If mastering basic commands is the entry point and being proficient with operational tools is intermediate, then true advanced Linux capability comes from your ability to gain insights into the system’s underlying architecture and precisely control performance bottlenecks.。

In high-concurrency business environments, where server resources are tight and system anomalies occur frequently, the ability to adjust kernel parameters, optimize performance, and troubleshoot at the lower levels determines whether you have the strength to “withstand the pressure”.

This article focuses on 24 high-frequency questions related to kernel and performance tuning, covering the following core modules:

• 📌 Kernel parameters and tuning configurations (e.g., sysctl)
• 📌 CPU/Memory/I/O performance bottleneck investigation
• 📌 Thread and process scheduling optimization
• 📌 Network stack tuning, maximum connection optimization
• 📌 System security and stability strategies

All questions are derived from practical experience; some you may have encountered but cannot articulate, while others you may not have touched upon yet. However, mastering them will help you stand out in the field!

31. What is the /proc file system?

<span>/proc</span> is a virtual file system that displays information about system and kernel data structures. It is an important interface for obtaining system information, debugging, and adjusting kernel parameters.

32. How to secure a Linux server?

Common security measures include:

• Creating strong passwords
• Regularly updating and patching
• Configuring SSH to use key authentication
• Enabling Intrusion Detection Systems (IDS)
• Configuring firewalls to limit port access
• Disabling unnecessary services
• Log auditing, regular backups, and encrypted transmission

33. What is the <span>strace</span> command?

<span>strace</span> is used to trace system calls and signals of a process, serving as a debugging tool. For example:

strace ls

This command will display all system calls made by the <span>ls</span> command along with their parameters and return values.

34. How to optimize Linux system performance?

Optimization strategies include:

• Updating the system and kernel
• Optimizing disk I/O and caching mechanisms
• Managing memory and CPU usage
• Simplifying services and using lightweight tools
• Adjusting kernel parameters (e.g., sysctl)
• Using <span>top</span>, <span>htop</span>, <span>pcp</span>, and other monitoring tools

35. How to manage a Linux server?

Recommended strategies include:

• User management and permission configuration
• Network and firewall settings
• Installing and configuring monitoring tools
• Implementing a regular backup plan
• Writing recovery process documentation

36. What is the Linux virtual memory system?

Virtual memory is a mechanism by which the operating system uses part of the disk space as RAM. It is used to:

• Compensate for insufficient physical memory
• Support concurrent multitasking
• Implement memory isolation and protection

37. What do you know about process scheduling in Linux?

Linux uses priority and preemptive scheduling algorithms to dynamically allocate CPU time to different processes. Scheduling strategies like CFS (Completely Fair Scheduler) ensure fair resource distribution.

38. What are the most commonly used Linux commands?

• <span>ls</span>: List directory contents
• <span>pwd</span>: Display current path
• <span>top</span>: View process resource usage
• <span>grep</span>: Text search
• <span>cat</span>: View file contents
• <span>tar</span>: Archive files
• <span>wget</span>: Network download
• <span>df/free</span>: Disk/memory usage
• <span>man</span>: View command manual

39. What is the iptables command? How is it used for network filtering?

<span>iptables</span> is used to set firewall rules in the Linux kernel:

iptables -L           # View current rules
iptables -A INPUT -p tcp --dport 22 -j ACCEPT  # Open port
iptables-save > /etc/iptables/rules.v4  # Persist rules

40. How to troubleshoot a Linux operating system that won’t start?

Steps to take include:

• Check boot logs and error messages
• Use GRUB to boot an old kernel
• Check hardware connections
• Rollback recent changes
• Use a live CD or rescue mode for repairs

41. What is the init process in Linux?

<span>init</span> is the first process started by the system (PID 1), used to initialize system services. The current mainstream is <span>systemd</span>, which replaces the older SysV init.

42. What is SMTP?

SMTP (Simple Mail Transfer Protocol) is a protocol used for email transmission, with:

• End-to-end model (cross-organization communication)
• Store-and-forward model (internal communication)

43. What is LVM?

LVM (Logical Volume Manager) is used for dynamic disk management, supporting:

• Dynamic resizing of partitions
• Snapshots
• Volume extension and migration

44. What are the differences between UDP and TCP?

Feature	UDP	TCP
Connection-oriented	No	Yes
Reliability	Unreliable	Reliable, supports retransmission and ordering
Application scenarios	Video conferencing, DNS, online gaming	File transfer, Web, email, etc.

45. What is /etc/resolv.conf?

This file is used to configure DNS server addresses and resolution behavior, and is a key configuration file for domain name resolution in Linux systems.

46. What is the difference between absolute and relative paths?

• Absolute path: Starts from the root directory <span>/</span>, such as <span>/home/user/file.txt</span>
• Relative path: Based on the current working directory, such as <span>./documents/file.txt</span>

47. What is the purpose of the grep command?

<span>grep</span> is used to search for matching text lines in files, for example:

grep "test" file.txt

48. How to check the status of a service or daemon?

Use the <span>systemctl</span> command:

systemctl status apache2

49. What is the difference between /etc/passwd and /etc/shadow?

• <span>/etc/passwd</span>: Stores user information (username, UID, Shell)
• <span>/etc/shadow</span>: Stores encrypted user password information, with stricter permissions

50. How to compress and decompress files?

# Compress
tar -czvf archive.tar.gz file

# Decompress
tar -xzvf archive.tar.gz

51. What is the difference between a process and a daemon?

• Process: Can be a foreground or background task
• Daemon: Runs in the background, requires no user interaction, starts with the system

52. How to schedule recurring tasks?

Use <span>crontab</span>:

crontab -e
# Execute script daily at 3:30
30 3 * * * /path/to/geeks.sh

53. What is the function of the sed command?

Used for stream editing and text replacement:

sed 's/foo/bar/g' file.txt

54. What are runlevels in Linux?

Runlevels define system states:

• 0: Shutdown
• 1: Single-user mode
• 3: Multi-user without graphical interface
• 5: Multi-user graphical interface
• 6: Reboot

The essence of advanced Linux capability is the ability to delve into the system’s underlying architecture to identify “invisible problems” and use data and strategies to precisely tune system performance。

These seemingly complex issues are, in fact, the foundation for the stable operation of large systems. Incorrect adjustments to kernel parameters can lead to slow services or, in severe cases, system crashes; with proper tuning, even an ordinary server can achieve peak performance!

This series is part of the complete set of “100 Linux Interview Questions”, covering a comprehensive system from beginner to advanced levels.

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