ch2.pptx

Operating System Services  Operating systems provide an environment for execution of programs and services to programs and users  One set of operating-system services provides functions that are helpful to the user:...

Operating System Services  Operating systems provide an environment for execution of programs and services to programs and users  One set of operating-system services provides functions that are helpful to the user: User interface - Almost all operating systems have a user interface (UI).  Varies between Command-Line (CLI), Graphics User Interface (GUI), touch-screen, Batch Program execution - The system must be able to load a program into memory and to run that program, end execution, either normally or abnormally (indicating error) I/O operations - A running program may require I/O, which may involve a file or an I/O device File-system manipulation - The file system is of particular interest. Programs need to read and write files and directories, create and delete them, search them, list file Information, permission management. Operating System Concepts – 10th Edition 2.1 Silberschatz, Galvin and Gagne ©2018  Operating System Services (Cont.)  One set of operating-system services provides functions that are helpful to the user (Cont.): Communications – Processes may exchange information, on the same computer or between computers over a network  Communications may be via shared memory or through message passing (packets moved by the OS) Error detection – OS needs to be constantly aware of possible errors  May occur in the CPU and memory hardware, in I/O devices, in user program  For each type of error, OS should take the appropriate action to ensure correct and consistent computing  Debugging facilities can greatly enhance the user’s and programmer’s abilities to efficiently use the system Operating System Concepts – 10th Edition 2.2 Silberschatz, Galvin and Gagne ©2018  Operating System Services (Cont.)  Another set of OS functions exists for ensuring the efficient operation of the system itself via resource sharing Resource allocation - When multiple users or multiple jobs running concurrently, resources must be allocated to each of them  Many types of resources - CPU cycles, main memory, file storage, I/O devices. Logging - To keep track of which users use how much and what kinds of computer resources Protection and security - The owners of information stored in a multiuser or networked computer system may want to control use of that information, concurrent processes should not interfere with each other  Protection involves ensuring that all access to system resources is controlled  Security of the system from outsiders requires user authentication, extends to defending external I/O devices from invalid access attempts Operating System Concepts – 10th Edition 2.3 Silberschatz, Galvin and Gagne ©2018  Command Line interpreter  CLI allows direct command entry  Sometimes implemented in kernel, sometimes by systems program  Sometimes multiple flavors implemented – shells  Primarily fetches a command from user and executes it  Sometimes commands built-in, sometimes just names of programs If the latter, adding new features doesn’t require shell modification Operating System Concepts – 10th Edition 2.4 Silberschatz, Galvin and Gagne ©2018  User Operating System Interface - GUI  User-friendly desktop metaphor interface Usually mouse, keyboard, and monitor Icons represent files, programs, actions, etc Various mouse buttons over objects in the interface cause various actions (provide information, options, execute function, open directory (known as a folder) Invented at Xerox PARC  Many systems now include both CLI and GUI interfaces Microsoft Windows is GUI with CLI “command” shell Apple Mac OS X is “Aqua” GUI interface with UNIX kernel underneath and shells available Unix and Linux have CLI with optional GUI interfaces (CDE, KDE, GNOME) Operating System Concepts – 10th Edition 2.5 Silberschatz, Galvin and Gagne ©2018  Touchscreen Interfaces  Touchscreen devices require new interfaces Mouse not possible or not desired Actions and selection based on gestures Virtual keyboard for text entry  Voice commands Operating System Concepts – 10th Edition 2.6 Silberschatz, Galvin and Gagne ©2018  System Calls  Programming interface to the services provided by the OS  Typically written in a high-level language (C or C++)  Mostly accessed by programs via a high-level Application Programming Interface (API) rather than direct system call use  Three most common APIs are Win32 API for Windows, POSIX API for POSIX-based systems (including virtually all versions of UNIX, Linux, and Mac OS X), and Java API for the Java virtual machine (JVM) Note that the system-call names used throughout this text are generic Operating System Concepts – 10th Edition 2.7 Silberschatz, Galvin and Gagne ©2018  System Call Implementation  Typically, a number is associated with each system call System-call interface maintains a table indexed according to these numbers  The system call interface invokes the intended system call in OS kernel and returns status of the system call and any return values  The caller need know nothing about how the system call is implemented Just needs to obey API and understand what OS will do as a result call Most details of OS interface hidden from programmer by API  Managed by run-time support library (set of functions built into libraries included with compiler) Operating System Concepts – 10th Edition 2.8 Silberschatz, Galvin and Gagne ©2018  System Call Parameter Passing  Often, more information is required than simply identity of desired system call Exact type and amount of information vary according to OS and call  Three general methods used to pass parameters to the OS Simplest: pass the parameters in registers  In some cases, may be more parameters than registers Parameters stored in a block, or table, in memory, and address of block passed as a parameter in a register  This approach taken by Linux and Solaris Parameters placed, or pushed, onto the stack by the program and popped off the stack by the operating system Block and stack methods do not limit the number or length of parameters being passed Operating System Concepts – 10th Edition 2.9 Silberschatz, Galvin and Gagne ©2018  System Services  System programs provide a convenient environment for program development and execution. They can be divided into: File manipulation Status information sometimes stored in a file Programming language support Program loading and execution Communications Background services Application programs  Most users’ view of the operating system is defined by system programs, not the actual system calls Operating System Concepts – 10th Edition 2.10 Silberschatz, Galvin and Gagne ©2018  System Services (Cont.)  