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
• 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
• Linux logging, Cisco IOS logging
• Logs, Log collector, log management, log explorer, Linux logging, docker logs, minikube logs, Vector, Logstash, Filebeat, promtail, logfmt, Elasticsearch, fluentd, Mezmo (LogDNA), Scalyr, Loggly, Loki, tlog, cockpit, NXLog, Winston, Amazon CloudWatch Logs Insights, Logz.io, Logflare

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