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157 lines
4.5 KiB
157 lines
4.5 KiB
4 years ago
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<!DOCTYPE html>
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<html lang="en">
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<head>
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<meta charset="UTF-8">
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<meta http-equiv="X-UA-Compatible" content="IE=edge">
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<meta name="viewport" content="width=device-width, initial-scale=1.0">
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<meta name="generator" content="Asciidoctor 2.0.12">
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<meta name="description" content="Linux process management">
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<meta name="keywords" content="ps aux">
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<meta name="author" content="Apostolos rootApostolos@swarmlab.io">
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<title>Linux process management !</title>
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<link rel="stylesheet" href="http://cdnjs.cloudflare.com/ajax/libs/asciidoctor.js/1.5.9/css/asciidoctor.min.css">
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</head>
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<body class="article toc2 toc-right">
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<div id="header">
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<h1>Linux process management !</h1>
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<div class="details">
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<span id="author" class="author">Apostolos rootApostolos@swarmlab.io</span><br>
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</div>
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<div id="toc" class="toc2">
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<div id="toctitle">Table of contents</div>
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<ul class="sectlevel1">
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<li><a href="#_process">1. process</a></li>
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<li><a href="#_linux_process_management">2. Linux process management</a>
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<ul class="sectlevel2">
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<li><a href="#_life_cycle_of_a_process">2.1. Life cycle of a process</a></li>
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<li><a href="#_process_state">2.2. process state</a></li>
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</ul>
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</li>
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</ul>
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</div>
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</div>
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<div id="content">
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<div class="sect1">
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<h2 id="_process">1. process</h2>
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<div class="sectionbody">
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<div class="paragraph">
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<p>An instance of a running program is called a process.
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Every time you run a shell command, a program is run and a process is created for it.</p>
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</div>
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<div class="paragraph">
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<p>In any modern operating system there can be more than one instance of a program loaded in memory at the same time.</p>
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</div>
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</div>
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</div>
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<div class="sect1">
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<h2 id="_linux_process_management">2. Linux process management</h2>
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<div class="sectionbody">
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<div class="paragraph">
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<p>Operating systems need some ways to create processes.</p>
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</div>
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<div class="ulist">
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<ul>
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<li>
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<p>In a very simple system designed for running only a single application (e.g., the controller in a microwave oven), it may be possible to have all the processes that will ever be needed be present when the system comes up.</p>
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</li>
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<li>
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<p>In general-purpose systems, however, some way is needed to create and terminate processes as needed during operation.</p>
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</li>
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</ul>
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</div>
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<div class="admonitionblock note">
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<table>
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<tr>
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<td class="icon">
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<i class="fa icon-note" title="Note"></i>
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</td>
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<td class="content">
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<div class="paragraph">
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<p><strong>There are four principal events that cause a process to be created:</strong></p>
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</div>
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<div class="ulist">
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<ul>
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<li>
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<p>System initialization.</p>
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</li>
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<li>
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<p>Execution of process creation system call by a running process.</p>
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</li>
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<li>
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<p>A user request to create a new process.</p>
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</li>
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<li>
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<p>Initiation of a batch job.</p>
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</li>
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</ul>
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</div>
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</td>
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</tr>
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</table>
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</div>
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<div class="paragraph">
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<p>Process creation in UNIX and Linux are done through <strong>fork()</strong> or <strong>clone()</strong> system calls.</p>
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</div>
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<div class="paragraph">
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<p>There are several steps involved in process creation.</p>
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</div>
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<div class="ulist">
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<ul>
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<li>
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<p>process scheduling,</p>
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</li>
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<li>
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<p>interrupt handling,</p>
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</li>
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<li>
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<p>signaling,</p>
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</li>
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<li>
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<p>process prioritization,</p>
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</li>
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<li>
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<p>process switching,</p>
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</li>
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<li>
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<p>process state,</p>
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</li>
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<li>
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<p>process memory</p>
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</li>
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</ul>
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</div>
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<div class="sect2">
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<h3 id="_life_cycle_of_a_process">2.1. Life cycle of a process</h3>
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<div class="admonitionblock note">
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<table>
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<tr>
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<td class="icon">
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<i class="fa icon-note" title="Note"></i>
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</td>
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<td class="content">
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<strong>1→</strong> creation <strong>2→</strong> execution <strong>3→</strong> termination <strong>4→</strong> removal
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</td>
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</tr>
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</table>
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</div>
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</div>
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<div class="sect2">
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<h3 id="_process_state">2.2. process state</h3>
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<div class="paragraph">
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<p>An operating system kernel that allows multitasking needs processes to have certain states. Names for these states are not standardised, but they have similar functionality.</p>
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</div>
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</div>
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</div>
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</div>
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