Provide a convenient environment for program development and execution Some of them are simply user interfaces to system calls; others are considerably more complex  File management - Create, delete, copy, rename, print, dump, list, and generally manipulate files and directories  Status information Some ask the system for info - date, time, amount of available memory, disk space, number of users Others provide detailed performance, logging, and debugging information Typically, these programs format and print the output to the terminal or other output devices Some systems implement a registry - used to store and retrieve configuration information Operating System Concepts – 10th Edition 2.11 Silberschatz, Galvin and Gagne ©2018  System Services (Cont.)  File modification Text editors to create and modify files Special commands to search contents of files or perform transformations of the text  Programming-language support - Compilers, assemblers, debuggers and interpreters sometimes provided  Program loading and execution- Absolute loaders, relocatable loaders, linkage editors, and overlay-loaders, debugging systems for higher-level and machine language  Communications - Provide the mechanism for creating virtual connections among processes, users, and computer systems Allow users to send messages to one another’s screens, browse web pages, send electronic-mail messages, log in remotely, transfer files from one machine to another Operating System Concepts – 10th Edition 2.12 Silberschatz, Galvin and Gagne ©2018  System Services (Cont.)  Background Services Launch at boot time Some for system startup, then terminate   Some from system boot to shutdown Provide facilities like disk checking, process scheduling, error logging, printing Run in user context not kernel context Known as services, subsystems, daemons  Application programs Don’t pertain to system Run by users Not typically considered part of OS Launched by command line, mouse click, finger poke Operating System Concepts – 10th Edition 2.13 Silberschatz, Galvin and Gagne ©2018  Linkers and Loaders  Source code compiled into object files designed to be loaded into any physical memory location – relocatable object file  Linker combines these into single binary executable file Also brings in libraries  Program resides on secondary storage as binary executable  Must be brought into memory by loader to be executed Relocation assigns final addresses to program parts and adjusts code and data in program to match those addresses  Modern general purpose systems don’t link libraries into executables Rather, dynamically linked libraries (in Windows, DLLs) are loaded as needed, shared by all that use the same version of that same library (loaded once)  Object, executable files have standard formats, so operating system knows how to load and start them Operating System Concepts – 10th Edition 2.14 Silberschatz, Galvin and Gagne ©2018  Operating System Structure  General-purpose OS is very large program  Various ways to structure ones Simple structure – MS-DOS More complex – UNIX Layered – an abstraction Microkernel – Mach Operating System Concepts – 10th Edition 2.15 Silberschatz, Galvin and Gagne ©2018  Monolithic Structure – Original UNIX  UNIX – limited by hardware functionality, the original UNIX operating system had limited structuring.  The UNIX OS consists of two separable parts Systems programs The kernel  Consists of everything below the system-call interface and above the physical hardware  Provides the file system, CPU scheduling, memory management, and other operating-system functions; a large number of functions for one level Operating System Concepts – 10th Edition 2.16 Silberschatz, Galvin and Gagne ©2018  Layered Approach  The operating system is divided into a number of layers (levels), each built on top of lower layers. The bottom layer (layer 0), is the hardware; the highest (layer N) is the user interface.  With modularity, layers are selected such that each uses functions (operations) and services of only lower-level layers Operating System Concepts – 10th Edition 2.17 Silberschatz, Galvin and Gagne ©2018  Microkernels  Moves as much from the kernel into user space  Mach is an example of microkernel Mac OS X kernel (Darwin) partly based on Mach  Communication takes place between user modules using message passing  Benefits: Easier to extend a microkernel Easier to port the operating system to new architectures More reliable (less code is running in kernel mode) More secure  Detriments: Performance overhead of user space to kernel space communication Operating System Concepts – 10th Edition 2.18 Silberschatz, Galvin and Gagne ©2018  Modules  Many modern operating systems implement loadable kernel modules (LKMs) Uses object-oriented approach Each core component is separate Each talks to the others over known interfaces Each is loadable as needed within the kernel  Overall, similar to layers but with more flexible Linux, Solaris, etc. Operating System Concepts – 10th Edition 2.19 Silberschatz, Galvin and Gagne ©2018  Hybrid Systems  Most modern operating systems are not one pure model Hybrid combines multiple approaches to address performance, security, usability needs Linux and Solaris kernels in kernel address space, so monolithic, plus modular for dynamic loading of functionality Windows mostly monolithic, plus microkernel for different subsystem personalities  Apple Mac OS X hybrid, layered, Aqua UI plus Cocoa programming environment Below is kernel consisting of Mach microkernel and BSD Unix parts, plus I/O kit and dynamically loadable modules (called kernel extensions) Operating System Concepts – 10th Edition 2.20 Silberschatz, Galvin and Gagne ©2018  System Boot  When power initialized on system, execution starts at a fixed memory location  Operating system must be made available to hardware so hardware can start it Small piece of code – bootstrap loader, BIOS, stored in ROM or EEPROM locates the kernel, loads it into memory, and starts it Sometimes two-step process where boot block at fixed location loaded by ROM code, which loads bootstrap loader from disk Modern systems replace BIOS with Unified Extensible Firmware Interface (UEFI)  Common bootstrap loader, GRUB, allows selection of kernel from multiple disks, versions, kernel options  Kernel loads and system is then running  Boot loaders frequently allow various boot states, such as single user mode Operating System Concepts – 10th Edition 2.21 Silberschatz, Galvin and Gagne ©2018