# List files
ls # Basic list
ls -l # Long format
ls -la # All files (including hidden)
ls -lah # Human readable sizes
ls -lht # Sorted by time
ls -lhS # Sorted by size
ls -lR # Recursive
ls -d */ # Directories only
ls *.txt # Pattern matching
ls -1 # One per line# Change directory
cd /path/to/directory # Absolute path
cd .. # Parent directory
cd ~ # Home directory
cd - # Previous directory
cd # Home directory
# Show current directory
pwd# Create files/directories
touch file.txt # Create empty file
mkdir directory # Create directory
mkdir -p path/to/create # Create with parents
mkdir dir1 dir2 dir3 # Multiple directories
# Copy files
cp source dest # Copy file
cp -r source dest # Copy directory
cp -p source dest # Preserve attributes
cp -a source dest # Archive mode
cp -u source dest # Update only
cp -v source dest # Verbose
# Move/rename
mv oldname newname # Rename
mv file /path/to/ # Move
mv -i file dest # Interactive
# Remove
rm file # Remove file
rm -f file # Force
rm -r directory # Remove directory
rm -rf directory # Force recursive (careful!)
rm -i file # Interactive
rm -v file # Verbose# Find files
find /path -name "*.log" # By name
find /path -type f # Files only
find /path -type d # Directories only
find /path -mtime -7 # Modified in last 7 days
find /path -mtime +30 # Modified more than 30 days ago
find /path -size +100M # Larger than 100MB
find /path -size -1k # Smaller than 1KB
find /path -user username # By owner
find /path -perm 644 # By permissions
find /path -name "*.log" -delete # Find and delete
# Locate (faster, requires database)
locate filename
updatedb # Update locate database# View files
cat file # Display entire file
cat file1 file2 # Multiple files
cat -n file # With line numbers
tac file # Reverse order
less file # Page through file
more file # Page through file
head -n 20 file # First 20 lines
tail -n 20 file # Last 20 lines
tail -f file # Follow (watch) file
tail -F file # Follow with retry# Search in files
grep "pattern" file # Search pattern
grep -r "pattern" /path # Recursive
grep -i "pattern" file # Case insensitive
grep -v "pattern" file # Invert match
grep -n "pattern" file # With line numbers
grep -c "pattern" file # Count matches
grep -l "pattern" /path # List files with matches
grep -E "pattern" file # Extended regex
grep -A 3 "pattern" file # 3 lines after
grep -B 3 "pattern" file # 3 lines before
grep -C 3 "pattern" file # 3 lines context
# Text manipulation
cut -d: -f1 file # Cut by delimiter
cut -c1-10 file # Cut by characters
awk '{print $1}' file # Print first field
awk -F: '{print $1}' file # Custom delimiter
sed 's/old/new/g' file # Replace text
sed -i 's/old/new/g' file # In-place edit
sort file # Sort lines
sort -r file # Reverse sort
sort -n file # Numeric sort
uniq file # Remove duplicates
uniq -c file # Count occurrences
wc -l file # Count lines
wc -w file # Count words
wc -c file # Count characters# List processes
ps # Current user processes
ps aux # All processes
ps aux | grep nginx # Filter processes
ps -ef # Full format
ps -p PID # Specific process
ps -u username # By user
# Interactive process viewer
top # Process viewer
htop # Better top (install separately)
top -p PID # Specific process
top -u username # By user# Kill processes
kill PID # Kill process
kill -9 PID # Force kill
killall process_name # Kill by name
pkill -f pattern # Kill by pattern
kill -HUP PID # Send HUP signal
kill -TERM PID # Send TERM signal
# Process priority
nice -n 10 command # Run with lower priority
renice 10 PID # Change priority# Background jobs
command & # Run in background
nohup command & # Run detached
jobs # List jobs
fg %1 # Bring to foreground
bg %1 # Send to background
disown %1 # Disown job# System info
uname -a # System information
uname -r # Kernel version
hostname # Hostname
uptime # Uptime and load
whoami # Current user
id # User and group IDs
w # Who is logged in
who # Logged in users
last # Last logged in users# Memory
free # Memory usage
free -h # Human readable
free -m # Megabytes
cat /proc/meminfo # Detailed memory info
vmstat 1 # Virtual memory stats
# CPU
top # CPU usage
htop # Better interface
mpstat 1 # CPU statistics
lscpu # CPU information
cat /proc/cpuinfo # CPU details
# Disk
df -h # Disk usage
df -i # Inode usage
du -h /path # Directory size
du -sh /path # Summary
du -h --max-depth=1 /path # One level deep
du -h --max-depth=1 /path | sort -h # Sorted
lsblk # Block devices
fdisk -l # Partitions# I/O statistics
iostat 1 # I/O stats
iostat -x 1 # Extended stats
iotop # I/O by process# IP addresses
ip addr show # Show IP addresses
ip addr add 192.168.1.100/24 dev eth0 # Add IP
ip link show # Show interfaces
ip route show # Show routing table
ifconfig # Network interfaces (deprecated)
hostname -I # IP address
# Network connections
netstat -tulpn # All connections
ss -tulpn # Modern netstat
ss -tulpn | grep :80 # Filter by port
lsof -i :80 # Processes using port 80
lsof -i -P -n # All network connections# Connectivity
ping host # Ping host
ping -c 4 host # 4 packets
ping -i 2 host # 2 second interval
ping6 host # IPv6 ping
# Route tracing
traceroute host # Trace route
tracepath host # Trace path
mtr host # My traceroute
