Linux Interview: Expert Tips & Real-Time Q&A

Must-Know Linux Questions for Stress-Free Job Preparation

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Question 1:

Your boss asks you to create 100 directories named project1, project2, …, up to project100 in a specific directory /home/user/projects. How would you achieve this in a single command?

Answer:

mkdir -p /home/user/projects/project{1..100}

Explanation:

• The mkdir command creates directories.
• The -p flag ensures the parent directory exists.
• {1..100} generates numbers from 1 to 100 automatically.

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Question 2:

Your boss wants you to find and list all .log files larger than 50MB in the /var/log directory. How would you do this?

Answer:

find /var/log -type f -name "*.log" -size +50M

Explanation:

• find /var/log: Search within the /var/log directory.
• -type f: Look for files only.
• -name "*.log": Match files with the .log extension.
• -size +50M: Find files larger than 50MB.

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Question 3:

Your boss asks you to archive and compress the entire /var/www/html directory into a tarball named website_backup.tar.gz. How would you do this?

Answer:

tar -czvf website_backup.tar.gz /var/www/html

Explanation:

• tar: Command to create archives.
• -c: Create an archive.
• -z: Compress with gzip.
• -v: Verbose mode to show progress.
• -f: Specify the file name.
• /var/www/html: Directory to be archived.

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Question 4:

Your boss wants you to change the permissions of all files in /home/user/data so that only the owner has read and write permissions. How would you do it?

Answer:

chmod -R 600 /home/user/data

Explanation:

• chmod: Change file permissions.
• -R: Apply changes recursively to all files and directories.
• 600: Permissions where the owner has read and write permissions only.

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Question 5:

Your boss asks you to write a one-liner to display the 10 most memory-consuming processes on the system. How would you do this?

Answer:

ps aux --sort=-%mem | head -n 11

Explanation:

• ps aux: Displays detailed information about running processes.
• --sort=-%mem: Sort processes by memory usage in descending order.
• head -n 11: Show the top 10 processes plus the header row.

Question 6

Your boss asks you to create 100 empty files named file1.txt, file2.txt, …, up to file100.txt inside the /home/user/docs directory in a single command. How would you do this?

Answer:

touch /home/user/docs/file{1..100}.txt

Explanation:

• touch: Command to create empty files.
• /home/user/docs/file{1..100}.txt: Generates filenames from file1.txt to file100.txt.

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Question 7

Your boss wants you to find and delete all .tmp files older than 30 days in /var/tmp. How would you do it?

Answer:

find /var/tmp -type f -name "*.tmp" -mtime +30 -exec rm {} \;

Explanation:

• -type f: Search for files.
• -name "*.tmp": Match files ending with .tmp.
• -mtime +30: Files modified more than 30 days ago.
• -exec rm {} \;: Delete the matched files.

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Question 8

Your boss asks you to find and count the number of lines containing the word ERROR in a log file /var/log/syslog. How would you do this?

Answer:

grep -c "ERROR" /var/log/syslog

Explanation:

• grep: Searches for patterns in files.
• -c: Counts matching lines.
• "ERROR": The pattern to search for.

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Question 9

Your boss asks you to continuously monitor the disk usage of /dev/sda1 every 5 seconds and output the result to the terminal. How would you do this?

Answer:

watch -n 5 df -h /dev/sda1

Explanation:

• watch -n 5: Run a command every 5 seconds.
• df -h: Show disk space usage in human-readable format.
• /dev/sda1: Disk partition to monitor.

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Question 10

Your boss asks you to replace all occurrences of localhost with 127.0.0.1 in the file /etc/hosts. How would you achieve this using a single command?

Answer:

sed -i 's/localhost/127.0.0.1/g' /etc/hosts

Explanation:

• sed: Stream editor for text manipulation.
• -i: Edit the file in place.
• 's/localhost/127.0.0.1/g': Substitute localhost with 127.0.0.1.

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Question 11

Your boss asks you to check the number of active connections to a web server running on port 80. How would you do this?

Answer:

netstat -an | grep ':80' | grep ESTABLISHED | wc -l

Explanation:

• netstat -an: Show network connections.
• grep ':80': Filter connections on port 80.
• grep ESTABLISHED: Find active connections.
• wc -l: Count the number of lines.

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Question 12

Your boss wants you to schedule a cron job that backs up the /home/user/docs directory every day at midnight. How would you configure this?

Answer:

1. Open the crontab editor:bashCopyEditcrontab -e
2. Add the following line to schedule the job 0 0 * * * tar -czf /home/user/backup_$(date +\%F).tar.gz /home/user/docs

Explanation:

• 0 0 * * *: Schedule the job at midnight every day.
• tar -czf: Create a compressed tarball.
• $(date +%F): Add the current date to the backup file name.

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Question 13

Your boss asks you to display the top 5 largest files in the /var directory. How would you do this?

Answer:

du -ah /var | sort -rh | head -n 5

Explanation:

• du -ah /var: Show sizes of all files and directories.
• sort -rh: Sort in reverse order by size.
• head -n 5: Display the top 5 results.

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Question 14

Your boss wants you to check whether the service nginx is running and restart it if it isn’t. How would you do this in a single command?

Answer:

systemctl is-active --quiet nginx || systemctl restart nginx

Explanation:

• systemctl is-active --quiet nginx: Check if the nginx service is active without producing output.
• || systemctl restart nginx: Restart the service if it is not active.

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Question 15

Your boss wants you to archive and transfer the /home/user/data directory to a remote server 192.168.1.100 using scp. How would you do this?

Answer:

tar -czf - /home/user/data | ssh user@192.168.1.100 "cat > data_backup.tar.gz"

Explanation:

• tar -czf -: Create an archive and write it to standard output.
• ssh user@192.168.1.100: Connect to the remote server.
• "cat > data_backup.tar.gz": Save the archive on the remote server.

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