Process Control (Chapter 8 )
Total Page:16
File Type:pdf, Size:1020Kb
Load more
Recommended publications
-
Parallel Programming in Unix, Many Programs Run in at the Same Time
parallelism parallel programming! to perform a number of tasks simultaneously! these can be calculations, or data transfer or…! In Unix, many programs run in at the same time handling various tasks! we like multitasking…! we don’t like waiting… "1 simplest way: FORK() Each process has a process ID called PID.! After a fork() call, ! there will be a second process with another PID which we call the child. ! The first process, will also continue to exist and to execute commands, we call it the mother. "2 fork() example #include <stdio.h> // printf, stderr, fprintf! ! #include <sys/types.h> // pid_t ! } // end of child! #include <unistd.h> // _exit, fork! else ! #include <stdlib.h> // exit ! { ! #include <errno.h> // errno! ! ! /* If fork() returns a positive number, we int main(void)! are in the parent process! {! * (the fork return value is the PID of the pid_t pid;! newly created child process)! pid = fork();! */! ! int i;! if (pid == -1) {! for (i = 0; i < 10; i++)! fprintf(stderr, "can't fork, error %d\n", {! errno);! printf("parent: %d\n", i);! exit(EXIT_FAILURE);! sleep(1);! }! }! ! exit(0);! if (pid == 0) {! }// end of parent! /* Child process:! ! * If fork() returns 0, it is the child return 0;! process.! } */! int j;! for (j = 0; j < 15; j++) {! printf("child: %d\n", j);! sleep(1);! }! _exit(0); /* Note that we do not use exit() */! !3 why not to fork fork() system call is the easiest way of branching out to do 2 tasks concurrently. BUT" it creates a separate address space such that the child process has an exact copy of all the memory segments of the parent process. -
Freebsd-And-Git.Pdf
FreeBSD and Git Ed Maste - FreeBSD Vendor Summit 2018 Purpose ● History and Context - ensure we’re starting from the same reference ● Identify next steps for more effective use / integration with Git / GitHub ● Understand what needs to be resolved for any future decision on Git as the primary repository Version control history ● CVS ○ 1993-2012 ● Subversion ○ src/ May 31 2008, r179447 ○ doc/www May 19, 2012 r38821 ○ ports July 14, 2012 r300894 ● Perforce ○ 2001-2018 ● Hg Mirror ● Git Mirror ○ 2011- Subversion Repositories svnsync repo svn Subversion & Git Repositories today svn2git git push svnsync git svn repo svn git github Repositories Today fork repo / Freebsd Downstream svn github github Repositories Today fork repo / Freebsd Downstream svn github github “Git is not a Version Control System” phk@ missive, reproduced at https://blog.feld.me/posts/2018/01/git-is-not-revision-control/ Subversion vs. Git: Myths and Facts https://svnvsgit.com/ “Git has a number of advantages in the popularity race, none of which are really to do with the technology” https://chapmanworld.com/2018/08/25/why-im-now-using-both-git-and-subversion-for-one-project/ 10 things I hate about Git https://stevebennett.me/2012/02/24/10-things-i-hate-about-git Git popularity Nobody uses Subversion anymore False. A myth. Despite all the marketing buzz related to Git, such notable open source projects as FreeBSD and LLVM continue to use Subversion as the main version control system. About 47% of other open source projects use Subversion too (while only 38% are on Git). (2016) https://svnvsgit.com/ Git popularity (2018) Git UI/UX Yes, it’s a mess. -
The Linux Kernel Module Programming Guide
The Linux Kernel Module Programming Guide Peter Jay Salzman Michael Burian Ori Pomerantz Copyright © 2001 Peter Jay Salzman 2007−05−18 ver 2.6.4 The Linux Kernel Module Programming Guide is a free book; you may reproduce and/or modify it under the terms of the Open Software License, version 1.1. You can obtain a copy of this license at http://opensource.org/licenses/osl.php. This book is distributed in the hope it will be useful, but without any warranty, without even the implied warranty of merchantability or fitness for a particular purpose. The author encourages wide distribution of this book for personal or commercial use, provided the above copyright notice remains intact and the method adheres to the provisions of the Open Software License. In summary, you may copy and distribute this book free of charge or for a profit. No explicit permission is required from the author for reproduction of this book in any medium, physical or electronic. Derivative works and translations of this document must be placed under the Open Software License, and the original copyright notice must remain intact. If you have contributed new material to this book, you must make the material and source code available for your revisions. Please make revisions and updates available directly to the document maintainer, Peter Jay Salzman <[email protected]>. This will allow for the merging of updates and provide consistent revisions to the Linux community. If you publish or distribute this book commercially, donations, royalties, and/or printed copies are greatly appreciated by the author and the Linux Documentation Project (LDP). -
