1. The Linux Operating System C. Blane Adcock Bryan Knehr Kevin Estep Jason Niesz

2. Multiprocessing Multiprocessing available from Linux 2.0 and above via Symmetric-Multiprocessing (SMP) Multiple hardware platforms supported by SMP System Administrator must construct their own SMP Kernel

3. User Levels and Threads User Levels –Single User –Multi User Thread Types –User Level –Kernel Level Multitasking OS

4. Hardware Platforms X86 Based –Intel –AMD –Other RISC, Alpha, SPARC, etc…

5. Command Language Control Statements –Shell reads and interprets control statements. –Commands E.g. “ls”, “cd”, “netstat”, etc… Separators, e.g. “|” –Shell Scripts

6. Graphical User Interface Desktop Environments –KDE/GNOME are both based off XFree86 X Windows System –Client/Server Interface –Platform Independent –Provides API –Implements X Protocol

7. X Protocol X Client –Device Independent –Displayed on X Server –Run Local/Non-Local X Server –Device Dependent –Device Independent Advantages/Disadvantages

8. Process Control Block In Linux, processes have the following attributes: –Owner’s ID –Process Name –Process ID –Process State –Process ID of the parent process –Total time the process has been in the system

9. Synchronization Signals –Processes put themselves on wait queues, waiting for an event. Counting Semaphores –Multiple processes can share large numbers of semaphores Mutexes –Process locks

10. CPU Scheduling Preemptive Simple priority based algorithm Two types of processes –Real time (two types) First in first out (FIFO) Round Robin (RR) –Normal (non real time)

11. CPU Scheduling (Con’t) Real time processes always have priority over normal processes When the scheduler gets invoked it begins to calculate a “goodness” value for each process in the run queue The process with the highest goodness value is selected to run, providing it is “ready to run” A process is ready to run if it is not waiting for anything, such as a keyboard input

12. Calculating the Goodness Value for Real Time Processes All processed marked SCHED_FIFO or SCHED_RR (real time processes) automatically start with a value of 1000 to ensure priority over normal processes The value of the priority field is then added to make up the goodness value

13. Calculating the Goodness Value for Normal Processes The goodness value for normal process is based on 4 factors: –The task counter If the counter is zero the goodness value for the process is zero If not zero the goodness value is set to the counter value –The priority value The task’s priority value is added to the goodness value –A 1 point bonus for processes that share memory maps –A 15 point bonus for tasks that ran on the current processor the last time they ran

14. Calculating the Goodness Value for Normal Processes (Con’t) If all the processes in the queue have a goodness value of zero, the scheduler has the counter values recalculated and the recalculates the goodness values Problems –Every time the scheduler is invoked all the goodness values are recalculated –This is a O(n) operation, n is the number of tasks in the queue, therefore is n is large this will be costly to the CPU (as high as 30% total CPU time)

15. Deadlock Detection and Resolution The nmi_watchdog command –Runs non-maskable interrupts to detect deadlock and display error messages Open source watchdogs

16. Approach to Memory Management Virtual to Physical Address mapping –Fixed Size Pages Offset Virtual Page Frame Number –Translation Process Page Table –Valid Flag, Physical Page Frame Number, Access Control Information

17. Page Replacement Algorithm Buddy algorithm –Page Allocation –Page Deallocation

18. File System Organization Hierarchal directory structure Every directory and subdirectory is a subdirectory of the root directory, symbolized “/” This forms an inverted tree structure with the root at the top and everything stemming from there Creates a parent-child relationship between directories and their subdirectories

19. The ext3 File System An extension of the ext2 file system, but adds journaling –Journaling adds quick recovery from crash Customization of data protection –data=writeback –data=ordered –data=journal ext3 is backward compatible