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General OS

File System Navigation​

Basic Navigation​

pwd                      # Print working directory
cd /path/to/directory    # Change directory
cd ~                     # Go to home directory
cd -                     # Go to previous directory
cd ..                    # Go up one directory
ls                       # List directory contents
ls -la                   # List with details and hidden files
ls -lh                   # List with human-readable sizes
tree                     # Display directory tree

File Operations​

# Creating files and directories
touch filename           # Create empty file
mkdir dirname           # Create directory
mkdir -p path/to/dir    # Create directory with parents
mktemp                  # Create temporary file

# Copying and moving
cp file1 file2          # Copy file
cp -r dir1 dir2         # Copy directory recursively
mv file1 file2          # Move/rename file
mv file1 /path/to/      # Move file to directory

# Removing files
rm filename             # Remove file
rm -rf dirname          # Remove directory recursively (dangerous!)
rmdir dirname           # Remove empty directory

File Permissions​

# View permissions
ls -l filename          # View file permissions
stat filename           # Detailed file information

# Change permissions
chmod 755 filename      # Set permissions (rwxr-xr-x)
chmod +x filename       # Add execute permission
chmod -w filename       # Remove write permission
chmod u+x,g-w,o-r file  # Multiple permission changes

# Change ownership
chown user:group file   # Change owner and group
chown user file         # Change owner only
chgrp group file        # Change group only

Text Processing​

Viewing Files​

cat filename            # Display entire file
less filename           # View file with pagination
head -n 10 filename     # Show first 10 lines
tail -n 10 filename     # Show last 10 lines
tail -f filename        # Follow file changes (logs)

Searching and Filtering​

grep "pattern" file     # Search for pattern in file
grep -r "pattern" dir   # Recursive search in directory
grep -i "pattern" file  # Case-insensitive search
grep -v "pattern" file  # Invert match (exclude pattern)
grep -n "pattern" file  # Show line numbers

# Advanced grep
grep -E "pattern1|pattern2" file  # Extended regex (OR)
grep -A 5 -B 5 "pattern" file     # Show 5 lines before/after

# Other search tools
find /path -name "*.txt"           # Find files by name
locate filename                   # Find files using database
which command                     # Find command location
whereis command                   # Find command, source, manual

Text Manipulation​

sort filename           # Sort lines
sort -n filename        # Numeric sort
sort -r filename        # Reverse sort
sort -u filename        # Sort and remove duplicates

uniq filename           # Remove duplicate lines
uniq -c filename        # Count occurrences

cut -d',' -f1 file.csv  # Extract first column (CSV)
cut -c1-10 filename     # Extract characters 1-10

awk '{print $1}' file   # Print first column
awk -F',' '{print $2}' file.csv  # Use comma as delimiter

sed 's/old/new/g' file  # Replace all occurrences
sed -i 's/old/new/g' file  # Edit file in place

System Information​

System Details​

uname -a                # Complete system information
uname -r                # Kernel version
hostname                # System hostname
hostnamectl             # Detailed host information
lsb_release -a          # Distribution information
cat /etc/os-release     # OS release information

Hardware Information​

lscpu                   # CPU information
lshw                    # Hardware information
lshw -short             # Hardware summary
lspci                   # PCI devices
lsusb                   # USB devices
lsblk                   # Block devices
fdisk -l                # Disk partitions

System Resources​

free -h                 # Memory usage (human-readable)
df -h                   # Disk usage by filesystem
du -h /path             # Directory size
du -sh *                # Size of all items in current directory
lsof                    # List open files
lsof -i :80             # Show what's using port 80

Process Management​

Process Information​

ps aux                  # All processes
ps -ef                  # All processes (different format)
ps -u username          # Processes for specific user
pgrep process_name      # Find process ID by name
pidof process_name      # Get PID of process

Process Control​

kill PID                # Terminate process
kill -9 PID             # Force kill process
killall process_name    # Kill all instances of process
pkill process_name      # Kill process by name

# Job control
command &               # Run in background
jobs                    # List background jobs
fg %1                   # Bring job 1 to foreground
bg %1                   # Send job 1 to background
nohup command &         # Run command immune to hangups

Process Monitoring​

top                     # Real-time process viewer
htop                    # Enhanced process viewer
atop                    # Advanced process monitor
iotop                   # I/O monitoring

Network Commands​

Network Information​

ip addr show            # Show IP addresses
ip route show           # Show routing table
ifconfig                # Network interface configuration
netstat -tuln           # Show listening ports
ss -tuln                # Modern replacement for netstat
lsof -i                 # Show network connections

Network Utilities​

ping hostname           # Test connectivity
traceroute hostname     # Trace network path
wget URL                # Download file
curl URL                # Transfer data from server
ssh user@hostname       # Secure shell connection
scp file user@host:path # Secure copy over network

Archive and Compression​

Tar Archives​

tar -cvf archive.tar files      # Create tar archive
tar -xvf archive.tar            # Extract tar archive
tar -tvf archive.tar            # List archive contents
tar -czvf archive.tar.gz files  # Create compressed archive
tar -xzvf archive.tar.gz        # Extract compressed archive

Compression​

gzip filename           # Compress file
gunzip filename.gz      # Decompress file
zip archive.zip files   # Create zip archive
unzip archive.zip       # Extract zip archive

Environment and Variables​

Environment Variables​

env                     # Show all environment variables
echo $PATH              # Show PATH variable
export VAR=value        # Set environment variable
unset VAR               # Remove environment variable

Shell Configuration​

source ~/.bashrc        # Reload bash configuration
alias ll='ls -la'       # Create command alias
unalias ll              # Remove alias
history                 # Show command history
!n                      # Execute command n from history
!!                      # Execute last command

Package Management​

Debian/Ubuntu (apt)​

sudo apt update         # Update package list
sudo apt upgrade        # Upgrade packages
sudo apt install package  # Install package
sudo apt remove package   # Remove package
sudo apt search pattern   # Search for packages

Red Hat/CentOS (yum/dnf)​

sudo yum update         # Update packages
sudo yum install package  # Install package
sudo yum remove package   # Remove package
sudo yum search pattern   # Search for packages

System Services​

Systemd Services​

systemctl status service    # Check service status
systemctl start service     # Start service
systemctl stop service      # Stop service
systemctl restart service   # Restart service
systemctl enable service    # Enable service at boot
systemctl disable service   # Disable service at boot
systemctl list-units       # List all units

Cron Jobs​

Cron Management​

crontab -l              # List cron jobs
crontab -e              # Edit cron jobs
crontab -r              # Remove all cron jobs

# Cron syntax: minute hour day month day-of-week command
# Example: 0 2 * * * /path/to/script  # Run daily at 2 AM

Input/Output Redirection​

Redirection​

command > file          # Redirect stdout to file
command >> file         # Append stdout to file
command 2> file         # Redirect stderr to file
command &> file         # Redirect both stdout and stderr
command < file          # Use file as input
command | command2      # Pipe output to another command

Useful Combinations​

find /path -name "*.log" | xargs rm  # Find and remove files
ps aux | grep process_name           # Find specific process
cat file | sort | uniq              # Sort and remove duplicates