Process and Memory Management Commands
Process and Memory Management Commands This chapter describes the Cisco IOS XR software commands used to manage processes and memory. For more information about using the process and memory management commands to perform troubleshooting tasks, see Cisco ASR 9000 Series Aggregation Services Router Getting Started Guide. • clear context, on page 2 • dumpcore, on page 3 • exception coresize, on page 6 • exception filepath, on page 8 • exception pakmem, on page 12 • exception sparse, on page 14 • exception sprsize, on page 16 • follow, on page 18 • monitor threads, on page 25 • process, on page 29 • process core, on page 32 • process mandatory, on page 34 • show context, on page 36 • show dll, on page 39 • show exception, on page 42 • show memory, on page 44 • show memory compare, on page 47 • show memory heap, on page 50 • show processes, on page 54 Process and Memory Management Commands 1 Process and Memory Management Commands clear context clear context To clear core dump context information, use the clear context command in the appropriate mode. clear context location {node-id | all} Syntax Description location{node-id | all} (Optional) Clears core dump context information for a specified node. The node-id argument is expressed in the rack/slot/module notation. Use the all keyword to indicate all nodes. Command Default No default behavior or values Command Modes Administration EXEC EXEC mode Command History Release Modification Release 3.7.2 This command was introduced. Release 3.9.0 No modification. Usage Guidelines To use this command, you must be in a user group associated with a task group that includes appropriate task IDs. -
Writing Your First Linux Kernel Module
Writing your first Linux kernel module Praktikum Kernel Programming University of Hamburg Scientific Computing Winter semester 2014/2015 Outline ● Before you start ● Hello world module ● Compile, load and unload ● User space VS. kernel space programing ● Summary Before you start ● Define your module’s goal ● Define your module behaviour ● Know your hardware specifications ○ If you are building a device driver you should have the manual ● Documentation ○ /usr/src/linux/Documentation ○ make { htmldocs | psdocs | pdfdocks | rtfdocks } ○ /usr/src/linux/Documentation/DocBook Role of the device driver ● Software layer between application and device “black boxes” ○ Offer abstraction ■ Make hardware available to users ○ Hide complexity ■ User does not need to know their implementation ● Provide mechanism not policy ○ Mechanism ■ Providing the flexibility and the ability the device supports ○ Policy ■ Controlling how these capabilities are being used Role of the device driver ● Policy-free characteristics ○ Synchronous and asynchronous operations ○ Exploit the full capabilities of the hardware ○ Often a client library is provided as well ■ Provides capabilities that do not need to be implemented inside the module Outline ● Before you start ● Hello world module ● Compile, load and unload ● User space VS. kernel space programing ● Summary Hello world module /* header files */ #include <linux/module.h> #include <linux/init.h> /* the initialization function */ /* the shutdown function */ static int __init hello_init(void) { static void __exit hello_exit(void) -
Name Synopsis Description
Perl version 5.10.0 documentation - vmsish NAME vmsish - Perl pragma to control VMS-specific language features SYNOPSIS use vmsish; use vmsish 'status';# or '$?' use vmsish 'exit'; use vmsish 'time'; use vmsish 'hushed'; no vmsish 'hushed'; vmsish::hushed($hush); use vmsish; no vmsish 'time'; DESCRIPTION If no import list is supplied, all possible VMS-specific features areassumed. Currently, there are four VMS-specific features available:'status' (a.k.a '$?'), 'exit', 'time' and 'hushed'. If you're not running VMS, this module does nothing. vmsish status This makes $? and system return the native VMS exit statusinstead of emulating the POSIX exit status. vmsish exit This makes exit 1 produce a successful exit (with status SS$_NORMAL),instead of emulating UNIX exit(), which considers exit 1 to indicatean error. As with the CRTL's exit() function, exit 0 is also mappedto an exit status of SS$_NORMAL, and any other argument to exit() isused directly as Perl's exit status. vmsish time This makes all times relative to the local time zone, instead of thedefault of Universal Time (a.k.a Greenwich Mean Time, or GMT). vmsish hushed This suppresses printing of VMS status messages to SYS$OUTPUT andSYS$ERROR if Perl terminates with an error status. and allowsprograms that are expecting "unix-style" Perl to avoid having to parseVMS error messages. It does not suppress any messages from Perlitself, just the messages generated by DCL after Perl exits. The DCLsymbol $STATUS will still have the termination status, but with ahigh-order bit set: EXAMPLE:$ perl -e"exit 44;" Non-hushed error exit%SYSTEM-F-ABORT, abort DCL message$ show sym $STATUS$STATUS == "%X0000002C" $ perl -e"use vmsish qw(hushed); exit 44;" Hushed error exit $ show sym $STATUS $STATUS == "%X1000002C" The 'hushed' flag has a global scope during compilation: the exit() ordie() commands that are compiled after 'vmsish hushed' will be hushedwhen they are executed. -
