Understanding operating systems 5th ed ch16

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Understanding operating systems 5th ed ch16

  1. 1. Understanding Operating Systems Fifth Edition Chapter 16 Linux Operating System
  2. 2. Learning Objectives <ul><li>The design goals for the Linux operating system </li></ul><ul><li>The significance of using files to manipulate devices </li></ul><ul><li>The differences between command-driven and menu-driven interfaces </li></ul><ul><li>The roles of the Memory, Device, File, Processor, and Network Managers </li></ul><ul><li>Some strengths and weaknesses of Linux </li></ul>Understanding Operating Systems, Fifth Edition
  3. 3. Overview <ul><li>POSIX-compliant </li></ul><ul><li>Portable </li></ul><ul><ul><li>Versions for cell phones, supercomputers, and computing systems in between </li></ul></ul><ul><li>Source code: freely available </li></ul><ul><ul><li>Configurable: run any device, meet any specification </li></ul></ul><ul><li>User interface </li></ul><ul><ul><li>Powerful desktop GUIs attracts users </li></ul></ul><ul><li>Highly modular </li></ul><ul><ul><li>Multiple modules load and unload on demand </li></ul></ul><ul><ul><ul><li>Technically robust operating system </li></ul></ul></ul>Understanding Operating Systems, Fifth Edition
  4. 4. History <ul><li>Developed by Linus Torvalds (1991) </li></ul><ul><li>Original purpose </li></ul><ul><ul><li>Maximize Intel 80386 microprocessor’s limited capabilities </li></ul></ul><ul><ul><li>Roots </li></ul></ul><ul><ul><ul><li>Minix: miniature UNIX with more functionality </li></ul></ul></ul><ul><li>First version meant for small microcomputer </li></ul><ul><ul><li>Expensive commercial computer features </li></ul></ul><ul><ul><ul><li>Flexibility and functionality </li></ul></ul></ul><ul><ul><li>Brought UNIX features to small computer </li></ul></ul>Understanding Operating Systems, Fifth Edition
  5. 5. History (continued) <ul><li>Open-source program </li></ul><ul><ul><li>Updates accepted from anyone </li></ul></ul><ul><li>User interface </li></ul><ul><ul><li>Originally typed and cryptic commands </li></ul></ul><ul><ul><li>Today </li></ul></ul><ul><ul><ul><li>Command-driven interface (Terminal mode) </li></ul></ul></ul><ul><ul><ul><li>Graphical user interface (GUI) </li></ul></ul></ul><ul><li>Red Hat Linux provided initial primary support </li></ul><ul><ul><li>World’s leading Linux distributor (until 2003) </li></ul></ul><ul><li>GNU General Public License </li></ul>Understanding Operating Systems, Fifth Edition
  6. 6. Understanding Operating Systems, Fifth Edition
  7. 7. History (continued) Understanding Operating Systems, Fifth Edition
  8. 8. Design Goals <ul><li>Three goals </li></ul><ul><ul><li>Modularity </li></ul></ul><ul><ul><li>Simplicity </li></ul></ul><ul><ul><li>Portability </li></ul></ul><ul><li>Numerous standard utilities </li></ul><ul><ul><li>Eliminates need to write special code </li></ul></ul><ul><ul><li>Used in combination for specific tasks </li></ul></ul><ul><li>Numerous functions </li></ul><ul><li>Conforms to IEEE POSIX specifications </li></ul><ul><ul><li>Portable Operating System Interface for Computer Environments </li></ul></ul>Understanding Operating Systems, Fifth Edition
  9. 9. Design Goals (continued) Understanding Operating Systems, Fifth Edition
