Linux Command Reference

cd                  # Change to home directory
cd /                # Change to root directory
cd ..               # Change to parent directory
cd ~                # Change to home directory
cd "linux command line"  # Navigate to directory with spaces

pwd                 # Displays your current location

ls                  # List files in current directory
ls -l                # Long listing format with details
ls -la               # List all files including hidden ones
ls -S                # Sort by file size
ls -lF               # Indicate file types with symbols
ls -p | grep -v / | tr '\n' ','  # List with comma separation
ls -lFd */           # List only directories

touch file.txt      # Create a new file or update timestamp
touch a b c          # Create multiple files
touch -c file.txt    # Update timestamp only if file exists
touch last_week -d "1 week ago"  # Create with specific timestamp

mkdir directory     # Create a directory
mkdir -p path/to/directory  # Create nested directories as needed

cp file1 file2      # Copy file1 to file2
cp file1 file2 directory/  # Copy files to directory
cp -r dir1/ dir2/   # Copy directory recursively
cp -a /source/. /dest/   # Copy with all attributes preserved

mv file1 file2      # Rename file1 to file2
mv directory1/ directory2/  # Rename directory
mv file1 file2 directory/  # Move files to directory

rm file.txt         # Remove a file
rm -r directory     # Remove directory recursively
rm -ri directory    # Remove with confirmation
rm file*.txt        # Remove all files starting with "file"

rmdir directory     # Remove empty directory
rmdir -p path/to/directory  # Remove nested empty directories

cat file.txt        # Display file contents
cat file1 file2     # Concatenate and display multiple files
cat -n file.txt     # Display with line numbers

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

Navigation in less:

• Space or f: Forward one page
• b: Back one page
• Enter or down arrow: Down one line
• q: Quit
• /pattern: Search for pattern
• n: Next search result
• 50%: Go to 50% of file

head file.txt       # Display first 10 lines
head -n 20 file.txt # Display first 20 lines
head -c 100 file.txt # Display first 100 bytes

tail file.txt       # Display last 10 lines
tail -n 20 file.txt # Display last 20 lines
tail -f log.txt     # Follow file updates in real-time

wc file.txt         # Display lines, words, bytes
wc -l file.txt      # Count lines only
wc -w file.txt      # Count words only
wc -m file.txt      # Count characters

su username         # Change to another user
su - username       # Change to user with their environment
exit                # Exit from switched user

sudo command        # Run command with superuser privileges
sudo -s             # Start a shell as superuser
sudo -i             # Login as root user
sudo -l             # List allowed commands

passwd              # Change your password
sudo passwd username  # Change another user's password

sudo adduser username  # Create a new user with interactive prompts

usermod -L username  # Lock a user's password
usermod -U username  # Unlock a user's password

id                  # Show current user ID and groups
id -un              # Display only username (same as whoami)

who                 # Display logged-in users
who -b              # Show time of last system boot

lastlog             # Show all users' last login times
lastlog -b 90       # Show logins in last 90 days

chmod u+x file.txt  # Add execute permission for owner
chmod g+w file.txt  # Add write permission for group
chmod a-w file.txt  # Remove write permission for all
chmod 755 file.txt  # Set to rwxr-xr-x (using octal)

Permissions Reference

sudo chown user file.txt  # Change owner
sudo chown user:group file.txt  # Change owner and group
sudo chown :group file.txt  # Change only group

chgrp group file.txt  # Change file's group

grep "pattern" file.txt  # Search for pattern
grep -i "pattern" file.txt  # Case-insensitive search
grep -r "pattern" directory/  # Recursive search
grep -n "pattern" file.txt  # Show line numbers
grep -A2 "pattern" file.txt  # Show 2 lines after match
grep -B1 "pattern" file.txt  # Show 1 line before match
grep -C1 "pattern" file.txt  # Show 1 line before and after match
grep -w "word" file.txt  # Match whole words only
grep -c "pattern" file.txt  # Count matching lines

sort file.txt       # Sort lines alphabetically
sort -r file.txt    # Sort in reverse order
sort -n file.txt    # Sort numerically
sort -u file.txt    # Sort and remove duplicates
sort -k2 file.txt   # Sort by second column

cat file.txt | tr 'a' 'A'  # Replace 'a' with 'A'
cat file.txt | tr a-z A-Z  # Convert to uppercase
cat file.txt | tr -d ','   # Delete all commas
cat file.txt | tr -d [:blank:]  # Delete all spaces

sed 's/old/new/g' file.txt  # Replace all occurrences
sed -i 's/old/new/g' file.txt  # Replace and update file
sed '/pattern/d' file.txt  # Delete lines with pattern
sed '/^$/d' file.txt  # Delete empty lines
sed '1d' file.txt  # Delete first line
sed 's/\t/ /g' file.txt  # Replace tabs with spaces

awk '{print}' file.txt  # Print all lines
awk '{print $1}' file.txt  # Print first column
awk '/pattern/ {print}' file.txt  # Print lines matching pattern
awk '{print NR, $0}' file.txt  # Print with line numbers
awk 'NR==3, NR==6 {print}' file.txt  # Print lines 3-6

find . -name "*.txt"  # Find text files in current directory
find /home -user username  # Find files owned by user
find . -type f -name "*.png"  # Find PNG files
find . -type d  # Find directories
find . -size +10M  # Find files larger than 10MB
find . -mtime -7  # Find files modified in last 7 days
find . -empty  # Find empty files
find . -name "*.txt" -exec cp {} {}_backup \;  # Find and copy

locate filename  # Find all files named "filename"
locate -i pattern  # Case-insensitive search
locate -e pattern  # Only show existing files
locate -l 10 pattern  # Limit to 10 results

which ls  # Show full path of ls command

uname -a  # Print all system information

date  # Show current date and time
date -u  # Show UTC time
date +%Y-%m-%d  # Format date as YYYY-MM-DD

ncal  # Display calendar for current month
ncal -3  # Display calendar for 3 months
ncal -A1 -B1  # Show previous, current, and next month
ncal -j  # Display Julian dates
ncal july 1969  # Display calendar for July 1969

ps  # Show your processes
ps -ef  # Show all processes in full format
ps aux  # Show all processes with user information
ps -ef | grep firefox  # Find Firefox processes

du -h file.txt  # Show human-readable file size
du -sh directory  # Show total directory size
du -h --max-depth=1 /  # Show size of root directories

ifconfig  # Display network interfaces
ip addr show  # Modern replacement for ifconfig
ip a  # Short version

ping google.com  # Check connection to Google
ping -c 4 google.com  # Send only 4 packets

traceroute google.com  # Trace route to Google
tracepath google.com  # Similar to traceroute but without root

curl url  # Get contents of URL
curl -o file.html url  # Save output to file
curl ifconfig.me  # Show your public IP address

command | tee file.txt  # Display output and save to file
command | tee -a file.txt  # Append to file

crontab -e  # Edit crontab
crontab -l  # List current jobs