Troubleshooting Linux Problems: A Beginner's Guide

[Chetan_Tiwary_]

Troubleshooting Linux systems can be a challenging task, especially for beginners and L1/L2 level administrators. However, with a systematic approach and some fundamental knowledge, you can effectively diagnose and resolve issues that may arise. Here is a step-by-step guide to help you navigate the world of Linux troubleshooting:

1. Understand the Problem: The first step in troubleshooting any issue is to gain a clear understanding of the problem. Ask questions and gather as much information as possible from the user or system logs. Knowing the symptoms and the context in which the issue occurred can be immensely helpful.

What exactly is the user experiencing? Is there an error message? What is the general expectation of running a command or service or process? What is not working ? eg. the working webserver is now down.

2. Check the logs : Based on the gathered information or the error message , you should check the logs for any info/error. Linux systems generate a lot of logs, which can be a valuable source of information for troubleshooting problems. The most important logs to check are the kernel log, application logs and the system logs. These logs can contain error messages, warnings, and other information that can help you to identify the cause of the problem. /var/log/ is the main key folder to check the system wide logs of various processes. Have a good knowledge of this folder.

3. Check the Basics: Before diving into complex diagnostics, ensure that you've covered the basics of the component reporting the error message or issues. Reproducing the error can give a nice idea of what could potentially be wrong.

eg. verify network connectivity to rule out any network-related problems/disruptions. Check if the required services are running, or confirm that there is enough disk space available or the relevant package was installed or the configuration was correct. Check the file system info / corruption, cpu load , any I/O bottlenecks or any firewall related settings etc based on the logs you got.

4. Utilize Command-Line Tools: Linux provides a plethora of command-line tools and utilities that can help you diagnose issues. Tools like 'top' for monitoring system resources, 'netstat' or 'ss' for network troubleshooting, and 'ps' for process management are your allies. 'free' for memory related info , 'tail' or 'head' command to read the logs, 'grep' to catch / filter the requred strings in the logs like error or warn etc,  'dmesg' for kernel logs , 'df' or 'du' for disk related info, 'yum' for package management, 'systemctl' for service related tasks like service start or stop, 'mount' for mounting the disks etc.  Teach yourself and your team how to effectively use these tools. 'man' command to check the manual pages for commands can be a really helpful guide to know more about the commands use cases.

Suppose there is a scenario : ssh to a server is not working 

• What is the error message ? connection timed out or connection refused 
• If the error is connectin timed out : we should check the ssh logs to get an idea of the error, then we can check if the host IP address is correct or check the firewall rules or verify if DNS is properly configured. We can do ssh with -vv option to check the more detailed information, including a detailed trace of the connection process to see if we can get an idea of the potential cause.
• If the error is connection refused: we should check the ssh logs , verify the firewall rules , verify if the port ( 22 ) is allowed by the firewall service, verify if the ssh service is running or not etc.
• If you have a permission denied error while doing ssh : It happens when the user is not authorized to logging into the server or there is a mismatched key pair. Verify the correct key pair configuration and permission & ownership of the key files is set. It is mainly due to the sshd_config file that contains SSH server configuration. Configuration like PasswordAuthentication and PubkeyAuthentication , Port , PermitRootLogin and other related configurations. Restart the ssh service if you change anything. 

This way you can eliminate the error related to the ssh login in a methodological manner.

5. Leverage Online Resources: The Linux community is vast and active. Encourage your team to explore online forums, communities, and knowledge bases. Often, you'll find that someone else has encountered a similar issue and shared their solution. Collaborative problem-solving can save valuable time. Be cautious to not apply any random solution to your system without doing the due diligence or the analysis of the resultant impacts it can have on your system performance.

6. Document Everything: Documenting the troubleshooting process is crucial. It not only helps in keeping track of what you've tried but also aids in knowledge sharing within your team. A well-documented troubleshooting procedure can become a valuable resource for future reference or to take help from the vendor.

7. Stay Calm and Patient: Troubleshooting can be frustrating, especially when the problem seems elusive. Encourage yourself and your team to stay calm and patient. Avoid making hasty decisions or changes that could potentially worsen the situation. Instead, approach the problem methodically. Engage teams and the vendor should you need support to recover your production systems.

8. Learn from Mistakes: In the world of Linux, mistakes are part of the learning process. When troubleshooting, it's possible to make errors or try solutions that don't work. Encourage a culture of learning from these experiences and using them to become better administrators.

9. Automate Routine Checks: If you have knowledge of automation tools like Ansible, consider automating routine checks and maintenance tasks. This can help prevent common issues and reduce the workload on your team. Always do a QA tests of any automation before applying it to the production systems.