Process Management
Princeton University Computer Science 217: Introduction to Programming Systems Process Management 1 Goals of this Lecture Help you learn about: • Creating new processes • Waiting for processes to terminate • Executing new programs • Shell structure Why? • Creating new processes and executing new programs are fundamental tasks of many utilities and end-user applications • Assignment 7… 2 System-Level Functions As noted in the Exceptions and Processes lecture… Linux system-level functions for process management Function Description exit() Terminate the process fork() Create a child process wait() Wait for child process termination execvp() Execute a program in current process getpid() Return the process id of the current process 3 Agenda Creating new processes Waiting for processes to terminate Executing new programs Shell structure 4 Why Create New Processes? Why create a new process? • Scenario 1: Program wants to run an additional instance of itself • E.g., web server receives request; creates additional instance of itself to handle the request; original instance continues listening for requests • Scenario 2: Program wants to run a different program • E.g., shell receives a command; creates an additional instance of itself; additional instance overwrites itself with requested program to handle command; original instance continues listening for commands How to create a new process? • A “parent” process forks a “child” process • (Optionally) child process overwrites itself with a new program, after performing appropriate setup 5 fork System-Level -
Getting Started With... Berkeley Software for UNIX† on the VAX‡ (The Third Berkeley Software Distribution)
Getting started with... Berkeley Software for UNIX† on the VAX‡ (The third Berkeley Software Distribution) A package of software for UNIX developed at the Computer Science Division of the University of California at Berkeley is installed on our system. This package includes a new version of the operating sys- tem kernel which supports a virtual memory, demand-paged environment. While the kernel change should be transparent to most programs, there are some things you should know if you plan to run large programs to optimize their performance in a virtual memory environment. There are also a number of other new pro- grams which are now installed on our machine; the more important of these are described below. Documentation The new software is described in two new volumes of documentation. The first is a new version of volume 1 of the UNIX programmers manual which has integrated manual pages for the distributed software and incorporates changes to the system made while introducing the virtual memory facility. The second volume of documentation is numbered volume 2c, of which this paper is a section. This volume contains papers about programs which are in the distribution package. Where are the programs? Most new programs from Berkeley reside in the directory /usr/ucb. A major exception is the C shell, csh, which lives in /bin. We will later describe how you can arrange for the programs in the distribution to be part of your normal working environment. Making use of the Virtual Memory With a virtual memory system, it is no longer necessary for running programs to be fully resident in memory. -
Processes Process States
Processes • A process is a program in execution • Synonyms include job, task, and unit of work • Not surprisingly, then, the parts of a process are precisely the parts of a running program: Program code, sometimes called the text section Program counter (where we are in the code) and other registers (data that CPU instructions can touch directly) Stack — for subroutines and their accompanying data Data section — for statically-allocated entities Heap — for dynamically-allocated entities Process States • Five states in general, with specific operating systems applying their own terminology and some using a finer level of granularity: New — process is being created Running — CPU is executing the process’s instructions Waiting — process is, well, waiting for an event, typically I/O or signal Ready — process is waiting for a processor Terminated — process is done running • See the text for a general state diagram of how a process moves from one state to another The Process Control Block (PCB) • Central data structure for representing a process, a.k.a. task control block • Consists of any information that varies from process to process: process state, program counter, registers, scheduling information, memory management information, accounting information, I/O status • The operating system maintains collections of PCBs to track current processes (typically as linked lists) • System state is saved/loaded to/from PCBs as the CPU goes from process to process; this is called… The Context Switch • Context switch is the technical term for the act -
