Understanding Operating Systems Fifth Edition

1. Understanding Operating Systems Fifth Edition Chapter 16Linux Operating System

2. Learning Objectives • The design goals for the Linux operating system • The significance of using files to manipulate devices • The differences between command-driven and menu-driven interfaces • The roles of the Memory, Device, File, Processor, and Network Managers • Some strengths and weaknesses of Linux Understanding Operating Systems, Fifth Edition

3. Overview • POSIX-compliant • Portable • Versions for cell phones, supercomputers, and computing systems in between • Source code: freely available • Configurable: run any device, meet any specification • User interface • Powerful desktop GUIs attracts users • Highly modular • Multiple modules load and unload on demand • Technically robust operating system Understanding Operating Systems, Fifth Edition

4. History • Developed by Linus Torvalds (1991) • Original purpose • Maximize Intel 80386 microprocessor’s limited capabilities • Roots • Minix: miniature UNIX with more functionality • First version meant for small microcomputer • Expensive commercial computer features • Flexibility and functionality • Brought UNIX features to small computer Understanding Operating Systems, Fifth Edition

5. History (continued) • Open-source program • Updates accepted from anyone • User interface • Originally typed and cryptic commands • Today • Command-driven interface (Terminal mode) • Graphical user interface (GUI) • Red Hat Linux provided initial primary support • World’s leading Linux distributor (until 2003) • GNU General Public License Understanding Operating Systems, Fifth Edition

6. Understanding Operating Systems, Fifth Edition

7. History (continued) Understanding Operating Systems, Fifth Edition

8. Design Goals • Three goals • Modularity • Simplicity • Portability • Numerous standard utilities • Eliminates need to write special code • Used in combination for specific tasks • Numerous functions • Conforms to IEEE POSIX specifications • Portable Operating System Interface for Computer Environments Understanding Operating Systems, Fifth Edition

9. Design Goals (continued) Understanding Operating Systems, Fifth Edition

10. Memory Management • Space allocation • Kernel: 1 GB high order memory • Executing processes: 3 GB memory • Process execution • Segment fixed size • System calls change segment size • Memory protection • Based on information type stored in address space region for process Understanding Operating Systems, Fifth Edition

11. Memory Management (continued) • Page loading • Least recently used algorithm (LRU) • Maintains a dynamically managed memory area and page cache (new and old pages inserted and deleted) • System page tables • Tracks free and busy pages • Virtual memory • Managed using multiple-level table hierarchy • 64- and 32-bit architectures • Added flexibility with swap devices • May deactivate without rebooting Understanding Operating Systems, Fifth Edition

12. Memory Management (continued) • Virtual memory managed using multiple-level table hierarchy • Four fields in virtual address Understanding Operating Systems, Fifth Edition

13. Memory Management (continued) Understanding Operating Systems, Fifth Edition

14. Memory Management (continued) • Buddy algorithm • Grouping and splitting equal-sized page frames • Give more contiguous space to job • Page replacement algorithm • Clock page replacement policy expanded version • Uses eight-bit byte to track page’s activity • Referred to as “age” Understanding Operating Systems, Fifth Edition

15. Memory Management (continued) Understanding Operating Systems, Fifth Edition

16. Processor Management • Uses same parent-child process management design found in UNIX • “Personality” concept • Allow processes from other operating systems to be executed Understanding Operating Systems, Fifth Edition

17. Organization of Table of Processes • Descriptor: references process • Contains approximately 70 fields • Describes process attributes • Information needed to manage process • Dynamically allocated by kernel • Process execution time • Organized by doubly linked lists • “Next run” field • “Previously run” field • Scheduler manages and updates descriptors • Macros Understanding Operating Systems, Fifth Edition

18. Process Synchronization • Wait queues and semaphores • Synchronize two processes with each other • Wait queue • Linked circular list of process descriptors • Problems solved • Mutual exclusion and producers and consumers • Semaphore structure • Three fields (semaphore counter, number of waiting processes, list of processes waiting for semaphore) • Counter contains binary values • Except if several units of one resource available Understanding Operating Systems, Fifth Edition

19. Process Management • Linux scheduler • Scans processes list in READY state • Chooses process to execute • Using predefined criteria • Three scheduling types • Real-time processes (two) • Normal processes (one) • Process scheduling policy determination • Combination of type and priority Understanding Operating Systems, Fifth Edition

20. Process Management (continued) Understanding Operating Systems, Fifth Edition

21. Process Management (continued) • First type • Highest priority (SCHED_FIFO) • First in, first out algorithm • Not preemptible • Runs to completion unless: • Process goes into WAIT state • Process relinquishes processor voluntarily • All FIFO processes complete • Scheduler processes lower priority types Understanding Operating Systems, Fifth Edition

22. Process Management (continued) • Second type • Medium priority (SCHED_RR) • Round robin algorithm with small time quantum • Time quantum expires • Other higher priority processes (FIFO, RR ) selected and executed • Before first process allowed to complete • Third type • Low priority (SCHED_OTHER) • Executed if no higher priority processes in READY queue Understanding Operating Systems, Fifth Edition

23. Device Management • Device independent • Improves portability • Device drivers • Supervise data transmission • Between main memory and peripheral unit • Devices assigned • Name • Descriptors • Further identify each device • Stored in device directory Understanding Operating Systems, Fifth Edition

24. Device Management (continued) Understanding Operating Systems, Fifth Edition

25. Device Management (continued) • Device drivers • Comprehensive collection in Linux • Required driver not available • Obtain from another source • Install separately • Manually write the driver • Requires skilled programmer Understanding Operating Systems, Fifth Edition

