Linux Fundamentals

Linux is a operating system just like Windows, mac etc. Linux share similarities with Unix which is another operating system has comparable components. Linux is open-source Operating system which is free to use, and its source code is available for anyone to view, modify, and distribute. Linux is known for being stable, secure, and customizable, and is widely used for servers, desktops, and embedded systems.

Core Components of Linux:

1. Hardware Layer:

   This layer consists of Physical components of computer like CPU,RAM,DISK etc

   The OS interacts with hardware using device drivers

2. Kernel:

   The kernel is the core of the Linux operating system. It acts as an interface between hardware and software. It manages system resources, such as the CPU, memory, and I/O devices. The kernel controls how programs interact with hardware and ensures efficient multitasking and security.

3. Shell:

   The shell is a command-line interface (CLI) that allows users to interact with the operating system. It interprets commands typed by the user and communicates with the kernel to execute them. Examples include Bash (Bourne Again Shell) and Zsh.

4. User Applications:

   It is the tool you use on a Linux system to get work done—whether it's browsing the web, coding, watching videos, or editing documents. They depend on the underlying Linux components (like the kernel and libraries) but provide the features and interfaces that make the system usable and productive for everyday tasks.

Linux Distributions:

A Linux Distribution also called Distros are different versions of linux that pacakge complete operating system built around the linux kernel. It includes the kernel, system libraries, utilities, software management tools (like package managers), and often a desktop environment or other user applications. Some of the popular linux distributions are

Folder Structure:

User Management:

User management in Linux is all about controlling who can access the system, what they can do, and how resources are shared. It involves creating users, setting permissions, managing groups, and securing user accounts.

Basic User Management Commands:

Group Management:

File Management:

File management in Linux is all about creating, moving, copying, deleting, and organizing files and directories using the command line (or GUI tools). Since everything in Linux is treated as a file, mastering file management is essential.

File and Directory Management

1. ls – Lists files and directories in the current location.

2. cd /path/to/directory – Changes the working directory.

3. pwd – Prints the current working directory.

4. mkdir new_folder – Creates a new directory.

5. rmdir empty_folder – Removes an empty directory.

6. rm file.txt – Deletes a file.

7. rm -r folder – Deletes a folder and its contents.

8. cp file1.txt file2.txt – Copies a file.

9. cp -r dir1 dir2 – Copies a directory recursively.

10. mv old_name new_name – Moves or renames a file or directory.

File Viewing and Editing

11. cat file.txt – Displays file content.

12. tac file.txt – Displays file content in reverse order.

13. less file.txt – Opens a file for viewing with scrolling support.

14. more file.txt – Similar to less, but only moves forward.

15. head -n 10 file.txt – Displays the first 10 lines of a file.

16. tail -n 10 file.txt – Displays the last 10 lines of a file.

17. nano file.txt – Opens a simple text editor.

18. vi file.txt – Opens a powerful text editor.

19. echo 'Hello' > file.txt – Writes text to a file, overwriting existing content.

20. echo 'Hello' >> file.txt – Appends text to a file without overwriting.

Using VI Editor:

Modes in VI Editor

• Normal Mode (default) – Used for navigation and command execution.

• Insert Mode – Used for text editing (press i to enter, Esc to exit).

• Command Mode – Used for saving, quitting, and searching (press : in Normal mode).

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Basic Navigation

• h – Move left

• l – Move right

• j – Move down

• k – Move up

• 0 – Move to the beginning of the line

• ^ – Move to the first non-blank character of the line

• $ – Move to the end of the line

• w – Move to the next word

• b – Move to the previous word

• gg – Move to the start of the file

• G – Move to the end of the file

• :n – Move to line number n

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Insert Mode Shortcuts

• i – Insert before cursor

• I – Insert at the beginning of the line

• a – Append after cursor

• A – Append at the end of the line

• o – Open a new line below

• O – Open a new line above

• Esc – Exit insert mode

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Editing Text

• x – Delete a character

• X – Delete a character before cursor

• dw – Delete a word

• dd – Delete a line

• d$ – Delete from cursor to end of line

• d0 – Delete from cursor to beginning of line

• D – Delete from cursor to end of line

• u – Undo last action

• Ctrl + r – Redo an undone change

• yy – Copy (yank) a line

• yw – Copy (yank) a word

• p – Paste after the cursor

• P – Paste before the cursor

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Search and Replace

• /pattern – Search forward for a pattern

• ?pattern – Search backward for a pattern

• n – Repeat last search forward

• N – Repeat last search backward

• :%s/old/new/g – Replace all occurrences of "old" with "new"

• :s/old/new/g – Replace all occurrences in the current line

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Working with Multiple Files

• :e filename – Open a new file

• :w – Save file

• :wq – Save and exit

• :q! – Quit without saving

• :split filename – Split screen horizontally and open another file

• :vsplit filename – Split screen vertically

• Ctrl + w + w – Switch between split screens

File Permissions in Linux:

File permissions control who can read, write, or execute a file or directory. It's a core part of Linux security and user management.

