File Formats
Total Page：16
File Type：pdf, Size：1020Kb
Load more
Recommended publications
-
IT1100 : Introduction to Operating Systems Chapter 15 What Is a Partition? What Is a Partition? Linux Partitions What Is Swap? M
IT1100 : Introduction to Operating Systems Chapter 15 What is a partition? A partition is just a logical division of your hard drive. This is done to put data in different locations for flexibility, scalability, ease of administration, and a variety of other reasons. One reason might be so you can install Linux and Windows side-by-side. What is a partition? Another reason is to encapsulate your data. Keeping your system files and user files separate can protect one or the otherfrom malware. Since file system corruption is local to a partition, you stand to lose only some of your data if an accident occurs. Upgrading and/or reformatting is easier when your personal files are stored on a separate partition. Limit data growth. Runaway processes or maniacal users can consume so much disk space that the operating system no longer has room on the hard drive for its bookkeeping operations. This will lead to disaster. By segregating space, you ensure that things other than the operating system die when allocated disk space is exhausted. Linux Partitions In Linux, a minimum of 1 partition is required for the / . Mounting is the action of connecting a filesystem/partition to a particular point in the / root filesystem. I.e. When a usb stick is inserted, it is assigned a particular mount point and is available to the filesytem tree. - In windows you might have an A:, or B:, or C:, all of which point to different filesystems. What is Swap? If RAM fills up, by running too many processes or a process with a memory leak, new processes will fail if your system doesn’t have a way to extend system memory. -
What Is Peer-To-Peer File Transfer? Bandwidth It Can Use
sharing, with no cap on the amount of commonly used to trade copyrighted music What is Peer-to-Peer file transfer? bandwidth it can use. Thus, a single NSF PC and software. connected to NSF’s LAN with a standard The Recording Industry Association of A peer-to-peer, or “P2P,” file transfer 100Mbps network card could, with KaZaA’s America tracks users of this software and has service allows the user to share computer files default settings, conceivably saturate NSF’s begun initiating lawsuits against individuals through the Internet. Examples of P2P T3 (45Mbps) internet connection. who use P2P systems to steal copyrighted services include KaZaA, Grokster, Gnutella, The KaZaA software assesses the quality of material or to provide copyrighted software to Morpheus, and BearShare. the PC’s internet connection and designates others to download freely. These services are set up to allow users to computers with high-speed connections as search for and download files to their “Supernodes,” meaning that they provide a How does use of these services computers, and to enable users to make files hub between various users, a source of available for others to download from their information about files available on other create security issues at NSF? computers. users’ PCs. This uses much more of the When configuring these services, it is computer’s resources, including bandwidth possible to designate as “shared” not only the and processing capability. How do these services function? one folder KaZaA sets up by default, but also The free version of KaZaA is supported by the entire contents of the user’s computer as Peer to peer file transfer services are highly advertising, which appears on the user well as any NSF network drives to which the decentralized, creating a network of linked interface of the program and also causes pop- user has access, to be searchable and users. -
Where Do You Want to Go Today? Escalating
Where Do You Want to Go Today? ∗ Escalating Privileges by Pathname Manipulation Suresh Chari Shai Halevi Wietse Venema IBM T.J. Watson Research Center, Hawthorne, New York, USA Abstract 1. Introduction We analyze filename-based privilege escalation attacks, In this work we take another look at the problem of where an attacker creates filesystem links, thereby “trick- privilege escalation via manipulation of filesystem names. ing” a victim program into opening unintended files. Historically, attention has focused on attacks against priv- We develop primitives for a POSIX environment, provid- ileged processes that open files in directories that are ing assurance that files in “safe directories” (such as writable by an attacker. One classical example is email /etc/passwd) cannot be opened by looking up a file by delivery in the UNIX environment (e.g., [9]). Here, an “unsafe pathname” (such as a pathname that resolves the mail-delivery directory (e.g., /var/mail) is often through a symbolic link in a world-writable directory). In group or world writable. An adversarial user may use today's UNIX systems, solutions to this problem are typ- its write permission to create a hard link or symlink at ically built into (some) applications and use application- /var/mail/root that resolves to /etc/passwd. A specific knowledge about (un)safety of certain directories. simple-minded mail-delivery program that appends mail to In contrast, we seek solutions that can be implemented in the file /var/mail/root can have disastrous implica- the filesystem itself (or a library on top of it), thus providing tions for system security. -
