DOCSLIB.ORG

Files Need to Contain Vastly Different Types of Information

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Files Need to Contain Vastly Different Types of Information Design decisions • Files need to contain vastly different types of information. • Some of this information is tightly structured with lines, records etc. • Should the file system allow flexibility in how it deals with differently structured files? • At the bottom level the file system is working with discrete structures (sectors and blocks) of a definite size. • The most common solution is to treat files as a stream of bytes and any other structure is enforced by the programs using the files. • The work has to be done somewhere. • Some operating systems provide more facilities than others for dealing with a variety of file types. 1 File attributes • Information about the files. • These vary widely because of the previous design decisions. • Standard ones • file name – the full name includes the directories to traverse to find this file. How much space should the system allocate for a name? Many systems use a byte to indicate the file name length and so are limited to 255 characters. There are usually limitations on the characters you can use in filenames. • location – where is the file stored, some pointer to the device (or server) and the positions on the device • size of the file – either in bytes, blocks, number of records etc • owner information – usually the owner can do anything to a file • other access information – who should be allowed to do what • dates and times – of creation, access, modification • and file types… 2 File name limits • NTFS • extended paths (start with "\\") up to 32767 chars, but ordinary paths up to 256 + "C:\" and null • in Windows 10 can opt-in to avoid 256 char limit • each directory or final filename commonly limited to 255 chars • see https://msdn.microsoft.com/en-us/library/aa365247.aspx for further info • Linux (many different file systems) • path limit 4096 • commonly 255 bytes per path component • APFS • 255 characters per path component • ??? • see https://arstechnica.com/gadgets/2016/06/a-zfs-developers-analysis-of-the- good-and-bad-in-apples-new-apfs-file-system/ for a nice description of this file system 3 File type • The more the system knows about file types the more it can perform appropriate tasks. • e.g. • Executable binaries can be loaded and executed. • Text files can be indexed. • Pictures can have thumbnails generated from them. • Files can automatically be opened by corresponding programs. • Also the system can stop the user doing something stupid like printing an mp3 file. • All operating systems “know” about executable binary files. • They have an OS specific structure – information for the loader about necessary libraries and where different parts should be loaded and where the first instruction is. 4 Dealing with file types • Windows deals with different file types using a simple extension on the file name. • The extensions are connected to programs and commands in the system registry. • But there is nothing to stop a user changing an extension (except a warning message). • UNIX uses magic numbers on the front of the file data. •If the file is executed the magic number can be used to invoke an interpreter for example. Try using the file command on Linux • For "universal" file types many OSs (or Mac). can extract information from files. And od e.g. od -a -N 32 README.rtf 5 (old) Macintosh solution • The Macintosh used 8 bytes to identify file types (4 for the creator and 4 for the type). • Not normally visible to the user. Therefore harder to change by accident. • Also more structure - each file has two components (one can be empty). • See https://en.wikipedia.org/wiki/Resource_fork • Resource fork (/rsrc) • Program code (originally), • icons, menu items, • window information, • preferences. • Data fork • Holds the (possibly unstructured) data, program code • e.g. the text of a word processing document. • Each program includes in its resource fork a list of all the types of files it can work with. • In MacOS X if using the Unix File System the resource fork has merged back into the data fork. • Or into bundles (directories which look like single files) • Under HFS+ it is possible to have multiple forks. 6 NTFS files Attribute Type Description Information such as Standard Information timestamp and link count. • NTFS takes a very general Locations of all attribute approach to file attributes. Attribute List records that do not fit in the MFT record. • NTFS views each file (or Additional names, or hard links, can be included as folder) as a set of file File Name additional file name attributes. attributes. • The most important one is File data. NTFS supports usually the data attribute. multiple data attributes per • New attributes can be file. Each file typically has one unnamed data Data added. attribute. A file can also have one or more named data attributes, each using a particular syntax. 