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Linux commands form the backbone of server administration, software development, and system management tasks. Whether you’re deploying applications, managing files, troubleshooting issues, or automating workflows, mastering these commands will dramatically improve your productivity and technical capabilities. This guide covers 25+ essential Linux commands with practical examples, common pitfalls, and real-world use cases that every developer should have in their toolkit.

File and Directory Operations

The foundation of Linux command-line work starts with navigating and manipulating files and directories. These commands handle everything from basic file operations to complex directory traversals.

ls – List Directory Contents

The ls command displays directory contents with various formatting options. Beyond basic listing, it provides detailed file information crucial for debugging permission issues and understanding file structures.

# Basic directory listing
ls

# Detailed listing with permissions, ownership, and timestamps
ls -la

# Sort by modification time (newest first)
ls -lt

# Show file sizes in human-readable format
ls -lh

# Display hidden files and directories
ls -a

# Recursive listing of subdirectories
ls -R

Common pitfall: Many developers forget that ls -l shows symbolic link targets, which can be confusing when troubleshooting broken symlinks. Use ls -lL to follow symbolic links and show the actual file information.

cd – Change Directory

Directory navigation seems simple but includes powerful shortcuts that speed up development workflows.

# Navigate to home directory
cd ~
cd

# Go back to previous directory
cd -

# Navigate to parent directory
cd ..

# Navigate to root directory
cd /

# Navigate using absolute path
cd /var/log

# Navigate using relative path
cd ../documents

pwd – Print Working Directory

Essential for script debugging and understanding your current location in the filesystem hierarchy.

# Show current directory path
pwd

# Show physical path (resolves symbolic links)
pwd -P

mkdir – Create Directories

Directory creation with advanced options for setting permissions and creating nested structures.

# Create single directory
mkdir project

# Create nested directory structure
mkdir -p /var/www/html/assets/images

# Create directory with specific permissions
mkdir -m 755 secure_folder

# Create multiple directories
mkdir dir1 dir2 dir3

rmdir and rm – Remove Directories and Files

File and directory removal with safety considerations for production environments.

# Remove empty directory
rmdir empty_folder

# Remove file
rm filename.txt

# Remove directory and all contents (use with extreme caution)
rm -rf directory_name

# Remove files interactively (prompts for confirmation)
rm -i *.log

# Remove files matching pattern
rm *.tmp

**Critical warning**: Always double-check paths before using rm -rf. Consider using trash-cli as a safer alternative that moves files to trash instead of permanent deletion.

File Content Operations

These commands handle reading, searching, and manipulating file contents – essential for log analysis, configuration management, and code review.

cat – Display File Contents

# Display file contents
cat file.txt

# Display multiple files
cat file1.txt file2.txt

# Number all lines
cat -n file.txt

# Show non-printing characters
cat -A file.txt

less and more – Paginated File Viewing

# View large files with pagination
less large_file.log

# Search within less (type /search_term)
# Navigate: Space (next page), b (previous page), q (quit)

# View file with line numbers
less -N file.txt

head and tail – View File Portions

# Show first 10 lines
head file.txt

# Show first 20 lines
head -n 20 file.txt

# Show last 10 lines
tail file.txt

# Follow file changes in real-time (essential for monitoring logs)
tail -f /var/log/apache2/access.log

# Show last 50 lines and follow
tail -n 50 -f application.log

grep – Search Text Patterns

One of the most powerful tools for searching and filtering text data.

# Basic text search
grep "error" log_file.txt

# Case-insensitive search
grep -i "ERROR" log_file.txt

# Search recursively in directories
grep -r "function_name" /path/to/source/

# Show line numbers
grep -n "TODO" *.js

# Count matching lines
grep -c "failed" access.log

# Search for exact word matches
grep -w "test" file.txt

# Use regular expressions
grep -E "[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}" access.log

# Exclude lines matching pattern
grep -v "debug" application.log

Option	Description	Use Case
-i	Case insensitive	Searching logs with mixed case
-r	Recursive search	Finding code patterns across projects
-n	Show line numbers	Debugging and code review
-v	Invert match	Filtering out noise from logs
-E	Extended regex	Complex pattern matching

find – Locate Files and Directories

Advanced file searching with powerful filtering capabilities.

