
  - Sometimes includes contact info
- Reporting bugs
  - Details how to report bugs
- Copyright
  - Provides copyright information
- See also
  - Helps find additional information related to the command
Searching a man page
- Use / to search through man pages
- Press n to move to the next match
- Press SHIFT+N to move to the previous match
Category sections
- Man pages are split into various sections
- Next to the command you'll see a number (eg. CAL(1)) that identifies the category
- Sections:
  1. General commands
  2. System calls
  3. Library calls
  4. Special files
  5. File formats and conventions
  6. Games
  7. Miscellaneous
  8. System administration commands
  9. Kernel routines

Finding stuff

locate
- Searches a database of all files/directories
  - The database is generated ~nightly
  - Can manually update the database with updatedb
- -c shows how many files/directories match the search term
- -b only includes listings that have the search term in the base name of the filename
- \ in the search term only outputs filenames that exactly match
info
- Documentation with an organizational structure
- More conducive for learning vs man pages which are more reference

Filesystem

Directories are files
- They store the names of the files within them and the inode number for where that file is on disk

Home directory

/home
When opening a shell, users are automatically placed in their home directory - They have full control to create/modify/delete files and directories here
~ is an alias for a user's home directory - ~<username> will take you to a specific user's home directory

Listing files and directories

ls
- -a shows hidden files
- -l lists metadata for the files/directories
- -h shows the file size in a human-readable size
  - Must be used with -l
- -d refers to the current directory
  - Not really useful without -l
- -R performs recursive listing
- -S sorts by file size
- -t sorts by timestamp
- --full-time will list complete timestamps
- -r reverse the sort
The ? can be used to match exactly 1 character in a name
- eg. ls -d /etc/???? - list all files in /etc that are exactly 4 characters long
[ ] can be used to match any character from a set
- eg. ls -d /etc/[abcd]* - display all files in /etc that start with a, b, c, or d

Long listing

**sysadmin@localhost:~$** ls -l /var/log/
total 900                                                                       
-rw-r--r-- 1 root   root  15322 Dec 10 21:33 alternatives.log
drwxr-xr-x 1 root   root   4096 Jul 19 06:52 apt
-rw-r----- 1 syslog adm     371 Dec 15 16:38 auth.log
-rw-r--r-- 1 root   root  35330 May 26  2018 bootstrap.log
-rw-rw---- 1 root   utmp      0 May 26  2018 btmp
-rw-r----- 1 syslog adm     197 Dec 15 16:38 cron.log
-rw-r--r-- 1 root   adm   85083 Dec 10 21:33 dmesg
-rw-r--r-- 1 root   root 351960 Jul 19 06:52 dpkg.log
-rw-r--r-- 1 root   root  32064 Dec 10 21:33 faillog
drwxr-xr-x 2 root   root   4096 Jul 19 06:51 journal
-rw-rw-r-- 1 root   utmp 292584 Dec 15 16:38 lastlog
-rw-r----- 1 syslog adm   14185 Dec 15 16:38 syslog
-rw------- 1 root   root  64128 Dec 10 21:33 tallylog
-rw-rw-r-- 1 root   utmp    384 Dec 15 16:38 wtmp

File type
- First character of each line
- Types of files:
  - d - directory
  - - - regular file
  - l - symbolic link
  - s - socket
    - Allows for communication between processes
  - p - pipe
    - Allows for communication between processes
  - b - block file
    - Used to communicate with hardware
  - c - character file
    - Used to communicate with hardware
Permissions
- Next nine characters
Hard link count
- How many hard links there are to the file
User owner
- Every file is owned by a user account
- Owner can set permissions on the file
Group owner
- Which group owns the file
- Any member of a group inherits the permissions to the file
File size
- Size of file in bytes
- For directories, how many bytes are reserved to keep track of the filenames in the directory
  - Not useful for directories
Timestamp
- When the contents were last modified
- For directories, when a file was added/removed
File name

Archiving and compression

Archiving
- Combine multiple files into one
Compression
- Make files smaller by removing redundant information
- Two types:
  - Lossless
  - Lossy
gzip
- Most common Linux tool used for compression
- -l provides info about the compression
  - Compression ratio shows how much the file was reduced
- Uses the Lempel-Ziv data compression algorithm
gunzip
- Used to decompress
- Same as gzip -d
tar
- tar -c [-f ARCHIVE] [OPTIONS] [FILE...]
- Used to archive files
- Short for TApe aRchive
- Has three modes:
  - Create
    - Make a new archive
  - Extract
    - Pull one or more files out of an archive
  - List
    - Show contents of an archive witout extracting
- Options
  - -c (create mode)
    - Create an archive
  - -t (list mode)
    - List files in an archive
  - -x (extract mode)
    - Extract files from an archive
    - -v
      - Verbosely list processed files
  - -f ARCHIVE
    - Specify the archive file to operate on
  - -z
    - Compress/decompress using gzip
  - -j
    - Compress/decompress using bzip2

Backlinks

wgu

D281 - Linux Foundations

Resources

What is Linux?

FLOSS and FOSS

Operating systems

Decision points

Linux

Working in Linux

Major applications

Server applications

Email servers

File sharing

Desktop applications

Console tools

Shells

Text editors

Package managers

Debian

RPM

Linux in the cloud

Open source software and licensing

Licensing

Creative Commons

Command line skills

Variables

Command types

Quotes

Control statements

Helpful commands

Getting help

Man pages

Finding stuff

Filesystem

Home directory

Listing files and directories

Long listing

Archiving and compression

Backlinks