File Permissions Do Not Restrict Root
Filesystem Security 1 General Principles • Files and folders are managed • A file handle provides an by the operating system opaque identifier for a • Applications, including shells, file/folder access files through an API • File operations • Access control entry (ACE) – Open file: returns file handle – Allow/deny a certain type of – Read/write/execute file access to a file/folder by – Close file: invalidates file user/group handle • Access control list (ACL) • Hierarchical file organization – Collection of ACEs for a – Tree (Windows) file/folder – DAG (Linux) 2 Discretionary Access Control (DAC) • Users can protect what they own – The owner may grant access to others – The owner may define the type of access (read/write/execute) given to others • DAC is the standard model used in operating systems • Mandatory Access Control (MAC) – Alternative model not covered in this lecture – Multiple levels of security for users and documents – Read down and write up principles 3 Closed vs. Open Policy Closed policy Open Policy – Also called “default secure” • Deny Tom read access to “foo” • Give Tom read access to “foo” • Deny Bob r/w access to “bar” • Give Bob r/w access to “bar • Tom: I would like to read “foo” • Tom: I would like to read “foo” – Access denied – Access allowed • Tom: I would like to read “bar” • Tom: I would like to read “bar” – Access allowed – Access denied 4 Closed Policy with Negative Authorizations and Deny Priority • Give Tom r/w access to “bar” • Deny Tom write access to “bar” • Tom: I would like to read “bar” – Access -
21Files2.Pdf
Here is a portion of a Unix directory tree. The ovals represent files, the rectangles represent directories (which are really just special cases of files). A simple implementation of a directory consists of an array of pairs of component name and inode number, where the latter identifies the target file’s inode to the operating system (an inode is data structure maintained by the operating system that represents a file). Note that every directory contains two special entries, “.” and “..”. The former refers to the directory itself, the latter to the directory’s parent (in the case of the slide, the directory is the root directory and has no parent, thus its “..” entry is a special case that refers to the directory itself). While this implementation of a directory was used in early file systems for Unix, it suffers from a number of practical problems (for example, it doesn’t scale well for large directories). It provides a good model for the semantics of directory operations, but directory implementations on modern systems are more complicated than this (and are beyond the scope of this course). Here are two directory entries referring to the same file. This is done, via the shell, through the ln command which creates a (hard) link to its first argument, giving it the name specified by its second argument. The shell’s “ln” command is implemented using the link system call. Here are the (abbreviated) contents of both the root (/) and /etc directories, showing how /unix and /etc/image are the same file. Note that if the directory entry /unix is deleted (via the shell’s “rm” command), the file (represented by inode 117) continues to exist, since there is still a directory entry referring to it. -
Legacy Character Sets & Encodings
Legacy & Not-So-Legacy Character Sets & Encodings Ken Lunde CJKV Type Development Adobe Systems Incorporated bc ftp://ftp.oreilly.com/pub/examples/nutshell/cjkv/unicode/iuc15-tb1-slides.pdf Tutorial Overview dc • What is a character set? What is an encoding? • How are character sets and encodings different? • Legacy character sets. • Non-legacy character sets. • Legacy encodings. • How does Unicode fit it? • Code conversion issues. • Disclaimer: The focus of this tutorial is primarily on Asian (CJKV) issues, which tend to be complex from a character set and encoding standpoint. 15th International Unicode Conference Copyright © 1999 Adobe Systems Incorporated Terminology & Abbreviations dc • GB (China) — Stands for “Guo Biao” (国标 guóbiâo ). — Short for “Guojia Biaozhun” (国家标准 guójiâ biâozhün). — Means “National Standard.” • GB/T (China) — “T” stands for “Tui” (推 tuî ). — Short for “Tuijian” (推荐 tuîjiàn ). — “T” means “Recommended.” • CNS (Taiwan) — 中國國家標準 ( zhôngguó guójiâ biâozhün) in Chinese. — Abbreviation for “Chinese National Standard.” 15th International Unicode Conference Copyright © 1999 Adobe Systems Incorporated Terminology & Abbreviations (Cont’d) dc • GCCS (Hong Kong) — Abbreviation for “Government Chinese Character Set.” • JIS (Japan) — 日本工業規格 ( nihon kôgyô kikaku) in Japanese. — Abbreviation for “Japanese Industrial Standard.” — 〄 • KS (Korea) — 한국 공업 규격 (韓國工業規格 hangug gongeob gyugyeog) in Korean. — Abbreviation for “Korean Standard.” — ㉿ — Designation change from “C” to “X” on August 20, 1997. 15th International Unicode Conference Copyright © 1999 Adobe Systems Incorporated Terminology & Abbreviations (Cont’d) dc • TCVN (Vietnam) — Tiu Chun Vit Nam in Vietnamese. — Means “Vietnamese Standard.” • CJKV — Chinese, Japanese, Korean, and Vietnamese. 15th International Unicode Conference Copyright © 1999 Adobe Systems Incorporated What Is A Character Set? dc • A collection of characters that are intended to be used together to create meaningful text. -
