Master Linux Basics with Daily Practice

Table of Contents

Introduction to Linux

Linux is a powerful, open-source operating system that forms the backbone of countless servers, embedded systems, and desktop computers worldwide. Understanding Linux fundamentals is essential for system administrators, developers, and IT professionals. The command-line interface provides direct control over system operations and enables automation through scripting.

The Linux file system follows a hierarchical structure starting from the root directory (/). Unlike Windows, Linux treats everything as a file, including hardware devices, processes, and system resources. This unified approach simplifies system management and provides consistent interfaces for various operations.

Key Linux Concepts

| Concept | Description | Example | |---------|-------------|---------| | Root Directory | Top-level directory in Linux hierarchy | / | | Home Directory | User's personal directory | /home/username | | Working Directory | Current directory location | pwd command shows current location | | Path | Location specification for files/directories | /usr/local/bin/program | | Shell | Command interpreter interface | bash, zsh, fish |

File System Navigation

Navigation forms the foundation of Linux command-line proficiency. Understanding how to move through directories efficiently enables all other operations.

Essential Navigation Commands

#### pwd (Print Working Directory) `bash pwd ` Purpose: Displays the absolute path of current directory Output Example: /home/user/documents

#### cd (Change Directory) `bash cd /path/to/directory # Absolute path navigation cd relative/path # Relative path navigation cd .. # Move to parent directory cd ~ # Move to home directory cd - # Return to previous directory `

Notes: - Absolute paths start with forward slash (/) - Relative paths are relative to current directory - Tilde (~) represents user home directory - Dash (-) toggles between current and previous directory

#### ls (List Directory Contents) `bash ls # Basic listing ls -l # Long format with details ls -la # Include hidden files ls -lh # Human-readable file sizes ls -lt # Sort by modification time ls -lr # Reverse order listing `

Long Format Explanation: ` -rw-r--r-- 1 user group 1024 Jan 15 10:30 filename │││││││││ │ │ │ │ │ │ │││││││││ │ │ │ │ │ └─ filename │││││││││ │ │ │ │ └─ modification time │││││││││ │ │ │ └─ file size │││││││││ │ │ └─ group ownership │││││││││ │ └─ user ownership │││││││││ └─ number of links └─────────── file permissions `

Directory Structure Overview

| Directory | Purpose | Contents | |-----------|---------|----------| | / | Root directory | System foundation | | /home | User directories | Personal files and settings | | /etc | Configuration files | System and application configs | | /var | Variable data | Logs, databases, temporary files | | /usr | User programs | Applications and utilities | | /bin | Essential binaries | Core system commands | | /sbin | System binaries | Administrative commands | | /tmp | Temporary files | Temporary storage | | /opt | Optional software | Third-party applications | | /proc | Process information | Virtual filesystem for processes |

File and Directory Operations

File and directory manipulation represents core Linux functionality. These operations enable creation, modification, and organization of data.

Creating Files and Directories

#### touch (Create Empty Files) `bash touch filename.txt # Create single file touch file1.txt file2.txt # Create multiple files touch /path/to/new/file.txt # Create with full path `

Notes: - Creates empty file if it doesn't exist - Updates timestamp if file exists - Useful for creating placeholder files

#### mkdir (Make Directories) `bash mkdir directory_name # Create single directory mkdir dir1 dir2 dir3 # Create multiple directories mkdir -p path/to/nested/dirs # Create nested directories mkdir -m 755 secure_dir # Create with specific permissions `

Options Explanation: - -p: Creates parent directories if they don't exist - -m: Sets directory permissions during creation

Copying and Moving Operations

#### cp (Copy Files and Directories) `bash cp source.txt destination.txt # Copy file cp source.txt /path/to/destination/ # Copy to directory cp -r source_dir destination_dir # Copy directory recursively cp -i source.txt destination.txt # Interactive mode (prompt before overwrite) cp -u source.txt destination.txt # Update mode (copy if newer) `

Important Options: - -r or -R: Recursive copy for directories - -i: Interactive mode for safety - -u: Update only if source is newer - -v: Verbose output showing operations

#### mv (Move/Rename Files) `bash mv oldname.txt newname.txt # Rename file mv file.txt /path/to/destination/ # Move file to directory mv directory_old directory_new # Rename directory mv *.txt /backup/ # Move multiple files using wildcards `

