Linux-Introduction-Course

What is Linux?

Linux is a family of open-source Unix-like operating systems based on the Linux kernel, created by Linus Torvalds in 1991. It is most used operating system on servers.

Key Features of Linux:

• Open-Source: Anyone can view, modify, and distribute the source code.
• Secure and Stable: Linux is widely used in servers due to its robustness.
• Versatile: Linux runs on various hardware platforms, from desktops to supercomputers.

Why Use Linux?

• It’s free and community-driven.
• Offers excellent performance and customization options.
• Provides extensive developer tools and scripting capabilities.

Linux Distributions and Package Management

A Linux distribution (distro) is a customized version of Linux that combines the Linux kernel with specific software, configurations, and package managers.

Popular Linux Distributions:

1. Debian-based: Debian, Ubuntu, Linux Mint
   • Package Manager: apt
   • Example command: sudo apt install package_name
2. Red Hat-based: Red Hat Enterprise Linux (RHEL), CentOS, Fedora
   • While CentOS/RHEL are mostly used in servers, Fedora is more user-friendly approach to RHEL-based distros
   • Package Manager: dnf or yum
   • Example command: sudo dnf install package_name
3. Arch-based: Arch Linux (use if you love pain & suffering)
   • Package Manager: pacman
   • Example command: sudo pacman -S package_name

How Package Formats Are Different:

• Debian (.deb): Precompiled binaries for Debian-based systems.
• Red Hat (.rpm): Red Hat-based binary format.
• Source Packages: Some distros like Gentoo compile software from source, allowing optimization for your hardware.

Crazy big linux distribution tree

https://en.wikipedia.org/wiki/List_of_Linux_distributions#/media/File:Linux_Distribution_Timeline.svg

What is Ubuntu?

Ubuntu is one of the most popular Linux distributions, based on Debian. It is designed to be user-friendly and is widely used for development, education, and production-ready systems

Key Features of Ubuntu:

• User-Friendly: Aimed at beginners, with a graphical user interface (GUI) and pre-installed software.
• Long-Term Support (LTS): LTS versions receive five years of updates and support.
• Community Support: A vibrant community and extensive documentation.
• Wide Application: Great for servers, desktops, and cloud computing.

Common Use Cases:

• Development and programming.
• Running web servers and databases.
• Hosting virtual machines and containers.

What is Bash?

Bash (Bourne Again SHell) is the default command-line shell for most Linux distributions. It allows users to interact with the system and automate tasks through scripting.

Why Use Bash?

• Pre-installed on almost all Linux systems.
• Supports complex scripts with loops, conditions, and functions.
• Compatible with numerous Unix utilities.

Common Bash Features:

• Variables: Store data for use in scripts or commands.
• Redirection: Direct output/input to/from files or other commands.
• Job Control: Manage background and foreground processes.

So, let's learn how to use terminal

Every command in bash has its own options. Options are used to modify behavior of that command. As an example, let's take rm command, which is used for removing things around file system.

Let's say we have test-1 directory and 2 files/folders inside of it, if you try to use rm -fv to remove folder and contents inside of it, you'll fail and get this error:

rm: cannot remove 'test-1': Is a directory

-f - force (ignore nonexistent files and arguments) -v - verbose (shows what is being done)

But, if you use rm -rvf test-1, it will remove folder itself and all contents inside of that folder. You can always access options of specific command with command --help, Example:

• rm --help
• ls --help OR
• man rm
• man ls

man means manual and it'll show you:

• description
• authors
• naming
• usage
• etc. about that specific command

Also every command in bash has its own opening. rm (remove), ls (list), and etc.

Basic Navigation

• pwd - print working directory

  • Prints current working directory (the folder you're in)

• ls - list

  • Lists all files and folders in the current directory
  • Except files that starts with ., because in most of the UNIX-based operating systems you can hide any file with adding dot in front of file name (MacOS, Linux, BSD)
  • Options for ls
    • -l - long (display file metadata)
    • -t - time (sorting based on modified time)
    • -r - reverse (reverse the order of the sort)
  • If you use ls -ltr, you'll see last modified at the end of the list, but if you don't use -r then you'll see last modified on top of the list

• cd - change directory

  • Changes the current directory to the specified one.
  • cd ~ - back to the home folder
  • cd .. - will go one folder back
    • if use this command in /home/user/Downloads/folder/ you will go back to the /home/user/Downloads/
  • cd test_1/ - enter test_1 folder (if it exists in your current directory)
  • cd - - go back to the previous folder

TIP: Use zoxide instead of cd. It's written in Rust, faster than cd and you don’t need to be in a specific location to jump to a directory. It learns your usage patterns and lets you quickly navigate to frequently used directories.

