How can you use log files to debug software?

Log files are extremely important during your defect detection investigation process. Log files equivalent to your "blood test" results where you can get meaningful data to understand application "health".

Log files always help as investigation reports. I have seen best-in-class programmers struggle without log files for troubleshooting. While developing and testing developers can not imagine how code might run into an accident when it runs into production. If there are no log files, it's extremely difficult to understand the failure reason and replicate scenarios. As an Integration consultant log files acted as a savior for me always. Most of the time integration failed due to data issues or incorrect processing of data and log files acted as evidence to troubleshoot and take the next steps to move forward. Same time, need to be careful to get rid of redundant logs, this might result in meaningless log files.

Log files are the basic material all developer needs to understand what is going wrong in a software. Some software behaviors are user-blocking which are generally visible to the user like a crash, feature not working, etc.) while others are more subtle and may turn later into further issues (e.g., memory leaks, data corruption). In all cases, these hints are key for developers to start investigating. It can be challenging sometimes for the development team as they need to look at both back (server side) and front (client side, typically in the browser's console). The reason why ease of access as well as flexibility in the level of logs (e.g., only errors, errors and warning, etc.) are important for quicker problem resolution.

Yes, if log is done properly, it can certainly help to debug the code. The primary objective of logs is to ensure the flow of information and identify where is it getting stuck. Sadly lot of junk is written in logs which is because the programmer didn't get an explicit direction on what to log and what to ignore so most of the folks end up writing logs only for their own program test missing out the holistic view of the entire project. I think it is the most powerful tool for maintenance team provided logs capture key flow inputs and not just anything that is not relevant for the program.

Log files are the text document and as the name says they contains log / details about the various operations/movements happened on the software system. Details can be the operations user performed, inputs they provided, details about the configuration of users system and many more things. These are extremely helpful for developers to trace the root cause while working on fixing any faliure / defect and acts as first source of information to them.

You should also decide when to log and how much to log as it can be overwhelming to determine the issue from log. Most importantly it should be dynamic and can be turned on and off on the fly. Avoid logging PU/SPI as well as any information which can identify the source system and business process especially if it’s outside the DMZ.

Log files can be confusing because they were written by someone for a purpose that may not be aligned with your task at hand. SO First think what steps the user is doing. Think what the machine or application steps are, and how they are broken down into the component services, then read the logs in that context, and patterns as well as understanding will emerge. Use time stamps to sequence different logs together, include user steps. And remember to check the time stamps between systems are aligned. You may need offsets or translations for time zones or even inaccuracies.

Log files serve as invaluable breadcrumbs in the debugging process, providing a trail of events and errors. They offer insights into the program's execution, helping developers pinpoint issues and streamline the troubleshooting journey.

Log files tell the story (in technical detail) about what actually happened with the system or application of your concern. They are the forensic evidence needed for the technical detective trying to solve the crime (of system or application failure).

Properly created log files can also help to verify if processes are followed. You can use Process Mining techniques to verify what is the real life process your organization follow. Maybe this is not entirely related to the debugging but we should treat it as organization level debugging.

Log Editor/viewer are helpful for General Application. But for Security function it need a real time co-relation and analytics hence you need tools with log ++ functions Like SIEM, EDR, XDR which also help in faster threat detection and response.

Knowledge of log aggregators is quite useful today. Software such as splunk, and ELK tools are very helpful in this regard. Regex based searches can be used for tokenizing and filtering within the log output. This can further be used to generate powerful visualizations of the data in the form of dashboards etc. that can be used for monitoring system health, and other relevant metrics.

Unix/Linux commands are helpful when reading logs because there could be extremely long files and you want to zero in on the issue. For example grep can be used to find only lines in the log which have the word Error or Exception.

Log files can be located in various locations depending on the developer and operating system and can be various file format including text, ascii etc. Log files locations will generally be made known under the technical specification section to be accessible by debuggers or at times data technicians for analysis purposes .

Ok today world we roll forward the log files to centralise tool like spunk, cloud watch and create various dashboards and metrics which can give insight to code as well performance

Often, the best way to read and interpret files is just using a plain old text editor. Sometimes, in the case of big disasters, your last message is at the end of the file. For more complex jobs, tools exist to help find patterns and interpret results.

Automate the access and the selection of key (meaningful/important) messages by using a monitoring tool with log reader capability. You can get alerted when some message you’re concerned with appears in the log.

