What is a Log File Format?

What is a Log File Format

What is a Log File Format? – Log files are plain-text documents that record events within your system and can contain anything that the software or operating system deems relevant to record.

W3C Extended Log Format (ASCII text file format) enables you to customize what properties are logged, thus reducing log size and saving disk space on web servers. It is frequently used by organizations using W3C services.

What is a Log File Format?

Log files provide an organized method of recording information in an easily-read and understandable format, and can be used to log events or monitor system performance. Often these logs provide valuable insight into what happened within an application or server and can help when troubleshooting problems.

Log files are usually plain-text documents and can be opened using any text editor, including Windows Notepad. If you need to convert one into another format such as PDF or CSV, however, specialized software programs that support such formats should be utilized instead.

Though logs differ across systems, applications, and tools, there are some widespread formats used for logs. Some formats may be semi-structured to facilitate easy human reading while others have defined schema or patterns requiring parsers for splitting events and extracting relevant data.

For your log file to remain human-readable, it’s essential that each event entry includes its timestamp in an easily recognizable format, such as YYYYMMDD. Furthermore, try including process or computer ID numbers whenever possible as this will make parsing easier and enable faster issue identification.

Commonly Used Log Formats

Logs can be stored and transmitted in various formats, from plain text to XML and JSON. Some formats are human readable while others can be processed by various software applications.

One of the most widely used log formats, known as Syslog, is generated by various devices and systems. It consists of both a header and extension that store log data as key-value pairs.

CSV files, which store values as comma-separated lists, are another popular format used for log file importation into databases regardless of which software system generated them.

W3C Extended format is another popular approach to structured logging, offering flexible control over which properties should be recorded and which should not. This enables you to keep log file sizes down while still collecting crucial information.

JSON is an increasingly popular logging format that provides both machine- and human-readable entries. Based on JavaScript object notation, it can be parsed by almost all programming languages and supports multiple keys and values for each entry to enable logs to be filtered according to various criteria.

Customized Log Formats

Log files are created by almost every device, system and application that generates logs for monitoring network traffic or security programs, or simply serving as a record of what has occurred over time on a computer – such as events occurring and their handling.

Customized log formats offer greater flexibility for recording data. They can reduce file sizes by eliminating unnecessary fields, as well as include extra information such as referrer and user agent information. When used in combination with other techniques such as rule-based logging, customized formats provide another tool to capture more data and enhance cybersecurity defenses of an organization.

JSON is one of the most commonly-used customized log formats, offering flexible data logging. As it uses nestable name/value pairs to arrange data in virtually any fashion, it offers far greater freedom than structured formats like CEF that use fixed structures that limit flexibility.

Create customized log formats using Kiwi Syslog Server’s Custom File Formats node of its Setup menu and then use these when sending log messages directly to files.

Miscellaneous Log Formats

While these log file formats are the most prevalent, system administrators may also come across other formats. These may include XML-based formats like JSON that allow administrators to store structured data while also offering the capability of querying for specific fields.

W3C Extended Log Format is a text-based log file format with a header listing which field names should be used for each entry, enabling log handlers to more efficiently parse these log entries.

Unstructured log files defy established formats and structures, making them difficult to analyze using existing tools and creating additional work for engineers during log management. Such logs typically require custom parsing processes which can be time-consuming and error-prone.

No matter the log file format, having an automated way of processing them is key for effective management. A modern log management platform offers instant visibility across multiple systems and applications allowing faster troubleshooting as well as prevention of security incidents before they become major issues. Start searching and filtering logs easily with our simple yet familiar query syntax which supports standard Boolean operators like Falcon LogScale Community Edition (formerly Humio).

1. Last Log-in Time

The Last Login Time field can provide crucial insight into when users last logged in or out. You can access this data using the NET USER USERNAME> command which updates /var/adm/acct/sumx/loginlog file with date/time information of when specific users logged on or out.

With PowerShell commands, it is possible to obtain similar information by entering this command:

Log files are an indispensable component of any IT system, and creating easily digestible logs is key for diagnosing issues quickly. To ensure that your logs are easily understood, follow these seven best practices for log file formatting.