Notes: - Single command for both moving and renaming - Works with both files and directories - Automatically overwrites unless using -i option

Removing Files and Directories

#### rm (Remove Files and Directories) `bash rm filename.txt # Remove single file rm file1.txt file2.txt # Remove multiple files rm -i filename.txt # Interactive removal rm -r directory_name # Remove directory recursively rm -rf directory_name # Force remove without prompts `

Critical Safety Notes: - -r: Required for directory removal - -f: Forces removal without prompts (dangerous) - -i: Prompts before each removal (safer) - No built-in recovery mechanism - deletions are permanent

#### rmdir (Remove Empty Directories) `bash rmdir empty_directory # Remove single empty directory rmdir -p path/to/empty/nested/dirs # Remove nested empty directories `

File Content Operations

#### cat (Display File Contents) `bash cat filename.txt # Display entire file cat file1.txt file2.txt # Display multiple files cat -n filename.txt # Display with line numbers cat -b filename.txt # Number non-empty lines only `

#### less and more (Paginated File Viewing) `bash less filename.txt # View file with navigation more filename.txt # Simple paginated viewing `

less Navigation: - Space: Next page - b: Previous page - /pattern: Search forward - ?pattern: Search backward - q: Quit

#### head and tail (Partial File Display) `bash head filename.txt # First 10 lines head -n 20 filename.txt # First 20 lines tail filename.txt # Last 10 lines tail -n 15 filename.txt # Last 15 lines tail -f logfile.txt # Follow file changes (useful for logs) `

Text Processing and Manipulation

Text processing capabilities make Linux powerful for data manipulation and system administration tasks.

Search and Pattern Matching

#### grep (Global Regular Expression Print) `bash grep "pattern" filename.txt # Search for pattern in file grep -i "pattern" filename.txt # Case-insensitive search grep -r "pattern" directory/ # Recursive search in directory grep -n "pattern" filename.txt # Show line numbers grep -v "pattern" filename.txt # Invert match (exclude pattern) grep -c "pattern" filename.txt # Count matching lines `

Advanced grep Examples: `bash grep "^start" file.txt # Lines starting with "start" grep "end$" file.txt # Lines ending with "end" grep -E "pattern1|pattern2" file.txt # Multiple patterns (extended regex) grep -A 3 -B 2 "pattern" file.txt # Show 3 lines after, 2 lines before match `

#### find (Locate Files and Directories) `bash find /path -name "filename" # Find by name find /path -name "*.txt" # Find by pattern find /path -type f # Find files only find /path -type d # Find directories only find /path -size +100M # Find files larger than 100MB find /path -mtime -7 # Find files modified in last 7 days `

Complex find Examples: `bash find /home -name "*.log" -size +10M -delete # Find and delete large log files find /tmp -type f -atime +30 -exec rm {} \; # Remove files not accessed in 30 days `

Text Manipulation Tools

#### sed (Stream Editor) `bash sed 's/old/new/' filename.txt # Replace first occurrence per line sed 's/old/new/g' filename.txt # Replace all occurrences sed -i 's/old/new/g' filename.txt # Edit file in-place sed '1,5s/old/new/g' filename.txt # Replace in lines 1-5 only sed '/pattern/d' filename.txt # Delete lines matching pattern `

#### awk (Text Processing Language) `bash awk '{print $1}' filename.txt # Print first column awk '{print $1, $3}' filename.txt # Print first and third columns awk '/pattern/ {print $0}' filename.txt # Print lines matching pattern awk '{sum+=$1} END {print sum}' data.txt # Sum first column values `

#### sort and uniq (Data Organization) `bash sort filename.txt # Sort lines alphabetically sort -n numbers.txt # Numerical sort sort -r filename.txt # Reverse sort sort -k 2 data.txt # Sort by second column uniq filename.txt # Remove duplicate adjacent lines sort filename.txt | uniq # Sort then remove duplicates sort filename.txt | uniq -c # Count occurrences of each line `

Input/Output Redirection

#### Redirection Operators

| Operator | Purpose | Example | |----------|---------|---------| | > | Redirect output to file (overwrite) | ls > filelist.txt | | >> | Redirect output to file (append) | echo "text" >> file.txt | | < | Redirect input from file | sort < unsorted.txt | | \| | Pipe output to another command | ls \| grep ".txt" | | 2> | Redirect error output | command 2> errors.txt | | &> | Redirect both output and errors | command &> all_output.txt |

#### Practical Redirection Examples `bash ls -la > directory_listing.txt # Save directory listing to file cat file1.txt file2.txt > combined.txt # Combine files grep "error" /var/log/syslog >> errors.log # Append errors to log file command 2>/dev/null # Discard error messages `

Process Management

Understanding process management enables effective system resource utilization and troubleshooting.

