Monday, April 13, 2026

Cohort 3 | Project CloudIgnite Topics: Linux File Management Duration: ~3 hours

📌 CLF-C02 Relevance Notice Most of this lecture covers Linux OS fundamentals (file system, permissions, CLI commands), which are not directly tested on the AWS Certified Cloud Practitioner (CLF-C02) exam. However, two areas are relevant:

• File permissions (chmod) — understanding permission models is foundational to AWS IAM concepts (least privilege, resource access control).
• SSH key management (chmod 400) — directly used when connecting to Amazon EC2 instances, which is tested on CLF-C02 under compute services. See the CLF-C02 Exam Guide for full domain coverage.

Key Takeaways

• Linux file system: everything is a file (processes in /proc, hardware in /dev)
• File permissions: rwx for owner/group/others; chmod 400 for SSH keys on EC2
• Core commands: ls, cat, less, head, tail, cp, mv, rm, mkdir, touch
• Search: find locates files by name/attributes; grep searches text inside files
• Hard links point to inode (survive deletion); symbolic links point to path (break on deletion)
• Lab 233: Practical exercises on EC2 via SSH — create dirs, files, copy/move/delete

Table of Contents

1. Knowledge Check Review — Vim Text Editor
2. Linux File System Fundamentals
3. File Permissions
4. Linux Directory Structure
5. File Viewing Commands
6. File & Directory Management Commands
7. Navigating the File System
8. Advanced File Operations
9. Links — Hard Links & Symbolic Links
10. Lab 233 Summary — Practical Exercises
11. Quick Reference Cheat Sheet

1. Knowledge Check Review — Vim Text Editor

Vim is the default terminal-based text editor for virtually all Linux distributions.

Other text editors mentioned:

• nano — simpler terminal editor
• gedit — GUI-based editor (GNOME desktop only, e.g., GNOME, Xfce)
• vi — older predecessor to Vim

2. Linux File System Fundamentals

"Everything is a File" Philosophy

A core Linux principle: almost everything in Linux is represented as a file, including:

• Regular files and folders
• Running processes (found under /proc/<PID>)
• Physical hardware devices (found under /dev)

Example: To see Zoom's process ID, navigate to /proc and locate the Zoom directory — the folder name is the process ID.

File Naming Rules

• Linux filenames are case-sensitive (File.txt ≠ file.txt)
• Avoid spaces in filenames
• Avoid forward slashes / in filenames
• File extensions are optional — a file can exist without one (defaults to plain text)

3. File Permissions

Permission String Format

When you run ls -l, you see something like:

drwxrwxrwx

Each permission: r = read, w = write, x = execute

Numeric (Octal) Permission Values

Permissions are represented in binary, then converted to a single digit:

Format: Three digits — [owner][group][others]

⚠️ CLF-C02 Relevance: chmod 400 labsuser.pem is the exact command used to secure your EC2 SSH key before connecting — a real-world AWS task.

4. Linux Directory Structure

Starting from / (root — the top of the entire filesystem):

Tip: /home is where users store personal files. /root is only for the superuser and should not be used for general file storage.

5. File Viewing Commands

ls — List Directory Contents

cat — Display File Contents

Prints the full content of a file to the terminal.

cat file.txt

more — Paginated File View

• Loads the entire file into RAM at once
• Use for small files only
• Allows forward scrolling

less — Efficient Paginated View

• Loads content page by page (memory-efficient)
• Use for large files
• Supports both forward and backward scrolling
• -N flag: show line numbers
• -X flag: clear screen before loading
• -F flag: watch mode — shows live updates as file changes

Rule of thumb: Use less for large files, more for small ones. less works well for both.

head — View Beginning of File

• Shows the first 10 lines by default
• -n <number>: specify how many lines to show

head -n 20 file.txt

tail — View End of File

• Shows the last 10 lines by default
• -n <number>: specify lines
• -f: follow/monitor mode — live updates as file changes (useful for log monitoring)

tail -f /var/log/syslog

6. File & Directory Management Commands

cp — Copy Files

cp source destination
cp file.txt /home/user/backup/

mv — Move or Rename Files

mv oldname.txt newname.txt        # Rename
mv file.txt /home/user/folder/    # Move

Same -i, -f, -v options as cp.

rm — Remove (Delete) Files

rm file.txt               # Delete a file
rm -R directory/          # Delete a non-empty directory
rmdir directory/          # Delete an EMPTY directory only

⚠️ Warning: rm in terminal is permanent. There is no Recycle Bin from the CLI. GUI deletion moves to trash; terminal deletion does not.

mkdir — Create Directory

mkdir foldername
mkdir -p parent/child/grandchild   # Create nested directories in one command
mkdir -m 755 foldername            # Create with specific permissions

touch — Create Empty File

touch filename.txt
touch file1.csv file2.csv          # Create multiple files at once

rmdir — Remove Empty Directory

rmdir foldername

Only works if the folder is completely empty.

7. Navigating the File System

pwd — Print Working Directory

Shows your current location in the file system.

pwd
# Output: /home/ec2-user/companyA

cd — Change Directory

Absolute vs Relative Paths

Shortcut: ~ is an alias for /home/username (your home directory).