Filtering records that contain personally identifiable information (PII), like usernames or IP addresses, from log file analysis can be challenging but essential in protecting user privacy. This guide will cover some of the most frequent use cases for log file analysis with search engines like Google in mind; although, its principles will likely apply to most other search engines as well. With log file analysis you can identify issues impacting SEO performance before taking steps to enhance rankings with changes implemented through log file analysis.

2. X-Request-ID

Timestamps are essential components of log files, providing an indication of when something occurred. Since dates and times can take on various formats, it is crucial that one chosen be universally understood without any ambiguities or surprises.

Log files provide more than just dates and times; they often also provide other data that allows us to trace back the activity that took place. For instance, they might record user login IDs or the host names from where actions originated – information which allows analysis tools to create log summaries by grouping together results of similar events.

An NCSA HTTPd server might use the Common Log Format (also referred to as NCSA Common Log Format, after its development company) when producing log files for web analysis programs to read and interpret easily. This standard text format makes for smooth reading and interpretation.


SNMP allows network managers to gather device information without overwhelming the network with large data transfers. Unlike traditional system logs, which store device status updates in an unstructured way and periodically, SNMP stores them standardized format allowing managers to view and analyze them at will. In addition, managers have access to a graphical interface which helps visualize this data for them.

At first glance, the inner workings of SNMP may appear complex. One key element is its hierarchical data system called Management Information Base (MIB). Each network device that supports SNMP has an OID number identifying itself uniquely (for instance: Cisco products have OID numbers like, along with human-readable labels which serve as codebooks in your SNMP manager’s codebook.

SNMP polls network equipment to collect various metrics, such as workload details and performance metrics such as queue lengths or packet drop rates. Furthermore, it monitors topologies to detect interconnections that help network administrators quickly spot problems and address them quickly. Finally, traps or GETs may be sent out automatically by SNMP to network equipment for automated tasks such as activating backup air-conditioning systems in server rooms to prevent overheating.

What Are the Different Log File Formats?

Log files are an integral component of modern applications. They keep a record of everything that takes place within them and enable developers to gain an insight into what’s taking place behind-the-scenes.

Ideal log files should be easily understandable by both humans and machines alike; an effective way of doing this is with structured log formats like JSON.

Commonly Used Log Formats

Log files are an indispensable asset when it comes to troubleshooting and monitoring software, providing valuable insights into how a system is operating – but only if they’re formatted properly; improper formatting or inconsistent data can make these files hard to read or interpret, leading to errors or inaccurate results.

A log file is typically an ordinary text file that can be opened using any text editor like Windows Notepad, used to record information such as antivirus scan results or software modifications and bug fixes. These logs may also serve as logs of changes.

There are multiple different log file formats, each offering distinct advantages and disadvantages. It is important to understand their inner workings so you can choose one best suited to your needs.


JSON (JavaScript Object Notation) is an open data format designed for easy reading and writing by humans and machines alike, offering an alternative to XML for web applications. Transferring JSON files is simple with numerous programming languages supporting it – making them suitable for systems running across different platforms.

JSON file format features an extremely straightforward structure based on text using UTF-8 character set. It offers support for integer and floating-point numbers as well as array data types (including nested arrays ), pointer syntax that enables elements to reference other elements using slashes referencing, whitespace is permitted but should be used sparingly since too much whitespace may confuse parsers; whitespace should also be avoided since too much may cause parsers to misread your file; whitespace in JSON files must be avoided as this can lead parsers misreading what it contains; trends on Stack Overflow show this; more questions relating to JSON than any other format ( including XML ).

Windows Event logs

Windows event logs are records that detail hardware and software actions taking place on your computer, including installation operations, system setup operations, error messages and security breaches. They serve as an invaluable way of troubleshooting potential issues with the operating system and installed applications; each log event contains five levels of information: Critical, Error, Warning, Information and Verbose that can be found in your registry. Each event also has a unique identification number so ISVs can utilize Windows event logging service to ensure their software issues are recorded appropriately in Windows Event Logs.

