Linux Directory Structure

The Filesystem Hierarchy

Linux organizes everything as files in a single directory tree starting from the root /. Understanding this structure helps you navigate test environments, find configuration files, and locate logs quickly.

/                   Root of the filesystem
├── home/user/      Your home directory (~)
├── etc/            Configuration files
├── var/
│   ├── log/        Application and system logs
│   └── lib/        Variable data (databases, packages)
├── tmp/            Temporary files (cleared on reboot)
├── opt/            Optional/third-party software
├── usr/
│   ├── bin/        User-installed binaries
│   └── local/      Locally compiled software
├── proc/           Virtual filesystem (process and kernel info)
├── dev/            Device files
└── srv/            Service data (web servers, FTP)

Directories QA Engineers Use Most

/home/user/ (Your Home Directory, ~)

This is where you work. Your scripts, test configurations, SSH keys, and shell customizations live here.

# Navigate to home directory
cd ~
# Or simply:
cd

# Common QA files in home directory
~/.ssh/config          # SSH connection shortcuts
~/.bashrc              # Shell customization (aliases, PATH)
~/.npmrc               # npm configuration
~/.env                 # Personal environment variables (not committed)
~/projects/            # Your cloned repositories

/var/log/ (Logs)

This is where you investigate failures. Application logs, system logs, and web server logs all live here.

# Common log locations
/var/log/syslog                    # System messages
/var/log/auth.log                  # Authentication events
/var/log/nginx/access.log          # Nginx access logs
/var/log/nginx/error.log           # Nginx error logs
/var/log/app/application.log       # Application-specific logs
/var/log/postgresql/postgresql.log # Database logs

/etc/ (Configuration)

Configuration files for system services and applications. When tests fail due to misconfiguration, this is where you look.

# Common configuration files
/etc/hosts                # DNS overrides (useful for test environments)
/etc/nginx/nginx.conf     # Nginx web server config
/etc/environment          # System-wide environment variables
/etc/postgresql/pg_hba.conf  # PostgreSQL access control
/etc/ssl/certs/           # SSL certificates

/tmp/ (Temporary Files)

Temporary data that is cleared on reboot. Useful for staging test data or storing intermediate results.

# Use /tmp for temporary test data
cp test-data.json /tmp/
# Run tests that use /tmp/test-data.json
# On reboot, the file is automatically cleaned up

/proc/ (Virtual Filesystem)

Not real files -- this is a window into the kernel and running processes. Useful for debugging.

# Check system memory
cat /proc/meminfo | head -5

# Check CPU information
cat /proc/cpuinfo | grep "model name" | head -1

# Check a specific process
cat /proc/1234/status | grep -E "(Name|State|VmRSS)"

Navigating the Filesystem

Basic Navigation Commands

# Print current directory
pwd

# List files (basic)
ls

# List files with details (permissions, size, date)
ls -la

# List files sorted by modification time (newest first)
ls -lt

# List files with human-readable sizes
ls -lh

# Change directory
cd /var/log
cd ..           # Go up one level
cd -            # Go to previous directory
cd ~/projects   # Go to projects in home directory

Finding Files

# Find a file by name (recursive search)
find / -name "playwright.config.ts" 2>/dev/null

# Find files modified in the last 24 hours
find /var/log -mtime -1 -type f

# Find files larger than 100MB (hunt for disk space issues)
find / -size +100M -type f 2>/dev/null

# Find all .spec.ts files in the project
find ~/projects/webapp -name "*.spec.ts" -type f

# Faster alternative: locate (uses a pre-built index)
locate playwright.config.ts

Disk Usage

# Disk usage summary
df -h

# Directory size
du -sh /var/log/

# Top 10 largest directories
du -h /var/log/ | sort -rh | head -10

# Check if disk is full (common cause of test failures)
df -h | grep -E "9[0-9]%|100%"

File Operations

# Create directories (including parents)
mkdir -p tests/integration/api

# Copy files
cp source.json destination.json
cp -r tests/ tests-backup/       # Recursive copy

# Move/rename files
mv old-name.ts new-name.ts
mv test-results/ archive/test-results-sprint23/

# Remove files
rm unwanted-file.txt
rm -r old-directory/              # Recursive remove
rm -rf node_modules/              # Force recursive remove (use carefully!)

# Create an empty file
touch new-test.spec.ts

# View file content
cat small-file.txt                # Entire file
head -20 large-file.log           # First 20 lines
tail -50 large-file.log           # Last 50 lines
tail -f /var/log/app.log          # Follow file in real-time (live log monitoring)
less large-file.log               # Paginated viewer (press q to quit)

Understanding Paths

Absolute vs Relative Paths

# Absolute path: starts from root (/)
/home/qa/projects/webapp/tests/login.spec.ts

# Relative path: relative to current directory
tests/login.spec.ts                # If you are in /home/qa/projects/webapp/
../webapp/tests/login.spec.ts      # If you are in /home/qa/projects/api/

Special Path Symbols

Hands-On Exercise

1. Open a terminal and navigate to /var/log/. List the files and identify which logs belong to which service.
2. Find all .log files modified in the last 24 hours anywhere on the system.
3. Check disk usage on your machine. Which directory is the largest?
4. Navigate to your home directory and explore what configuration files (dotfiles) exist.
5. Create a directory structure: ~/qa-practice/tests/unit/, ~/qa-practice/tests/integration/, ~/qa-practice/tests/e2e/
6. Use tail -f to monitor a log file in real-time while performing an action that generates log entries.