Process Viewing and Monitoring

#### ps (Process Status) `bash ps # Show current user processes ps aux # Show all processes with details ps -ef # Alternative detailed format ps -u username # Show processes for specific user ps -C program_name # Show processes by command name `

ps aux Output Explanation: ` USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND root 1 0.0 0.1 19696 1234 ? Ss Jan15 0:01 /sbin/init │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ │ └─ command │ │ │ │ │ │ │ │ │ └─ CPU time used │ │ │ │ │ │ │ │ └─ start time │ │ │ │ │ │ │ └─ process state │ │ │ │ │ │ └─ terminal │ │ │ │ │ └─ resident memory (KB) │ │ │ │ └─ virtual memory (KB) │ │ │ └─ memory percentage │ │ └─ CPU percentage │ └─ process ID └─ user owner `

#### top and htop (Real-time Process Monitoring) `bash top # Real-time process viewer htop # Enhanced process viewer (if installed) `

top Interactive Commands: - q: Quit - k: Kill process - r: Renice process - M: Sort by memory usage - P: Sort by CPU usage - u: Filter by user

Process Control

#### Background and Foreground Jobs `bash command & # Run command in background jobs # List active jobs fg %1 # Bring job 1 to foreground bg %1 # Send job 1 to background Ctrl+Z # Suspend current foreground job `

#### Process Termination

#### kill (Terminate Processes) `bash kill PID # Terminate process by ID kill -9 PID # Force kill process kill -15 PID # Graceful termination (SIGTERM) killall program_name # Kill all processes by name pkill -f "pattern" # Kill processes matching pattern `

Common Kill Signals:

| Signal | Number | Purpose | |--------|--------|---------| | SIGTERM | 15 | Graceful termination (default) | | SIGKILL | 9 | Force termination | | SIGHUP | 1 | Hang up signal | | SIGINT | 2 | Interrupt (Ctrl+C) | | SIGSTOP | 19 | Stop process |

System Information and Monitoring

System monitoring commands provide insights into hardware resources, system performance, and operational status.

System Resource Monitoring

#### System Load and Performance `bash uptime # System uptime and load average free -h # Memory usage (human-readable) df -h # Disk space usage du -sh directory/ # Directory size summary iostat # I/O statistics vmstat # Virtual memory statistics `

Load Average Explanation: Load averages show system load over 1, 5, and 15-minute intervals. Values represent average number of processes either running or waiting for resources.

#### Hardware Information `bash lscpu # CPU information lsblk # Block device information lsusb # USB device information lspci # PCI device information dmidecode # Hardware DMI information `

#### System Information Commands

| Command | Purpose | Example Output | |---------|---------|----------------| | uname -a | Complete system information | Linux hostname 5.4.0 x86_64 GNU/Linux | | whoami | Current username | username | | id | User and group IDs | uid=1000(user) gid=1000(user) | | w | Logged-in users | Shows users and their activities | | last | Login history | Recent login records |

Log File Monitoring

#### Common Log Locations `bash /var/log/syslog # System messages /var/log/auth.log # Authentication logs /var/log/kern.log # Kernel messages /var/log/apache2/access.log # Apache access logs /var/log/mysql/error.log # MySQL error logs `

#### Log Monitoring Commands `bash tail -f /var/log/syslog # Follow system log journalctl -f # Follow systemd journal journalctl -u service_name # Show logs for specific service dmesg # Kernel ring buffer messages `

Network Commands

Network troubleshooting and configuration commands are essential for system connectivity management.

