Top Linux Server Administrator Interview Questions and Answers

Landing a job as a Linux server administrator requires strong technical skills and the ability to demonstrate those skills during the interview process Here are some of the most common Linux admin interview questions and examples of good responses

Overview of Key Linux Server Admin Interview Topics

Some of the key topics covered in Linux admin interviews include

• Linux vs Windows operating systems
• Linux distributions
• Linux filesystem and file permissions
• User and group management
• Process monitoring and management
• Network configuration
• Security practices like firewall setup
• Bash scripting
• Automation tools like Ansible
• Databases like MySQL and PostgreSQL
• Web servers like Apache and Nginx
• Email servers like Postfix
• Virtualization technologies like KVM
• Containerization with Docker and Kubernetes
• Troubleshooting skills
• DevOps methodologies

Before your Linux admin interview, make sure you know more about all of these things.

Common Linux Interview Questions and Answers

Here are some specific questions you might be asked as a Linux administrator, along with good answers:

Q: What are the key differences between the Linux and Windows operating systems?

The Linux operating system is based on a decentralized open source model, while Windows is a closed system made by Microsoft.

Some other key differences include:

• Linux uses the Linux kernel while Windows has its own kernel and architecture.
• Linux allows more customization and access to core system components. Windows provides less flexibility to alter the base system.
• Linux uses package managers and repositories for software installation and updates. Windows uses installers and software updates managed more centrally.
• Linux supports more programming languages and environments out of the box like Python, Ruby, Java, etc.
• Linux traditionally has better security and malware resistance than Windows.
• Linux is used more for servers, cloud environments, and computer clusters while Windows is still common for desktop/laptop use.

Q: Explain the differences between a UNIX and a Linux system.

While Linux is based on UNIX concepts and paradigms, there are some key differences:

• Linux is open source, free to use, and can be modified/distributed freely. UNIX is proprietary software owned by AT&T.
• Linux distributions bring together different open source components like the Linux kernel, GNU tools, graphical environments, etc. The core UNIX system is developed as a single integrated proprietary unit.
• Linux supports journaling filesystems like ext3, ext4 for better data integrity. Filesystems like ZFS provide advanced features like snapshots and data deduplication.
• Linux provides out of the box support for scripting languages like Python, Perl, Ruby, etc which can directly invoke kernel system calls.
• Linux has native portability across different hardware architectures. UNIX historically was tied closely to proprietary hardware architectures.

Q: What are the basic components that make up a Linux operating system?

The key components of a Linux OS include:

• The Linux kernel – This interfaces with computer hardware and manages system resources like CPU, memory, IO devices, etc.
• System library and daemons – These provide core system services. For example, systemd starts other services during bootup.
• The filesystem hierarchy with directories like /etc, /var, /bin, /usr etc.
• Shells like Bash and other CLI tools for administration.
• Desktop environments like GNOME, KDE provide graphical interfaces.

Some other components include software package managers, development tools and various applications that give the OS added functionality.

Q: Can you explain what the LILO bootloader is?

LILO (Linux Loader) is one of the bootloaders used to load the Linux operating system into memory during system startup. It contains information on available operating systems or kernels, reads boot parameters, loads the kernel image into RAM and passes control to the kernel.

Some key facts about LILO:

• Stands for Linux Loader.
• Master boot record based bootloader.
• Configured via /etc/lilo.conf file.
• Provides dual boot capabilities – can configure multiple OS like Windows.
• Uses either linear or disk mapping for locating kernel images.
• Lacks advanced features like graphical menus that newer bootloaders like GRUB provide.

Q: Describe a service you might disable on a Linux server and why.

One example of a non-essential service that is a candidate for disabling is the Cups print service which allows sharing of printers over the network.

Reasons you may want to disable Cups:

• The server is being used as a backend application server not connected to any printers.
• You want to minimize open ports/services and potential entry points for attackers as part of security hardening.
• To conserve system resources like RAM, CPU by disabling unneeded services.

To disable cups, stop the service and disable auto-start on system boot:

$ sudo systemctl stop cups$ sudo systemctl disable cups

Q: How would you check memory and CPU usage statistics on a Linux server?

Some common ways to check memory and CPU usage on Linux include:

• Use the free command to view information about free and used memory and swap. Can use -h to display human readable format.

• Use top to get an overall view of current processes with info on CPU, memory, and swap usage. Can press Shift+P to sort processes by CPU usage.

• Install and use htop for an interactive view with ability to scroll, sort, filter. Provides visual indication of CPU/memory heavy processes.

• Check the vmstat summary output for data on memory, swap, I/O, CPU usage.

• Use sar to get historic statistics on CPU, memory usage over different time intervals.

• Monitor utilization with dstat which gives useful system statistics and metrics.

• Use the /proc/meminfo virtual file for up-to-date memory usage statistics.

Q: You get a “Disk full” alert. How would you investigate and fix this?

Steps to investigate and fix a full disk alert:

1. Use the df command to check disk usage for different filesystems and identify which partition is full.

2. Use du to check which folder is taking up space. Example du -sh /* to scan top folders.

3. Delete unneeded files, packages cached in package manager, core dumps, log files if no longer required.

4. Uninstall unneeded applications.

5. Move files to another partition if space available.

6. Compress folders using Zip, RAR or tar gzip to recover space.

7. Increase partition size using utilities like gparted if still inadequate space.

8. As a last resort, migrate data and reinstall OS. Set up LVM or ZFS next time for easier storage management.

Q: Your server was hacked. What are the steps you would take?

If a server is hacked or compromised, I would follow these response steps:

1. Take it offline immediately by disconnecting from network to prevent further attacks or lateral movement.

2. Take disk and memory snapshots/images for forensics analysis based on policy.

3. Restore server from clean OS images and validated backups after taking snapshots.

4. Notify stakeholders and check for signs of data breach. Notify authorities as applicable.

5. Inspect backups closely and run anti-virus scans to ensure no malware.

6. Review logs, files, network traffic captures for signs of intrusion.

7. Change all credentials and encrypt/reset sensitive customer data if needed.

8. Patch vulnerabilities, review and harden security configurations to prevent reoccurrence.

9. Monitor network, user activity, new vulnerabilities closely.

10. Develop measures like intrusion detection systems to improve breach response.

Q: How would you troubleshoot network connectivity issues on a Linux server?

Steps to troubleshoot network connectivity issues on a Linux server:

1. Use ping and traceroute to check connectivity to known good hosts. This helps identify general network issues.

2. Verify interface status and IP addressing using ip addr command. Check for interfaces being down, IP conflicts, etc.

3. Inspect network daemon logs like syslog for errors. Look for DHCP failures, firewall rules blocking traffic, etc.

4. Check DNS resolution using nslookup or dig to see if hostnames are resolving IPs. Update resolve.conf if needed.

5. Verify correct firewall rules are applied on the server for expected traffic. Flush inactive/invalid rules.

6. Check routing table with route -n for issues. Update default gateway if missing.

7. Restart network services/daemons like network manager, DNS, firewall if needed and test connectivity.

8. Replace network cables, check switch/router ports ifhardware related.

9. Capture packets if necessary to analyze network traffic flows for unusual activity.

10. Compare configurations with a known good server for differences that could cause issues.

This covers some of the most common Linux admin interview questions and examples of strong responses. Make sure you are well prepared in all aspects of Linux administration including storage, security, networking, automation, troubleshooting, etc.