26. Device Classifications • Device identification • Minor device number • Passed to device driver as an argument • Accesses one of several identical physical devices • Major device number • Index to array to access appropriate code • Configuration table for each class • Entry point into driver • Only connection between system code and driver • Importance • Allows quick creation of device drivers Understanding Operating Systems, Fifth Edition

27. Device Drivers • Support for standard classes introduced by UNIX • Allow new device classes supporting new technology • Device classes not rigid • Create large, complex, multiple function drivers • Discouraged because: • Users share code, demand simple drivers • Modular code supports system scalability and extendibility goal • Encouraged: drivers maximizing system’s effective device usage Understanding Operating Systems, Fifth Edition

28. Device Drivers (continued) • Notable feature • Accept new device drivers on the fly • System up and running • No reboot necessary Understanding Operating Systems, Fifth Edition

29. Device Classes • Three standard classes Understanding Operating Systems, Fifth Edition

30. Device Classes (continued) • Character (char) devices • Accessed as a stream of bytes • Communications port, monitor, other byte-stream-fed device • Implement open, close, read, write system calls • Accessed by file system nodes • Look like ordinary data area • Drivers treated as ordinary files • Exception: drivers are data channels accessed sequentially Understanding Operating Systems, Fifth Edition

31. Device Classes (continued) • Block devices • Host a file system (hard disk) • Accessed by file system nodes in /dev directory • Transfer in blocks of data • Similarity to char driver • Appear as ordinary files • Dissimilarity to char driver • Access file system in connection with device (not possible with char device) Understanding Operating Systems, Fifth Edition

32. Device Classes (continued) • Network interfaces • Function • Send and receive information packets • Directed by network subsystem • Network device functions • Relate to packet transmission • Not read and write calls • Dissimilar from block and char • System device handled by device driver • Under direction of Linux subsystem Understanding Operating Systems, Fifth Edition

33. Device Classes (continued) • Open and release • Allocate and deallocate the appropriate device • Open operation example • Verify device available and working • Increase device usage counter by one (subsystem knows module cannot be unloaded until file appropriately closed) • Initialize device so old data is removed and device ready to accept new data • Identify minor number and update appropriate pointer (if necessary) • Allocate appropriate data structure Understanding Operating Systems, Fifth Edition

34. Device Classes (continued) • Open and release (continued) • Release operation example • Deallocate resources allocated with open function • Shut down device • Reduce usage counter by one (device released to another module) Understanding Operating Systems, Fifth Edition

35. File Management • Data structures • Filename conventions • Directory listings Understanding Operating Systems, Fifth Edition

36. Data Structures • Files organized in directories • Connected in treelike structure • Five file types Understanding Operating Systems, Fifth Edition

37. Filename Conventions • Case sensitive • Recognizes uppercase and lowercase letters • Up to 255 characters long • Contain alphabetic characters, underscores, numbers • File suffixes: optional • Can include space • Complications if running command-line programs • Uses file hierarchy • First slash indicates an absolute path name Understanding Operating Systems, Fifth Edition

38. Filename Conventions (continued) Understanding Operating Systems, Fifth Edition

39. Filename Conventions (continued) • Path name rules • Path name starting with slash (at root directory) • Path name • One name or list of names separated by slashes • Last name on list • Name of file requested • Preceding names must be directory names • Two periods (..) in path name • Move upward in hierarchy (closer to root) • Only way to go up hierarchy • Other path names go down tree Understanding Operating Systems, Fifth Edition

40. Filename Conventions (continued) • Data structures: Virtual File System (VFS) • Kernel • Allows processes to access files in a consistent manner • Maintains interface between file related system calls and file management code • Virtual file system layer • Receives process-initiated system call to files • Performs file operations • Independent of file system format • Redirects request to module managing file Understanding Operating Systems, Fifth Edition

41. Directory Listings • Creation • ls or ls -l command • GUI interface • Displays: • File or directory name • Size • Modification date and time • Permissions column • Code: file’s type and access privileges • Order of letters indicates the specific access granted Understanding Operating Systems, Fifth Edition

42. Directory Listings (continued) Understanding Operating Systems, Fifth Edition

43. Directory Listings (continued) Understanding Operating Systems, Fifth Edition

44. Directory Listings (continued) • First column character: nature of folder entry • Dash (-) indicates a file • d indicates a directory file • l indicates a link • b indicates a block special file • c indicates a character special file • Next three characters (rwx): file owner privileges • r indicates read access • w indicates write access • x indicates execute access Understanding Operating Systems, Fifth Edition

45. Directory Listings (continued) • Next three characters • Group access privileges • Group: set of users, excluding owner, having something in common (project, class, department) • System-wide group of users: “world” • Last three characters • Access privileges granted to “others” • Others: users at large (excluding owner and group member) Understanding Operating Systems, Fifth Edition

46. Directory Listings (continued) • Change file security • Owner (and only the owner) opens file properties to be protected • File-Properties from the File menu • Click on Permissions tab • Choose the appropriate access • For owner, group, others Understanding Operating Systems, Fifth Edition

47. Directory Listings (continued) Understanding Operating Systems, Fifth Edition

48. User Interface • Early Linux versions • Required typed commands • Thorough knowledge of valid commands required • Current versions • Include powerful and intuitive GUI desktops • Novice user can use successfully • Navigate operating system • Can still use Terminal mode • Type commands similar to those used for UNIX Understanding Operating Systems, Fifth Edition

49. Command-Driven Interfaces • Typed command general syntax • command arguments filename • Command: legal operating system command • Arguments: required or optional • Filename: filename • Relative or absolute path name • Shell (bash shell) • Command interpreter • Interprets and executes command • Key to system program coordination and combination Understanding Operating Systems, Fifth Edition

50. Command-Driven Interfaces (continued) Understanding Operating Systems, Fifth Edition