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Linux Terminal Basics

The terminal (command line) is a powerful interface for interacting with Linux. This guide covers essential commands to get you productive quickly.

Opening the Terminal​

  • Ubuntu/Debian: Ctrl + Alt + T
  • Menu: Search for "Terminal" or "Console"
  • Right-click: Desktop → "Open Terminal"

Command Structure​

command [options] [arguments]

Example:

ls -la /home
  • ls = command
  • -la = options (flags)
  • /home = argument

Essential Navigation Commands​

pwd (Print Working Directory)​

Shows your current location:

pwd
# Output: /home/username

ls (List)​

Lists files and directories:

ls                  # List files
ls -l               # Long format (detailed)
ls -a               # Show hidden files (starting with .)
ls -la              # Long format + hidden files
ls -lh              # Human-readable file sizes
ls -lt              # Sort by modification time
ls -lS              # Sort by size
ls /path/to/dir     # List specific directory

Common output:

-rw-r--r-- 1 user group 4096 Jan 15 10:30 file.txt
drwxr-xr-x 2 user group 4096 Jan 15 10:30 directory

cd (Change Directory)​

Navigate between directories:

cd /path/to/directory    # Go to specific path
cd ..                    # Go up one level
cd ~                     # Go to home directory
cd -                     # Go to previous directory
cd                       # Go to home directory (no arguments)
cd ../..                 # Go up two levels

File and Directory Operations​

mkdir (Make Directory)​

Create directories:

mkdir dirname              # Create single directory
mkdir -p path/to/dir       # Create nested directories
mkdir dir1 dir2 dir3       # Create multiple directories

touch​

Create empty files or update timestamps:

touch file.txt            # Create new file
touch file1 file2 file3   # Create multiple files

cp (Copy)​

Copy files and directories:

cp source.txt dest.txt              # Copy file
cp -r sourcedir destdir             # Copy directory recursively
cp -i file.txt dest.txt             # Interactive (prompt before overwrite)
cp -v file.txt dest.txt             # Verbose (show what's being copied)
cp *.txt /destination/              # Copy all .txt files

mv (Move/Rename)​

Move or rename files:

mv oldname.txt newname.txt          # Rename file
mv file.txt /new/location/          # Move file
mv -i file.txt destination/         # Interactive mode
mv *.txt /destination/              # Move all .txt files

rm (Remove)​

Delete files and directories:

rm file.txt                # Delete file
rm -i file.txt             # Interactive (confirm deletion)
rm -f file.txt             # Force deletion (no confirmation)
rm -r directory/           # Delete directory recursively
rm -rf directory/          # Force delete directory (DANGEROUS!)
rm *.log                   # Delete all .log files

⚠️ Warning: rm -rf is dangerous and permanent. No trash/recycle bin!

File Viewing Commands​

cat (Concatenate)​

Display entire file content:

cat file.txt                    # Display file
cat file1.txt file2.txt         # Display multiple files
cat -n file.txt                 # Show line numbers

less​

View files page by page:

less file.txt

Navigation in less:

  • Space or Page Down - Next page
  • b or Page Up - Previous page
  • /search_term - Search forward
  • ?search_term - Search backward
  • q - Quit

View first lines of a file:

head file.txt               # First 10 lines
head -n 20 file.txt         # First 20 lines

tail​

View last lines of a file:

tail file.txt               # Last 10 lines
tail -n 20 file.txt         # Last 20 lines
tail -f log.txt             # Follow file (watch for changes)

File Permissions​

Understanding Permissions​

-rw-r--r--
  • Position 1: File type (- = file, d = directory)
  • Positions 2-4: Owner permissions (rwx)
  • Positions 5-7: Group permissions (rwx)
  • Positions 8-10: Others permissions (rwx)

Permission letters:

  • r = read (4)
  • w = write (2)
  • x = execute (1)

chmod (Change Mode)​

Change file permissions:

chmod 755 script.sh              # rwxr-xr-x
chmod 644 file.txt               # rw-r--r--
chmod +x script.sh               # Add execute permission
chmod -w file.txt                # Remove write permission
chmod u+x script.sh              # User: add execute
chmod g-w file.txt               # Group: remove write
chmod o-r file.txt               # Others: remove read

Common permissions:

  • 755 - Directories and executables
  • 644 - Regular files
  • 600 - Private files (only owner)
  • 777 - All permissions (avoid this!)

chown (Change Owner)​

Change file ownership:

sudo chown user:group file.txt       # Change owner and group
sudo chown user file.txt             # Change owner only
sudo chown -R user:group directory/  # Recursive

Searching​

find​

Search for files and directories:

find /path -name "filename"              # Find by name
find . -name "*.txt"                     # Find all .txt files
find /home -type f -name "*.log"         # Find files only
find /home -type d -name "docs"          # Find directories only
find . -size +100M                       # Files larger than 100MB
find . -mtime -7                         # Modified in last 7 days
find . -name "*.tmp" -delete             # Find and delete

grep​

Search text within files:

grep "search_term" file.txt              # Search in file
grep -r "search_term" /path              # Recursive search
grep -i "search_term" file.txt           # Case-insensitive
grep -n "search_term" file.txt           # Show line numbers
grep -v "search_term" file.txt           # Invert match (exclude)
grep -c "search_term" file.txt           # Count matches
grep -l "search_term" *.txt              # List filenames only

