1. Understanding Operating Systems Seventh Edition
Chapter 15 Linux Operating Systems

2. Learning Objectives
After completing this chapter, you should be able to describe:
The design goals for the Linux operating system
The flexibility offered by using files to manipulate devices
The roles of the Memory, Device, File, Processor, and Network Managers
The impact of open source software
Some strengths and weaknesses of Linux
Understanding Operating Systems, 7e

3. Introduction Linux Portable Source code: freely available Open source
Originally based on a version of UNIX
Powerful
Inexpensive or free to use
Portable
Versions for cell phones, supercomputers, and computing systems in between
Source code: freely available
Configurable: runs any device; meets any specification
Open source
Source code freely available to anyone for improvement
Under constant development
Contributors around the world: not paid for their work
Understanding Operating Systems, 7e

4. Brief History Developed by Linus Torvalds (1991) Original purpose
Maximize Intel 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, 7e

5. Brief History (cont'd.) User interface
First Linux operating systems: command-driven interface
Sometimes cryptic commands
Recent years
Graphical user interfaces (GUI)
Written and distributed under the GNU General Public License
Fedora Project responsible for the open-source development of the Linux kernel
Common \ popular distributions: Fedora, Ubuntu, Cent OS
The foundation of Android operating system (most popular mobile OS)
Understanding Operating Systems, 7e

6. Understanding Operating Systems, 7e
(table 15.1)
Selected releases of Ubuntu Linux. New releases are scheduled every 6 months. Normal Ubuntu releases are supported for 18 months; LTS releases are supported longer. (adapted from
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Understanding Operating Systems, 7e

7. Design Goals Three goals Numerous standard utilities
Modularity
Simplicity
Portability
Numerous standard utilities
Eliminate need to write special code
Used in combination for specific tasks
Numerous functions
IEEE POSIX (Portable Operating System Interface) specifications conformity
Programs’ portability
Understanding Operating Systems, 7e

8. Understanding Operating Systems, 7e
(table 15.2)
Select system functions supported by Linux.
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Understanding Operating Systems, 7e

9. Understanding Operating Systems, 7e
(table 15.2) (cont’d.)
Select system functions supported by Linux.
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Understanding Operating Systems, 7e

10. Memory Management Space allocation (32 bit) Process execution
Kernel: 1 GB high order memory
Executing processes: 3 GB memory
Process execution
Fixed-size segment
System calls change segment size
Memory protection
Based on information type stored in address space region for process
Memory limits vary with 64 bit Linux distributions but generally in terabytes (TB) – 1,000s of GBs
Understanding Operating Systems, 7e

11. Processor Management
Uses same parent-child process management design found in UNIX
Supports “personality” concept
Allows processes from other operating systems to be executed
Understanding Operating Systems, 7e

12. Device Management Device independent Device drivers Devices assigned
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, 7e

13. Device Drivers Support for standard classes introduced by UNIX
Allow new device classes supporting new technology
Device classes not rigid
Creating large, complex, and multiple function drivers is discouraged because:
Users share code: wider demand for simple drivers
Modular code supports system scalability and extendibility goals
Encouraged: drivers maximizing system’s effective device usage
Notable feature
Accept new device drivers on the fly
System up and running
No reboot necessary
Understanding Operating Systems, 7e

14. Device Classes Three standard classes Character devices Block devices
Network devices
Understanding Operating Systems, 7e

15. Understanding Operating Systems, 7e
Character (char) devices
Accessed as a stream of bytes
Communications port, monitor, or other byte-stream-fed device
Implement open, release, read, and 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
Block devices
Host a file system (e.g., 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)
Network interfaces
Function
Send and receive information packets
Directed by network subsystem
Network device functions
Relate to packet transmission
System device handled by device driver
Under Linux subsystem’s direction
(figure 15.5)
This example of the three primary classes of device drivers shows how device drivers receive direction from different subsystems of Linux.
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Understanding Operating Systems, 7e

16. Device Classes (cont'd.)
Character (char) devices
Accessed as a stream of bytes
Communications port, monitor, or other byte-stream-fed device
Implement open, release, read, and 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, 7e

17. Device Classes (cont'd.)
Block devices
Host a file system (e.g., 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, 7e

18. Device Classes (cont'd.)
Network interfaces
Function
Send and receive information packets
Directed by network subsystem
Network device functions
Relate to packet transmission
System device handled by device driver
Under Linux subsystem’s direction
Understanding Operating Systems, 7e