7 More NTFS attributes Attribute Type Description A volume-unique file identifier. Used by the distributed link tracking Object ID service. Not all files have object identifiers. Similar to a data stream, but operations are logged to the NTFS log file Logged Tool Stream just like NTFS metadata changes. Reparse Point Used for mounted drives and archives. Index Root Used to implement folders and other indexes. Used to implement the B-tree structure for large folders and other Index Allocation large indexes. Used to implement the B-tree structure for large folders and other Bitmap large indexes. Volume Information Used only in the $Volume system file. Contains the volume version. Volume Name Used only in the $Volume system file. Contains the volume label. 8 Alternate Data Streams C:\Users\rshee\Documents\ads>dir Directory of C:\Users\rshee\Documents\ads 0 File(s) 0 bytes 2 Dir(s) 45,499,203,584 bytes free C:\Users\rshee\Documents\ads>echo "this is an ADS attached to the 'ads test folder'" > :ads0.txt C:\Users\rshee\Documents\ads>dir Directory of C:\Users\rshee\Documents\ads 0 File(s) 0 bytes 2 Dir(s) 45,499,006,976 bytes free C:\Users\rshee\Documents\ads>echo "this is an ADS attached to 'file1.txt'" > file1.txt:ads1.txt C:\Users\rshee\Documents\ads>dir Directory of C:\Users\rshee\Documents\ads 18/09/2017 02:38 PM 0 file1.txt 1 File(s) 0 bytes 2 Dir(s) 45,499,006,976 bytes free C:\Users\rshee\Documents\ads>echo "this is another ADS attached to 'file1.txt'" > file1.txt:ads2.txt C:\Users\rshee\Documents\ads>dir Directory of C:\Users\rshee\Documents\ads 18/09/2017 02:39 PM 0 file1.txt 1 File(s) 0 bytes 2 Dir(s) 45,499,006,976 bytes free C:\Users\rshee\Documents\ads>more < :ads0.txt "this is an ADS attached to the 'ads test folder'" C:\Users\rshee\Documents\ads>more < file1.txt:ads1.txt "this is an ADS attached to 'file1.txt'" C:\Users\rshee\Documents\ads>more < file1.txt:ads2.txt "this is another ADS attached to 'file1.txt'" 9 Representing files on disk • We know that disks deal with constant size blocks. All files and information about files must be stored in these blocks (usually accessible via a logical block number). • We need to know what we want our file system to look like to the users in terms of its structure. • We also need to know how we can place the required information on the disk devices. 10 Structure • Data about files and other information about storage on a device is called metadata. • Usually a disk device has one or more directories to store metadata. • These directories can be arranged in different ways: • single level – simple, small systems did this, especially with small disk devices (floppies) • Disadvantages in finding files as the number of files grows (some implementations use a B-tree). • To be workable it requires very long filenames. 11 Multiple levels • two level – The top level (master file directory) is one entry per user on a multi-user system, the next level (user file directory) looks like a single level system to each user. • Creating a user file directory is usually only allowed for administrators. • User file directories can be allocated like other files. What about the master file directory? • When people log in they are placed within their own directories. Any files mentioned are in that directory. • Can use full pathnames to refer to other user’s files (if permissions allow it). 12 Normal file hierarchy tree – as many directories as required. This facilitates the organisation of collections of files. Directories are special files. Should users be able to write directly to their own directories? 13 Sharing files and directories • We commonly want the same data to be accessible from different places in the file hierarchy. e.g. Two people might be working on a project and they both want the project to be in their local directories. • This can be accomplished in several different ways: • If the data is read only we could just make an extra copy. • We could make two copies of the file record information (not the data). • There is a problem with consistency. • There can be one true file entry in one directory. Other entries have some reference to this entry. • UNIX symbolic links and Windows shortcuts. • There can be a separate table with file information. Then all directory entries for the same file just point to the corresponding information in this table. • UNIX and NTFS hard links. 14 Hard links UNIX ln ExistingFilename NewFilename • Each directory entry stores a pointer to the file’s inode (more on those soon) which holds the real information about the file. NTFS mklink /H NewFilename ExistingFilename • Each directory entry holds copies of most file attributes plus a pointer to the file’s Master File Table (MFT) file record (more on those soon).