  10. 10. Memory Management <ul><li>Space allocation </li></ul><ul><ul><li>Kernel: 1 GB high order memory </li></ul></ul><ul><ul><li>Executing processes: 3 GB memory </li></ul></ul><ul><li>Process execution </li></ul><ul><ul><li>Segment fixed size </li></ul></ul><ul><ul><li>System calls change segment size </li></ul></ul><ul><li>Memory protection </li></ul><ul><ul><li>Based on information type stored in address space region for process </li></ul></ul>Understanding Operating Systems, Fifth Edition
  11. 11. Memory Management (continued) <ul><li>Page loading </li></ul><ul><ul><li>Least recently used algorithm (LRU) </li></ul></ul><ul><ul><li>Maintains a dynamically managed memory area and page cache (new and old pages inserted and deleted) </li></ul></ul><ul><li>System page tables </li></ul><ul><ul><li>Tracks free and busy pages </li></ul></ul><ul><li>Virtual memory </li></ul><ul><ul><li>Managed using multiple-level table hierarchy </li></ul></ul><ul><ul><ul><li>64- and 32-bit architectures </li></ul></ul></ul><ul><ul><li>Added flexibility with swap devices </li></ul></ul><ul><ul><ul><li>May deactivate without rebooting </li></ul></ul></ul>Understanding Operating Systems, Fifth Edition
  12. 12. Memory Management (continued) <ul><li>Virtual memory managed using multiple-level table hierarchy </li></ul><ul><ul><li>Four fields in virtual address </li></ul></ul>Understanding Operating Systems, Fifth Edition
  13. 13. Memory Management (continued) Understanding Operating Systems, Fifth Edition
  14. 14. Memory Management (continued) <ul><li>Buddy algorithm </li></ul><ul><ul><li>Grouping and splitting equal-sized page frames </li></ul></ul><ul><ul><ul><li>Give more contiguous space to job </li></ul></ul></ul><ul><li>Page replacement algorithm </li></ul><ul><ul><li>Clock page replacement policy expanded version </li></ul></ul><ul><ul><li>Uses eight-bit byte to track page’s activity </li></ul></ul><ul><ul><ul><li>Referred to as “age” </li></ul></ul></ul>Understanding Operating Systems, Fifth Edition
  15. 15. Memory Management (continued) Understanding Operating Systems, Fifth Edition
  16. 16. Processor Management <ul><li>Uses same parent-child process management design found in UNIX </li></ul><ul><li>“ Personality” concept </li></ul><ul><ul><li>Allow processes from other operating systems to be executed </li></ul></ul>Understanding Operating Systems, Fifth Edition
  17. 17. Organization of Table of Processes <ul><li>Descriptor: references process </li></ul><ul><li>Contains approximately 70 fields </li></ul><ul><ul><li>Describes process attributes </li></ul></ul><ul><ul><ul><li>Information needed to manage process </li></ul></ul></ul><ul><ul><li>Dynamically allocated by kernel </li></ul></ul><ul><ul><ul><li>Process execution time </li></ul></ul></ul><ul><ul><li>Organized by doubly linked lists </li></ul></ul><ul><ul><ul><li>“ Next run” field </li></ul></ul></ul><ul><ul><ul><li>“ Previously run” field </li></ul></ul></ul><ul><ul><li>Scheduler manages and updates descriptors </li></ul></ul><ul><ul><ul><li>Macros </li></ul></ul></ul>Understanding Operating Systems, Fifth Edition
  18. 18. Process Synchronization <ul><li>Wait queues and semaphores </li></ul><ul><ul><li>Synchronize two processes with each other </li></ul></ul><ul><li>Wait queue </li></ul><ul><ul><li>Linked circular list of process descriptors </li></ul></ul><ul><ul><li>Problems solved </li></ul></ul><ul><ul><ul><li>Mutual exclusion and producers and consumers </li></ul></ul></ul><ul><li>Semaphore structure </li></ul><ul><ul><li>Three fields (semaphore counter, number of waiting processes, list of processes waiting for semaphore) </li></ul></ul><ul><ul><ul><li>Counter contains binary values </li></ul></ul></ul><ul><ul><ul><li>Except if several units of one resource available </li></ul></ul></ul>Understanding Operating Systems, Fifth Edition
