Systemlog

Systemlog, or system log, is the collection of records produced by an operating system and its installed software to document events and conditions that occur within a computer system. It serves as a central source of information for troubleshooting, auditing, monitoring, and capacity planning. System logs can be generated locally on a device or aggregated from multiple machines.

Entries typically record a timestamp, the host name, the originating component or process (such as the kernel or a daemon), a severity level, and a human readable message. Severity levels commonly range from emergency or critical through error, warning, notice, info, to debug.

Historically, Unix-like systems used the syslog facility to write logs to local files and/or remote servers via the syslog protocol. Modern implementations include rsyslog and syslog-ng, while systemd-based systems use journald, which can export messages in syslog format. The syslog protocol is defined in RFC 3164 and RFC 5424, providing a standard message structure.

Log files are usually stored in system-specific locations, such as /var/log on Unix-like systems, with files like messages, syslog, or dmesg. Windows maintains a separate System log accessible through Event Viewer.

Logs are often rotated and archived to manage disk usage, and may be centralized for monitoring and analysis with tools such as log shippers, aggregators, or SIEM platforms. Proper access control and retention policies support security and compliance.