1. Linux Operating System
4/17/2017
4/17/2017
Linux Operating System
Review
Chapter 10
cs431-cotter
cs431-cotter
cs431-cottercs431-cotter 1

2. Overview System Overview Linux Processes CPU Scheduler
4/17/2017
4/17/2017
System Overview
Linux Processes
CPU Scheduler
Process Synchronization
Memory Management
Input / Output
File Systems
Security
cs431-cotter
cs431-cottercs431-cotter
cs431-cotter 2

3. Figure 10-1. The layers in a Linux system.
Interfaces to Linux
4/17/2017
Figure The layers in a Linux system.
cs431-cotter
Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc. All rights reserved
cs431-cottercs431-cotter

4. Linux Utility Programs
4/17/2017
Figure A few of the common Linux utility programs required by POSIX.
cs431-cotter
Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc. All rights reserved
cs431-cottercs431-cotter

5. Figure 10-3. Structure of the Linux kernel
Kernel Structure
4/17/2017
Figure Structure of the Linux kernel
cs431-cotter
Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc. All rights reserved
cs431-cottercs431-cotter

6. Overview System Overview Linux Processes CPU Scheduler
4/17/2017
4/17/2017
System Overview
Linux Processes
CPU Scheduler
Process Synchronization
Memory Management
Input / Output
File Systems
Security
cs431-cotter
cs431-cottercs431-cotter
cs431-cotter 6

7. Linux Processes int pid; : pid = fork (); //create a child process
if (pid < 0) // fork failed!!
errexit(); // handle error
else if (pid == 0) {
: //child process work goes here }
else //pid must be > 0 {
: //parent process work goes here
cs431-cotter

8. Process Management System Calls in Linux
4/17/2017
Figure Some system calls relating to processes.
cs431-cotter
Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc. All rights reserved
cs431-cottercs431-cotter

9. Implementation of Exec
4/17/2017
Figure The steps in executing the command ls typed to the shell.
cs431-cotter
Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc. All rights reserved
cs431-cottercs431-cotter

10. Overview System Overview Linux Processes CPU Scheduler
4/17/2017
4/17/2017
System Overview
Linux Processes
CPU Scheduler
Process Synchronization
Memory Management
Input / Output
File Systems
Security
cs431-cotter
cs431-cottercs431-cotter
cs431-cotter 10

11. Linux Scheduling Algorithm
4/17/2017
4/17/2017
Linux Scheduling Algorithm
SCHED_FIFO Designed for static priority. Soft real-time processes.
SCHED_RR designed for real-time processes that require fair assignment of CPU time.
SCHED_OTHER designed for normal user processes. Preemptible. Priority determined by base priority and time remaining in quantum.
cs431-cotter
cs431-cotter
cs431-cottercs431-cotter 11

12. Scheduling in Linux
4/17/2017
Figure Illustration of Linux runqueue and priority arrays.
cs431-cotter
Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc. All rights reserved
cs431-cottercs431-cotter

13. Overview System Overview Linux Processes CPU Scheduler
4/17/2017
4/17/2017
System Overview
Linux Processes
CPU Scheduler
Process Synchronization
Memory Management
Input / Output
File Systems
Security
cs431-cotter
cs431-cottercs431-cotter
cs431-cotter 13

14. Figure 10-5. The signals required by POSIX.
Signals in Linux (1)
4/17/2017
Figure The signals required by POSIX.
cs431-cotter
Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc. All rights reserved
cs431-cottercs431-cotter

15. Signals must be captured with signal handler
4/17/2017
4/17/2017
Signals must be captured with signal handler
Program must explicitly handle signals, if it does not want to use default handling (usually termination)
sigaction (signal_to_catch, new_action, old_action)
struct sigaction {
void * sa_handler; // What function do we call?
sigset_t mask; // Mask of signals to block when called
int sa_flags; // Special flags to set. };
Will be executed automatically on reception of appropriate signal
cs431-cotter
cs431-cotter
cs431-cottercs431-cotter 15