  19. 19. Process Management <ul><li>Linux scheduler </li></ul><ul><ul><li>Scans processes list in READY state </li></ul></ul><ul><ul><li>Chooses process to execute </li></ul></ul><ul><ul><ul><li>Using predefined criteria </li></ul></ul></ul><ul><li>Three scheduling types </li></ul><ul><ul><li>Real-time processes (two) </li></ul></ul><ul><ul><li>Normal processes (one) </li></ul></ul><ul><li>Process scheduling policy determination </li></ul><ul><ul><li>Combination of type and priority </li></ul></ul>Understanding Operating Systems, Fifth Edition
  20. 20. Process Management (continued) Understanding Operating Systems, Fifth Edition
  21. 21. Process Management (continued) <ul><li>First type </li></ul><ul><ul><li>Highest priority (SCHED_FIFO) </li></ul></ul><ul><ul><ul><li>First in, first out algorithm </li></ul></ul></ul><ul><ul><li>Not preemptible </li></ul></ul><ul><ul><li>Runs to completion unless: </li></ul></ul><ul><ul><ul><li>Process goes into WAIT state </li></ul></ul></ul><ul><ul><ul><li>Process relinquishes processor voluntarily </li></ul></ul></ul><ul><ul><li>All FIFO processes complete </li></ul></ul><ul><ul><ul><li>Scheduler processes lower priority types </li></ul></ul></ul>Understanding Operating Systems, Fifth Edition
  22. 22. Process Management (continued) <ul><li>Second type </li></ul><ul><ul><li>Medium priority (SCHED_RR) </li></ul></ul><ul><ul><ul><li>Round robin algorithm with small time quantum </li></ul></ul></ul><ul><ul><li>Time quantum expires </li></ul></ul><ul><ul><ul><li>Other higher priority processes (FIFO, RR ) selected and executed </li></ul></ul></ul><ul><ul><ul><li>Before first process allowed to complete </li></ul></ul></ul><ul><li>Third type </li></ul><ul><ul><li>Low priority (SCHED_OTHER) </li></ul></ul><ul><ul><li>Executed if no higher priority processes in READY queue </li></ul></ul>Understanding Operating Systems, Fifth Edition
  23. 23. Device Management <ul><li>Device independent </li></ul><ul><ul><li>Improves portability </li></ul></ul><ul><li>Device drivers </li></ul><ul><ul><li>Supervise data transmission </li></ul></ul><ul><ul><ul><li>Between main memory and peripheral unit </li></ul></ul></ul><ul><li>Devices assigned </li></ul><ul><ul><li>Name </li></ul></ul><ul><ul><li>Descriptors </li></ul></ul><ul><ul><ul><li>Further identify each device </li></ul></ul></ul><ul><ul><ul><li>Stored in device directory </li></ul></ul></ul>Understanding Operating Systems, Fifth Edition
  24. 24. Device Management (continued) Understanding Operating Systems, Fifth Edition
  25. 25. Device Management (continued) <ul><li>Device drivers </li></ul><ul><ul><li>Comprehensive collection in Linux </li></ul></ul><ul><li>Required driver not available </li></ul><ul><ul><li>Obtain from another source </li></ul></ul><ul><ul><ul><li>Install separately </li></ul></ul></ul><ul><ul><li>Manually write the driver </li></ul></ul><ul><ul><ul><li>Requires skilled programmer </li></ul></ul></ul>Understanding Operating Systems, Fifth Edition
  26. 26. Device Classifications <ul><li>Device identification </li></ul><ul><ul><li>Minor device number </li></ul></ul><ul><ul><ul><li>Passed to device driver as an argument </li></ul></ul></ul><ul><ul><ul><li>Accesses one of several identical physical devices </li></ul></ul></ul><ul><ul><li>Major device number </li></ul></ul><ul><ul><ul><li>Index to array to access appropriate code </li></ul></ul></ul><ul><li>Configuration table for each class </li></ul><ul><ul><li>Entry point into driver </li></ul></ul><ul><ul><li>Only connection between system code and driver </li></ul></ul><ul><ul><li>Importance </li></ul></ul><ul><ul><ul><li>Allows quick creation of device drivers </li></ul></ul></ul>Understanding Operating Systems, Fifth Edition
