unix_prog_web/unix_prog_web_02.xhtml

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   7     <title>Systèmes d'exploitation (2/2)</title>
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  12           content="Copyright &#169; 2013 Kim Nguyễn" />
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  43   <body>
  44     <a href="unix_prog_web_01.xhtml" class="sws-previous" />
  45     <div class="sws-slide sws-cover sws-option-nofooter">
  46       <h1>Unix et Programmation Web</h1>
  47       <h1>Cours 2</h1>
  48       <a href="mailto:kn@lri.fr">kn@lri.fr</a><br/>
  49       <a href="http://www.lri.fr/~kn/">http://www.lri.fr/~kn</a>
  50     </div>
  51 <h1> Gestion des processus</h1>
  52
  53     <div class="sws-slide">
  54       <h1> Définitions </h1>
  55       <table class="desc">
  56         <tr>
  57           <td style="width:6.5em;">Programme</td> <td>séquences d'instructions effectuant
  58             une tâche sur un ordinateur</td>
  59         </tr>
  60         <tr>
  61           <td>Exécutable</td> <td>fichier binaire contenant des
  62             instructions machines interprétables par le
  63             microprocesseur</td>
  64         </tr>
  65         <tr>
  66           <td><i>Thread</i> </td>
  67           <td>plus petite unité de traitement (≡
  68             séquence d'instructions) pouvant être ordonnancée par
  69             l'OS
  70           </td>
  71         </tr>
  72         <tr>
  73           <td>Processus</td>
  74           <td> instance d'un programme (≡ « un
  75             programme en cours d'exécution »). Un processus est constitué
  76             de un ou plusieurs <i>threads</i>.</td>
  77         </tr>
  78       </table>
  79     </div>
  80
  81     <div class="sws-slide">
  82       <h1> Exemple: programme </h1>
  83       <p>Dans un fichier « <tt> counter.c </tt> »
  84         (<span style="color:red;">attention c'est du pseudo
  85           C</span>)</p>
  86       <div style="float:left;clear:both;vertical-align:top;width:45%;display:inline-block;border-right: 1pt solid #494948;">
  87 <code > int count = 0;
  88  int exit = 0;
  89  void <span style="color:green;">display()</span> {
  90     while (exit == 0) {
  91       sleep (3);
  92       printf("%i\n", count);
  93     }
  94  }
  95  void <span style="color:red;">listen()</span> {
  96     while (exit == 0) {
  97       wait_connect(80);
  98       count++;
  99   }
 100  }</code>
 101       </div> <div style="vertical-align:top;display:inline-block;width:45%;">
 102 <code> void <span style="color:blue;">main ()</span> {
 103     run_function(display);
 104     run_function(listen);
 105     while (getc () != '\n') { };
 106     exit = 1;
 107     return;
 108  }</code>
 109       </div>
 110     </div>
 111     <div class="sws-slide">
 112       <h1> Exemple: programme </h1>
 113       <p>Compilation <br/>
 114         <code>
 115           gcc -o counter.exe counter.c
 116         </code><br/>
 117         Le <em>fichier</em> « <tt>counter.exe</tt> » est un
 118         exécutable (fichier binaire contenant du code machine)<br/>
 119         <code>
 120           ./counter.exe <span style="margin-left:2em;font-size:smaller;color:red;"> ← il faut la permission +x sur le fichier</span>
 121         </code>
 122         <br/>
 123         Le contenu de l'exécutable est copié en mémoire et le processeur
 124         commence à exécuter la première instruction du programme.
