Telephonic / F2F Interview Linux Administrator Questions asked in HCL

1. Tell me about yourself and current project you are supporting ?
2. How many servers you are handling/managing ?
3. What type of applications are hosted on those servers ?
4. What exactly you are managing on those servers ?
5. Explain about Server Hardening steps ?
6. How will you install any rpm packages ?
7. Difference between Hardlink & Softlink ?
8. What is the “lsof” command ?
9. What is the Swap Space ? Your swap space utilisation is full and How would you investigate and troubleshoot ?
10. How would you schedule the jobs ?
11. What is the syntax for crontab ?
12. Different run levels in Linux ?
13. What are the tools you are working ?
14. How do you check the disk utilization ?
15. What is “chown” command ?
16. What are the different owners for any file ? How did you find the permissions of any file ?
17. What is autofs and NFS ?
18. How you recover /etc/passwd file ?
19. What is NIC bonding ? why we use ?
20. How can you extend SWAP with LVM and without LVM ?
21. Booting issues you faced ?
22. Assign cronjob for every 1 hour ?
23. Explain about patching ?

Linux Administration Q&A

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1. Explain About Server Hardening Steps

Server hardening means securing a server by minimizing vulnerabilities. Key steps:

• Update & Patch OS regularly.
• Disable unused services/ports with systemctl or chkconfig.
• Strong password & account policies (enforce complexity, lockout policy).
• Firewall rules (iptables/firewalld).
• Enable SELinux/AppArmor for mandatory access control.
• Disable root SSH login; use key-based authentication.
• Audit logs with auditd, logrotate, monitoring.
• File permissions: apply chmod, chown.
• Remove unnecessary packages.
• Backup and recovery plan in place.

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2. How Will You Install Any RPM Packages?

Use rpm or yum/dnf:

rpm -ivh package.rpm      # Install  
rpm -Uvh package.rpm      # Upgrade  
rpm -e package_name       # Remove  

But yum/dnf is preferred as it resolves dependencies automatically:

yum localinstall package.rpm

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3. Difference Between Hardlink & Softlink

• Hardlink: Points to the same inode. File continues to exist even if original is deleted. Cannot span across filesystems.
• Softlink (Symlink): Shortcut pointing to a filename. If original deleted, link breaks. Can span filesystems.

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4. What is the “lsof” Command?

lsof = List Open Files.
It shows processes using files, sockets, ports. Example:

lsof -i :80    # Show process using port 80
lsof /var/log/messages

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5. What is Swap Space? How Do You Troubleshoot High Swap Usage?

• Swap Space is disk space used when RAM is full.
• To investigate: free -m swapon -s top / htop vmstat 1
• Steps:
  • Identify memory-hungry processes → kill/tune.
  • Add more RAM or swap space.
  • Adjust swappiness (/proc/sys/vm/swappiness).

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6. How Would You Schedule Jobs?

• Use cron for recurring jobs.
• Use at command for one-time jobs.

Example:

crontab -e
30 2 * * * /usr/local/bin/backup.sh

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7. What is the Syntax for Crontab?

*  *  *  *  *  command
|  |  |  |  |
|  |  |  |  +---- Day of week (0-6, Sun=0)
|  |  |  +------- Month (1-12)
|  |  +---------- Day of month (1-31)
|  +------------- Hour (0-23)
+---------------- Minute (0-59)

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8. Different Run Levels in Linux

Runlevels define system state:

• 0 → Halt
• 1 → Single-user mode
• 2 → Multi-user (no network, older systems)
• 3 → Multi-user with CLI
• 4 → Unused (custom)
• 5 → Multi-user with GUI
• 6 → Reboot

In systemd, runlevels replaced by targets.

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9. What Are the Tools You Are Working With?

Depends on project, but common:

• Monitoring: Nagios, Zabbix, Prometheus.
• Configuration: Ansible, Puppet, Chef.
• Version Control: Git.
• Logging: ELK stack (Elasticsearch, Logstash, Kibana), Splunk.
• Ticketing: ServiceNow, JIRA.