1. Understanding Permission Notation

Use ls -l to view file permissions:

bashCopyEdit-rwxr-xr-- 1 user group 1234 Apr 23 10:00 example.sh

Breakdown of -rwxr-xr--:

So, this file:

• Can be read, written, and executed by the owner.

• Can be read and executed by the group.

• Can only be read by others.

2. Permission Categories

3. Changing Permissions – chmod

You can set permissions using symbolic or numeric (octal) notation.

✅ Symbolic Mode

bashCopyEditchmod u+x file.txt     # Add execute for owner (u = user)
chmod g-w file.txt     # Remove write for group
chmod o=r file.txt     # Set read-only for others

✅ Numeric Mode

Example:

bashCopyEditchmod 755 script.sh
# = rwx (7) for owner
# = r-x (5) for group
# = r-x (5) for others

4. Changing Owner or Group – chown and chgrp

bashCopyEditchown newuser file.txt        # Change file owner
chown user:group file.txt     # Change owner and group
chgrp newgroup file.txt       # Change group only

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5. Special Permission Bits

Set with chmod, e.g.:

bashCopyEditchmod +t /sharedfolder     # Add sticky bit
chmod 4755 program         # Setuid (4), normal 755 permissions

Process Management:

In Linux, process management means monitoring, controlling, starting, stopping, and managing the programs (a.k.a. processes) running on your system. Below is a full list of commonly used process management commands, with explanations and examples.

1. Viewing Running Processes

2. Getting Process Info

3. Starting & Running Processes

4. Stopping / Killing Processes

5. Managing Background/Foreground Jobs

6. Process Priorities – nice and renice

Lower value = higher priority. -20 is highest, 19 is lowest.

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🔧 7. System Resource Monitoring

System Monitoring:

Linux system monitoring is the process of observing and analyzing various system resources to ensure the system is running efficiently and to detect issues early. It's crucial for system administrators and developers to keep servers or development environments stable, secure, and performant.

Index of Commands Covered

CPU and Memory Monitoring

• top – Real-time system monitoring

• htop – Interactive process viewer (requires installation)

• vmstat – Report system performance statistics

• free -m – Show memory usage

Disk Monitoring

• df -h – Check disk space usage

• du -sh /path – Show disk usage of a specific directory

• iostat – Display CPU and disk I/O statistics

Network Monitoring

• ifconfig – Show network interfaces (deprecated, use ip a)

• ip a – Show network interface details

• netstat -tulnp – Show active connections and listening ports

• ss -tulnp – Alternative to netstat for socket statistics

• ping hostname – Test network connectivity

• traceroute hostname – Show network path to a host

• nslookup domain – Get DNS resolution details

Log Monitoring

• tail -f /var/log/syslog – Live monitoring of system logs

• journalctl -f – Live system logs for systemd-based distros

• dmesg | tail – View kernel logs

Networking Commands:

1. ping google.com – Checks connectivity to a remote server.

2. ifconfig – Displays network interfaces (deprecated, use ip).

3. ip a – Shows IP addresses of network interfaces.

4. netstat -tulnp – Displays open network connections.

5. curl https://example.com – Fetches a webpage's content.

6. wget https://example.com/file.zip – Downloads a file from the internet.

Disk Management:

Managing disks and storage efficiently is crucial for system performance and stability. Linux provides various commands to monitor, partition, format, mount, and manage disk storage.

Index of Commands Covered

Viewing Disk Information

• lsblk – Display block devices

• fdisk -l – List disk partitions

• blkid – Show UUIDs of devices

• df -h – Check disk space usage

• du -sh /path – Show size of a directory

Partition Management

• fdisk /dev/sdX – Create and manage partitions

• parted /dev/sdX – Alternative to fdisk for GPT disks

• mkfs.ext4 /dev/sdX1 – Format a partition as ext4

• mkfs.xfs /dev/sdX1 – Format a partition as XFS

Mounting and Unmounting

• mount /dev/sdX1 /mnt – Mount a partition

• umount /mnt – Unmount a partition

• mount -o remount,rw /mnt – Remount a partition as read-write

Logical Volume Management (LVM)

• pvcreate /dev/sdX – Create a physical volume

• vgcreate vg_name /dev/sdX – Create a volume group

• lvcreate -L 10G -n lv_name vg_name – Create a logical volume

• mkfs.ext4 /dev/vg_name/lv_name – Format an LVM partition

• mount /dev/vg_name/lv_name /mnt – Mount an LVM partition

Swap Management

• mkswap /dev/sdX – Create a swap partition

• swapon /dev/sdX – Enable swap space

• swapoff /dev/sdX – Disable swap space