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System Log Analysis with journalctl

In this video, we’ll explore how to use journalctl for system log analysis. journalctl is a powerful command-line tool for exploring and analyzing logs collected by systemd-journald. It offers a unified way to view system, service, and kernel messages, making it essential for diagnosing and maintaining Linux systems. We’ll cover basic commands, filtering logs by priority, time, service, and process ID, as well as advanced options and practical examples. Let’s dive into the details and master journalctl! Learn: ⚙️ Basic Commands View all logs: journalctl (Displays all logs in chronological order) View logs from current boot: journalctl -b (Shows logs only from the latest boot) Follow logs live: journalctl -f (Streams new log entries in real time) 🔍 Filtering Logs By Priority journalctl -p err Shows only error-level logs. Priority levels: 0=emerg, 1=alert, 2=crit, 3=err, 4=warning, 5=notice, 6=info, 7=debug -By Time journalctl --since "1 hour ago" journalctl --until "2023-01-02 00:00:00" Supports both relative (yesterday, today) and absolute time formats. -By Service journalctl -u apache2 journalctl -u NetworkManager Filters logs for specific services. -By Process ID journalctl _PID=1234 Displays logs for a specific process. 🧠 Advanced Options Show newest entries first: journalctl -r Display last 50 entries: journalctl -n 50 Export logs in JSON or plain format: journalctl -o json-pretty / journalctl -o cat Check journal disk usage: journalctl --disk-usage 🧩 Practical Examples Find failed services: journalctl -b -p err Monitor network connections: journalctl -u NetworkManager -f Monitor Apache web server logs: journalctl -u apache2 -f View kernel messages: journalctl -k Search for specific keywords: journalctl | grep "error" View logs from previous boot: journalctl -b -1 🧹 Managing Journal Logs Clean Up Old Logs sudo journalctl --vacuum-time=2weeks sudo journalctl --vacuum-size=100M Deletes logs older than 2 weeks or keeps total size under 100 MB. 💡 Pro Tips Use grep to search patterns quickly: journalctl | grep "error" Combine filters for precision (e.g., -u apache2 -p err): journalctl -u apache2 -p err Use --no-pager to print directly to terminal: journalctl --no-pager Save important logs: journalctl -u apache2 〉 apache_logs.txt 🧾 List Available Services to Monitor You can list all active services to find which ones support journalctl: systemctl list-units --type=service Then use: journalctl -u 〈service-name〉 -f 🏁 Conclusion journalctl is an indispensable tool for Linux administrators. With it, you can monitor services, analyze errors, and keep your system healthy — all from one unified log viewer. Mastering journalctl will significantly enhance your ability to diagnose and maintain your Linux systems. GitLab Link: You can find the tutorial pdf used in this video at this GitLab link: https://gitlab.com/hatem-badawi/linux.... Hit subscribe for more Linux and productivity tips and like if this helped. Let us know: What’s your favorite journalctl command? 👉 Watch now and master system log analysis with journalctl! #LinuxTips #SystemLogs #Journalctl #ProductivityHacks #SystemAdministration (Short, clear, and packed with practical knowledge!)