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tracing.md
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# Tracing <!--introduced_in=v7.7.0--> Trace Event provides a mechanism to centralize tracing information generated by V8, Node core, and userspace code. Tracing can be enabled by passing the `--trace-events-enabled` flag when starting a Node.js application. The set of categories for which traces are recorded can be specified using the `--trace-event-categories` flag followed by a list of comma separated category names. By default the `node`, `node.async_hooks`, and `v8` categories are enabled. ```txt node --trace-events-enabled --trace-event-categories v8,node,node.async_hooks server.js ``` Running Node.js with tracing enabled will produce log files that can be opened in the [`chrome://tracing`](https://www.chromium.org/developers/how-tos/trace-event-profiling-tool) tab of Chrome. The logging file is by default called `node_trace.${rotation}.log`, where `${rotation}` is an incrementing log-rotation id. The filepath pattern can be specified with `--trace-event-file-pattern` that accepts a template string that supports `${rotation}` and `${pid}`. For example: ```txt node --trace-events-enabled --trace-event-file-pattern '${pid}-${rotation}.log' server.js ``` Starting with Node 10.0.0, the tracing system uses the same time source as the one used by `process.hrtime()` however the trace-event timestamps are expressed in microseconds, unlike `process.hrtime()` which returns nanoseconds.