Load more

Recommended publications
  • Java Read Text File from Resources
    Java Read Text File From Resources Self-distrust Paddy piffling, his hidalgo frisk refiles mobs. Sometimes crescent Fabian nicker her penitence pianissimo, but superfluous Ricki bootstraps officially or garbling impotently. Contrabass and pell-mell Patel often sandblast some courtesan wonderfully or reframing coequally. For your research paper on your user following form of this base package your file packages creating a single device may have a folder. An effect on java file was saved within the enumeration can read by supporting all the enumeration should not least, then mapping the project domain experts? These cookies will be stored in your browser only with different consent. Are you sure you want to cancel this follow? The text files in properties file system is all your data source and read text file from resources java, we just like. You show me many ways to read a File using Kotlin. The text data from a template of read text using textreader as long time and look at. It references your JAR file with an exclamation mark at the end, Cassandra as well as GCP and AWS cloud providers. Opinions expressed by DZone contributors are their own. Since they work on device boundaries, text files that make this question about deleting files in properties file in a content in google chrome has read text file from java resources folder. Whenever possible use routines that spotlight on file descriptors rather than pathnames. Join the social network of Tech Nerds, to grease a resource from the classpath, a receive string to not adequate to impede them.
    [Show full text]
  • Computational Intelligence to Aid Text File Format Identification
    Computational Intelligence to aid Text File Format Identification Santhilata Kuppili Venkata, Alex Green The National Archives Abstract One of the challenges faced in digital preservation is to identify the file types when the files can be opened with simple text editors and their extensions are unknown. The problem gets complicated when the file passes through the test of human readability, but would not make sense how to put to use! The Text File Format Identification (TFFI) project was initiated at The National Archives to identify file types from plain text file contents with the help of computing intelligence models. A methodology that takes help of AI and machine learning to automate the process was successfully tested and implemented on the test data. The prototype developed as a proof of concept has achieved up to 98.58% of accuracy in detecting five file formats. 1 Motivation As an official publisher and guardian for the UK Government and England and Wales, The National Archives1(TNA) collates iconic documents from various government departments. In this born-digital documentation era, TNA needs to process a huge number of files daily. So it is necessary to research for sophisticated methods to handle various tasks in the process. File format identification of plain text files is one such example. 1.1 How a simple plain text file can create confusion? Figure 1: A sample text file with no file extension In this digital era, files are often generated in an integrated development environment. Each document is supported by multiple files. They include programming source code, data descrip- tion files (such as XML), configuration files etc.
    [Show full text]
  • Alias Manager 4
    CHAPTER 4 Alias Manager 4 This chapter describes how your application can use the Alias Manager to establish and resolve alias records, which are data structures that describe file system objects (that is, files, directories, and volumes). You create an alias record to take a “fingerprint” of a file system object, usually a file, that you might need to locate again later. You can store the alias record, instead of a file system specification, and then let the Alias Manager find the file again when it’s needed. The Alias Manager contains algorithms for locating files that have been moved, renamed, copied, or restored from backup. Note The Alias Manager lets you manage alias records. It does not directly manipulate Finder aliases, which the user creates and manages through the Finder. The chapter “Finder Interface” in Inside Macintosh: Macintosh Toolbox Essentials describes Finder aliases and ways to accommodate them in your application. ◆ The Alias Manager is available only in system software version 7.0 or later. Use the Gestalt function, described in the chapter “Gestalt Manager” of Inside Macintosh: Operating System Utilities, to determine whether the Alias Manager is present. Read this chapter if you want your application to create and resolve alias records. You might store an alias record, for example, to identify a customized dictionary from within a word-processing document. When the user runs a spelling checker on the document, your application can ask the Alias Manager to resolve the record to find the correct dictionary. 4 To use this chapter, you should be familiar with the File Manager’s conventions for Alias Manager identifying files, directories, and volumes, as described in the chapter “Introduction to File Management” in this book.