Implementing Cross-Locale CJKV Code Conversion
Implementing Cross-Locale CJKV Code Conversion Ken Lunde CJKV Type Development Adobe Systems Incorporated bc ftp://ftp.oreilly.com/pub/examples/nutshell/ujip/unicode/iuc13-c2-paper.pdf ftp://ftp.oreilly.com/pub/examples/nutshell/ujip/unicode/iuc13-c2-slides.pdf Code Conversion Basics dc • Algorithmic code conversion — Within a single locale: Shift-JIS, EUC-JP, and ISO-2022-JP — A purely mathematical process • Table-driven code conversion — Required across locales: Chinese ↔ Japanese — Required when dealing with Unicode — Mapping tables are required — Can sometimes be faster than algorithmic code conversion— depends on the implementation September 10, 1998 Copyright © 1998 Adobe Systems Incorporated Code Conversion Basics (Cont’d) dc • CJKV character set differences — Different number of characters — Different ordering of characters — Different characters September 10, 1998 Copyright © 1998 Adobe Systems Incorporated Character Sets Versus Encodings dc • Common CJKV character set standards — China: GB 1988-89, GB 2312-80; GB 1988-89, GBK — Taiwan: ASCII, Big Five; CNS 5205-1989, CNS 11643-1992 — Hong Kong: ASCII, Big Five with Hong Kong extension — Japan: JIS X 0201-1997, JIS X 0208:1997, JIS X 0212-1990 — South Korea: KS X 1003:1993, KS X 1001:1992, KS X 1002:1991 — North Korea: ASCII (?), KPS 9566-97 — Vietnam: TCVN 5712:1993, TCVN 5773:1993, TCVN 6056:1995 • Common CJKV encodings — Locale-independent: EUC-*, ISO-2022-* — Locale-specific: GBK, Big Five, Big Five Plus, Shift-JIS, Johab, Unified Hangul Code — Other: UCS-2, UCS-4, UTF-7, UTF-8, -
Files and Processes (Review)
Files and Processes (review) Files and Processes (review) 1/61 Learning Objectives Files and Processes (review) I Review of files in standard C versus using system call interface for files I Review of buffering concepts I Review of process memory model I Review of bootup sequence in Linux and Microsoft Windows I Review of basic system calls under Linux: fork, exec, wait, exit, sleep, alarm, kill, signal I Review of similar basic system calls under MS Windows 2/61 Files Files and I Recall how we write a file copy program in standard C. Processes (review) #include <stdio.h> FILE *fopen(const char *path, const char *mode); size_t fread(void *ptr, size_t size, size_t nmemb, FILE *stream); size_t fwrite(const void *ptr, size_t size, size_t nmemb, FILE *stream); int fclose(FILE *fp); I We can also use character-based functions such as: #include <stdio.h> int fgetc(FILE *stream); int fputc(int c, FILE *stream); I With either approach, we can write a C program that will work on any operating system as it is in standard C. 3/61 Standard C File Copy Files and Processes (review) I Uses fread and fwrite. I files-processes/stdc-mycp.c 4/61 POSIX/Unix Files Files and Processes (review) I "On a UNIX system, everything is a file; if something is not a file, it is a process." I A directory is just a file containing names of other files. I Programs, services, texts, images, and so forth, are all files. I Input and output devices, and generally all devices, are considered to be files. -
The Application of File Identification, Validation, and Characterization Tools in Digital Curation
THE APPLICATION OF FILE IDENTIFICATION, VALIDATION, AND CHARACTERIZATION TOOLS IN DIGITAL CURATION BY KEVIN MICHAEL FORD THESIS Submitted in partial fulfillment of the requirements for the degree of Master of Science in Library and Information Science in the Graduate College of the University of Illinois at Urbana-Champaign, 2011 Urbana, Illinois Advisers: Research Assistant Professor Melissa Cragin Assistant Professor Jerome McDonough ABSTRACT File format identification, characterization, and validation are considered essential processes for digital preservation and, by extension, long-term data curation. These actions are performed on data objects by humans or computers, in an attempt to identify the type of a given file, derive characterizing information that is specific to the file, and validate that the given file conforms to its type specification. The present research reviews the literature surrounding these digital preservation activities, including their theoretical basis and the publications that accompanied the formal release of tools and services designed in response to their theoretical foundation. It also reports the results from extensive tests designed to evaluate the coverage of some of the software tools developed to perform file format identification, characterization, and validation actions. Tests of these tools demonstrate that more work is needed – particularly in terms of scalable solutions – to address the expanse of digital data to be preserved and curated. The breadth of file types these tools are anticipated to handle is so great as to call into question whether a scalable solution is feasible, and, more broadly, whether such efforts will offer a meaningful return on investment. Also, these tools, which serve to provide a type of baseline reading of a file in a repository, can be easily tricked. -
