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CLI & Linux Command Interview Questions

This Q&A bank contains 20 detailed questions and answers on Linux terminal operations, search patterns, log monitoring, process tracking, and connectivity validations.

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CLI & Linux Q&A​

Q1: What is the CLI (Command Line Interface) and why is it important for QA engineers?

Core Answer: The CLI is a text-based interface used to run programs, manage files, and execute scripts by typing commands instead of clicking a graphical interface.

Why it matters for QA:

  • Headless Servers: Most testing and staging environments (including CI/CD agents and cloud servers) are headless Linux machines with no GUI.
  • Log Inspection: Diagnosing server crashes or checking API events requires logging in via SSH and running commands.
  • Automation Runs: Executing test suites locally or in containers often requires running command runners (e.g. npm test, pytest, mvn test).
Q2: How do you list files and directories in a folder? List common flags.

Core Answer: Use the ls command to list files.

Common Options & Meanings:

  • ls -l: Displays a detailed list including file permissions, owner, size, and modification date.
  • ls -a: Lists all files, including hidden configuration files (prefixed with a dot, e.g. .gitignore).
  • ls -lh: Displays details with human-readable file sizes (e.g. 2K, 45M, 3G).
  • ls -t: Sorts files by modification time (newest first).
Q3: How do you check the absolute path of your current working directory?

Core Answer: Run the pwd command, which stands for Print Working Directory.

Command Output Example:

$ pwd
/Users/paywize/projects/test-framework/src/test

This is useful when configuring relative file paths in your automation framework scripts.

Q4: How do you change directories? What do dots represent?

Core Answer: Use the cd (Change Directory) command followed by your target path.

Navigation Shortcodes:

  • cd ..: Move up one level to the parent directory.
  • cd .: Refers to the current directory.
  • cd ~: Returns to the user's home directory.
  • cd -: Toggles back to the previous directory path.
Q5: How do you create a new directory? How do you create nested folders?

Core Answer: Use the mkdir (Make Directory) command.

Commands:

  • Create a single directory: mkdir reports
  • Create nested subdirectories at once: 
    mkdir -p target/surefire-reports/screenshots
    The -p flag creates any missing parent directories automatically.
Q6: How do you create a new file from the command line?

Core Answer: Use the touch command to create an empty file, or use redirections (> or >>) with echo or cat.

Commands:

  • Create empty file: touch test-data.csv
  • Create file with content: echo "env=staging" > config.properties
  • Append content: echo "threads=4" >> config.properties
Q7: What is the difference between cat, less, and more commands?

Core Answer: All are used to view file contents, but they differ in how they display data.

Key Differences:

  • cat: Prints the entire file content directly to the terminal screen at once. Best for short configuration files.
  • less: Opens an interactive reader allowing you to scroll up and down using arrow keys, search keywords, and quit (q). It does not load the entire file into memory, making it fast for large logs.
  • more: An older utility that displays file contents page by page, allowing forward scrolling only.
Q8: How do you search for a specific keyword in a file? Explain grep options.

Core Answer: Use the grep command, which searches text files for lines matching a regular expression.

Common Commands:

  • Search word: grep "NullPointerException" test-run.log
  • Case-insensitive search: grep -i "error" server.log
  • Count occurrences: grep -c "Failed" regression.log
  • Print line numbers: grep -n "TimeoutException" app.log
Q9: How do you copy, move, and delete files/directories in Linux?

Core Answer: Use cp to copy, mv to move/rename, and rm to delete.

Commands:

  • Copy file: cp config.env backup.env
  • Copy directory: cp -r src/ backup-src/ (the -r flag copies recursively)
  • Move/Rename: mv report.html old-reports/
  • Delete file: rm temp.log
  • Delete directory: rm -rf temp-dir/ (the -f flag forces deletion without confirmation). Use with caution.
Q10: How do you monitor running processes on a Linux machine?

Core Answer: Use ps for snapshots and top or htop for real-time CPU/memory process usage.

Commands:

  • Snapshot of all running processes: ps aux
  • Find a specific process by name: ps aux | grep "java"
  • Interactive monitoring: top (displays resource usage, sorted by CPU consumption). Press q to exit.
Q11: How do you check available disk space on your server?

Core Answer: Run the df command (Disk Free).

Flag usage:

df -h

The -h (human-readable) flag formats output columns into gigabytes (G), megabytes (M), and percentages, helping QA identify if automation builds are failing because the disk is full.

Q12: How do you check memory (RAM) usage on a Linux system?

Core Answer: Run the free command.

Flag usage:

free -h

This displays total, used, free, shared, buffer/cache, and available RAM configurations. It is crucial for debugging out-of-memory errors on build agents.

Q13: How do you monitor application logs in real time? Provide a QA search example.

Core Answer: Use the tail command with the follow -f flag.

QA Commands:

  • Stream logs live: tail -f app.log
  • Stream logs filtering for specific errors: 
    tail -f app.log | grep -i "500 Internal Error"

This is useful during manual exploratory testing to verify if user actions trigger errors in the backend.

Q14: How do you find files in the filesystem?

Core Answer: Use the find command, specifying the search directory and name pattern.

Command Examples:

  • Find files matching name: find . -name "*.json"
  • Find files modified in the last 24 hours: find /var/log -mtime -1
  • Find directories: find . -type d -name "screenshots"
Q15: How do you test network connectivity to an external API or server?

Core Answer: Use ping to test basic reachability, and curl or telnet to check HTTP endpoints and port access.

Commands:

  • Test server ping: ping -c 4 api.github.com
  • Fetch response headers: curl -I https://api.com/users
  • Check if port 8080 is open: nc -zv localhost 8080 (netcat).
Q16: How do you change file permissions in Linux?

Core Answer: Use the chmod (Change Mode) command to edit read (r), write (w), and execute (x) permissions.

Command Examples:

  • Make a script executable: chmod +x run-tests.sh
  • Grant read-write permissions to everyone: chmod 666 config.json
  • Full access to owner, read-only to others: chmod 755 gradlew
Q17: How do you check which process is listening on a specific port?

Core Answer: Use the lsof (List Open Files) or netstat command to trace active ports.

Commands:

  • Find process on port 8080: lsof -i :8080
  • Alternative: netstat -tulnp | grep 8080 This helps you identify and terminate processes blocking your local web or database servers.
Q18: How do you print only the beginning or the end of a log file?

Core Answer: Use head to read the top of a file, and tail to read the bottom of a file.

Commands:

  • Print first 15 lines: head -n 15 app.log
  • Print last 30 lines: tail -n 30 app.log
Q19: How do you chain multiple command executions together?

Core Answer: Chain commands using operators like ;, &&, or redirect them using piping |.

Operations:

  • ; (Run sequentially): mkdir test; cd test (runs second even if first fails).
  • && (Logical AND): mvn clean compile && mvn test (runs test only if compile succeeds).
  • | (Piping): cat logs.txt | grep "ERROR" (sends stdout of first as stdin to second).
Q20: How do you download files from a remote server using the CLI?

Core Answer: Use wget or curl to download files via HTTP/HTTPS protocols.

Commands:

  • Download using wget: wget https://example.com/testdata.zip
  • Download and rename using curl: curl -o data.zip https://example.com/testdata.zip