Seldaek/monolog · error · InvalidArgumentException

Invalid filename format - format must contain at least `{dat

Error message

Invalid filename format - format must contain at least `{date}`, because otherwise rotating is impossible.

What it means

Error "Invalid filename format - format must contain at least `{date}`, because otherwise rotating is impossible." thrown in Seldaek/monolog.

Source

Thrown at src/Monolog/Handler/RotatingFileHandler.php:87

        }
    }

    /**
     * @inheritDoc
     */
    public function reset(): void
    {
        parent::reset();
    }

    /**
     * @return $this
     */
    public function setFilenameFormat(string $filenameFormat, string $dateFormat): self
    {
        $this->setDateFormat($dateFormat);
        if (substr_count($filenameFormat, '{date}') === 0) {
            throw new InvalidArgumentException(
                'Invalid filename format - format must contain at least `{date}`, because otherwise rotating is impossible.'
            );
        }
        $this->filenameFormat = $filenameFormat;
        $this->url = $this->getTimedFilename();
        $this->close();

        return $this;
    }

    /**
     * @inheritDoc
     */
    protected function write(LogRecord $record): void
    {
        // on the first record written, if the log is new, we rotate (once per day) after the log has been written so that the new file exists
        if (null === $this->mustRotate) {
            $this->mustRotate = null === $this->url || !file_exists($this->url);

View on GitHub (pinned to 57eb102834)

When it happens

Trigger: Thrown at src/Monolog/Handler/RotatingFileHandler.php:87 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of Seldaek/monolog@57eb102834 (2026-08-17). Data as JSON: /api/errors/7adb47b523734508. Report an issue: GitHub.