Os lecture 7
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This document discusses operating system structures and system calls, specifically focusing on process control and file management calls. It provides examples of common process control calls like end, abort, load, execute, and create/terminate process. It also lists examples of file management calls such as create/delete file, open/close, read/write/reposition, and get/set file attributes. The document explains that system calls allow programs to interface with the operating system to control processes and manipulate files.
Os lecture 7
- 1. OPERATING SYSTEM 4th Stage , College of Education , KUFA University CHAPTER TWO – OPERATING-SYSTEM STRUCTURES provides new coverage of user interfaces for mobile devices, including discussions of iOS and Android, and expanded coverage of Mac OS X as a type of hybrid system. Prepared By: Dr. Ahmed J. Obaid Lecture :7
- 2. 4th stage, CS Dept. Operating System, CH2 Dr. Ahmed J. Obaid Operating System Structure 2.4 System Calls System calls can be grouped roughly into six major categories: Process control, file manipulation, device manipulation, information maintenance, communications, and protection. 2.4.1 Process Control A running program needs to be able to halt its execution either normally (end ()) or abnormally (abort ()). If a system call is made to terminate the currently running program abnormally, or if the program runs into a problem and causes an error trap كمين او ,شرك a dump مهمل جزء of memory is sometimes taken and an error message generated. The dump is written to disk and may be examined by a debugger—a system program designed to aid the programmer in finding and correcting errors, or bugs—to determine the cause of the problem. Under either normal or abnormal circumstances, the operating system must transfer control to the invoking command interpreter. The command interpreter then reads the next command. In an interactive system, the command interpreter simply continues with the next command; it is assumed that the user will issue an appropriate command to respond to any error. In a GUI system, a pop-up window might alert the user to the error and ask for guidance. In a batch system, the command interpreter usually terminates the entire job and continues with the next job. Some systems may allow for special recovery actions in case an error occurs. If the program discovers an error in its input and wants to terminate abnormally, it may also want to define an error level.
- 3. 4th stage, CS Dept. Operating System, CH2 Dr. Ahmed J. Obaid Process Control Calls: ◦ end, abort ◦ load, execute ◦ create process, terminate process ◦ get process attributes, set process attributes ◦ wait for time ◦ wait event, signal event ◦ allocate and free memory ======================================================== LINUX: Process Control Linux is multi-tasking OS and it executes multiple processes simultaneous. One of the best futures of working at the terminal line is that we can easily manipulate this type of activity(processes). Why is important to control the processes in Linux Well, as administrator you will have to know and understand the Linux Processes and what types they are so you can manipulate then as you like. By manipulating we refer to the priority of running processes and termination of that processes.
- 4. 4th stage, CS Dept. Operating System, CH2 Dr. Ahmed J. Obaid What is Running Processes? Also called ‘running instance’ or ‘program’ the process is a program in execution. The processes consist in executing program code, resources such as open files, internal data, an address space, one or more threads of execution and a data section containing global variables. Every process has its own descriptors that keeps the information used to track the process in the memory. We will not look deep into the processes since this is a wide area in the Linux OS. We are going to describe and explain how we can see and manipulate the running processes. 2.4.2 File Management A running program needs to be able to halt its execution either normally (end ()) or abnormally (abort ()). We first need to be able to create() and delete() files. Either system call requires the name of the file and perhaps some of the file’s attributes. Once the file is created, we need to open() it and to use it. We may also read(), write(), or reposition() (rewind or skip to the end of the file, for example). Finally, we need to close() the file, indicating that we are no longer using it. We may need these same sets of operations for directories if we have a directory structure for organizing files in the file system. In addition, for either files or directories, we need to be able to determine the values of
- 5. 4th stage, CS Dept. Operating System, CH2 Dr. Ahmed J. Obaid various attributes and perhaps to reset them if necessary. File attributes include the file name, file type, protection codes, accounting information, and so on. Some operating systems provide many more calls, such as calls for file move() and copy(). Others might provide an API that performs those operations using code and other system calls, and others might provide system programs to perform those tasks. If the system programs are callable by other programs, then each can be considered an API by other system programs. File management Calls ◦ create file, delete file ◦ open, close ◦ read, write, reposition ◦ get file attributes, set file attributes