Chapter 3: Processes
Chapter 3: Processes Operating System Concepts – 9th Edition Silberschatz, Galvin and Gagne ©2013 Chapter 3: Processes Process Concept Process Scheduling Operations on Processes Interprocess Communication Examples of IPC Systems Communication in Client-Server Systems Operating System Concepts – 9th Edition 3.2 Silberschatz, Galvin and Gagne ©2013 Objectives To introduce the notion of a process -- a program in execution, which forms the basis of all computation To describe the various features of processes, including scheduling, creation and termination, and communication To explore interprocess communication using shared memory and message passing To describe communication in client-server systems Operating System Concepts – 9th Edition 3.3 Silberschatz, Galvin and Gagne ©2013 Process Concept An operating system executes a variety of programs: Batch system – jobs Time-shared systems – user programs or tasks Textbook uses the terms job and process almost interchangeably Process – a program in execution; process execution must progress in sequential fashion Multiple parts The program code, also called text section Current activity including program counter, processor registers Stack containing temporary data Function parameters, return addresses, local variables Data section containing global variables Heap containing memory dynamically allocated during run time Operating System Concepts – 9th Edition 3.4 Silberschatz, Galvin and Gagne ©2013 Process Concept (Cont.) Program is passive entity stored on disk (executable -
Practical Session 1, System Calls a Few Administrative Notes…
Operating Systems, 142 Tas: Vadim Levit , Dan Brownstein, Ehud Barnea, Matan Drory and Yerry Sofer Practical Session 1, System Calls A few administrative notes… • Course homepage: http://www.cs.bgu.ac.il/~os142/ • Contact staff through the dedicated email: [email protected] (format the subject of your email according to the instructions listed in the course homepage) • Assignments: Extending xv6 (a pedagogical OS) Submission in pairs. Frontal checking: 1. Assume the grader may ask anything. 2. Must register to exactly one checking session. System Calls • A System Call is an interface between a user application and a service provided by the operating system (or kernel). • These can be roughly grouped into five major categories: 1. Process control (e.g. create/terminate process) 2. File Management (e.g. read, write) 3. Device Management (e.g. logically attach a device) 4. Information Maintenance (e.g. set time or date) 5. Communications (e.g. send messages) System Calls - motivation • A process is not supposed to access the kernel. It can’t access the kernel memory or functions. • This is strictly enforced (‘protected mode’) for good reasons: • Can jeopardize other processes running. • Cause physical damage to devices. • Alter system behavior. • The system call mechanism provides a safe mechanism to request specific kernel operations. System Calls - interface • Calls are usually made with C/C++ library functions: User Application C - Library Kernel System Call getpid() Load arguments, eax _NR_getpid, kernel mode (int 80) Call sys_getpid() Sys_Call_table[eax] syscall_exit return resume_userspace return User-Space Kernel-Space Remark: Invoking int 0x80 is common although newer techniques for “faster” control transfer are provided by both AMD’s and Intel’s architecture. -
UNIX X Command Tips and Tricks David B
SESUG Paper 122-2019 UNIX X Command Tips and Tricks David B. Horvath, MS, CCP ABSTRACT SAS® provides the ability to execute operating system level commands from within your SAS code – generically known as the “X Command”. This session explores the various commands, the advantages and disadvantages of each, and their alternatives. The focus is on UNIX/Linux but much of the same applies to Windows as well. Under SAS EG, any issued commands execute on the SAS engine, not necessarily on the PC. X %sysexec Call system Systask command Filename pipe &SYSRC Waitfor Alternatives will also be addressed – how to handle when NOXCMD is the default for your installation, saving results, and error checking. INTRODUCTION In this paper I will be covering some of the basics of the functionality within SAS that allows you to execute operating system commands from within your program. There are multiple ways you can do so – external to data steps, within data steps, and within macros. All of these, along with error checking, will be covered. RELEVANT OPTIONS Execution of any of the SAS System command execution commands depends on one option's setting: XCMD Enables the X command in SAS. Which can only be set at startup: options xcmd; ____ 30 WARNING 30-12: SAS option XCMD is valid only at startup of the SAS System. The SAS option is ignored. Unfortunately, ff NOXCMD is set at startup time, you're out of luck. Sorry! You might want to have a conversation with your system administrators to determine why and if you can get it changed.