19. File Management Very similar to UNIX Files organized in directories
Easy transition for programmers and administrators who are familiar with one operating system to move to the other
Files organized in directories
Connected in treelike structure
Understanding Operating Systems, 7e

20. Understanding Operating Systems, 7e
(table 15.5)
The file type indicates how each file is to be used.
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Understanding Operating Systems, 7e

21. Filename Conventions Case sensitive Up to 255 characters long
Recognizes uppercase and lowercase letters
Up to 255 characters long
Contain alphabetic characters, underscores, and numbers
File suffixes: optional
Can include space
Complications if running command-line programs
File hierarchy
First slash indicates an absolute path name
Understanding Operating Systems, 7e

22. Understanding Operating Systems, 7e
(figure 15.6)
A sample file hierarchy. The forward slash (/ ) at the top represents the root directory.
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Understanding Operating Systems, 7e

23. Filename Conventions (cont'd.)
Path name rules
Path name starting with slash: begins at root directory
Path name
One name or list of names separated by slashes
Last name on list: name of file requested
Two periods (..) in path name
Move upward in hierarchy: closer to root
Only way to go up the hierarchy
Understanding Operating Systems, 7e

24. Filename Conventions (cont'd.)
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 the file
Understanding Operating Systems, 7e

25. New Versions Linux operating systems: patched between version releases
Downloaded on request or
System setup checks for available updates
Patch management
Replaces or changes parts of the operating system that need to be enhanced or replaced
Understanding Operating Systems, 7e

26. New Versions (cont'd.) Reasons for operating system patches
Security precautions: constantly changing system threats
System compliance: government regulations regarding privacy and financial accountability
Peak efficiency
System manager must:
Maintain vigilance: security vulnerabilities
Assess patch’s criticality
If important, apply immediately
Understanding Operating Systems, 7e

27. User Interface Early Linux versions Current versions
Required typed commands
Thorough knowledge of valid commands required
Current versions
Include powerful and intuitive menu-driven interfaces
Several graphical user interfaces available
Can still use Terminal mode - type commands similar to those used for UNIX
Many Linux versions
Equipped with Windows-compatible word processors, spreadsheet, and presentation applications
Understanding Operating Systems, 7e

28. System Monitor System Monitor window Moment-by-moment system status
Immediate history: CPUs, memory, and network usage
Other information
Supported file systems
Currently running processes information
Understanding Operating Systems, 7e

29. Understanding Operating Systems, 7e
(figure 15.9)
This Linux system monitor shows the recent history of both CPUs, shown in the top graph. © Cengage Learning 2014
Understanding Operating Systems, 7e

30. System Logs Provide detailed description of activity on system
Invaluable to administrators
Tracking system malfunction
Firewall failure
Disabled device
Found in /var/log directory
Seen using a log viewer
Understanding Operating Systems, 7e

31. Understanding Operating Systems, 7e
(figure 15.10)
The system log viewer shows details of all activity.
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Understanding Operating Systems, 7e

32. Understanding Operating Systems, 7e
(table 15.6)
A few of the many available Linux log files. See the documentation for your system for specifics.
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Understanding Operating Systems, 7e

33. File Listings Understanding Operating Systems, 7e (figure 15.11)
Directories are shown in the left-most column, and the contents of the currently highlighted folder are displayed in the window on the right.
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Understanding Operating Systems, 7e

34. File Listings (cont'd.) Explore directory’s or file’s contents
Double click its icon
Establish the directory’s or file’s access control settings
Right click on item’s icon
Terminal window
Display directory details: type command ls-l
Understanding Operating Systems, 7e

35. Understanding Operating Systems, 7e
(figure 15.12)
Directory details shown in Terminal mode, which is another way to explore Linux.
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Understanding Operating Systems, 7e

36. Setting Permissions Network administrators Three levels of access
Full control: manage access to files and directories
Three levels of access
Owner
Group
Others
Access level settings: under properties option
Access types
Create and delete files, list files only, access files, and none
Understanding Operating Systems, 7e

37. Understanding Operating Systems, 7e
(figure 15.13)
User activity can be restricted by using document properties options.
© Cengage Learning 2014
Understanding Operating Systems, 7e

38. Conclusion
Originally designed to gain more power from a 1990s computer
Evolved into powerful, flexible operating system: runs supercomputers, cell phones, and many other 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
Viable marketplace player
Popularity expected to grow for many years
Android operating system foundation
Understanding Operating Systems, 7e