Understanding Operating Systems Fifth Edition

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Understanding Operating Systems Fifth Edition

• Linux Operating System

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History

• Developed by Linus Torvalds (1991)
• Original purpose
• Maximize Intel 80386 microprocessors 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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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
• Worlds leading Linux distributor (until 2003)
• GNU General Public License

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Design Goals

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

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Design Goals (continued)
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Device Management
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Device Classes

• Three standard classes

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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

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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

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File Management

• Data structures
• Filename conventions
• Directory listings

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Data Structures

• Files organized in directories
• Connected in treelike structure
• Five file types

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Filename Conventions
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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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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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Directory Listings

• Creation
• ls or ls -l command
• GUI interface
• Displays
• File or directory name
• Size
• Modification date and time
• Permissions column
• Code files 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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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)