Basic Linux Commands

# View manual page for a command
man <command>

# Quick help for many commands
<command> --help

# Search manual pages by keyword
apropos <keyword>

# Basic directory listing
ls

# Detailed list with permissions, size, and timestamps
ls -l

# Show all files including hidden ones (starting with .)
ls -la

# Human-readable file sizes
ls -lh

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

# Change to specific directory
cd /path/to/directory

# Go to home directory
cd
# or
cd ~

# Go up one directory level
cd ..

# Go to previous directory
cd -

# Show current working directory
pwd

# Print entire file content to terminal
cat filename

# View file page by page (press q to quit)
less filename

# Show first 10 lines of file
head filename

# Show last 10 lines of file
tail filename

# Follow file changes in real-time (useful for logs)
tail -f filename

# Create empty file
touch filename

# Create directory
mkdir directory_name

# Create nested directories
mkdir -p path/to/nested/directory

# Copy files
cp source_file destination

# Copy directories recursively
cp -r source_directory destination_directory

# Move/rename files or directories
mv old_name new_name

# Remove files
rm filename

# Remove directories and their contents
rm -rf directory_name

# List all available shells on the system
cat /etc/shells

# Check current shell
echo $SHELL

# Change shell for current user
chsh -s /path/to/new/shell

# Change shell for specific user (requires sudo)
sudo chsh -s /path/to/new/shell username

# Example: Change to Fish shell
chsh -s /usr/bin/fish

# Display system information
uname -a

# Show disk usage
df -h

# Show directory size
du -h /path/to/directory

# Display memory usage
free -h

# Show running processes
ps aux

# Show system uptime
uptime