Operating Systems (202-1-3031) Meni Adler Office: Alon, 211 adlerm@cs.bgu.ac.il Office hours: Wed.. Danny Hendler Office: Alon, 218 hendlerd@cs.bgu.ac.il Office hours: 11:30-13:30 Amnon Meisels Office: Alon, 206 am@cs.bgu.ac.il Office hours: Wed. 9-11 Lecturers: Meni Adler, Danny Hendler and Amnon Meisels TAs: Vadim Levit, Ehud Barnea, Matan Drori, Yeri Sofer and Dan Brownstein (Zohar Komarovski & Tomer Sidi) Course site: http://www.cs.bgu.ac.il/~os142/main 1
Assignments and grade structure Assignment Programming 1 + 2 Programming 3 + 4 Midterm Final Subject Scheduling + Synchronization Memory Management + Files Processes, scheduling, synchronization, memory (TBD) All Weight 15% 15% 15% 55% Assignments and exams are mandatory Must pass final exam 2
Textbooks A. Tanenbaum: Modern Operating Systems, Prentice-Hall, 3 rd Edition, 2008 A. Silbetschatz et al.: Operating System Concepts (9th ed.), Addison Wesley, 2012 G. Nutt: Operating Systems (a modern perspective) (3rd ed.), Addison Wesley, 2003 W. Stallings: Operating Systems (6th ed.), Prentice-Hall, 2009 Operating Systems, 2014, Meni Adler, Danny Hendler & Amnon Meisels 3
Syllabus 1. Introduction - History; Views; Concepts; Structure 2. Process Management - Processes; State + Resources; Threads; Unix implementation of Processes 3. Scheduling Paradigms; Unix; Modeling 4. Synchronization - Synchronization primitives and their equivalence; Deadlocks 5. Memory Management - Virtual memory; Page replacement algorithms; Segmentation 6. File Systems - Implementation; Directory and space management; Unix file system; Distributed file systems (NFS) 7. Distributed Synchronization (if there's time) Operating Systems, 2014, Meni Adler, Danny Hendler & Amnon Meisels 4
Introduction: outline What is an operating system? Some history OS concepts OS structure Operating Systems, 2014, Meni Adler, Danny Hendler & Amnon Meisels 5
Layered Hardware-Software Machine Model Operating Systems, 2014, Meni Adler, Danny Hendler & Amnon Meisels 6
Computer-System Architecture Operating Systems, 2014, Meni Adler, Danny Hendler & Amnon Meisels 7
What is an Operating System? An operating system is: 1. An Extended Machine 2. A Resource manager Operating Systems, 2014, Meni Adler, Danny Hendler & Amnon Meisels 8
Operating Systems as extended Machines The problems: Bare machine has complex structure o Processors o Many difficult-to-program devices Primitive Instruction Set Different for Different Machines OS provides: Abstraction! Simple, easier to use interface (machine-independent) Hiding of unnecessary details Operating Systems, 2014, Meni Adler, Danny Hendler & Amnon Meisels 9
OS abstraction example: read from disk Read file data from disk (simplified) Read linear sector 17,403 from disk 2 Convert linear sector number to: cylinder, sector, head (may be complicated outer cylinders have more sectors, bad sectors remapped, etc.) Move disk arm to requested cylinder Wait for proper sector to appear OS abstraction return-code = read(fd, buff, nbytes) Operating Systems, 2014, Meni Adler, Danny Hendler & Amnon Meisels 10
UNIX high-level architecture User Interface Operating Systems, 2014, Meni Adler, Danny Hendler & Amnon Meisels 11
Operating Systems as Resource Managers Multiple resources o Processors; Memory o Disks; Tapes; Printers o Network interfaces; Terminals Controlled allocation of Resources among: o Groups, Users; Processes, Threads, Means of control: sharing/multiplexing/scheduling, monitoring, protection, report/payment Operating Systems, 2014, Meni Adler, Danny Hendler & Amnon Meisels 12
Introduction: outline What is an operating system? Some history OS concepts OS structure Operating Systems, 2014, Meni Adler, Danny Hendler & Amnon Meisels 13
History of Operating Systems First generation 1945-1955 o vacuum tubes, plug boards user plugs-in program Operating Systems, 2014, Meni Adler, Danny Hendler & Amnon Meisels 14
The first computers Electronic Numerical Integrator And Computer (ENIAC) Mathematical Analyzer, Numeric Integrator And Computer(MANIAC) Operating Systems, 2014, Meni Adler, Danny Hendler & Amnon Meisels 15
History of Operating Systems (cont d) Second generation 1955-1965 o transistors, batch systems multiple programs on Disk Third generation 1965 1980 o ICs and multiprogramming - user interaction (time-sharing) Fourth generation 1980 present o personal computers graphic user-interface o Networks file & computing services o Web-computing, Handheld devices, Cellular phones, Cloud computing Operating Systems, 2014, Meni Adler, Danny Hendler & Amnon Meisels 16
How Bill Gates became rich 1974: Intel releases the 8080 processor, needs an OS Please! develop an OS CP/M OS Gary Kildall Operating Systems, 2014, Meni Adler, Danny Hendler & Amnon Meisels 17
How Bill Gates became rich (cont d) 1974: Intel releases the 8080 processor, needs an OS CP/M OS Can you grant me CP/M rights? Sure! Gary Kildall Operating Systems, 2014, Meni Adler, Danny Hendler & Amnon Meisels 18
