How to read and edit systemd logs using journalctl in linux : FAQs

1. What is journalctl and what does it do?

journalctl is a command-line tool used to view and manage system logs on systems that use systemd. It allows you to see logs from various sources, including the kernel, services, and applications.

2. How do I see all system logs with journalctl?

Simply run the command journalctl in your terminal. This will display all logs, starting with the oldest entries.

3. How can I filter the log output to specific services or timeframes?

journalctl offers various options for filtering. We can:

Use the –unit option to see logs for a specific service (e.g., journalctl –unit sshd).

Use the –since and –until options to filter by time (e.g., journalctl –since yesterday).

Combine multiple filters for more precise results.

4. How do I view kernel logs only?

We use the -k option with journalctl. This will display entries specifically from the kernel as follows.

journalctl -k

5. Can I clear or delete old system logs?

While journalctl itself doesn’t have a direct delete function, systemd manages journald logs with a specific policy. We can use the systemctl command with the cleanup argument to manage disk space used by logs.

6. What is Journal?

The journal acts as a repository for all system and process logs. The journald daemon is responsible for collecting and storing log messages from various sources. Journal entries have a structured format with fields like timestamps, severity levels, unit names, and message content.

In the realm of Linux system administration, managing logs is an indispensable task. System logs are crucial for understanding the health, performance, and troubleshooting of a system. Systemd, the init system widely adopted by modern Linux distributions, introduced a centralized logging system called the Journal. `journalctl` is the primary tool provided by Systemd for accessing and managing these logs. In this article, we will delve into the intricacies of `journalctl`, learning how to read, filter, and edit Systemd logs effectively.