  27. 27. Device Drivers <ul><li>Support for standard classes introduced by UNIX </li></ul><ul><li>Allow new device classes supporting new technology </li></ul><ul><li>Device classes not rigid </li></ul><ul><ul><li>Create large, complex, multiple function drivers </li></ul></ul><ul><ul><li>Discouraged because: </li></ul></ul><ul><ul><ul><li>Users share code, demand simple drivers </li></ul></ul></ul><ul><ul><ul><li>Modular code supports system scalability and extendibility goal </li></ul></ul></ul><ul><ul><li>Encouraged: drivers maximizing system’s effective device usage </li></ul></ul>Understanding Operating Systems, Fifth Edition
  28. 28. Device Drivers (continued) <ul><li>Notable feature </li></ul><ul><ul><li>Accept new device drivers on the fly </li></ul></ul><ul><ul><ul><li>System up and running </li></ul></ul></ul><ul><ul><ul><li>No reboot necessary </li></ul></ul></ul>Understanding Operating Systems, Fifth Edition
  29. 29. Device Classes <ul><li>Three standard classes </li></ul>Understanding Operating Systems, Fifth Edition
  30. 30. Device Classes (continued) <ul><li>Character (char) devices </li></ul><ul><ul><li>Accessed as a stream of bytes </li></ul></ul><ul><ul><ul><li>Communications port, monitor, other byte-stream-fed device </li></ul></ul></ul><ul><ul><li>Implement open, close, read, write system calls </li></ul></ul><ul><ul><li>Accessed by file system nodes </li></ul></ul><ul><ul><ul><li>Look like ordinary data area </li></ul></ul></ul><ul><ul><li>Drivers treated as ordinary files </li></ul></ul><ul><ul><ul><li>Exception: drivers are data channels accessed sequentially </li></ul></ul></ul>Understanding Operating Systems, Fifth Edition
  31. 31. Device Classes (continued) <ul><li>Block devices </li></ul><ul><ul><li>Host a file system (hard disk) </li></ul></ul><ul><ul><li>Accessed by file system nodes in /dev directory </li></ul></ul><ul><ul><ul><li>Transfer in blocks of data </li></ul></ul></ul><ul><ul><li>Similarity to char driver </li></ul></ul><ul><ul><ul><li>Appear as ordinary files </li></ul></ul></ul><ul><ul><li>Dissimilarity to char driver </li></ul></ul><ul><ul><ul><li>Access file system in connection with device (not possible with char device) </li></ul></ul></ul>Understanding Operating Systems, Fifth Edition
  32. 32. Device Classes (continued) <ul><li>Network interfaces </li></ul><ul><ul><li>Function </li></ul></ul><ul><ul><ul><li>Send and receive information packets </li></ul></ul></ul><ul><ul><ul><li>Directed by network subsystem </li></ul></ul></ul><ul><ul><li>Network device functions </li></ul></ul><ul><ul><ul><li>Relate to packet transmission </li></ul></ul></ul><ul><ul><ul><li>Not read and write calls </li></ul></ul></ul><ul><ul><ul><li>Dissimilar from block and char </li></ul></ul></ul><ul><li>System device handled by device driver </li></ul><ul><ul><li>Under direction of Linux subsystem </li></ul></ul>Understanding Operating Systems, Fifth Edition
