Linux

【Linux】查看 Log

Posted by 西维蜀黍 on 2021-06-28, Last Modified on 2021-09-21

Log Files

  • /var/log/syslog or /var/log/messages: general messages, as well as system-related information. Essentially, this log stores all activity data across the global system.

  • /var/log/auth.log or /var/log/secure: store authentication logs, including both successful and failed logins and authentication methods. Again, the system type dictates where authentication logs are stored; Debian/Ubuntu information is stored in /var/log/auth.log, while Redhat/CentrOS is stored in /var/log/secure.

  • /var/log/boot.log: a repository of all information related to booting and any messages logged during startup.

  • /var/log/maillog or var/log/mail.log: stores all logs related to mail servers, useful when you need information about postfix, smtpd, or any email-related services running on your server.

  • /var/log/kern: stores Kernel logs and warning data. This log is valuable for troubleshooting custom kernels as well.

  • /var/log/dmesg: messages relating to device drivers. The command dmesg can be used to view messages in this file.

  • /var/log/faillog: contains information all failed login attempts, which is useful for gaining insights on attempted security breaches, such as those attempting to hack login credentials as well as brute-force attacks.

  • /var/log/cron: stores all Crond-related messages (cron jobs), such as when the cron daemon initiated a job, related failure messages, etc.

  • /var/log/messages : General message and system related stuff

  • /var/log/auth.log : Authenication logs

  • /var/log/kern.log : Kernel logs

  • /var/log/cron.log : Crond logs (cron job)

journalctl - Query the systemd journal

# Show all messages from this boot:
$ journalctl -b

# Show all messages from last boot:
$ journalctl -b -1

# Show all messages with priority level 3 (errors) from this boot:
$journalctl -b --priority=3

# Follow new messages (like tail -f for traditional syslog):
$ journalctl -f

# Show all messages by a specific unit:
$ journalctl -u unit

# Filter messages within a time range (either timestamp or placeholders like "yesterday"):
$ journalctl --since now|today|yesterday|tomorrow --until YYYY-MM-DD HH:MM:SS

# Show all messages by a specific process:
$ journalctl _PID=pid

# Show all messages by a specific executable:
$ journalctl path/to/executable

Reference

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