Combining Commands

cd companyA && mkdir finance    # Second command runs ONLY if first succeeds
cd companyA ; mkdir finance     # Both commands run independently

8. Advanced File Operations

hash — Recently Used Commands

Displays a table of recently executed commands, their file locations, and how many times they've been run.

hash

Most standard Linux commands (like ls, mv, cp) are actually executable files stored in /usr/bin/.

Checksum — File Integrity Verification (CRC)

Used to verify a downloaded file has not been corrupted or tampered with.

• Website provides a checksum file alongside the download
• After downloading, generate the checksum of your file and compare it to the provided value
• If they match → file is intact

find — Search for Files

find /path -name "filename.txt"          # Find by exact name
find . -iname "filename.txt"             # Case-insensitive search
find . -name "*.csv"                     # Find all CSV files (wildcard)
find . -user ec2-user                    # Find files owned by a user
find . -type f -name "*.jpg"             # Find by file type
find . -mtime -7                         # Modified within last 7 days

grep — Search Inside File Contents

grep "search_term" file.txt              # Basic search
grep -i "search_term" file.txt           # Case-insensitive
grep -n "search_term" file.txt           # Show line numbers
grep -c "search_term" file.txt           # Count matching lines
grep -l "search_term" *.txt              # Show only filenames with match
cat file.txt | grep "search_term"        # Piped usage

find vs grep: find locates files by name/attributes. grep searches for text content inside files.

diff — Compare Two Files

diff file1.txt file2.txt

Shows the lines that differ between two files. Output shows exact position of differences.

9. Links — Hard Links & Symbolic Links

inode — The Actual File

• In Linux, every file has an inode: a data structure storing the file's metadata
  • File type, size, owner, permissions
  • Exact physical location on disk
• The inode number is the system's internal identifier for the file

Hard Link

• A human-readable filename that points to an inode
• Every filename you see (e.g., file.txt) is actually a hard link
• Multiple hard links can point to the same inode (same file, multiple names)
• The file is only truly deleted when ALL hard links to its inode are removed

ln file.txt backup.txt           # Create a hard link
ls -i                            # View inode numbers (same number = same file)

Key behaviour: Changing content through one hard link updates all others — they share the same inode.

Symbolic Link (Soft Link)

• Similar to a Windows shortcut
• Stores the path/location of another file — not the data itself
• If the original file is deleted, the symbolic link breaks

ln -s /path/to/original linkname

10. Lab 233 Summary — Practical Exercises

Lab Goal: Practice Linux file management on an EC2 instance via SSH.

Connection Steps (Windows)

# 1. Navigate to Downloads folder
cd Downloads

# 2. Delete old key file (if exists)
rm labsuser.pem

# 3. Download new labsuser.pem from lab environment

# 4. Set correct permission on key
chmod 400 labsuser.pem

# 5. Connect via SSH
ssh -i labsuser.pem ec2-user@<Public-IP>

If you get "Permission denied (publickey)": You likely have an old key file conflicting. Delete all old .pem files in your home directory and retry.

Lab Tasks Practiced

1. Create folder structure:

   mkdir companyA
   cd companyA
   mkdir finance HR management
   

2. Create files inside directories:

   cd HR
   touch assessment.csv "trial period.csv"
   cd ../finance
   touch salary.csv "profit and loss statement.csv"
   

3. Create files without navigating into directory:

   touch management/budget.csv management/headcount.csv
   

4. View directory tree:

   ls -laR    # Long format, all hidden files, recursive
   

5. Copy, move, rename, and delete:

   cp -R finance HR/              # Copy folder into another
   mv assessment.csv employees/   # Move file
   mv wrongname.csv correctname.csv  # Rename
   rm salary.csv                  # Delete file
   rm -R finance/                 # Delete folder
   

11. Quick Reference Cheat Sheet

NAVIGATION
pwd               → Show current directory
cd <dir>          → Change directory
cd ..             → Go up one level
cd ~              → Go to home directory

LISTING
ls                → List files
ls -l             → Long format
ls -a             → Show hidden files
ls -lh            → Human-readable sizes

FILE OPERATIONS
touch <file>      → Create empty file
cat <file>        → Show file contents
less <file>       → Page through large file
head -n N <file>  → Show first N lines
tail -n N <file>  → Show last N lines
tail -f <file>    → Monitor live changes

COPY / MOVE / DELETE
cp <src> <dst>    → Copy file
cp -R <dir> <dst> → Copy directory
mv <src> <dst>    → Move or rename
rm <file>         → Delete file
rm -R <dir>       → Delete directory
rmdir <dir>       → Delete EMPTY directory
mkdir <dir>       → Create directory
mkdir -p a/b/c    → Create nested directories

PERMISSIONS
chmod 400 <file>  → Owner read-only (SSH keys)
chmod 600 <file>  → Owner read+write
chmod 755 <file>  → Standard executable
chmod 777 <file>  → Full access for all (avoid!)

SEARCH
find . -name "*.txt"       → Find files by name
grep "term" file.txt       → Search inside file
diff file1 file2           → Compare two files

LINKS
ln <src> <link>            → Hard link
ln -s <src> <link>         → Symbolic (soft) link
ls -i                      → Show inode numbers

MISC
hash                       → Recently used commands

Notes compiled from live lecture — April 13, 2026 AWS/Restart Program | Cohort 3: Project CloudIgnite