How Bill Gates became rich (cont d) 1980: IBM designs IMB PC, needs an OS Can you find an OS for our PC? Please meet IBM, they need an OS Gary Kildall Operating Systems, 2014, Meni Adler, Danny Hendler & Amnon Meisels 19
How Bill Gates became rich (cont d) 1980: IBM designs IMB PC, needs an OS Kildall too busy. Please develop an OS! I de like to buy the DOS OS Sure, it s yours for $75,000 Operating Systems, 2014, Meni Adler, Danny Hendler & Amnon Meisels 20
How Bill Gates became rich (cont d) 1980: IBM designs IMB PC, needs an OS May I retain the rights for MS- DOS? Sure, why not!! Operating Systems, 2014, Meni Adler, Danny Hendler & Amnon Meisels 21
How Bill Gates became rich (cont d) Well, this is 20:20 hind vision Operating Systems, 2014, Meni Adler, Danny Hendler & Amnon Meisels 22
Introduction: outline What is an operating system? Some history OS concepts OS structure Operating Systems, 2014, Meni Adler, Danny Hendler & Amnon Meisels 23
OS Key Functions Process management o process creation; deletion; suspension/preemption o process synchronization; communication; scheduling Main-memory management o Manage used parts and their current users o Select processes to load from secondary storage o Allocate memory to running processes Secondary storage management o Free-space management o Storage allocation Operating Systems, 2014, Meni Adler, Danny Hendler & Amnon Meisels 24
OS Key Functions (cont d) File system management o File + directory - creation; deletion o File manipulation primitives o Mapping files onto secondary storage I/O system management o General device-driver interface o Drivers for specific hardware devices Protection system o Distinguish between authorized and unauthorized usage o Provide means of enforcement Operating Systems, 2014, Meni Adler, Danny Hendler & Amnon Meisels 25
Processes - a key concept Resource container for program in execution Timesharing, process suspension/preemption Process Table Process Groups Signals Operating Systems, 2014, Meni Adler, Danny Hendler & Amnon Meisels 26
Why do we need multiple processes? Single application: We want things to happen concurrently (E.g.: paging and typing in a text editor) Multiple applications: processes running in the background (e.g., Anti Virus) Multiple users: The departmental computer; all types of Servers Operating Systems, 2014, Meni Adler, Danny Hendler & Amnon Meisels 27
Multiprogramming: how is it done? CPU much faster than I/O o Computation/communication overlap Memory large enough requires memory protection! Scheduler which manages flow of jobs in and out and shares CPU between jobs requires Timer Operating Systems, 2014, Meni Adler, Danny Hendler & Amnon Meisels 28
Process trees A process tree A created two child processes, B and C B created three child processes, D, E, and F Operating Systems, 2014, Meni Adler, Danny Hendler & Amnon Meisels 29
Inter-Process Communication (IPC) Two processes communicating via a pipe Operating Systems, 2014, Meni Adler, Danny Hendler & Amnon Meisels 30
Files: non volatile data File types and operations on files Directories - hierarchical structure Working directories Root directory Students Faculty Amnon Gil Roni Or Papers Progs G rants Operating Systems, 2014, Meni Adler, Danny Hendler & Amnon Meisels 31
Files: non volatile data (cont d) Protection and Security Unix - user; group; other (rwx bits) File descriptors (handles) I/O as a special file Block & Character special files Standard input; output; error Pipes Links Operating Systems, 2014, Meni Adler, Danny Hendler & Amnon Meisels 32
I/O is performed in kernel mode All I/O instructions are privileged instructions I/O devices and CPU can execute concurrently CPU moves data between main memory and device controllers' buffers (done by device drivers) Device controllers interrupt upon completion Interrupts or Traps enable mode switching Operating systems are interrupt-driven Traps/signals: software interrupts Operating Systems, 2014, Meni Adler, Danny Hendler & Amnon Meisels 33
Interrupts and the fetch-decode-execute loop Do forever{ IR = memory[pc]; execute(ir); PC++; If(Interrupt_Request) { memory[0] = PC; PC = memory[1] } } An interrupt is an asynchronous event The kernel interrupt handling routine may use a disable_interrupts instruction to avoid losing data while processing an interrupt request Interrupt handler is typically called indirectly via the interrupt vector Operating Systems, 2014, Meni Adler, Danny Hendler & Amnon Meisels 34
Synchronous vs. Asynchronous I/O execute Operating Systems, 2014, Meni Adler, Danny Hendler & Amnon Meisels 35
Steps in Making a System Call There are 11 steps in making the system call: read (fd, buffer, nbytes) Is this call Synchronous or Asynchronous? Operating Systems, 2014, Meni Adler, Danny Hendler & Amnon Meisels 36
