Understanding Operating Systems Fifth Edition

1. Understanding Operating Systems Fifth Edition Linux Operating System

2. 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

3. 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

4. Design Goals • Three goals • Modularity • Simplicity • Portability • Conforms to IEEE POSIX specifications • Portable Operating System Interface for Computer Environments

5. Design Goals (continued)

6. Device Management

7. Device Classes • Three standard classes

8. 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 • Drivers treated as ordinary files • Exception: drivers are data channels accessed sequentially

9. 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

10. File Management • Data structures • Filename conventions • Directory listings

11. Data Structures • Files organized in directories • Connected in treelike structure • Five file types

12. Filename Conventions

13. 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

14. 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

15. 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

16. Directory Listings (continued)

17. Directory Listings (continued)

18. 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

19. 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)

20. 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

21. Directory Listings (continued)

22. 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

23. Command-Driven Interfaces (continued)

24. Graphical User Interfaces • Multiple graphical user interfaces (often free) • Allowing choice for end users • Different GUIs used by different users on same system (certain environments) • Flexibility • Spurring Linux acceptance • Sophisticated Windows-compatible word processors, spreadsheet, presentation applications (some at no cost) • Spurring Linux popularity

25. System Monitor • System Monitor window • System well-being information • Immediate history • CPU, memory, network usage • Other information • Supported file systems • Currently running processes information

26. System Monitor (continued)

27. Service Settings • Variety of services help manage system • Linux distribution dependent (see documentation)

28. System Logs • System logs • Provide detailed description of activity on system • Invaluable to administrators • Tracking system malfunction • Firewall failure • Disabled device • Found in /var/log directory • System log viewer to see data

29. System Logs (continued)

30. Keyboard Shortcuts • Users easily switch from one task to another • Keyboard shortcuts • Many identical to commonly used Windows operating systems’ shortcuts • Ease operating system transition • Example: CTRL-V • Quick way to issue PASTE command • Linux, UNIX, and Windows

31. Keyboard Shortcuts (continued)