filemd5¶The filemd5 command returns the md5 hash for a single file stored using the GridFS specification. Client libraries use this command to verify that files are correctly written to MongoDB. The command takes the files_id of the file in question and the name of the GridFS root collection as arguments. For example:例如：
MongoDB computes the filemd5 using all data in the GridFS file object pulled sequentially from each chunk in the chunks collection.