Advanced Questions¶
How to use these interview questions
🧠 Read each question carefully.
Try answering it yourself before expanding the answer to compare with the ideal response.
Level: Advanced
🔴 Complex Scenarios & Architecture.
Tackle high-level design, production-grade scaling, security, and advanced internals.
1. Which command is used to test network connectivity to a host?
ping [hostname/IP].
It sends ICMP ECHO_REQUEST packets to the target. Note that some firewalls block ICMP.
2. How do you check listening ports and active connections?
ss -tln (or netstat -tln on older systems).
- t: TCP
- l: Listening
- n: Numeric (show port numbers instead of service names)
3. Which command is used to debug HTTP responses (headers)?
curl -I [URL].
This fetches only the HTTP headers (HEAD request), allowing you to see status codes (200, 404, 500) without downloading the body.
4. What is grep used for?
Global Regular Expression Print.
It searches generally for text patterns within files.
* grep "error" file.log: Search for "error".
* grep -i "error" file.log: Case-insensitive search.
* grep -r "error" .: Recursive search in directory.
5. How do you find the line number of a matching string in a file?
grep -n "string" [file].
The -n option prints the line number along with the matched line.
6. Which command is used for specific column extraction?
awk or cut.
awk '{print $1}' file.txt: Prints the first column (space-separated).cut -d: -f1 /etc/passwd: Prints the first column (colon-separated).
7. What is sed used for?
Stream Editor.
It is mostly used for search-and-replace operations.
* sed 's/old/new/g' file.txt: Replaces all occurrences of "old" with "new".
8. How do you view the last 10 lines of a log file and follow updates?
tail -f [logfile].
The -f (follow) flag keeps the stream open and prints new lines as they are appended to the file.
9. What is a Crontab?
A list of commands meant to be run at specified times.
Format: * * * * * command_to_execute
(Minute, Hour, Day of Month, Month, Day of Week).
10. How do you list the current user's cron jobs?
crontab -l.
To edit the crontab, use crontab -e.
11. How do you check the exit status of the last executed command?
echo $?.
0: Success- Non-zero (e.g.,
1,127): Failure/Error.
12. How do you find all files modified in the last 3 days?
find . -type f -mtime -3.
-type f: Search for files only.-mtime -3: Modified less than 3 days ago.
13. What is the difference between hard link and soft link?
Soft Link (Symbolic Link): A pointer to the original file path. If original is deleted, link is broken. (ln -s target link).
Hard Link: A direct reference to the underlying inode. The file data remains as long as at least one hard link exists. (ln target link).
14. How do you run a script in the background?
Append & to the command.
Example: ./script.sh &.
To keep it running after logout, use nohup ./script.sh &.
15. How do you pass arguments to a shell script?
./script.sh arg1 arg2.
Inside the script:
* $1: First argument (arg1)
* $2: Second argument (arg2)
* $#: Total number of arguments.
16. How do you debug a shell script?
Run with bash -x script.sh or add set -x inside the script.
This prints each command and its arguments as they are executed.
17. What is awk commonly used for in DevOps?
Text processing and report generation.
Example: checking for processes consuming high memory:
ps aux | awk '$4 > 50.0 {print $0}' (Print processes using > 50% memory).
18. How do you check if a port is open on a remote server?
nc -zv [host] [port] (Netcat), or telnet [host] [port].
Example: nc -zv google.com 80.
19. How do you redirect both STDOUT and STDERR to the same file?
command > file.log 2>&1.
2>&1 redirects File Descriptor 2 (Stderr) to where File Descriptor 1 (Stdout) is pointing.
20. How do you get unique entries from a sorted file?
sort file.txt | uniq.
uniq removes adjacent duplicates, so sorting first is usually required.
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