File Management

• mkdir folder_name - make directory

  • Creates folder in your current directory
  • Options for mkdir
    • -v - verbose (print a message for each created directory)
    • -m - mode (set file mode for user permissions)

• rm file or folder name - remove

  • Removes file/directory you enter
  • Options for rm
    • -r - recursive. remove directories and their contents recursively
    • -v - verbose. show what has been done.
    • -f - force. ignore non-existent files
    • -I - interactive. used for removing three or more files
    • -d - dir (directory). remove empty directories

• touch file_name

  • Generally used for creating files.
  • Options for touch
    • Generally (at least in my experience) I haven't used any options with touch. It exists, but generally not used.

• mv - move

  • You can move files around directories and/or move files to different file
  • Options for mv
    • -b - backup. make a backup of each existing destination file
    • -f - force. don't prompt before overwriting

• cat file_name - concatenate file and print on the standard output

  • Generally used for printing content of the file
  • Options for cat
    • -n - number. show numbers for every line for file

• cp - copy file or directory

  • Used to copy files or directories from one location to another.
  • Options for cp
    • -r - recursive. copy directories and their contents
    • -v - verbose. show the files being copied
    • -i - interactive. prompt before overwriting files
    • -f - force. overwrite files without prompting
    • -u - update. copy only if the source is newer or doesn’t exist

Text Manipulation and Viewing

• less file_name

  • Opens the file in a viewer, allowing you to scroll through the content without editing it.

• more file_name

  • Similar to less, but only allows forward navigation.

• head file_name

  • Displays the first few lines of a file.
  • Options for head:
    • -n - Specify the number of lines to display (default is 10).

• tail file_name

  • Displays the last few lines of a file.
  • Options for tail:
    • -n - Specify the number of lines to display.
    • -f - Follow the file, displaying new lines as they are added (useful for logs).

• grep pattern file_name

  • Searches for lines in a file that match the specified pattern.
  • Options for grep:
    • -i - Ignore case.
    • -v - Invert match (show lines that do not match the pattern).
    • -r - Recursive search in directories.

Permissions and Ownership

• chmod mode file_name

  • Changes file permissions.
  • Modes can be specified numerically (e.g., chmod 755) or symbolically (e.g., chmod u+x).

• chown user:group file_name

  • Changes the ownership of a file or directory.
  • Example: chown user1:group1 myfile.

Permission Symbols:

• r - Read

• w - Write

• x - Execute

• Example: -rwxr-xr--

  • Owner: Read, Write, Execute
    • Admin - opus/ (Owner)
  • Group: Read, Execute
    • Researchers - opus/ (read, write, execute)
    • Developers - opus/ (read)
    • Students - X
  • Others: Read

• drwxr-xr-x

  • d - directory
  • r - read
  • w - write
  • x - execute

• Example:

  • 755
    • 7 - owner
    • 5 - group
    • 5 - others

• 0 = no permissions whatsoever; this person cannot read, write, or execute the file

• 1 = execute only

• 2 = write only

• 3 = write and execute (1+2)

• 4 = read only

• 5 = read and execute (4+1)

• 6 = read and write (4+2)

• 7 = read and write and execute (4+2+1)

Process Management

• ps

  • Displays active processes.
  • Options for ps:
    • -e - Show all processes.
    • -f - Full format listing.

• top

  • Interactive process viewer showing CPU/memory usage.

• htop or btop (this one is cooler)

  • A more user-friendly version of top (requires installation).

• kill pid

  • Terminates a process by its process ID.

• killall process_name

  • Terminates all processes with a specific name.

Tools and Links

• https://github.com/eld4niz/helixis/tree/main - Helix tutorial and config
• https://www.redhat.com/en/blog/navigating-filesystem-linux-terminal - Red Hat File Navigation Tutorial