# Find files by name
find /path -name "*.log"

# Find files modified in last 7 days
find /var/log -mtime -7

# Find files larger than 100MB
find /home -size +100M

# Find and execute commands on results
find /tmp -name "*.tmp" -exec rm {} \;

# Find files by permissions
find /var/www -perm 644

# Find files by user ownership
find /home -user username

# Combine multiple criteria
find /var/log -name "*.log" -size +10M -mtime -30

System Information and Process Management

Understanding system resources and managing processes is crucial for application deployment and troubleshooting.

ps – Process Status

# Show all running processes
ps aux

# Show processes in tree format
ps auxf

# Show processes for specific user
ps -u username

# Show specific process details
ps -p 1234

top and htop – System Monitoring

# Real-time process monitoring
top

# Enhanced process monitoring (if installed)
htop

# Show processes for specific user
top -u username

kill and killall – Process Termination

# Terminate process by PID
kill 1234

# Force kill process
kill -9 1234

# Terminate processes by name
killall firefox

# Send specific signal to process
kill -HUP 1234

df – Disk Space Usage

# Show disk usage for all mounted filesystems
df -h

# Show specific filesystem
df -h /var

# Show inode usage
df -i

du – Directory Space Usage

# Show directory sizes in current location
du -h

# Show total size only
du -sh

# Show sizes of specific directories
du -h /var/log/*

# Sort by size
du -h | sort -hr

free – Memory Usage

# Show memory usage in human-readable format
free -h

# Show memory usage with continuous updates
free -h -s 5

File Permissions and Ownership

Understanding and managing file permissions is critical for security and proper application functionality.

chmod – Change Permissions

# Set specific permissions using numeric notation
chmod 755 script.sh

# Add execute permission for owner
chmod u+x script.sh

# Remove write permission for group and others
chmod go-w file.txt

# Set permissions recursively
chmod -R 644 /var/www/html/

# Common permission combinations
chmod 644 file.txt    # rw-r--r-- (files)
chmod 755 directory/  # rwxr-xr-x (directories and executables)
chmod 600 private.key # rw------- (sensitive files)

Numeric	Symbolic	Permissions	Use Case
644	rw-r–r–	Owner: read/write, Others: read	Regular files
755	rwxr-xr-x	Owner: full, Others: read/execute	Executables, directories
600	rw——-	Owner: read/write only	Private keys, config files
777	rwxrwxrwx	Full permissions for all	Temporary directories (use cautiously)

chown – Change Ownership

# Change file owner
chown username file.txt

# Change owner and group
chown username:groupname file.txt

# Change ownership recursively
chown -R www-data:www-data /var/www/html/

Network and Connectivity Commands

Essential for troubleshooting network issues and managing remote connections.

ping – Test Network Connectivity

# Test connectivity to host
ping google.com

# Send specific number of packets
ping -c 4 google.com

# Set packet interval
ping -i 2 google.com

wget and curl – Download Files and Test APIs

# Download file with wget
wget https://example.com/file.tar.gz

# Download with custom filename
wget -O custom_name.tar.gz https://example.com/file.tar.gz

# Basic HTTP request with curl
curl https://api.example.com/data

# POST request with data
curl -X POST -d "key=value" https://api.example.com/endpoint

# Include response headers
curl -i https://example.com

# Follow redirects
curl -L https://example.com

# Save to file
curl -o output.json https://api.example.com/data

ssh – Secure Shell

# Connect to remote server
ssh user@hostname

# Connect using specific key
ssh -i ~/.ssh/private_key user@hostname

# Execute command remotely
ssh user@hostname 'ls -la'

# Connect to specific port
ssh -p 2222 user@hostname

# Enable X11 forwarding
ssh -X user@hostname

scp – Secure Copy

# Copy file to remote server
scp file.txt user@hostname:/path/to/destination/

# Copy from remote server
scp user@hostname:/path/to/file.txt ./

# Copy directory recursively
scp -r directory/ user@hostname:/path/to/destination/

# Use specific SSH key
scp -i ~/.ssh/private_key file.txt user@hostname:/path/

Archive and Compression

Managing compressed files and creating backups efficiently.

tar – Archive Files

# Create tar archive
tar -cvf archive.tar directory/

# Create compressed tar.gz archive
tar -czvf archive.tar.gz directory/

# Extract tar archive
tar -xvf archive.tar

# Extract tar.gz archive
tar -xzvf archive.tar.gz

# List contents without extracting
tar -tvf archive.tar

# Extract specific files
tar -xvf archive.tar specific_file.txt

Option	Description	Usage
-c	Create archive	Making backups
-x	Extract archive	Restoring files
-v	Verbose output	Seeing progress
-f	Specify filename	Archive file name
-z	Gzip compression	Saving space

