Understanding Operating Systems Fifth Edition Chapter 16 Linux Operating System.
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Transcript of Understanding Operating Systems Fifth Edition Chapter 16 Linux Operating System.
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Understanding Operating Systems Fifth Edition
Chapter 16Linux Operating System
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Understanding Operating Systems, Fifth Edition 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
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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
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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
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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
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Understanding Operating Systems, Fifth Edition 6
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Understanding Operating Systems, Fifth Edition 7
History (continued)
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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
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Understanding Operating Systems, Fifth Edition 9
Design Goals (continued)
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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
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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
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Understanding Operating Systems, Fifth Edition 12
Memory Management (continued)
• Virtual memory managed using multiple-level table hierarchy– Four fields in virtual address
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Understanding Operating Systems, Fifth Edition 13
Memory Management (continued)
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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”
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Understanding Operating Systems, Fifth Edition 15
Memory Management (continued)
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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
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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
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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
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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
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Understanding Operating Systems, Fifth Edition 20
Process Management (continued)
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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
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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
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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
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Understanding Operating Systems, Fifth Edition 24
Device Management (continued)
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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
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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
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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
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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
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Understanding Operating Systems, Fifth Edition 29
Device Classes
• Three standard classes
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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
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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)
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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
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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
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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)
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Understanding Operating Systems, Fifth Edition 35
File Management
• Data structures
• Filename conventions
• Directory listings
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Understanding Operating Systems, Fifth Edition 36
Data Structures
• Files organized in directories– Connected in treelike structure
• Five file types
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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
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Understanding Operating Systems, Fifth Edition 38
Filename Conventions (continued)
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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
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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
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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
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Directory Listings (continued)
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Directory Listings (continued)
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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
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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)
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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
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Directory Listings (continued)
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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
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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
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Command-Driven Interfaces (continued)
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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
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System Monitor
• System Monitor window – System well-being information– Immediate history
• CPU, memory, network usage
• Other information– Supported file systems – Currently running processes information
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System Monitor (continued)
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Service Settings
• Variety of services help manage system– Linux distribution dependent (see documentation)
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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
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System Logs (continued)
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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
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Keyboard Shortcuts (continued)
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Summary
• Originally designed to gain more microcomputer chip power– Evolved into powerful, flexible operating system
• Runs supercomputers, cell phones, many devices
• Unparalleled popularity among programmers– Contribute standard code set enhancements
• Supports broad range of applications– Available for minimal cost and easy to install– Growing acceptance among non-programmers
• Large organizations– Commercial Linux products available