Logging (computing): Difference between revisions

Revision as of 22:04, 10 November 2023

Revision as of 22:05, 10 November 2023

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{{distinguish|Data logger}}

In [[computing]], '''logging''' is the act of keeping a [[wikt:log#Etymology 2|log]] of [[Event (computing)|events]] that occur in a computer system, such as problems, errors or just information on current operations. These events may occur in the [[operating system]] or in other [[software]]. A message or '''log entry''' is recorded for each such event. These log messages can then be used to monitor and understand the operation of the system, to [[debugging|debug]] problems, or during an [[audit]]. Logging is particularly important in [[multi-user software]], to have a central overview of the operation of the system.

In the simplest case, messages are written to a file, called a '''log file'''.<ref>{{cite web |url= https://blog.pandorafms.org/log-monitoring/ |title= Log Monitoring: not the ugly sister |access-date = February 14, 2018 |last= DeLaRosa |first= Alexander |date= February 8, 2018 |website= [[Pandora FMS]] |language = english |quote= A log file is a text file or XML file used to register the automatically produced and time-stamped documentation of events, behaviors and conditions relevant to a particular system. |archive-url= https://web.archive.org/web/20180214153657/https://blog.pandorafms.org/log-monitoring/

|archive-date= February 14, 2018}}</ref> Alternatively, the messages may be written to a dedicated logging system or to a [[log management]] software, where it is stored in a database or on a different computer system.

Specifically, a '''transaction log''' is a log of the communications between a system and the users of that system,<ref>Peters, T. (1993). The history and development of transaction log analysis. Library Hi Tech., 42(11), 41−66</ref> or a data collection method that automatically captures the type, content, or time of transactions made by a person from a terminal with that system.<ref>Rice, R. E., & Borgman, C. L. (1983). The use of computer-monitored data in information science. Journal of the American Society for Information Science, 44, 247−256</ref> For Web searching, a transaction log is an electronic record of interactions that have occurred during a searching episode between a Web search engine and users searching for information on that Web search engine.

Many operating systems, software frameworks and programs include a logging system. A widely used logging standard is [[Syslog]], defined in Internet Engineering Task Force (IETF) [[Request for Comments|RFC]] 5424). The Syslog standard enables a dedicated, standardized subsystem to generate, filter, record, and analyze log messages. This relieves software developers of having to design and code their ad hoc logging systems.<ref>{{Cite web|url=https://winscp.net/eng/docs/logging_xml|title=XML Logging :: WinSCP|website=winscp.net}}</ref><ref>{{Cite web|url=https://www.codeproject.com/Articles/28752/Use-XML-for-Log-Files|title=Use XML for Log Files|date=August 22, 2008|website=CodeProject}}</ref><ref>{{Cite web|url=https://learn.microsoft.com/en-us/previous-versions/dotnet/articles/ms972965(v=msdn.10)|title=Turn Your Log Files into Searchable Data Using Regex and the XML Classes|website=learn.microsoft.com}}</ref>

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== Event logs ==

'''Event logs''' record events taking place in the execution of a system in order to provide an [[audit trail]] that can be used to understand the activity of the system and to diagnose problems. They are essential to understand the activities of complex systems, particularly in the case of applications with little user interaction (such as [[Server (computing)|server]] applications).

It can also be useful to combine log file entries from multiple sources. This approach, in combination with [[statistical analysis]], may yield [[Statistical correlation|correlations]] between seemingly unrelated events on different servers. Other solutions employ network-wide querying and [[report]]ing.<ref>{{Cite web|url=https://learn.microsoft.com/en-us/sql/relational-databases/logs/log-file-viewer|title=Log File Viewer - SQL Server|website=learn.microsoft.com}}</ref><ref name="auto">{{Cite web |title=Extended Log File Format |url=https://www.org/pm --0 user/TR/WD-logfile.html |website=www.w3.org}}</ref>

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{{Main|Transaction log}}

Most [[Database|database systems]] maintain some kind of '''transaction log''', which are not mainly intended as an audit trail for later analysis, and are not intended to be [[human-readable]]. These logs record changes to the stored data to allow the database to recover from [[Crash (computing)|crashes]] or other data errors and maintain the stored data in a consistent state. Thus, database systems usually have both general event logs and transaction logs.<ref>{{Cite web|url=https://learn.microsoft.com/en-us/sql/relational-databases/logs/the-transaction-log-sql-server|title=The Transaction Log (SQL Server) - SQL Server|website=learn.microsoft.com}}</ref><ref>{{Cite web|url=https://www.sqlshack.com/beginners-guide-sql-server-transaction-logs/|title=A beginner’s guide to SQL Server transaction logs|first=Ivan|last=Stankovic|date=February 11, 2014}}</ref><ref>{{Cite web|url=https://www.techrepublic.com/article/understanding-the-importance-of-transaction-logs-in-sql-server/|title=Understanding the importance of transaction logs in SQL Server|date=November 11, 2004|website=TechRepublic}}</ref><ref>{{Cite web|url=https://www.neurobs.com/pres_docs/html/03_presentation/07_data_reporting/01_logfiles/index.html|title=Logfiles|website=www.neurobs.com}}</ref>

=== Transaction log analysis ===

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==Server log{{anchor|Server}}==

[[File:Apache Log.png|thumb|Apache access log showing Wordpress vulnerability bots]]

A '''server log''' is a log file (or several files) automatically created and maintained by a [[Server (computing)|server]] consisting of a list of activities it performed.

A typical example is a [[Webserver directory index|web server]] log which maintains a history of page requests. The [[World Wide Web Consortium|W3C]] maintains a standard format (the [[Pm 0--user Common Log Format|Common Log Format]]) for web server log files, but other proprietary formats exist.<ref name="auto"/>Some servers can log information to computer readable formats (such as [[JSON]]) versus the human readable standard.<ref>{{Cite web|url=https://caddyserver.com/|title=How Logging Works - Caddy Documentation|first=Caddy Web|last=Server|website=caddyserver.com}}</ref> More recent entries are typically appended to the end of the file. Information about the request, including [[client (computing)|client]] [[IP address]], request [[Calendar date|date]]/[[time]], [[webpage|page]] requested, [[HTTPs|HTTP]] code, bytes served, [[Pm 0--User agent|user agent]], and [[HTTP referrer|referrer]] are typically added. This data can be combined into a single file, or separated into distinct logs, such as an access log, [[error]] log, or referrer log. However, server logs typically do not collect user-specific information.

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== References ==

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