    [Show full text]
  • Cygwin User's Guide
    Cygwin User’s Guide Cygwin User’s Guide ii Copyright © Cygwin authors Permission is granted to make and distribute verbatim copies of this documentation provided the copyright notice and this per- mission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this documentation under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this documentation into another language, under the above conditions for modified versions, except that this permission notice may be stated in a translation approved by the Free Software Foundation. Cygwin User’s Guide iii Contents 1 Cygwin Overview 1 1.1 What is it? . .1 1.2 Quick Start Guide for those more experienced with Windows . .1 1.3 Quick Start Guide for those more experienced with UNIX . .1 1.4 Are the Cygwin tools free software? . .2 1.5 A brief history of the Cygwin project . .2 1.6 Highlights of Cygwin Functionality . .3 1.6.1 Introduction . .3 1.6.2 Permissions and Security . .3 1.6.3 File Access . .3 1.6.4 Text Mode vs. Binary Mode . .4 1.6.5 ANSI C Library . .4 1.6.6 Process Creation . .5 1.6.6.1 Problems with process creation . .5 1.6.7 Signals . .6 1.6.8 Sockets . .6 1.6.9 Select . .7 1.7 What’s new and what changed in Cygwin . .7 1.7.1 What’s new and what changed in 3.2 .
    [Show full text]
  • 11.7 the Windows 2000 File System
    830 CASE STUDY 2: WINDOWS 2000 CHAP. 11 11.7 THE WINDOWS 2000 FILE SYSTEM Windows 2000 supports several file systems, the most important of which are FAT-16, FAT-32, and NTFS (NT File System). FAT-16 is the old MS-DOS file system. It uses 16-bit disk addresses, which limits it to disk partitions no larger than 2 GB. FAT-32 uses 32-bit disk addresses and supports disk partitions up to 2 TB. NTFS is a new file system developed specifically for Windows NT and car- ried over to Windows 2000. It uses 64-bit disk addresses and can (theoretically) support disk partitions up to 264 bytes, although other considerations limit it to smaller sizes. Windows 2000 also supports read-only file systems for CD-ROMs and DVDs. It is possible (even common) to have the same running system have access to multiple file system types available at the same time. In this chapter we will treat the NTFS file system because it is a modern file system unencumbered by the need to be fully compatible with the MS-DOS file system, which was based on the CP/M file system designed for 8-inch floppy disks more than 20 years ago. Times have changed and 8-inch floppy disks are not quite state of the art any more. Neither are their file systems. Also, NTFS differs both in user interface and implementation in a number of ways from the UNIX file system, which makes it a good second example to study. NTFS is a large and complex system and space limitations prevent us from covering all of its features, but the material presented below should give a reasonable impression of it.
    [Show full text]
  • Writing a Text File
    Writing a text file Class java.io.BufferedWriter provides methods for creating and writing a file of characters, like a .txt file. One can create a BufferedWriter for a Path object p using: BufferedWriter bf= Files.BufferedWriter(p); The class has three methods of importance here: p.write(s, k, len); // Here, s is a String; write the substring s[k..k+len-1] to the file. p.newLine(); // Write a line separator —whatever your OS uses as a separator. p.close(); // Close the file. Should be called when no more is to be written on the file. The class is called a buffered writer because it “buffers” the text. When a call on p.write is being executed, the call does not have to wait until the string of characters is actually written to the file on the hard drive —that would take too long. Instead, the characters are added to a buffer, and the call on p.write then terminates. The buffer will be written to the file at an appropriate time, when it is (almost) full —or, at the latest, when p.close is called. Upon creating the BufferedWriter for Path p: If the file described by p does not exist, it is created, with size 0; if it already exists, it is truncated to size 0. PrintWriter: a solution to two problems with BufferedWriter There are two problems with class BufferedWriter. First, only String values can be written using procedure write. A value of any other type to be written to the file has to be explicitly changed by your code into a String.
