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Log file

lastmod 2026-03-13created 2018-10-0219 edits

In computing, a logfile is a file that records events that occur while an operating system or other software runs, or messages between the communication software of different users. The act of keeping a log is called logging.

A transaction log is a file of the communication between a system and its users, or a data collection method that automatically captures the type, content, and time of transactions made by users at terminals belonging to the system.

Many operating systems, software frameworks, and programs include a logging system. A widely used logging standard is syslog, defined in IETF RFC 5424.

Log level

0 (KERN_EMERG)
The system is unusable.
When the system can no longer be used. That is, the system is about to crash.
1 (KERN_ALERT)
Actions that must be taken care of immediately.
When a serious problem occurs that requires immediate resolution.
2 (KERN_CRIT)
Critical conditions.
A critical problem. (It does not have to be resolved immediately, but it should be resolved as soon as possible)
3 (KERN_ERR)
Non-critical error conditions.
When a non-critical but definite problem occurs. (The application may keep running. It just doesn't work properly...)
4 (KERN_WARNING)
Warning conditions that should be taken care of.
A situation the system can resolve, but which carries potential risk.
For example, a malformed input value (such as entering 2010-1-21 when the date format is yyyy-MM-dd)
5 (KERN_NOTICE)
Normal, but significant events.
Normal. But a significant event has occurred. It is assumed that the user is notified.
6 (KERN_INFO)
Informational messages that require no action.
Additional information. No further action is needed after checking.
7 (KERN_DEBUG)
Kernel debugging messages, output by the kernel if the developer enabled debugging at compile time.
For debugging.

List of Log Aggregator

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