System Calls processes files directories miscellaneous Operating Systems, 2014, Meni Adler, Danny Hendler & Amnon Meisels 37
The Shell Command Language sort < file1 > file2 cat file1 sort lpr The Shell is a process which executes its commands as offspring processes Processes may call shell commands by using the system system call Operating Systems, 2014, Meni Adler, Danny Hendler & Amnon Meisels 38
Shell structure Parent & child A stripped-down shell: while (TRUE) { /* repeat forever */ type_prompt( ); /* display prompt */ read_command (command, parameters) /* input from terminal */ } if (fork() > 0) { /* fork off child process */ /* Parent code */ wait(); /* wait for child to exit */ } else { /* Child code */ execvp (command, parameters); /* execute command */ } Operating Systems, 2014, Meni Adler, Danny Hendler & Amnon Meisels 39
Linux Shell initialization The init program (process 1) runs getty on all ports Upon detecting a terminal, getty runs login Typing in a user name and a password login checks the passwd file and if correct runs a shell the one specified in the UID entry The shell is run with that user ID environment parameters Operating Systems, 2014, Meni Adler, Danny Hendler & Amnon Meisels 40
Running user commands User types: grep some_word file_name Shell parses the command, inserts the strings grep, some_word, file_name into argv and their number to argc Next, the shell uses fork() to create a process (same user ID) Now, it takes the executable name grep and the arguments, all from argv, and uses execvp() (or a similar system call) to run the grep executable On foreground execution, the shell would use the wait() system call and continue its session only after the child process terminates Operating Systems, 2014, Meni Adler, Danny Hendler & Amnon Meisels 41
UNIX Utility Programs A few of the more common UNIX utility programs required by POSIX Operating Systems, 2014, Meni Adler, Danny Hendler & Amnon Meisels 42
Introduction: outline What is an operating system? Some history OS concepts )חומר העשרה ) structure OS Operating Systems, 2014, Meni Adler, Danny Hendler & Amnon Meisels 43
Operating system structure 1. Monolithic systems 2. Virtual machines 3. Client-server model Operating Systems, 2014, Meni Adler, Danny Hendler & Amnon Meisels 44
Monolithic systems Monolithic systems have little structure Main procedure for invoking OS service Service Routines Utility procedures Operating Systems, 2014, Meni Adler, Danny Hendler & Amnon Meisels 45
Monolithic systems Service routines are system calls Utility procedures serve multiple service routines All compiled into a single system Operating Systems, 2014, Meni Adler, Danny Hendler & Amnon Meisels 46
Virtual Machines Provide an interface identical to the underlying bare machine VM monitor creates multiple VMs, each executing on its own (virtual) processor and its own (virtual) memory Virtual machines provide complete protection of system resources - even separate resources Difficult to implement, due to the effort required to provide an exact duplicate of the underlying machine Well-known examples: o MS-DOS on top of Windows o JVM o VMWare Operating Systems, 2014, Meni Adler, Danny Hendler & Amnon Meisels 47
Virtual Machines: IBM 370 CMS CMS CMS VM/370 user kernel 370 bare hardware CMS: Conversational Monitor System, a single user OS Operating Systems, 2014, Meni Adler, Danny Hendler & Amnon Meisels 48
Virtual Machines (cont d) Operating Systems, 2014, Meni Adler, Danny Hendler & Amnon Meisels 49
Modern virtual machines Different legacy servers run on different OS Host sharing for web servers Use multiple operating systems on a single machine Security through isolation Operating Systems, 2014, Meni Adler, Danny Hendler & Amnon Meisels 50
Microkernels Small number of lines of code mostly in C Catching interrupts and switching processes in Assembly C code manages and schedules processes, interprocess communication, i/o interaction Offers few (~40) system calls for the rest of OS Device drivers (Disk, Network, ) in user mode Upper level contains Servers File, Process.. Operating Systems, 2014, Meni Adler, Danny Hendler & Amnon Meisels 51
Client-Server Model Client Process Client Process...... File Server Memory Server (Micro)Kernel Machine1 Machine2 Machine3 Machine4 Client File Server Process Server....... Kernel Kernel Kernel Kernel Network Distributed System Operating Systems, 2014, Meni Adler, Danny Hendler & Amnon Meisels 52
Client/server architecture: Mechanism vs. Policy Simple Kernel - modularity; minimal privileged operation Servers for files, memory, etc. - distribution; user mode operation good for distributed systems Mechanism in kernel - how to do things.. Policy outside - decide what to do; can be changed later.. Critical servers in kernel i/o disk server & the Scheduler who serves who. Operating Systems, 2014, Meni Adler, Danny Hendler & Amnon Meisels 53