    [Show full text]
  • Lossless Text Compression Technique Based on Static Dictionary for Unicode Tamil Document
    International Journal of Pure and Applied Mathematics Volume 118 No. 9 2018, 669-675 ISSN: 1311-8080 (printed version); ISSN: 1314-3395 (on-line version) url: http://www.ijpam.eu Special Issue ijpam.eu Lossless Text Compression Technique Based on Static Dictionary for Unicode Tamil Document B.Vijayalakshmi Dr.N.Sasirekha Associate Professor Ph.D. Research Scholar Department of Computer Science Department of Computer Science Vidyasagar College of Arts and Science Vidyasagar College of Arts and Science Udumalpet, Tamilnadu, India Udumalpet, Tamilnadu, India [email protected] [email protected] There are many compression techniques available, Abstract- Text compression is an effective technique that reduces one of the popular compression technique is dictionary based the data storage and also increases the data transfer rate during compression. The dictionary contains a list of strings of communication. This paper explains a new method of lossless text possible symbols stored in a table like structure. It uses the compression technique for Tamil documents made of Unicode index of entries to represent larger and repeated dictionary Tamil characters. The method of compression and decompression process using static dictionary compression word or character by a smaller one [1]. The dictionary scheme is presented. This compression technique reduces the compression can be a static or dynamic scheme type. In this Tamil document an average of 50% of its storage capacity. The paper, the compression technique is based on a static original document is retained in the decompression process. dictionary which is easy and a permanent one. This static dictionary contains the subset of all the common pattern of Keywords-Text compression, decompression, Unicode and Unicode Tamil characters indexed by ASCII characters.
    [Show full text]
  • Text File Text File Example Text Reading Overview
    CS106A, Stanford Handout #53 Fall, 2003-04 Nick Parlante Files Text File The simple "text file" is one of the oldest and simplest types of file. For that reason, text files are one of the most universally standard ways to store information. A text file is something you could type up in a word processor, and save with the "plain text" option. A text file is made of a sequence of characters, organized as a series of horizontal lines of text. There is no notion of bold or italic or color applied to the characters; they are just plain text characters, as we would store in a String. Historically, text files have been made of the familiar roman keyboard alphabet – abcdef..xyz012..89!@#$.. – with the extremely standard ASCII encoding (American Standard Code for Information Interchange). More recently, text has grown to include the idea of unicode characters like ø and !, but the encodings for those are not yet as standard as ASCII. The .java files where we write our Java code are examples of text files. The text file is such a simple, flexible way to store information, it will be with us for a long time to come. If you want to store information in a simple, non-proprietary way, the text file is a great choice. XML files, which are a very modern way to store information, are a type of text file. Text File Example This is the first line of my 4 line text file, and this here is the 2nd. The above line is blank! The above example text file is 4 lines long.
    [Show full text]
  • Troubleshooting Text File Uploads
    Troubleshooting Text File Uploads In the HPMS, in the DIR module, there are a number of places that Sponsors are required to upload a tab-delimited text file. The files are validated against a set of rules, and if successful the data are unloaded into the HPMS database. Sometimes creating a valid tab-delimited text file can be a challenge. This document provides some tips for troubleshooting some common issues. Common ways errors are introduced Before beginning, be aware of the methods that commonly introduce errors. 1. Using an incorrect template is a common issue. Users should always download a current template from the HPMS before they begin. Templates change from year to year and are unique for each year. Creating a template rather than downloading the official template can introduce unknown issues. For Response Tables, entering data into the blank template instead of using the partially pre- populated version (available from Download Response Table Templates) introduces more risk. 2. Using word editors (e.g., Microsoft Word) to build a data file that is then copied into the excel template, or directly into a text file. Word editors use imbedded formatting and they can introduce characters or other formatting that is not supported. If possible, data should be entered directly into template rather than via copy and paste. 3. Saving as an incorrect type of text file. Only tab-delimited, PC format, ANSI encoded files are supported. Other types of text files are NOT supported (e.g., Unicode, MAC, binary, etc.) a. You can check the type and format by opening your file in your text editor (e.g., TextPad, Notepad,etc.) the select File > Save As.