  33. 33. Device Classes (continued) <ul><li>Open and release </li></ul><ul><ul><li>Allocate and deallocate the appropriate device </li></ul></ul><ul><ul><li>Open operation example </li></ul></ul><ul><ul><ul><li>Verify device available and working </li></ul></ul></ul><ul><ul><ul><li>Increase device usage counter by one (subsystem knows module cannot be unloaded until file appropriately closed) </li></ul></ul></ul><ul><ul><ul><li>Initialize device so old data is removed and device ready to accept new data </li></ul></ul></ul><ul><ul><ul><li>Identify minor number and update appropriate pointer (if necessary) </li></ul></ul></ul><ul><ul><ul><li>Allocate appropriate data structure </li></ul></ul></ul>Understanding Operating Systems, Fifth Edition
  34. 34. Device Classes (continued) <ul><li>Open and release (continued) </li></ul><ul><ul><li>Release operation example </li></ul></ul><ul><ul><ul><li>Deallocate resources allocated with open function </li></ul></ul></ul><ul><ul><ul><li>Shut down device </li></ul></ul></ul><ul><ul><ul><li>Reduce usage counter by one (device released to another module) </li></ul></ul></ul>Understanding Operating Systems, Fifth Edition
  35. 35. File Management <ul><li>Data structures </li></ul><ul><li>Filename conventions </li></ul><ul><li>Directory listings </li></ul>Understanding Operating Systems, Fifth Edition
  36. 36. Data Structures <ul><li>Files organized in directories </li></ul><ul><ul><li>Connected in treelike structure </li></ul></ul><ul><li>Five file types </li></ul>Understanding Operating Systems, Fifth Edition
  37. 37. Filename Conventions <ul><li>Case sensitive </li></ul><ul><ul><li>Recognizes uppercase and lowercase letters </li></ul></ul><ul><li>Up to 255 characters long </li></ul><ul><li>Contain alphabetic characters, underscores, numbers </li></ul><ul><li>File suffixes: optional </li></ul><ul><li>Can include space </li></ul><ul><ul><li>Complications if running command-line programs </li></ul></ul><ul><li>Uses file hierarchy </li></ul><ul><ul><li>First slash indicates an absolute path name </li></ul></ul>Understanding Operating Systems, Fifth Edition
  38. 38. Filename Conventions (continued) Understanding Operating Systems, Fifth Edition
  39. 39. Filename Conventions (continued) <ul><li>Path name rules </li></ul><ul><ul><li>Path name starting with slash (at root directory) </li></ul></ul><ul><ul><li>Path name </li></ul></ul><ul><ul><ul><li>One name or list of names separated by slashes </li></ul></ul></ul><ul><ul><li>Last name on list </li></ul></ul><ul><ul><ul><li>Name of file requested </li></ul></ul></ul><ul><ul><ul><li>Preceding names must be directory names </li></ul></ul></ul><ul><ul><li>Two periods (..) in path name </li></ul></ul><ul><ul><ul><li>Move upward in hierarchy (closer to root) </li></ul></ul></ul><ul><ul><ul><li>Only way to go up hierarchy </li></ul></ul></ul><ul><ul><ul><li>Other path names go down tree </li></ul></ul></ul>Understanding Operating Systems, Fifth Edition
  40. 40. Filename Conventions (continued) <ul><li>Data structures: Virtual File System (VFS) </li></ul><ul><ul><li>Kernel </li></ul></ul><ul><ul><ul><li>Allows processes to access files in a consistent manner </li></ul></ul></ul><ul><ul><ul><li>Maintains interface between file related system calls and file management code </li></ul></ul></ul><ul><ul><li>Virtual file system layer </li></ul></ul><ul><ul><ul><li>Receives process-initiated system call to files </li></ul></ul></ul><ul><ul><ul><li>Performs file operations </li></ul></ul></ul><ul><ul><ul><li>Independent of file system format </li></ul></ul></ul><ul><ul><ul><li>Redirects request to module managing file </li></ul></ul></ul>Understanding Operating Systems, Fifth Edition