While a text editor can be used to inspect log files, it may not offer the same specialized features as dedicated log analysis tools. However, for smaller logs or quick checks, text editors like Vim, Emacs, or Sublime Text can still be valuable. Their search and navigation functionalities allow developers to manually review log entries, search for specific keywords, and get a quick overview. For larger logs or complex debugging scenarios, transitioning to tools explicitly designed for log analysis could provide a more efficient and comprehensive solution.

Important element to read through log file depends on your objective, if you are looking for error identification or information flow understanding accordingly look for right parameter, timestamp, error/message description, source which generated the event. Most of the log message are self explanatory to point out the issues. In my experience vi, tail, less are very useful commands while working on linux/unix systems.

The best way is built a dashboard and berate metrics and alert. Of course short analysis can be done by accessing it via command line interfaces

Essentially, the logs help you retrace the path to diagnose a malfunction. Recalling my experience as a coder and engineer: 1. We generously placed log lines throughout the flow of the code. 2. Each log statement was detailed enough with a view of the contents of the variables, lists, etc. 3. Such a lot of logging will likely slow down the system substantially. So, we defined log levels and applied them to each log statement. We kept the log level minimal (only key points) in a production environment and maximal (all log statements) in a lab environment. 4. Occasionally, when we cannot reproduce the bug in the lab, we may turn on a higher log level in production for some time to get some visibility on the cause of the defect.

Logs play a pivotal role in ensuring the sustainability of an application. Contrary to a common misconception that logs primarily serve development activities, their true significance lies in instilling confidence in the end user's experience within the application. As an architect, crafting an effective log strategy involves meticulous attention to log design, precise logging, thorough log analysis, and seamless log correlation. Additionally, the thoughtful planning and execution of log archival and purging are essential components to maintain the uninterrupted flow of a user's journey within the application.

Sometimes log files are live, so they're refreshing instantly. You will need any kind of advanced notepad engine (e.g. notepad++) with linux-like function "tail -f". This will let you trace logs in real time, once error in application will happen.

To use log files for debugging, start by identifying the issue you're trying to solve. Determine which log files might contain relevant information, such as application, system, or web server logs. Narrow your focus to the time period when the issue occurred, using timestamps in the logs to guide you. In cases of complex systems, it's important to compare logs from different sources to understand how different components interacted or failed. Based on your findings, develop hypotheses about what might be causing the issue. Test these hypotheses by modifying the code or configuration and observing the results.

Acquire database tools that will present log information in different formats and allow you to see log contents in different ways which will be useful in determining symptoms and assist in problem resolution.

What Not to Write in Log Files: Avoid logging redundant or unnecessary information. Ex: In process Connected to Database "How is it going to help me?" While detailed logs are beneficial, avoid excessive verbosity. Focus on key information. "What should I do with the queries you executed?" Maintain consistent log format for easy parsing and analysis. Event: Data processed successfully. Warning - Low resources detected. "How are you going to parse these?" Ensure log entries are complete and provide sufficient context. Error: Connection failed. "Where is the WHY part?" And I am not going to discuss DEBUG logs in Prod. *sigh*

It's fundamental to consider what to log starting from development, while writing code you should define a 'baseline' of log, that can help you to understand macro level of problems and that can allow you to collect informations about performance and errors, using also some log collection tools like splunk, ELK or Grafana/Loki framework, enabling you to define metrics, KPI and dashboards for monitoring se execution and predicting failures. Another important consideraton has to be made about identifying the source of the log, particularly in a multisession environment like an application server, in which many user sessions write their log in the same file. It's fundamental to be able to distinguish each chain of log rows to reconstruct

We had an application that periodically ran very slowly. The application crew wanted to blame the infrastructure. Logic told us that if the infrastructure works well 29 days out of the month, the one day a month is probably not caused by infrastructure. It is most likely a load problem caused by any number of factors. The app team had a log file, but they didn’t know how to troubleshoot. We wrote a script to identify when a process started and stopped so we could see frequency and duration. We found number of executions for one process changed dramatically on that one day. It was a flawed process, not infrastructure . Finger pointing occurred for months before we got access to the log files. Solved in a couple hours with log files.

I think we all have an affinity for logging. Having a thorough understanding of logging and how to utilize log data not only for troubleshooting, but for system scaling, security, performance metrics, preventative maintenance, etc. Proper logs can save your life and career.

Ability to set what type of information is being logged is important to increase log information when you might have problems with your system and set those parameters off when all is operating as expected to save disk space and increase system performance.