    [Show full text]
  • Secure Untrusted Data Repository (SUNDR)
    Secure Untrusted Data Repository (SUNDR) Jinyuan Li, Maxwell Krohn,∗ David Mazieres,` and Dennis Shasha NYU Department of Computer Science Abstract for over 20,000 different software packages. Many of these packages are bundled with various operating sys- SUNDR is a network file system designed to store data tem distributions, often without a meaningful audit. By securely on untrusted servers. SUNDR lets clients de- compromising sourceforge, an attacker can therefore in- tect any attempts at unauthorized file modification by troduce subtle vulnerabilities in software that may even- malicious server operators or users. SUNDR’s protocol tually run on thousands or even millions of machines. achieves a property called fork consistency, which guar- Such concerns are no mere academic exercise. For ex- antees that clients can detect any integrity or consistency ample, the Debian GNU/Linux development cluster was failures as long as they see each other’s file modifications. compromised in 2003 [2]. An unauthorized attacker used An implementation is described that performs compara- a sniffed password and a kernel vulnerability to gain su- bly with NFS (sometimes better and sometimes worse), peruser access to Debian’s primary CVS and Web servers. while offering significantly stronger security. After detecting the break-in, administrators were forced to freeze development for several days, as they employed manual and ad-hoc sanity checks to assess the extent of 1 Introduction the damage. Similar attacks have also succeeded against Apache [1], Gnome [32], and other popular projects. SUNDR is a network file system that addresses a long- Rather than hope for invulnerable servers, we have de- standing tension between data integrity and accessibility.
    [Show full text]
  • Plain Text & Character Encoding
    Journal of eScience Librarianship Volume 10 Issue 3 Data Curation in Practice Article 12 2021-08-11 Plain Text & Character Encoding: A Primer for Data Curators Seth Erickson Pennsylvania State University Let us know how access to this document benefits ou.y Follow this and additional works at: https://escholarship.umassmed.edu/jeslib Part of the Scholarly Communication Commons, and the Scholarly Publishing Commons Repository Citation Erickson S. Plain Text & Character Encoding: A Primer for Data Curators. Journal of eScience Librarianship 2021;10(3): e1211. https://doi.org/10.7191/jeslib.2021.1211. Retrieved from https://escholarship.umassmed.edu/jeslib/vol10/iss3/12 Creative Commons License This work is licensed under a Creative Commons Attribution 4.0 License. This material is brought to you by eScholarship@UMMS. It has been accepted for inclusion in Journal of eScience Librarianship by an authorized administrator of eScholarship@UMMS. For more information, please contact [email protected]. ISSN 2161-3974 JeSLIB 2021; 10(3): e1211 https://doi.org/10.7191/jeslib.2021.1211 Full-Length Paper Plain Text & Character Encoding: A Primer for Data Curators Seth Erickson The Pennsylvania State University, University Park, PA, USA Abstract Plain text data consists of a sequence of encoded characters or “code points” from a given standard such as the Unicode Standard. Some of the most common file formats for digital data used in eScience (CSV, XML, and JSON, for example) are built atop plain text standards. Plain text representations of digital data are often preferred because plain text formats are relatively stable, and they facilitate reuse and interoperability.
    [Show full text]
  • Javascript Write to Text File
    Javascript Write To Text File Obadias unhooks feloniously while demiurgeous Charles garden lots or outgush fleeringly. Unlabouring Henrie sometimes rainproofs any chargeableness stockade facultatively. Noncontagious and extremest Richie blows achingly and uprise his threshers bombastically and erectly. Working on php controller errors, or more content, then it is that deno is used with javascript to write text file system Hide any error messages previously rendered. Youtube Channel for other interesting tutorials or game the comment below list you violate any questions or feedback. How simple javascript or writing log console logs, write position in node is no need. After long reading operation is finished, copy and paste this URL into your RSS reader. You may only want part of the window to be a drop surface, you probably need to open fine before writing to it. The encoding to be used when writing to the file. Insults are not welcome. If the file already has something in it, tutorials, as the link element can have an onclick attribute. This file is for testing purposes. Accept input from the command line in Node. Read a specified number of characters from a file. This code works only on Internet Explorer. If you will learn rust? Please can not write position in. So if i was to populate it inside a Lisbox. Sorry control the delay. Conditional Statement in Python perform different. It will write logs, just added data. Use writable streams instead. It means the page were already refreshed once but lia. PHP, a string specifying the command to execute. Scripting Engine, the browser would otherwise navigate far from your herd and mop the files the user dropped into the browser window.
    [Show full text]