Text Processing and Manipulation

Advanced text processing commands for data analysis and file manipulation.

awk – Text Processing

# Print specific columns
awk '{print $1, $3}' file.txt

# Process CSV files
awk -F',' '{print $2}' data.csv

# Calculate sum of column
awk '{sum += $1} END {print sum}' numbers.txt

# Pattern matching with action
awk '/error/ {print $0}' log.txt

sed – Stream Editor

# Replace text in file
sed 's/old_text/new_text/g' file.txt

# Edit file in place
sed -i 's/old_text/new_text/g' file.txt

# Delete specific lines
sed '2d' file.txt

# Replace text only on specific lines
sed '1,10s/old/new/g' file.txt

sort – Sort Lines

# Sort file contents
sort file.txt

# Sort numerically
sort -n numbers.txt

# Sort by specific column
sort -k2 file.txt

# Reverse sort
sort -r file.txt

# Remove duplicates while sorting
sort -u file.txt

uniq – Remove Duplicate Lines

# Remove consecutive duplicate lines
uniq file.txt

# Count occurrences
uniq -c file.txt

# Show only duplicate lines
uniq -d file.txt

System Control and Service Management

Modern Linux systems use systemd for service management, making these commands essential for deployment and maintenance.

systemctl – Service Control

# Start service
systemctl start nginx

# Stop service
systemctl stop nginx

# Restart service
systemctl restart nginx

# Enable service to start at boot
systemctl enable nginx

# Check service status
systemctl status nginx

# List all services
systemctl list-units --type=service

# Reload service configuration
systemctl reload nginx

Environment and Variable Management

export – Set Environment Variables

# Set environment variable for current session
export API_KEY="your_api_key_here"

# Set PATH variable
export PATH=$PATH:/usr/local/bin

# View all environment variables
export

# View specific variable
echo $PATH

which and whereis – Locate Commands

# Find command location
which python3

# Find all related files
whereis nginx

Real-World Use Cases and Practical Examples

Here are some practical scenarios where these commands work together to solve common development problems:

Log Analysis Workflow

# Find large log files
find /var/log -name "*.log" -size +100M

# Monitor real-time errors
tail -f /var/log/nginx/error.log | grep -i "error"

# Count error types
grep -i "error" /var/log/application.log | awk '{print $4}' | sort | uniq -c

# Archive old logs
tar -czvf logs_backup_$(date +%Y%m%d).tar.gz /var/log/*.log

Deployment and Maintenance Script

#!/bin/bash
# Check disk space before deployment
df -h | grep -E "(8[0-9]|9[0-9])%" && echo "Warning: Disk space low"

# Backup current application
tar -czvf backup_$(date +%Y%m%d_%H%M%S).tar.gz /var/www/html/

# Update file permissions
chown -R www-data:www-data /var/www/html/
chmod -R 644 /var/www/html/
find /var/www/html/ -type d -exec chmod 755 {} \;

# Restart services
systemctl restart nginx
systemctl restart php7.4-fpm

Performance Considerations and Best Practices

• Use find with specific paths instead of searching from root to improve performance
• Pipe grep results to head or tail when dealing with large files
• Use less instead of cat for viewing large files to avoid memory issues
• Always test rm and chmod commands with ls first to verify target files
• Use nohup for long-running processes that should continue after logout
• Implement proper error handling in scripts using set -e and exit codes

Security Considerations

• Never use chmod 777 on production servers except for specific temporary directories
• Regularly audit file permissions with find /path -perm 777
• Use sudo instead of logging in as root for administrative tasks
• Secure SSH keys with chmod 600 permissions
• Monitor system logs regularly for suspicious activity using grep and awk

Integration with Development Workflows

These commands integrate seamlessly with modern development practices. Use them in CI/CD pipelines, Docker containers, and deployment scripts. Many developers create aliases for frequently used command combinations:

# Add to ~/.bashrc or ~/.zshrc
alias ll='ls -la'
alias grep='grep --color=auto'
alias df='df -h'
alias du='du -h'
alias ps='ps aux'

For comprehensive Linux command references, check the Linux man pages and the GNU Coreutils manual.

When deploying applications that rely on these commands, consider using reliable infrastructure like VPS services or dedicated servers that provide full root access and customization capabilities for optimal command-line workflows.

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