pinojs/pino · error · Error

only one of option.transport or stream can be specified

Error message

only one of option.transport or stream can be specified

What it means

Pino throws this when both a transport option and a stream argument are passed to pino(). A transport spawns a worker thread that builds its own destination stream, so a user-supplied stream would be contradictory. Only one output mechanism may be specified.

Source

Thrown at lib/tools.js:331

      stream.end()
    })
  } else {
    // For some reason istanbul is not detecting this, but it's there
    /* istanbul ignore next */
    // We do not have an event loop, so flush synchronously
    stream.flushSync()
  }
}

function createArgsNormalizer (defaultOptions) {
  return function normalizeArgs (instance, caller, opts = {}, stream) {
    // support stream as a string
    if (typeof opts === 'string') {
      stream = buildSafeSonicBoom({ dest: opts })
      opts = {}
    } else if (typeof stream === 'string') {
      if (opts && opts.transport) {
        throw Error('only one of option.transport or stream can be specified')
      }
      stream = buildSafeSonicBoom({ dest: stream })
    } else if (opts instanceof SonicBoom || opts.writable || opts._writableState) {
      stream = opts
      opts = {}
    } else if (opts.transport) {
      if (opts.transport instanceof SonicBoom || opts.transport.writable || opts.transport._writableState) {
        throw Error('option.transport do not allow stream, please pass to option directly. e.g. pino(transport)')
      }
      if (opts.transport.targets && opts.transport.targets.length && opts.formatters && typeof opts.formatters.level === 'function') {
        throw Error('option.transport.targets do not allow custom level formatters')
      }

      let customLevels
      if (opts.customLevels) {
        customLevels = opts.useOnlyCustomLevels ? opts.customLevels : Object.assign({}, opts.levels, opts.customLevels)
      }
      stream = transport({ caller, ...opts.transport, levels: customLevels })

View on GitHub (pinned to 5aa62305c5)

Solutions

Remove the second stream argument and configure the destination inside the transport options (e.g. target 'pino/file' with its options.destination).
Or drop opts.transport and keep passing the stream/destination string directly: pino('/path/to/log').
If using targets, put everything in transport.targets and pass no stream.
If the stream is required, wrap it with pino.destination and pass it as the sole stream argument instead of a transport.

Example fix

// before
const logger = pino({ transport: { target: 'pino/file', options: { destination: './app.log' } } }, './app.log')
// after
const logger = pino({ transport: { target: 'pino/file', options: { destination: './app.log' } } })

Defensive patterns

Strategy: validation

Validate before calling

function validatePinoArgs(opts, stream) {
  if (opts && opts.transport && stream != null) {
    throw new TypeError('Pass either opts.transport OR a stream, not both')
  }
  return true
}

Type guard

const isStreamLike = (s) => s && (typeof s === 'object') && (typeof s.writable === 'boolean' || '_writableState' in s)

Try / catch

try {
  const logger = pino(opts, stream)
} catch (err) {
  if (err.message.includes('only one of option.transport or stream')) {
    loggerFallback = pino(opts.transport ? opts : stream)
  } else throw err
}

Prevention

Pick one output mechanism per logger: transport OR stream, never both
In wrapper functions, assert the merged options don't contain both before calling pino
Prefer the transport API for new code and configure destinations inside the target options

When it happens

Trigger: Calling pino({ transport: { target: 'pino/file' } }, someStream) — i.e. opts.transport is truthy while the second argument is a string path or stream.

Common situations: Copying examples that use transport into code that already passes a destination string/file stream; migrating from pino(destination) to the newer transport API without removing the second argument; a wrapper function merging both config styles.

Related errors

AI-assisted analysis of pinojs/pino@5aa62305c5 (2026-09-02). Data as JSON: /api/errors/f717cccb5fe5754a. Report an issue: GitHub.