Chapter 10: File System
Chapter 10: File System Operating System Concepts – 9th Edition Silberschatz, Galvin and Gagne © 2013 Chapter 10: File System File Concept Access Methods Disk and Directory Structure File-System Mounting File Sharing Protection Operating System Concepts – 9th Edition 11.2 Silberschatz, Galvin and Gagne © 2013 Objectives To explain the function of file systems To describe the interfaces to file systems To discuss file-system design tradeoffs, including access methods, file sharing, file locking, and directory structures To explore file-system protection Operating System Concepts – 9th Edition 11.3 Silberschatz, Galvin and Gagne © 2013 File Concept Contiguous logical address space Types: Data numeric character binary Program Contents defined by file’s creator Many types Consider text file, source file, executable file Operating System Concepts – 9th Edition 11.4 Silberschatz, Galvin and Gagne © 2013 File Structure None - sequence of words, bytes Simple record structure Lines Fixed length Variable length Complex Structures Formatted document Relocatable load file Can simulate last two with first method by inserting appropriate control characters Who decides: Operating system Program Operating System Concepts – 9th Edition 11.5 Silberschatz, Galvin and Gagne © 2013 File Attributes Name – only information kept in human-readable form Identifier – unique tag (number) identifies file within file system Type – needed for systems that support different types Location – pointer to file location on device Size -
Man Pages Section 2 System Calls
man pages section 2: System Calls Part No: E29032 October 2012 Copyright © 1993, 2012, Oracle and/or its affiliates. All rights reserved. This software and related documentation are provided under a license agreement containing restrictions on use and disclosure and are protected by intellectual property laws. Except as expressly permitted in your license agreement or allowed by law, you may not use, copy, reproduce, translate, broadcast, modify, license, transmit, distribute, exhibit, perform, publish, or display any part, in any form, or by any means. Reverse engineering, disassembly, or decompilation of this software, unless required by law for interoperability, is prohibited. The information contained herein is subject to change without notice and is not warranted to be error-free. If you find any errors, please report them to us in writing. If this is software or related documentation that is delivered to the U.S. Government or anyone licensing it on behalf of the U.S. Government, the following notice is applicable: U.S. GOVERNMENT END USERS. Oracle programs, including any operating system, integrated software, any programs installed on the hardware, and/or documentation, delivered to U.S. Government end users are "commercial computer software" pursuant to the applicable Federal Acquisition Regulation and agency-specific supplemental regulations. As such, use, duplication, disclosure, modification, and adaptation of the programs, including anyoperating system, integrated software, any programs installed on the hardware, and/or documentation, shall be subject to license terms and license restrictions applicable to the programs. No other rights are granted to the U.S. Government. This software or hardware is developed for general use in a variety of information management applications. -
ERDA User Guide
User Guide 22. July 2021 1 / 116 Table of Contents Introduction..........................................................................................................................................3 Requirements and Terms of Use...........................................................................................................3 How to Access UCPH ERDA...............................................................................................................3 Sign-up.............................................................................................................................................4 Login................................................................................................................................................7 Overview..........................................................................................................................................7 Home................................................................................................................................................8 Files..................................................................................................................................................9 File Sharing and Data Exchange....................................................................................................15 Share Links...............................................................................................................................15 Workgroup Shared Folders.......................................................................................................19