Logs provide detailed data including source, username, time stamp, event ID, computer task category and level information that can help troubleshoot system and application errors, investigate security incidents and predict future problems. They can be sent remotely using the xm_syslog module which removes tab characters and newline sequences before converting the event description to BSD syslog format and forwarding via UDP.

Common Event Format CEF

The Common Event Format (CEF) is a standardized log file format designed to make integrating events across systems easier. Featuring standard data fields and severity levels for ease of troubleshooting issues or identifying trends.

CEF utilizes the Syslog protocol as its transport vehicle and consists of two parts, including a header and message. The header contains metadata about an event while its message provides its actual data. Each event has a defined type and severity level while CEF specifications also permit for more granular data assignment to each event.

Log Analytics’ Configuration Data Connectors gallery makes it easy to configure your syslog receiver to accept CEF logs, then once configured you can view them in Alerts table as PD-CEF alerts. Furthermore, Event Rules and Event Orchestration provide ways of dynamically suppressing non-actionable alerts with its dynamic alert suppression functionality.

Common Log Format CLF

Graylog supports all log file formats used by web servers and other applications, each offering specific advantages over another format for specific scenarios. Graylog provides full support for these log formats by analyzing and archiving them automatically.

Common Log Format (CLF) is an industry standard format for HTTP servers. It consists of an ASCII text file which contains fields associated with an individual HTTP transaction and any omitted fields are marked with an “-“.

ACLF is a flexible log file format that enables the definition of multiple custom time formats. Format strings may contain timezone-related tokens and separator characters for convenience when configuring this time format string via the ACLF configuration option.

An SIP CLF format would benefit the industry by facilitating the creation of tools to mine logs and produce trend analysis reports, while also allowing anomaly detection systems to use these events as input for situational awareness purposes.

Extended Log Format ELF

W3C Extended Log Format (ELF) is an industry standard method of recording events on IT systems, offering users flexibility in how they record them. By adding or omitting fields as desired, this helps reduce file sizes while making analysis simpler and scalability and compatibility more achievable. UTC dates also help facilitate compatibility.

Each entry consists of fields related to one HTTP transaction and separated by whitespace before being terminated with either LF or CRLF. Their meanings are determined by the preceding #Fields directive; any non-utilized fields will be marked with “-“.

Web servers produce vast log files filled with lots of data that take time to process, may contain personally identifiable information which must be protected for compliance reasons and require protection for compliance reasons. IRI offers solutions for transforming, migrating, protecting and reporting on web log data – JSON, NCSA Common and W3C Extended formats can make managing them more manageable.

W3C Extended Log File Format

The W3C Extended Log File Format is an ASCII text-based log format designed to record logging information more easily than IIS and NCSA Common formats do. It allows more flexibility while recording log data similarly, including including proxy servers’ use of an X-Forwarded-For field that records client IP addresses as an additional field in their logs.

This log format utilizes a semi-structured format, making it easier for humans to read but requiring a parser in order to extract event and field values. Furthermore, this log format provides standard fields, including one called Date that specifies when an entry took place in GMT timezone.

Graylog provides an ideal example of such a solution and supports all the most commonly used log formats to ensure reliable analysis without data loss or incomplete analysis.


Though log data offers organizations great insights, its use can sometimes prove challenging due to its sheer volume. One such challenge lies with data preparation for use in meaningful ways – which often takes complex processes and hours to accomplish.

Log file formats present another difficulty when it comes to analysis and search, making them hard to search through and analyze. Some log formats offer users help in reading and understanding data: plain text logs consist solely of ASCII characters while CSV logs use comma-separated values as data structures while JSON logs use key-value pairs as key/value representations of log messages.

XML extended log file format supports process accounting, which helps identify when a site is using too many resources. This feature can be enabled per-site; information in a process account includes its name, number of threads used by that process and total CPU resources consumed by that process.

Sam is an experienced information security specialist who works with enterprises to mature and improve their enterprise security programs. Previously, he worked as a security news reporter.