# DNS
nslookup host # DNS lookup
dig host # DNS lookup
dig @8.8.8.8 host # Use specific DNS
dig -x 192.168.1.1 # Reverse lookup
host host # Host lookup
getent hosts host # Get host entry
# HTTP testing
curl http://example.com # HTTP request
curl -I http://example.com # Headers only
curl -L http://example.com # Follow redirects
curl -O http://example.com/file # Download file
wget http://example.com/file # Download file
wget -r http://example.com # Recursive download# Network traffic
iftop -i eth0 # Interface top
nethogs # Network by process
vnstat -i eth0 # Network statistics
tcpdump -i eth0 # Packet capture
tcpdump -i eth0 port 80 # Filter by port
tcpdump -i eth0 -w capture.pcap # Save to file# Permission format: rwx rwx rwx
# owner group others
# r=4, w=2, x=1
# View permissions
ls -l file # Long format
stat file # Detailed info# chmod (change mode)
chmod 755 file # rwxr-xr-x
chmod +x file # Add execute
chmod -w file # Remove write
chmod u+x file # User execute
chmod g+w file # Group write
chmod o-r file # Others read
chmod a+x file # All execute
chmod -R 755 directory # Recursive
# chown (change owner)
chown user:group file # Change owner
chown user file # Change user only
chown :group file # Change group only
chown -R user:group directory # Recursive
# Special permissions
chmod +s file # Setuid/setgid
chmod +t directory # Sticky bit# Update package list
apt update
apt-get update
# Upgrade packages
apt upgrade
apt-get upgrade
apt full-upgrade
# Install package
apt install package
apt-get install package
apt install package1 package2 # Multiple packages
# Remove package
apt remove package
apt purge package # Remove with config
apt autoremove # Remove unused
# Search packages
apt search keyword
apt-cache search keyword
# Package information
apt show package
apt-cache show package
dpkg -l # List installed
dpkg -L package # Files in package# Update packages
yum update
dnf update
# Install package
yum install package
dnf install package
# Remove package
yum remove package
dnf remove package
# Search packages
yum search keyword
dnf search keyword
# Package information
yum info package
dnf info package
rpm -qa # List installed
rpm -ql package # Files in package# Service management
systemctl status service # Service status
systemctl start service # Start service
systemctl stop service # Stop service
systemctl restart service # Restart service
systemctl reload service # Reload configuration
systemctl enable service # Enable on boot
systemctl disable service # Disable on boot
systemctl is-enabled service # Check if enabled
systemctl is-active service # Check if active
# List services
systemctl list-units # All units
systemctl list-units --type=service # Services only
systemctl list-units --state=running # Running only
# Logs
journalctl -u service # Service logs
journalctl -f # Follow logs
journalctl --since "1 hour ago" # Since time
journalctl --since today # Since today
journalctl -p err # Errors only# Load average
uptime # Uptime and load
cat /proc/loadavg # Load average
# System resources
sar 1 # System activity
sar -u 1 # CPU
sar -r 1 # Memory
sar -d 1 # Disk
# Process monitoring
ps aux --sort=-%mem | head # Top memory
ps aux --sort=-%cpu | head # Top CPU# Common log locations
/var/log/syslog # System log
/var/log/messages # Messages
/var/log/auth.log # Authentication
/var/log/nginx/ # Nginx logs
/var/log/apache2/ # Apache logs
# View logs
tail -f /var/log/syslog # Follow log
tail -n 100 /var/log/syslog # Last 100 lines
grep "error" /var/log/syslog # Search in log
journalctl -f # Systemd logs# tar
tar -czf archive.tar.gz directory # Create gzip archive
tar -xzf archive.tar.gz # Extract gzip archive
tar -cjf archive.tar.bz2 directory # Create bzip2 archive
tar -xjf archive.tar.bz2 # Extract bzip2 archive
tar -tf archive.tar.gz # List contents
# zip
zip -r archive.zip directory # Create zip
unzip archive.zip # Extract zip
# gzip
gzip file # Compress
gunzip file.gz # Decompress# Compare files
diff file1 file2 # Differences
diff -u file1 file2 # Unified format
cmp file1 file2 # Compare files
comm file1 file2 # Common lines# View variables
env # All environment variables
echo $PATH # Specific variable
printenv VAR # Print variable
# Set variables
export VAR=value # Export to environment
VAR=value command # Set for command only# Find large files
find / -type f -size +100M 2>/dev/null
du -h / | sort -h | tail -20
# Find processes using port
lsof -i :80
netstat -tulpn | grep :80
ss -tulpn | grep :80
# Check disk space
df -h
du -sh /* | sort -h
# Check memory
free -h
cat /proc/meminfo | grep MemAvailable
# Check load
uptime
cat /proc/loadavgcommand > file # Redirect output
command >> file # Append output
command < file # Redirect input
command 2> file # Redirect errors
command &> file # Redirect all
command | command2 # Pipe
command | tee file # Output and saveCtrl+C # Cancel command
Ctrl+D # Exit shell
Ctrl+Z # Suspend process
Ctrl+L # Clear screen
Ctrl+R # Search history
Ctrl+A # Beginning of line
Ctrl+E # End of line
Ctrl+U # Clear to beginning
Ctrl+K # Clear to endRemember: Linux commands are powerful. Always verify before executing destructive operations. Use man command for help.