  41. 41. Directory Listings <ul><li>Creation </li></ul><ul><ul><li>ls or ls -l command </li></ul></ul><ul><ul><li>GUI interface </li></ul></ul><ul><li>Displays: </li></ul><ul><ul><li>File or directory name </li></ul></ul><ul><ul><li>Size </li></ul></ul><ul><ul><li>Modification date and time </li></ul></ul><ul><li>Permissions column </li></ul><ul><ul><li>Code: file’s type and access privileges </li></ul></ul><ul><ul><li>Order of letters indicates the specific access granted </li></ul></ul>Understanding Operating Systems, Fifth Edition
  42. 42. Directory Listings (continued) Understanding Operating Systems, Fifth Edition
  43. 43. Directory Listings (continued) Understanding Operating Systems, Fifth Edition
  44. 44. Directory Listings (continued) <ul><li>First column character: nature of folder entry </li></ul><ul><ul><li>Dash (-) indicates a file </li></ul></ul><ul><ul><li>d indicates a directory file </li></ul></ul><ul><ul><li>l indicates a link </li></ul></ul><ul><ul><li>b indicates a block special file </li></ul></ul><ul><ul><li>c indicates a character special file </li></ul></ul><ul><li>Next three characters (rwx): file owner privileges </li></ul><ul><ul><li>r indicates read access </li></ul></ul><ul><ul><li>w indicates write access </li></ul></ul><ul><ul><li>x indicates execute access </li></ul></ul>Understanding Operating Systems, Fifth Edition
  45. 45. Directory Listings (continued) <ul><li>Next three characters </li></ul><ul><ul><li>Group access privileges </li></ul></ul><ul><ul><ul><li>Group: set of users, excluding owner, having something in common (project, class, department) </li></ul></ul></ul><ul><ul><ul><li>System-wide group of users: “world” </li></ul></ul></ul><ul><li>Last three characters </li></ul><ul><ul><li>Access privileges granted to “others” </li></ul></ul><ul><ul><ul><li>Others: users at large (excluding owner and group member) </li></ul></ul></ul>Understanding Operating Systems, Fifth Edition
  46. 46. Directory Listings (continued) <ul><li>Change file security </li></ul><ul><ul><li>Owner (and only the owner) opens file properties to be protected </li></ul></ul><ul><ul><ul><li>File-Properties from the File menu </li></ul></ul></ul><ul><ul><li>Click on Permissions tab </li></ul></ul><ul><ul><li>Choose the appropriate access </li></ul></ul><ul><ul><ul><li>For owner, group, others </li></ul></ul></ul>Understanding Operating Systems, Fifth Edition
  47. 47. Directory Listings (continued) Understanding Operating Systems, Fifth Edition
  48. 48. User Interface <ul><li>Early Linux versions </li></ul><ul><ul><li>Required typed commands </li></ul></ul><ul><ul><ul><li>Thorough knowledge of valid commands required </li></ul></ul></ul><ul><li>Current versions </li></ul><ul><ul><li>Include powerful and intuitive GUI desktops </li></ul></ul><ul><ul><ul><li>Novice user can use successfully </li></ul></ul></ul><ul><ul><li>Navigate operating system </li></ul></ul><ul><ul><li>Can still use Terminal mode </li></ul></ul><ul><ul><ul><li>Type commands similar to those used for UNIX </li></ul></ul></ul>Understanding Operating Systems, Fifth Edition
  49. 49. Command-Driven Interfaces <ul><li>Typed command general syntax </li></ul><ul><ul><li>command arguments filename </li></ul></ul><ul><li>Command: legal operating system command </li></ul><ul><li>Arguments: required or optional </li></ul><ul><li>Filename: filename </li></ul><ul><ul><li>Relative or absolute path name </li></ul></ul><ul><li>Shell (bash shell) </li></ul><ul><ul><li>Command interpreter </li></ul></ul><ul><ul><li>Interprets and executes command </li></ul></ul><ul><ul><li>Key to system program coordination and combination </li></ul></ul>Understanding Operating Systems, Fifth Edition