16. Semaphores POSIX version of semaphores System V version of semaphores
4/17/2017
4/17/2017
Semaphores
POSIX version of semaphores
#include <semaphore.h>
classic semaphore implementation
System V version of semaphores
#include <sys/sem.h>
Enhanced version of semaphores to include sets
cs431-cotter
cs431-cotter
cs431-cottercs431-cotter 16

17. Figure 2-30. Some of the Pthreads calls relating to mutexes.
Mutexes in Pthreads
4/17/2017
Figure Some of the Pthreads calls relating to mutexes.
cs431-cotter
Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc. All rights reserved
cs431-cottercs431-cotter

18. Named Pipes Permanent objects
4/17/2017
4/17/2017
Named Pipes
Permanent objects
Available to processes that can access the filespace (same system or on a shared file system)
Processes do not have to be related.
cs431-cotter
cs431-cotter
cs431-cottercs431-cotter 18

19. Message Queues A “linked list of messages”
Message queue has kernel persistence
Supports asynchronous communications.
Messages are stored in the queue, independent of the sender (sender can close queue without losing messages).
Receiver can retrieve messages at a later time.
Messages have a priority
Higher priority messages are retrieved first (POSIX)
Max priority is 32768
cs431-cotter

20. Shared Memory
Allows 2 or more processes to share the same main memory space
Memory can be allocated as blocks (pages) of memory
Memory can be mapped as a file that is available in memory to multiple processes
cs431-cotter

21. Overview System Overview Linux Processes CPU Scheduler
4/17/2017
4/17/2017
System Overview
Linux Processes
CPU Scheduler
Process Synchronization
Memory Management
Input / Output
File Systems
Security
cs431-cotter
cs431-cottercs431-cotter
cs431-cotter 21

22. Memory Management in Linux (1)
4/17/2017
(a)
(b)
(c)
Figure (a) Process A’s virtual address space. (b) Physical memory. (c) Process B’s virtual address space.
cs431-cotter
Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc. All rights reserved
cs431-cottercs431-cotter

23. Memory Management in Linux (2)
4/17/2017
(a)
(b)
(c)
Figure Two processes can share a mapped file.
cs431-cotter
Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc. All rights reserved
cs431-cottercs431-cotter

24. Physical Memory Management (3)
4/17/2017
Figure Linux uses four-level page tables.
cs431-cotter
Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc. All rights reserved
cs431-cottercs431-cotter

25. Memory Allocation Mechanisms
4/17/2017
(a)
(b)
(c)
(d)
(e)
(f)
(g)
(h)
(i)
Figure Operation of the buddy algorithm.
cs431-cotter
Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc. All rights reserved
cs431-cottercs431-cotter

26. Overview System Overview Linux Processes CPU Scheduler
4/17/2017
4/17/2017
System Overview
Linux Processes
CPU Scheduler
Process Synchronization
Memory Management
Input / Output
File Systems
Security
cs431-cotter
cs431-cottercs431-cotter
cs431-cotter 26

27. Implementation of Input/Output
4/17/2017
Figure The Linux I/O system showing one file system in detail.
cs431-cotter
Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc. All rights reserved
cs431-cottercs431-cotter

28. Overview System Overview Linux Processes CPU Scheduler
4/17/2017
4/17/2017
System Overview
Linux Processes
CPU Scheduler
Process Synchronization
Memory Management
Input / Output
File Systems
Security
cs431-cotter
cs431-cottercs431-cotter
cs431-cotter 28

29. System Organization Like UNIX...
4/17/2017
4/17/2017
System Organization
Like UNIX...
Predefined root directory structure with preferred locations for kernel files
/ (root)
bin
dev
home
mnt
root
tmp
var
boot
etc
lib
proc
sbin
usr
cs431-cotter
cs431-cottercs431-cotter
cs431-cotter 29