Network Connectivity Testing

#### ping (Network Connectivity Test) `bash ping google.com # Test connectivity to host ping -c 4 google.com # Send only 4 packets ping -i 2 google.com # 2-second interval between packets ping6 ipv6.google.com # IPv6 ping `

#### Network Configuration `bash ip addr show # Show network interfaces ip route show # Show routing table ifconfig # Network interface configuration (legacy) netstat -tuln # Show listening ports ss -tuln # Modern alternative to netstat `

Network Information Commands

| Command | Purpose | Usage Example | |---------|---------|---------------| | wget | Download files from web | wget https://example.com/file.zip | | curl | Transfer data from servers | curl -O https://example.com/file.txt | | nslookup | DNS lookup | nslookup google.com | | dig | DNS lookup (detailed) | dig google.com MX | | traceroute | Trace network path | traceroute google.com |

Firewall and Security

#### iptables (Firewall Management) `bash iptables -L # List firewall rules iptables -A INPUT -p tcp --dport 22 -j ACCEPT # Allow SSH iptables -A INPUT -j DROP # Default deny rule `

#### SSH (Secure Shell) `bash ssh username@hostname # Connect to remote host ssh -p 2222 username@hostname # Connect using specific port scp file.txt username@hostname:/path/ # Copy file to remote host rsync -av local/ username@hostname:remote/ # Synchronize directories `

File Permissions and Ownership

Linux file permissions control access to files and directories, forming a crucial security mechanism.

Understanding Permissions

#### Permission Types - r (read): View file contents or list directory contents - w (write): Modify file contents or create/delete files in directory - x (execute): Run file as program or enter directory

#### Permission Categories - Owner (u): File owner permissions - Group (g): Group member permissions - Others (o): All other users permissions

Permission Representation

#### Symbolic Notation ` -rwxr-xr-- │││││││││ │└┴┴─ others permissions (r--) │ └┴┴─ group permissions (r-x) │ └┴┴─ owner permissions (rwx) └─ file type (- for regular file, d for directory) `

#### Numeric (Octal) Notation

| Permission | Binary | Octal | |------------|--------|-------| | --- | 000 | 0 | | --x | 001 | 1 | | -w- | 010 | 2 | | -wx | 011 | 3 | | r-- | 100 | 4 | | r-x | 101 | 5 | | rw- | 110 | 6 | | rwx | 111 | 7 |

Permission Management Commands

#### chmod (Change Mode) `bash chmod 755 filename # Set permissions using octal chmod u+x filename # Add execute for owner chmod g-w filename # Remove write for group chmod o=r filename # Set others to read-only chmod -R 644 directory/ # Recursive permission change `

Common Permission Combinations: - 644: rw-r--r-- (files) - 755: rwxr-xr-x (directories and executables) - 600: rw------- (private files) - 700: rwx------ (private directories)

#### chown (Change Ownership) `bash chown username filename # Change owner chown username:groupname filename # Change owner and group chown :groupname filename # Change group only chown -R username:group directory/ # Recursive ownership change `

#### chgrp (Change Group) `bash chgrp groupname filename # Change group ownership chgrp -R groupname directory/ # Recursive group change `

Package Management

Package management systems handle software installation, updates, and removal across different Linux distributions.

Debian/Ubuntu (APT)

#### Basic APT Commands `bash apt update # Update package lists apt upgrade # Upgrade installed packages apt install package_name # Install package apt remove package_name # Remove package apt purge package_name # Remove package and configuration apt search keyword # Search for packages apt show package_name # Show package information `

#### Advanced APT Operations `bash apt list --installed # List installed packages apt list --upgradable # List upgradable packages apt autoremove # Remove unnecessary packages apt autoclean # Clean package cache dpkg -i package.deb # Install local deb package dpkg -l # List installed packages `

Red Hat/CentOS (YUM/DNF)

#### YUM Commands `bash yum update # Update all packages yum install package_name # Install package yum remove package_name # Remove package yum search keyword # Search packages yum info package_name # Package information yum list installed # List installed packages `

#### DNF Commands (Modern replacement for YUM) `bash dnf update # Update packages dnf install package_name # Install package dnf remove package_name # Remove package dnf search keyword # Search packages dnf history # Show transaction history `

Package Management Comparison

| Distribution | Package Manager | Package Format | Configuration | |--------------|----------------|----------------|---------------| | Ubuntu/Debian | APT | .deb | /etc/apt/ | | Red Hat/CentOS | YUM/DNF | .rpm | /etc/yum.repos.d/ | | Arch Linux | Pacman | .pkg.tar.xz | /etc/pacman.conf | | SUSE | Zypper | .rpm | /etc/zypp/ |

