Feature Request: Log error when systemd logs are unable to be read due to permissions

[lizziemac]

Is your feature request related to a problem? Please describe.

I recently encountered an issue where fluent-bit was unable to access or read systemd logs due to permission or ownership issues, and there was no error or warning logged when trailing the fluent-bit logs. We spent a few days trying to understand if this was a server side issue, or a device side issue, tried changing the config, etc, before we realized it was a simple permissions problem related to grouping.

This happened months after the successful integration of fluent-bit, because we had removed a user from the system, causing the user/group IDs to be misaligned in our shared log partition (and systemd-resolve took ownership over from systemd-journal)

Describe the solution you'd like

I would like fluent-bit to log a clear error or warning when it encounters permission or ownership issues preventing access to systemd logs. This error should explicitly mention that log access was denied due to permissions and provide suggestions for correcting the issue, such as checking permissions or user configuration.

Describe alternatives you've considered

• Erroring out of fluent-bit completely. I wouldn't recommend because that would break other log source streams.

Additional context

This was on version 2.2.2, and fluent-bit was running as a service with its own user that had access to systemd-journal