Master Linux Interview Questions: 20 Essential Commands & Answers

Linux Interview Questions and Answers

1. How to view the current Linux server runlevel?

Use who -r or runlevel commands.

2. How to view Linux default gateway?

Run route -n or netstat -nr to display the routing table including the default gateway.

3. How to rebuild the initramfs image on Linux?

On CentOS/RHEL 5.x use:

# mkinitrd -f -v /boot/initrd-$(uname -r).img $(uname -r)

On CentOS/RHEL 6.x use dracut : # dracut -f For a specific kernel version:

# dracut -f initramfs-2.x.xx-xx.el6.x86_64.img 2.x.xx-xx.el6.x86_64

4. What is the cpio command?

cpio copies files to and from an archive, allowing creation, listing, and extraction of files.

5. What is the patch command and how to use it?

patch applies a diff file to update source files. Example: # diff -Naur old_file new_file > diff_file Then apply:

# patch < diff_file

6. What is aspell used for?

aspell is an interactive spell‑checking tool for Linux, often used by other programs or directly from the command line.

7. How to view a domain's SPF record from the command line?

Use dig -t TXT example.com .

8. How to identify the package providing a specific file (/etc/fstab)?

# rpm -qf /etc/fstab

9. Which command shows the status of bond0?

# cat /proc/net/bonding/bond0

10. What is the purpose of the /proc filesystem?

/proc is a memory‑based virtual filesystem exposing kernel and process information such as CPU, memory, I/O, and running processes.

11. How to find files larger than 10 MB under /usr?

# find /usr -size +10M

12. How to find files in /home modified more than 120 days ago?

# find /home -mtime +120

13. How to find files in /var not accessed in the last 90 days?

# find /var \! -atime -90

14. How to delete all "core" files in the entire directory tree?

# find / -name core -exec rm {} \;

15. What does the strings command do?

strings extracts printable text strings from binary files, useful for forensic analysis.

16. What is the purpose of the tee filter?

tee duplicates standard input to both a file and standard output, allowing simultaneous viewing and saving of command output.

ll /etc | nl | tee /tmp/ll.out

17. What does export PS1="$LOGNAME@hostname:$PWD:" do?

It changes the shell prompt to display the username, hostname, and current working directory.

18. What does ll | awk '{print $3,"owns",$9}' do?

It prints each file's owner and name from the long‑listing output.

19. What is the at command used for?

at schedules a one‑time command execution, storing jobs in /var/spool/at and executing them via the atd daemon.

20. What does the lspci command do?

lspci lists PCI devices; adding -v , -vv , or -vvv provides increasingly detailed output, and -r improves readability.