Advanced Commands and Concepts

Text Editors

#### vim (Vi Improved) `bash vim filename # Open file in vim `

Basic vim Commands: - i: Insert mode - Esc: Command mode - :w: Save file - :q: Quit - :wq: Save and quit - :q!: Quit without saving - dd: Delete line - yy: Copy line - p: Paste

#### nano (Simple Text Editor) `bash nano filename # Open file in nano `

nano Key Shortcuts: - Ctrl+O: Save file - Ctrl+X: Exit - Ctrl+K: Cut line - Ctrl+U: Paste line - Ctrl+W: Search

Archive and Compression

#### tar (Tape Archive) `bash tar -cvf archive.tar files/ # Create tar archive tar -czvf archive.tar.gz files/ # Create compressed archive tar -xvf archive.tar # Extract tar archive tar -xzvf archive.tar.gz # Extract compressed archive tar -tvf archive.tar # List archive contents `

tar Options: - c: Create archive - x: Extract archive - v: Verbose output - f: Specify filename - z: Gzip compression - j: Bzip2 compression

#### Compression Tools `bash gzip filename # Compress file gunzip filename.gz # Decompress file zip archive.zip files/ # Create zip archive unzip archive.zip # Extract zip archive `

System Services

#### systemctl (SystemD Service Control) `bash systemctl status service_name # Check service status systemctl start service_name # Start service systemctl stop service_name # Stop service systemctl restart service_name # Restart service systemctl enable service_name # Enable service at boot systemctl disable service_name # Disable service at boot systemctl list-units # List all units `

Environment Variables

#### Managing Environment Variables `bash env # List all environment variables echo $PATH # Display PATH variable export VARIABLE_NAME=value # Set environment variable unset VARIABLE_NAME # Remove environment variable `

Important Environment Variables: - PATH: Executable search paths - HOME: User home directory - USER: Current username - SHELL: Current shell program - PWD: Present working directory

Daily Practice Routine

Week 1: Foundation Building

#### Day 1-2: Navigation Mastery `bash

Practice these commands daily

#### Day 3-4: File Operations `bash

Daily file manipulation practice

#### Day 5-7: Text Processing `bash

Daily text processing exercises

Week 2: Intermediate Skills

#### Daily System Monitoring `bash

Morning system check routine

#### Permission Practice `bash

Daily permission exercises

Week 3: Advanced Operations

#### Automation Scripts `bash #!/bin/bash

Daily backup script example

#### Log Analysis `bash

Daily log analysis routine

Week 4: Integration and Mastery

#### Complex Command Combinations `bash

Advanced daily exercises

Monthly Assessment Checklist

#### Core Competencies Verification

| Skill Area | Assessment Task | Proficiency Level | |------------|----------------|-------------------| | Navigation | Navigate entire file system without assistance | Beginner/Intermediate/Advanced | | File Operations | Create, copy, move, delete files efficiently | Beginner/Intermediate/Advanced | | Text Processing | Use grep, sed, awk for data manipulation | Beginner/Intermediate/Advanced | | Process Management | Monitor and control system processes | Beginner/Intermediate/Advanced | | Permissions | Understand and modify file permissions | Beginner/Intermediate/Advanced | | System Monitoring | Interpret system performance metrics | Beginner/Intermediate/Advanced |

Best Practices for Daily Practice

#### Consistency Guidelines 1. Daily Commitment: Practice for at least 30 minutes daily 2. Progressive Learning: Build upon previous day's knowledge 3. Real-world Application: Use commands for actual tasks 4. Documentation: Keep notes of useful command combinations 5. Experimentation: Try variations of commands safely

#### Safety Considerations 1. Backup Important Data: Always backup before experimenting 2. Use Test Environments: Practice destructive commands safely 3. Understand Before Executing: Read command documentation 4. Verify Permissions: Check file permissions before modification 5. Monitor System Resources: Avoid overwhelming system resources

#### Learning Resources - Man Pages: Use man command_name for detailed documentation - Info Pages: Use info command_name for comprehensive guides - Online Documentation: Refer to distribution-specific documentation - Practice Environments: Use virtual machines for safe experimentation - Community Forums: Engage with Linux communities for problem-solving

This comprehensive guide provides the foundation for mastering Linux basics through structured daily practice. Regular application of these commands and concepts will develop proficiency in Linux system administration and command-line operations. Remember that mastery comes through consistent practice and real-world application of these fundamental skills.