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LOGGING.md

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Logging

By default, Mountpoint for Amazon S3 emits high-severity log information to syslog if available on your system. To view these logs on systems using journald (most modern Linux distributions, including Amazon Linux), run:

journalctl -e SYSLOG_IDENTIFIER=mount-s3

On other systems, syslog entries are likely written to a file such as /var/log/syslog.

When running mount-s3 in foreground mode (the -f, --foreground command-line argument), Mountpoint will emit logs to stdout in addition to syslog or any configured log directory (see below).

Logging to a file

You can direct logs to a file instead of syslog by providing a destination directory using the -l, --log-directory command-line argument with mount-s3.

mount-s3 <BUCKET> <MOUNT_PATH> --log-directory <LOG_DIRECTORY>

The directory will be created if it doesn't exist. A new log file will be created for each execution of mount-s3. Both the directory and log files are created with read/write access for the process owner and read access for the process owner's group. Log files are not automatically rotated or cleaned up.

Disabling logging

If you do not want to record any logs, use the --no-log command-line argument. This argument cannot be combined with other logging-related command-line arguments. The --no-log argument has no effect on messages sent to the standard output. If no output is desired, consider redirecting it.

Verbose logging

By default, Mountpoint only logs high-severity events. For reporting issues or debugging application problems, it can be helpful to increase this verbosity. You can enable more verbose logging with the --debug command-line argument. We recommend logging to a file (the -l, --log-directory argument above) when using this option.

Advanced logging verbosity options

To enable more verbose logging for the AWS Common Runtime that Mountpoint uses to communicate with S3, use the --debug-crt command-line argument. These logs are very verbose, and should be combined with the -l, --log-directory and --debug arguments described above.

For finer-grained control over log verbosity, Mountpoint uses the MOUNTPOINT_LOG environment variable, which overrides the verbosity options above. The MOUNTPOINT_LOG environment variable uses the tracing-subscriber directive syntax, and can be used to control log verbosity on a per-subject basis. For example, setting MOUNTPOINT_LOG to trace enables all trace-level logs, while trace,awscrt=warn enables trace-level logs for all log subjects except awscrt, which has only warning-level logging enabled.

Metrics

Mountpoint optionally collects metrics measuring various values across different components. For example, Mountpoint records the durations of FUSE operations and the number of S3 responses grouped by HTTP status code.

To opt-in, use the --log-metrics command-line argument. Metrics will be collected by Mountpoint and flushed to the logs every five seconds. See below an example of what the emitted metrics may look like in the logs.

[INFO] mountpoint_s3::metrics: fuse.io_size[type=read]: n=4: min=3184 p10=3199 p50=16511 avg=26494.00 p90=70143 p99=70143 p99.9=70143 max=70143
[INFO] mountpoint_s3::metrics: fuse.op_latency_us[op=lookup]: n=8: min=22912 p10=23039 p50=65023 avg=62632.00 p90=95231 p99=95231 p99.9=95231 max=95231
[INFO] mountpoint_s3::metrics: fuse.op_latency_us[op=open]: n=3: min=24448 p10=24575 p50=64255 avg=54037.33 p90=73727 p99=73727 p99.9=73727 max=73727
[INFO] mountpoint_s3::metrics: fuse.total_bytes[type=read]: 105584 (n=4)

We recommend using the metrics only for debugging at this time. Metrics are currently output in an unstructured format and are subject to change in future releases.