Logs (Linux)

Linux logs are save usually in /var/log folder. Most linux distribution uses syslog, syslog-ng or rsyslog software for logging or sending them to remote servers. Analytics and visualisation software such a Elasticsearch and Kibana can be used for log inspection.

Usage by Distribution:

• Debian/Ubuntu: rsyslog
• RHEL/Fedora:

Standard logs:

• Debian/Ubuntu: /var/log/syslog
• RHEL/Fedora: /var/log/message

SSH sessions logging:

• Debian/Ubuntu: /var/log/auth.log
• RHEL/Fedora: /var/log/secure

Misc:

• SUSE: /var/log/warn.log

/var/log/message – Where whole system logs or current activity logs are available.
/var/log/auth.log – Authentication logs.
/var/log/kern.log – Kernel logs.
/var/log/cron.log – Crond logs (cron job).
/var/log/maillog – Mail server logs.
/var/log/boot.log – System boot log.
/var/log/mysqld.log – MySQL database server log file.
/var/log/secure – Authentication log.
/var/log/utmp or /var/log/wtmp : Login records file.
/var/log/yum.log: Yum log files.

Rsyslog

Rsyslogd supports queued operations to handle offline outputs. Official documentation: https://www.rsyslog.com/doc/v8-stable/configuration/index.html

Rsyslog Configuration

Default configuration files by Distribution:

• Debian: /etc/rsyslog.conf man rsyslog.conf: https://linux.die.net/man/5/rsyslog.conf
• Ubuntu: /etc/rsyslog.d/50-default.conf

Docker

• docker logs command show docker logs.

See also https://stackoverflow.com/questions/30969435/where-is-the-docker-daemon-log/30970134#30970134 for further information about docker logs.

• docker container logs

See also

• Files: tail, mtail, promtail, aws logs tail, ktail, stern, kubectl logs
• systemd-journald: journalctl, /etc/systemd/journald.conf, journalctl logs, journalctl --list-boots, journalctl --disk-usage, journalctl -u kubelet, journalctl -u prometheus, journalctl --help
• logger and systemd-cat
• auditd: https://linux.die.net/man/8/auditd
• acct package
• Monitoring: On call, Monitoring software, Monitoring services, Resource monitoring, Metric colletion tools, network monitoring, SLA Management Monitoring Tools, Alarm/Alert, Resource starvation, Alerts and notifications, Monitoring Kubernetes, VictoriaMetrics, Sensu, LogicMonitor, Distributed tracing, Datadog Monitors
• Netflow for network logging
• Message Brokers for routing messages: NSQ, RabbitMQ, Apache Kafka, AWS Kinesis and NATS Messaging
• fluentd
• logstash and filebeat products from Elastic
• Logwatch
• Linux logging, Cisco IOS logging

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