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10. How Do You Check the Disk Utilization?

df -h          # Filesystem usage
du -sh *       # Directory size
iostat -x 1    # Disk I/O stats

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11. What is “chown” Command?

chown changes ownership of file/directory.

chown user:group file.txt

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12. What Are the Different Owners for Any File? How to Find Permissions?

Owners:

1. User (u) – File owner.
2. Group (g) – Group assigned.
3. Others (o) – Everyone else.

Find permissions:

ls -l file.txt
-rw-r--r-- 1 user group 123 Sep 6 10:00 file.txt

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13. What is autofs and NFS?

• NFS (Network File System): Protocol to share files across systems.
• autofs: Service that auto-mounts NFS directories on demand. Config: /etc/auto.master.

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14. How Do You Recover /etc/passwd File?

• If deleted/corrupted:
  • Boot into single-user/rescue mode.
  • Copy from backup /var/backups/passwd- (Debian/Ubuntu).
  • Manually recreate essential entries (root, system accounts).

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15. What is NIC Bonding? Why Do We Use It?

NIC Bonding = combining multiple NICs into one logical interface for:

• High availability (failover).
• Increased bandwidth (load balancing).

Config in /etc/sysconfig/network-scripts/ifcfg-bond0.

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16. How Can You Extend SWAP (With and Without LVM)?

• With LVM: lvextend -L +2G /dev/vg0/swap mkswap /dev/vg0/swap swapon /dev/vg0/swap
• Without LVM: Create swap file. dd if=/dev/zero of=/swapfile bs=1G count=2 chmod 600 /swapfile mkswap /swapfile swapon /swapfile

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17. Booting Issues You Faced?

• Kernel panic → missing initramfs/kernel modules.
• GRUB errors → corrupt bootloader.
• Filesystem corruption → run fsck.
• Disk full → clear logs/temp.

Troubleshoot with recovery mode, boot logs, rescue ISO.

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18. Assign Cronjob for Every 1 Hour

0 * * * * /path/to/script.sh

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19. Explain About Patching

• OS Patching = applying vendor security & bug fix updates.
  Steps:

1. Take backup/snapshot.
2. Check patch availability: yum update / apt upgrade.
3. Apply in staging/test environment.
4. Rollout in production (usually maintenance window).
5. Validate services post-patch.

About HCLTech

HCLTech (formerly HCL Technologies) is a leading global technology company that helps enterprises reimagine their businesses for the digital age. Founded in 1976 as part of the HCL Group, it has grown into one of India’s top IT services organizations, with headquarters in Noida, India, and operations in over 60 countries. The company is consistently ranked among the world’s most valuable IT service providers, with more than 225,000 employees worldwide.

HCLTech delivers a broad portfolio of services, including IT and business services, engineering and R&D, and digital transformation solutions. Its expertise spans cloud computing, data analytics, artificial intelligence, cybersecurity, enterprise applications, IoT, and next-generation digital platforms. By combining deep domain knowledge with strong technology partnerships, HCLTech enables organizations to modernize their IT infrastructure, build agile digital workplaces, and unlock new revenue streams.

One of HCLTech’s defining strengths is its Engineering and R&D Services (ERS), where it is a global leader in product engineering and innovation for industries like aerospace, automotive, telecom, and healthcare. Additionally, its Mode 1-2-3 strategy helps customers drive efficiency (Mode 1), adopt next-gen services (Mode 2), and create innovative ecosystems (Mode 3).

HCLTech maintains strategic partnerships with leading technology providers such as Microsoft, Google Cloud, AWS, IBM, SAP, and ServiceNow, enabling it to co-create solutions tailored for enterprise-scale challenges.

The company’s purpose is captured in its brand identity: “Supercharging Progress”—a commitment to empowering clients, employees, and communities through technology-driven transformation. With its culture of innovation, sustainability initiatives, and customer-first approach, HCLTech continues to be a trusted partner for global enterprises navigating the complexities of the digital economy.