1. 16 UNIX and Linux

2. Fig. 16.1: The shell and the kernel.

3. Images and Processes Image –an execution environment –the pseudo-computer concept –components text segment data segment stack segment Process –the execution of an image

4. Fig. 16.2: An image.

5. Fig. 16.3: The text segment is reentrant. The data and stack segments are private.

6. Process Creation Fig. 16.4a: The parent calls fork.

7. Fig. 16.4b: the child calls exec.

8. Fig. 16.4c: exec overlays the child’s text and data segments.

9. Fig. 16.4d: When the child dies, the parent resumes processing.

10. Fig. 16.5: The possible contents of memory on a system supporting four concurrent users.

11. Fig. 16.6: The process table contains one entry per process.

12. Events and Signals Event generated by death of a process Event produces signal event-wait routine activated –awaken all processes waiting for event –start highest priority ready process

13. Time-slicing and Interrupts Time-slicing –programs limited to a single time slice –exceeding time slice generates an event –event-wait starts highest priority process Interrupts –interrupt handling routines in kernel

14. Fig. 16.7: The swapping process is part of the kernel.

15. Fig. 16.8: A text table.

16. The File System Data treated as strings of bytes Device types –block devices hold files –character devices File types –ordinary files –special files

17. Fig. 16.9: A configuration table lists all the device drivers.

18. Fig. 16.10: A UNIX disk is divided into four regions.

19. Fig. 16.11: Associated with the file name is an i-number that points to a specific i-node.

20. Fig. 16.12: The process file table points to the system file table, which points to the file on disk.

21. The Buffer Pool All block I/O through buffer pool Read implies a buffer search Write –mark appropriate buffer dirty –transfer to disk when buffer reassigned Physical I/O asynchronous

22. Fig. 16.13: A summary of key UNIX system tables.

23. Linux The Linux kernel –deals directly with hardware –load/unload specific modules Linux processes –call fork or clone to create –personality identifier The Linux file system (ex2fs) –virtual file system (VFS)

24. Fig. 16.14: The virtual file system allows processes to access all file systems uniformly.