30. The Linux File System (2)
4/17/2017
Figure (a) Before linking. (b) After linking.
cs431-cotter
Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc. All rights reserved
cs431-cottercs431-cotter

31. The Linux File System (3)
4/17/2017
Figure (a) Separate file systems. (b) After mounting.
cs431-cotter
Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc. All rights reserved
cs431-cottercs431-cotter

32. The Linux Virtual File System
4/17/2017
Figure File system abstractions supported by the VFS.
cs431-cotter
Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc. All rights reserved
cs431-cottercs431-cotter

33. The Linux Ext2 File System (1)
4/17/2017
Figure Disk layout of the Linux ext2 file system.
cs431-cotter
Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc. All rights reserved
cs431-cottercs431-cotter

34. The Linux Ext2 File System (4)
4/17/2017
Figure The relation between the file descriptor table, the open file description table, and the i-node table.
cs431-cotter
Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc. All rights reserved
cs431-cottercs431-cotter

35. 4/17/2017
4/17/2017
Journal File Systems
Designed to speed file system recovery from system crashes.
Traditional systems use an fs recovery tool (e.g. fsck) to verify system integrity
As file system grows, recovery time grows.
Journal File Systems track changes in meta-data to allow rapid recovery from crashes
cs431-cotter
cs431-cotter
cs431-cottercs431-cotter 35

36. 4/17/2017
4/17/2017
Journal File System
Uses a version of a transaction log to track changes to file system directory records.
If a system crash occurs, the transaction log can be reviewed back to a check point to verify any pending work (either undo or redo).
For large systems, recovery time goes from hours or days to seconds.
cs431-cotter
cs431-cotter
cs431-cottercs431-cotter 36

37. Journal File System - Examples
4/17/2017
4/17/2017
Journal File System - Examples
ReiserFS
Designed originally for Linux (32 bit system)
Supports file systems to 2TB -> 16TB
Journal support of meta-data
Btree structure supports large file counts
Supports block packing for small files
No fixed inode allocation - more flexible.
cs431-cotter
cs431-cotter
cs431-cottercs431-cotter 37

38. NFS Protocols
4/17/2017
Figure Examples of remote mounted file systems. Directories shown as squares, files shown as circles.
cs431-cotter
Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc. All rights reserved
cs431-cottercs431-cotter

39. Figure 10-36. The NFS layer structure
NFS Implementation
4/17/2017
Figure The NFS layer structure
cs431-cotter
Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc. All rights reserved
cs431-cottercs431-cotter

40. Overview System Overview Linux Processes CPU Scheduler
4/17/2017
4/17/2017
System Overview
Linux Processes
CPU Scheduler
Process Synchronization
Memory Management
Input / Output
File Systems
Security
cs431-cotter
cs431-cottercs431-cotter
cs431-cotter 40

41. Figure 10-37. Some example file protection modes.
Security In Linux
4/17/2017
Figure Some example file protection modes.
cs431-cotter
Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc. All rights reserved
cs431-cottercs431-cotter

42. Security System Calls in Linux
4/17/2017
Figure system calls relating to security.
cs431-cotter
Tanenbaum, Modern Operating Systems 3 e, (c) 2008 Prentice-Hall, Inc. All rights reserved
cs431-cottercs431-cotter

43. Summary System Overview Linux Processes CPU Scheduler
Process Synchronization
Memory Management
Input / Output
File Systems
Security
cs431-cotter

44. Questions
What command would be needed to print the last 250 characters of a file “data.txt”
What function can a parent process use to capture the exit code from a child process?
In terms of Linux scheduling what is a runqueue?
How does Linux use the Buddy algorithm to allocate memory for a process?
What information is kept in an open file description table that isn’t kept anywhere else?
What is the primary advantage of a journaling file system over earlier file systems (such as ext2fs)?
cs431-cotter