Linux Operations from Scratch: 30 Essential Commands for Beginners

What Is Linux and Why Learn It?

Linux is an open-source Unix-like operating system whose kernel was first released by Linus Torvalds in 1991. It follows the POSIX standard, supports multi-user, multi-tasking, and multi-threading, and offers high stability and security, making it widely used in servers, embedded systems, and development environments.

Linux Filesystem Structure

The Linux filesystem adopts a tree structure where all files and directories are mounted from the root directory (/), and devices are also managed as files.

File Management

Navigation Commands

Core navigation commands include:

pwd          # Show current directory (Where am I?)
ls -l        # Detailed listing
ls -a        # Show hidden files
cd /home     # Go to home directory
cd ..        # Go up one level
cd ../..     # Go up two levels
cd .         # Current directory (rarely used alone)
cd ~         # Go to current user's home directory
/            # Root directory
~            # Shortcut for current user's home directory

Memory aid: pwd = where am I, ls = what's here, cd = where to go.

File Operations

Common file operations:

# Commands without a path operate in the current directory
# Example: mkdir xxx creates directory xxx in current directory
# Example: cp filename backup/ copies file to backup directory

# Create
mkdir dirname          # Create directory
mkdir fileName.txt     # Create file (touch works similarly)

# Copy and move
cp file.txt backup/    # Backup file
cp -a                  # Recursively copy files and directories
mv old.txt new.txt     # Rename
mv file.txt /tmp/      # Move file

# View content
cat file.txt           # Display entire file at once
more file.txt          # Page-by-page view (space to scroll)
tail -f log.txt        # Real-time log monitoring (ops essential!)

# Edit with vi/vim
vi                     # Basic editor; creates file if missing
vim                    # Enhanced version; both create file if missing
vi/vim fileName        # Enter command mode
Press i to enter insert mode
Save: Press Esc, then :w   # w = write
Exit: :q                 # q = quit
Save and exit: :wq
Discard changes and exit: :q!

Dangerous Commands

rm file.txt            # Delete file.txt
rm -r folder/          # Delete directory recursively (careful!)
rm -rf /               # DESTRUCTIVE! NEVER RUN!

# Options explained:
-r   Recursive deletion for directories and contents
-i   Interactive mode, prompts before each deletion
-d   Handle empty directories
-f   Force deletion, ignore non-existent files, no confirmation

Hard-earned lesson: Never use rm -rf lightly; "deleting the database and fleeing" is no joke.

Permission Management (Security Foundation)

Understanding Permissions

rwx r-x r-x
|   |   └── Others: read and execute
|   └───── Group: read and execute
└──────── Owner: read, write, execute

Numeric mode uses three octal digits (user, group, others). Each digit is the sum of:
4 = read (r)
2 = write (w)
1 = execute (x)

7

= 4+2+1 = read, write, execute 6 = 4+2 = read, write 5 = 4+1 = read, execute

Changing Permissions

# Symbolic mode (intuitive)
chmod u+x script.sh    # Add execute permission for owner
chmod o-w file.txt     # Remove write permission for others

# Numeric mode (efficient)
chmod 755 script.sh    # Owner full, others read/execute
chmod 644 config.txt   # Owner read/write, others read-only
chmod 777 script.sh    # All permissions for all (use cautiously)
chmod 644 file.txt     # Owner read/write, others read-only

# Options
chmod -R               # Recursively change directory and contents
chmod -v               # Verbose output showing changes

User Switching

# After each command you'll be prompted for password (input is hidden)
su          # Switch to another user (default root)
su -        # Load target user's environment (e.g., /root/.bashrc)
su - username   # Switch to specific user with environment
su username     # Switch without loading environment
sudo          # Execute command as another user
sudo -i       # Switch to root user (equivalent to sudo su)
sudo -u username command  # Run command as specific user

System Management (Daily Operations)

Disk and Memory Inspection

# Disk space
df
df -h          # Human-readable format
df -T          # Show filesystem type

# Memory usage
free
free -h        # Human-readable format

# Directory/file size
du
du -sh         # Show directory size in human-readable format

# Real-time process and resource view
top

Process Management

# View processes
ps
ps aux         # All processes
-e or -a       # Show all processes
-f             # Full format with command line arguments (combine with -e)
ps -ef         # All processes with full details
-u             # Processes for specific user
-p             # Process by specific PID

# Terminate processes
kill           # Graceful termination
kill -9 PID    # Force kill (use sparingly)
kill -s PID    # Request normal termination

File Search and Archiving

# Find files in directory tree
find
find /home -name "*.txt"

# Search text patterns in files
grep
grep "error" logfile   # Find lines containing "error"

# Archive and compress (commonly with gzip/bzip2)
# tar -czvf archive.tar.gz folder  (compress)
-c   Create archive
-z   Use gzip compression
-v   Verbose output
-f archive.tar.gz   Output filename

# tar -xzvf archive.tar.gz  (extract)
-x   Extract archive
-z   Handle gzip compression
-v   Verbose output
-f archive.tar.gz   Input filename

Practical Applications (Solving Real Problems)

Starting and Stopping Programs

# Basic: program exits when terminal closes
java -jar app.jar

# Advanced: runs after terminal closes with &
java -jar app.jar &

# Professional: with logging and process monitoring
nohup java -jar xxx.jar > /path/to/output.log 2>&1 &

# Breakdown:
nohup          # Ignore SIGHUP, keep running after terminal closes
java -jar xxx.jar   # Start Java application
>              # Redirect stdout to file
/path/to/output.log   # Custom log file path
2>&1           # Merge stderr into stdout (both go to output.log)
&              # Run in background

# Find and stop a Java program
ps -ef | grep java
kill pid

Log Analysis

# Find error logs
grep "ERROR" app.log

# Real-time monitoring with keyword filter
tail -f app.log | grep "important keyword"

# Count access lines
cat access.log | wc -l

# Find and delete log files older than 30 days (with confirmation per file)
find /var/log -name "*.log" -mtime +30 -exec rm -i {} \;

# Alternative using -ok for confirmation
find /var/log -name "*.log" -mtime +30 -ok rm {} \;

Learning Advice

Back up before operating – Good use of cp prevents system crashes and data loss.

Use tab completion heavily – Reduces typing errors.

Learn and understand continuously – Growth comes from hands-on work.

Never joke in production – Production is the lifeline of your system; a mistake can bring everything down.