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Checking Service Status and Logs

1. Introduction to Service Status and Logs​

In Linux, it is essential to monitor and troubleshoot running services to ensure they are operating correctly. You can check a service’s status to determine if it is running, inactive, or failed, and use logs to troubleshoot and examine service behavior.

This lesson will guide you through using systemctl to check service status and view logs to track service activity.

2. Checking Service Status with systemctl​

a. Using systemctl status​

The systemctl status command gives you detailed information about a service's current state. This includes whether the service is active, inactive, or in a failed state.

systemctl status apache2

This command provides a comprehensive status of the Apache2 web server, showing whether the service is running, the process ID (PID), uptime, and any error messages in the logs.

b. Interpreting the Status Output​

Here’s a sample output of systemctl status apache2:

● apache2.service - The Apache HTTP Server
   Loaded: loaded (/etc/systemd/system/apache2.service; enabled; vendor preset: enabled)
   Active: active (running) since Thu 2025-01-06 10:30:18 UTC; 2h 20min ago
 Main PID: 1234 (apache2)
   CGroup: /system.slice/apache2.service
           ├─1234 /usr/sbin/apache2 -k start
           └─5678 /usr/sbin/apache2 -k start

Explanation:

  • Loaded: Displays if the service configuration is properly loaded.
  • Active: Shows the current status of the service. In this case, it is active (running), which means the Apache2 service is working as expected.
  • Main PID: The process ID of the main service.
  • CGroup: Displays the control group and shows the list of processes running under this service.

Note: If the service isn’t running, you'll see something like inactive or failed, indicating the service didn’t start properly.

3. Checking Service Logs with journalctl​

Systemd uses the journald service to store logs for services. The logs contain vital information, including any error messages, service startup issues, or runtime problems.

a. Using journalctl for Service Logs​

You can use journalctl to view the logs related to a specific service. By filtering logs, you can easily find issues related to the service.

journalctl -u apache2

This command shows all logs associated with the Apache2 service. The -u flag filters logs by unit, so you can target a specific service.

b. Viewing Logs from the Current Boot​

If you only want to view logs from the current boot, you can add the -b flag:

journalctl -u apache2 -b

This will display only the logs for Apache2 from the current session, helping you troubleshoot without getting older, unrelated logs.

c. Filtering Logs by Time Range​

You can also filter logs to view messages from a specific time range. For example, to view logs from the past hour:

journalctl -u apache2 --since "1 hour ago"

This command will show logs that have occurred in the last hour, useful for narrowing down recent issues.

4. Viewing Real-Time Logs with journalctl -f​

If you need to monitor logs in real-time, for instance, when you're troubleshooting an issue as it happens, you can use the -f flag with journalctl.

journalctl -u apache2 -f

This command streams the logs in real-time, so you can see new log entries as they are generated. This is useful when you are debugging a service that’s running and want to track its activity as it happens.

5. Additional Log Management with systemctl​

While journalctl is the main tool for accessing service logs, systemctl also provides a simple way to view the logs associated with the service when checking its status.

a. Viewing Logs Directly in systemctl status​

When using systemctl status <service>, you may see the last few lines of logs directly under the service status output. This is helpful for quickly identifying issues without needing to run a separate journalctl command.

systemctl status apache2

Explanation: At the end of the status output, you will see log entries like the following (if any):

Sample Output:

Jan 06 12:30:18 myserver apache2[1234]: Starting Apache2 web server...
Jan 06 12:30:19 myserver apache2[1234]: Apache2 started successfully.

Note:If errors occurred, they would appear here as well.

7. Key Takeaways​

  • How to check the status of services with systemctl status.
  • Using journalctl to view service logs and filter them based on time or service.
  • Monitoring real-time logs with journalctl -f.
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