  50. 50. Command-Driven Interfaces (continued) Understanding Operating Systems, Fifth Edition
  51. 51. Graphical User Interfaces <ul><li>Multiple graphical user interfaces (often free) </li></ul><ul><ul><li>Allowing choice for end users </li></ul></ul><ul><ul><li>Different GUIs used by different users on same system (certain environments) </li></ul></ul><ul><ul><li>Flexibility </li></ul></ul><ul><ul><li>Spurring Linux acceptance </li></ul></ul><ul><li>Sophisticated Windows-compatible word processors, spreadsheet, presentation applications (some at no cost) </li></ul><ul><ul><li>Spurring Linux popularity </li></ul></ul>Understanding Operating Systems, Fifth Edition
  52. 52. System Monitor <ul><li>System Monitor window </li></ul><ul><ul><li>System well-being information </li></ul></ul><ul><ul><li>Immediate history </li></ul></ul><ul><ul><ul><li>CPU, memory, network usage </li></ul></ul></ul><ul><li>Other information </li></ul><ul><ul><li>Supported file systems </li></ul></ul><ul><ul><li>Currently running processes information </li></ul></ul>Understanding Operating Systems, Fifth Edition
  53. 53. System Monitor (continued) Understanding Operating Systems, Fifth Edition
  54. 54. Service Settings <ul><li>Variety of services help manage system </li></ul><ul><ul><li>Linux distribution dependent (see documentation) </li></ul></ul>Understanding Operating Systems, Fifth Edition
  55. 55. System Logs <ul><li>System logs </li></ul><ul><ul><li>Provide detailed description of activity on system </li></ul></ul><ul><ul><li>Invaluable to administrators </li></ul></ul><ul><ul><ul><li>Tracking system malfunction </li></ul></ul></ul><ul><ul><ul><li>Firewall failure </li></ul></ul></ul><ul><ul><ul><li>Disabled device </li></ul></ul></ul><ul><ul><li>Found in /var/log directory </li></ul></ul><ul><ul><li>System log viewer to see data </li></ul></ul>Understanding Operating Systems, Fifth Edition
  56. 56. System Logs (continued) Understanding Operating Systems, Fifth Edition
  57. 57. Keyboard Shortcuts <ul><li>Users easily switch from one task to another </li></ul><ul><li>Keyboard shortcuts </li></ul><ul><ul><li>Many identical to commonly used Windows operating systems’ shortcuts </li></ul></ul><ul><ul><ul><li>Ease operating system transition </li></ul></ul></ul><ul><ul><li>Example: CTRL-V </li></ul></ul><ul><ul><ul><li>Quick way to issue PASTE command </li></ul></ul></ul><ul><ul><ul><li>Linux, UNIX, and Windows </li></ul></ul></ul>Understanding Operating Systems, Fifth Edition
  58. 58. Keyboard Shortcuts (continued) Understanding Operating Systems, Fifth Edition
  59. 59. Summary <ul><li>Originally designed to gain more microcomputer chip power </li></ul><ul><ul><li>Evolved into powerful, flexible operating system </li></ul></ul><ul><ul><ul><li>Runs supercomputers, cell phones, many devices </li></ul></ul></ul><ul><li>Unparalleled popularity among programmers </li></ul><ul><ul><li>Contribute standard code set enhancements </li></ul></ul><ul><li>Supports broad range of applications </li></ul><ul><ul><li>Available for minimal cost and easy to install </li></ul></ul><ul><ul><li>Growing acceptance among non-programmers </li></ul></ul><ul><li>Large organizations </li></ul><ul><ul><li>Commercial Linux products available </li></ul></ul>Understanding Operating Systems, Fifth Edition

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