yii\log\FileTarget::rotateFiles PHP Method

    protected function rotateFiles()
    {
        $file = $this->logFile;
        for ($i = $this->maxLogFiles; $i >= 0; --$i) {
            // $i == 0 is the original log file
            $rotateFile = $file . ($i === 0 ? '' : '.' . $i);
            if (is_file($rotateFile)) {
                // suppress errors because it's possible multiple processes enter into this section
                if ($i === $this->maxLogFiles) {
                    @unlink($rotateFile);
                } else {
                    if ($this->rotateByCopy) {
                        @copy($rotateFile, $file . '.' . ($i + 1));
                        if ($fp = @fopen($rotateFile, 'a')) {
                            @ftruncate($fp, 0);
                            @fclose($fp);
                        }
                        if ($this->fileMode !== null) {
                            @chmod($file . '.' . ($i + 1), $this->fileMode);
                        }
                    } else {
                        @rename($rotateFile, $file . '.' . ($i + 1));
                    }
                }
            }
        }
    }