System Information​

df (Disk Free)​

Show disk space usage:

df                      # Disk usage
df -h                   # Human-readable (GB, MB)
df -T                   # Show filesystem type

du (Disk Usage)​

Show directory/file sizes:

du -h file.txt          # File size
du -sh directory/       # Directory size summary
du -h --max-depth=1     # Show one level deep

free​

Show memory usage:

free                    # Memory usage
free -h                 # Human-readable

top / htop​

Monitor system processes:

top                     # Process monitor
htop                    # Better process monitor (if installed)

top commands:

  • q - Quit
  • M - Sort by memory
  • P - Sort by CPU
  • k - Kill process

uname​

System information:

uname -a                # All system info
uname -r                # Kernel version
uname -m                # Architecture

Process Management​

ps​

List processes:

ps                      # Your processes
ps aux                  # All processes (detailed)
ps aux | grep process   # Find specific process

kill​

Terminate processes:

kill PID                # Graceful termination
kill -9 PID             # Force kill
killall process_name    # Kill by name

jobs / bg / fg​

Manage background jobs:

command &               # Run in background
jobs                    # List background jobs
fg %1                   # Bring job 1 to foreground
bg %1                   # Resume job 1 in background
Ctrl+Z                  # Suspend current process

Text Processing​

wc (Word Count)​

Count lines, words, characters:

wc file.txt             # Lines, words, characters
wc -l file.txt          # Count lines only
wc -w file.txt          # Count words only
wc -c file.txt          # Count bytes

sort​

Sort file content:

sort file.txt           # Sort alphabetically
sort -n file.txt        # Sort numerically
sort -r file.txt        # Reverse sort
sort -u file.txt        # Remove duplicates

uniq​

Remove duplicate lines:

uniq file.txt           # Remove adjacent duplicates
uniq -c file.txt        # Count occurrences
uniq -d file.txt        # Show only duplicates

Pipes and Redirection​

Pipes (|)​

Chain commands:

ls -l | grep ".txt"              # List files, filter .txt
ps aux | grep firefox            # Find firefox process
cat file.txt | sort | uniq       # Sort and remove duplicates

Output Redirection​

command > file.txt               # Overwrite file
command >> file.txt              # Append to file
command 2> error.log             # Redirect errors
command &> output.log            # Redirect all output

Input Redirection​

command < input.txt              # Read from file

Compression and Archives​

tar​

Create and extract archives:

tar -czf archive.tar.gz directory/       # Create compressed archive
tar -xzf archive.tar.gz                  # Extract compressed archive
tar -czf backup.tar.gz file1 file2       # Archive multiple files
tar -xzf archive.tar.gz -C /destination/ # Extract to specific location

tar flags:

  • -c - Create archive
  • -x - Extract archive
  • -z - Compress with gzip
  • -f - Filename
  • -v - Verbose

zip / unzip​

zip archive.zip file1 file2      # Create zip
zip -r archive.zip directory/    # Zip directory
unzip archive.zip                # Extract zip
unzip archive.zip -d /path/      # Extract to specific path

Network Commands​

wget​

Download files:

wget https://example.com/file.zip        # Download file
wget -O filename.zip https://url         # Save with custom name
wget -c https://example.com/file.zip     # Resume download

curl​

Transfer data:

curl https://example.com                 # Display content
curl -O https://example.com/file.zip     # Download file
curl -I https://example.com              # Headers only

ping​

Test network connectivity:

ping google.com                          # Test connection
ping -c 4 google.com                     # Send 4 packets only

ssh​

Secure shell connection:

ssh user@hostname                        # Connect to remote
ssh -p 2222 user@hostname                # Custom port
ssh -i key.pem user@hostname             # Use private key

scp​

Secure copy:

scp file.txt user@host:/path/            # Copy to remote
scp user@host:/path/file.txt ./          # Copy from remote
scp -r directory/ user@host:/path/       # Copy directory

Shortcuts and Tips​

Keyboard Shortcuts​

  • Ctrl + C - Cancel current command
  • Ctrl + D - Exit terminal / EOF
  • Ctrl + Z - Suspend process
  • Ctrl + L - Clear screen (same as clear)
  • Ctrl + A - Move to line beginning
  • Ctrl + E - Move to line end
  • Ctrl + U - Delete from cursor to beginning
  • Ctrl + K - Delete from cursor to end
  • Ctrl + R - Search command history
  • Tab - Auto-complete

Command History​

history                 # Show command history
!123                    # Run command #123 from history
!!                      # Run last command
!$                      # Last argument of previous command

Wildcards​

*                       # Match any characters
?                       # Match single character
[abc]                   # Match a, b, or c
[a-z]                   # Match range a through z

Useful Combinations​

command1 && command2    # Run command2 if command1 succeeds
command1 || command2    # Run command2 if command1 fails
command1 ; command2     # Run both regardless

Help and Documentation​

man command             # Manual page
command --help          # Help information
whatis command          # Brief description
which command           # Location of command
type command            # Command type

Resources​