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Red Hat Linux & Shell Scripting interview questions

Practice Linux & Shell Scripting questions specifically asked in Red Hat interviews – ideal for online test preparation, technical rounds and final HR discussions.

Company: Red HatSubject: Linux & Shell Scripting37 questions in this page

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Red Hat · Linux & Shell Scripting questions (37)

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1. What is the difference between a hard link and a symbolic link?

Difficulty: MediumType: MCQTopic: Filesystem Basics

Hard links create multiple directory entries pointing to the same inode (actual data on disk). All hard links are equal - deleting one doesn't affect others since they all reference the same data. Hard links cannot span filesystems or link to directories. Create with ln source target. Symbolic links (symlinks) are special files containing a path to another file or directory. They're like shortcuts - if the original file is deleted, the symlink breaks becoming a dangling pointer. Symlinks can span filesystems and link to directories. Create with ln -s source target. Use hard links when you need multiple references to the same data that persist even if one reference is deleted. Use symlinks for flexibility, creating shortcuts, or linking across filesystems. Most use cases prefer symlinks due to their flexibility, though hard links have performance advantages for large files since they don't add indirection.

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33. What are essential Linux security hardening practices? Discuss SSH security, firewall configuration, SELinux/AppArmor, and security updates.

Difficulty: HardType: SubjectiveTopic: Security Hardening

SSH hardening (/etc/ssh/sshd_config): disable root login (PermitRootLogin no), use key-based authentication only (PasswordAuthentication no, PubkeyAuthentication yes), change default port (Port 2222), limit users (AllowUsers user1 user2), use Protocol 2 only, set LoginGraceTime 30, MaxAuthTries 3, disable empty passwords (PermitEmptyPasswords no), disable X11 forwarding if not needed (X11Forwarding no). Firewall configuration: enable firewall (ufw, firewalld, iptables), default deny policy, whitelist necessary ports only. UFW: ufw default deny incoming, ufw allow 22/tcp, ufw allow 80/tcp, ufw enable. Iptables: iptables -P INPUT DROP, iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT, iptables -A INPUT -p tcp --dport 22 -j ACCEPT, persist with iptables-save. Minimize attack surface: disable unused services (systemctl disable service), remove unnecessary packages (apt remove or yum remove), close unnecessary ports, run services as non-root users, use chroot jails or containers for service isolation. SELinux/AppArmor: mandatory access control systems. SELinux (RHEL/CentOS): enforce policies restricting process actions, set to enforcing mode: setenforce 1, check status: getenforce, fix context: restorecon -Rv /path, audit logs in /var/log/audit/audit.log. AppArmor (Ubuntu): profile-based confinement, enable profile: aa-enforce /etc/apparmor.d/usr.bin.program, check status: aa-status. Security updates: enable automatic security updates (unattended-upgrades on Debian/Ubuntu, yum-cron on RHEL/CentOS), configure notification, test in staging before production, subscribe to security mailing lists (ubuntu-security-announce, centos-announce), monitor CVEs for installed software. Password policies: enforce strong passwords with PAM (pam_pwquality), set password expiration (chage -M 90 user), lock accounts after failed attempts (pam_faillock), audit passwords with john the ripper (authorized testing). File permissions: review world-writable files: find / -xdev -type f -perm -002, review setuid files: find / -xdev -type f -perm -4000 (potential security risks), protect sensitive files (600 for SSH keys, 640 for config files), audit with aide or tripwire detecting unauthorized changes. Audit logging: enable auditd for system call auditing, log important events (file access, authentication, privilege escalation), central log collection, regular log review, configure retention policy. Network security: disable IPv6 if not used, disable unnecessary network services, use TCP wrappers (/etc/hosts.allow, /etc/hosts.deny), configure reverse DNS, enable fail2ban for intrusion prevention (bans IPs with multiple failed logins). Monitoring: install intrusion detection (OSSEC, Snort), monitor logs for suspicious activity, set up alerts for critical events, regular security scans (nmap for open ports, nikto for web vulnerabilities - authorized testing only), vulnerability scanning (OpenVAS, Nessus). Understanding security hardening protects systems from attacks and ensures compliance with security standards.

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Red Hat Linux & Shell Scripting interview questions

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1. What is the difference between a hard link and a symbolic link?

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2. Explain the Linux filesystem hierarchy. What are the purposes of /home, /var, /usr, /tmp, and /opt directories?

3. What does systemctl enable do?

4. Explain Linux file permissions including special permissions (setuid, setgid, sticky bit). How do they work and when are they used?

5. What is stored in the /etc directory in Linux?

6. What is an inode in Linux? Explain its structure and how it relates to files and hard links.

7. Explain common directory navigation commands and shortcuts in Linux. Include cd, pushd, popd, and special directory references.

8. Explain the difference between a filesystem and a partition. What are common Linux filesystems and their use cases?

9. Explain advanced sed operations including multiple substitutions, line deletion, insertion, and using sed with regular expressions.

10. Explain basic and extended regular expressions in Linux. What are the differences and how do they affect grep, sed, and awk?

11. What package manager does RHEL/CentOS use?

12. Explain the complete process of creating, modifying, and deleting user accounts. Include commands, files involved, and best practices.

13. Which command is used to add a new user in Linux?

14. What information is stored in /etc/passwd file?

15. What does the sticky bit do on a directory?

16. Explain umask in Linux. How does it work and how do you calculate default permissions for new files and directories?

17. Explain firewall configuration in Linux using iptables and firewalld. How do you allow or block network traffic?

18. Explain the find command in Linux. How do you search for files by name, size, modification time, and permissions?

19. Explain the different process states in Linux (running, sleeping, stopped, zombie). How do you identify and handle zombie processes?

20. Explain the /proc filesystem in Linux. What information does it provide and how do you use it for process and system monitoring?

21. What is the difference between su and su - commands?

22. What are Access Control Lists (ACLs) in Linux?

23. Explain the /etc/sudoers file structure and how to configure granular sudo access. Include examples of different sudo configurations.

24. Explain setuid and setgid special permissions. Provide examples of when they're necessary and security implications.

25. What are best practices for managing a multi-user Linux system? Discuss user isolation, resource limits, and security hardening.

26. Explain advanced package management including repository configuration, package dependencies, and resolving package conflicts.

27. Explain systemd service management including creating custom service units, service dependencies, and troubleshooting service failures.

28. How do you ensure package security in Linux? Discuss package verification, security updates, and vulnerability scanning.

29. What can you do if a Linux system won't boot?

30. What command creates a new filesystem on a partition?

31. Explain common Linux signals (SIGTERM, SIGKILL, SIGHUP, SIGINT, SIGSTOP). When should you use each signal?

32. Explain password management in Linux including /etc/shadow, password policies, and the chage command. How do you enforce password complexity and expiration?

33. What are essential Linux security hardening practices? Discuss SSH security, firewall configuration, SELinux/AppArmor, and security updates.

34. What is LVM and what are its main components?

35. What is systemd in modern Linux systems?

36. Explain advanced cron usage including environment variables, output handling, error reporting, and alternatives like systemd timers.

37. Explain the chown and chgrp commands. How do you change file ownership and why is it important?

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