 125       </p>
 126     </div>
 127     <div class="sws-slide">
 128       <h1> Exemple: <i>threads</i> </h1>
 129       <ol>
 130         <li class="sws-pause" ><span style="color:white;background:blue">main</span> </li>
 131         <li class="sws-pause" ><span style="color:blue;">attente d'un évènement clavier
 132             →</span><span style="color:red;">←changement de <i>thread</i></span>
 133         </li>
 134         <li class="sws-pause" ><span style="color:white;background:red">listen</span> </li>
 135         <li class="sws-pause" ><span style="color:red;">attente de connexion →</span><span style="color:green;">←changement de <i>thread</i></span>
 136         </li>
 137         <li class="sws-pause" ><span style="color:white;background:green">display</span> (<span style="color:green;">affiche
 138             0 à l'écran)</span> </li>
 139         <li class="sws-pause" ><span style="color:green;">attente pendant 3s →</span> (les
 140           3 <i>threads</i> attendent un évènement externe)<br/>
 141           <span class="sws-pause" >nouvelle connexion sur le port 80</span> <span style="color:red;">←
 142             réveil du <i>thread</i> <code style="color:red;">listen</code></span>
 143         </li>
 144         <li class="sws-pause" ><span style="color:white;background:red">listen</span>
 145           (<span style="color:red;">incrémente <tt style="color:red">count</tt></span>)<br/>
 146           <span style="color:red;">attente de connexion →</span><br/>
 147           <span>… fin des 3s</span><br/>
 148           <span style="color:green;">←
 149             réveil du <i>thread</i> <tt style="color:green;">display</tt></span>
 150         </li>
 151         <li class="sws-pause" ><span style="color:white;background:green">display</span> (<span style="color:green;">affiche
 152             1 à l'écran)</span> </li>
 153       </ol>
 154       <p class="sws-pause" >Les <i>threads</i> partagent leur mémoire (variables communes)</p>
 155     </div>
 156     <div class="sws-slide">
 157       <h1>Exemple: processus</h1>
 158       <p>(différence: les processus
 159         <em>ne partagent pas leur espace mémoire</em>)</p>
 160       <ol>
 161         <li>Exécution de <code><span style="color:blue;">coun</span><span style="color:red;">ter</span><span style="color:green;">.exe</span></code> pendant 50㎲
 162         </li>
 163         <li > Exécution
 164           de <code><span style="color:orange;">firefox.exe</span></code>
 165           pendant 50㎲ </li>
 166         <li > Exécution du processus qui dessine le bureau pendant 50
 167           ㎲<br/> … </li>
 168
 169       </ol>
 170       <p>C'est le <em>gestionnaire de processus</em> qui décide quel
 171         programme a la main et pour combien de temps (priorité aux
 172         tâches critiques par exemple)<br/>
 173         Le système d'exploitation stocke pour chaque processus un
 174         ensemble d'informations, le PCB (<i>Process Control Block</i>).
 175       </p>
 176     </div>
 177     <div class="sws-slide">
 178       <h1>Proccess Control Block</h1>
 179       <p>Le PCB contient:</p>
 180       <ul>
 181         <li>l'<em>identificateur du processus</em> (pid)</li>
 182         <li>l'<em>l'état</em> du processus (en attente, en exécution,
 183           bloqué, …)</li>
 184         <li>le compteur d'instructions (<i>i.e.</i> où on en est dans
 185           le programme)</li>
 186         <li>le <em>contexte courant</em>(état des registres, …)</li>
 187         <li>position dans <em>la file d'attente de priorité
 188             globale</em></li>
 189         <li>informations mémoire (zones allouées, zones accessibles,
 190           zones partagées)</li>
 191         <li>listes des fichiers ouverts (en lecture, en écriture),
 192           liste des connexions ouvertes, … <br/> … </li>
 193       </ul>
 194     </div>
 195     <div class="sws-slide">
 196       <h1>Opérations sur les processus</h1>
 197       <ul>
 198         <li><em>création</em> et <em>destruction</em> de
 199           processus</li>
 200         <li><em>suspension</em> et <em>reprise</em></li>
 201         <li><em>duplication</em> (<i>fork</i>)</li>
 202         <li>modification de la <em>priorité</em></li>
 203         <li>modification des <em>permissions </em></li>
 204       </ul>
 205     </div>
 206     <div class="sws-slide">
 207       <h1>États d'un processus</h1>
 208       <p>Un processus change d'état au cours de son exécution</p>
 209       <table class="desc">
 210         <tr><td style="width:6em;">Nouveau</td> <td>le processus est en cours de création</td></tr>
 211         <tr><td>Exécution</td> <td>le processus s'exécute</td></tr>
 212         <tr><td>En attente</td> <td>le processus attend un évènement
 213             particulier (saisie au clavier, écriture sur le disque,
 214             …)</td></tr>
 215         <tr><td>Prêt</td> <td>le processus est prêt à reprendre son
 216             exécution et attend que l'OS lui rende la main</td></tr>
 217         <tr><td>terminé</td> <td>le processus a fini son exécution</td></tr>
 218       </table>
 219     </div>
 220     <div class="sws-slide">
 221       <h1>États d'un processus</h1>
 222       <p>L'OS détermine et modifie l'état d'un processus:</p>
 223       <ul>
 224         <li>En fonction d'évènements internes au processus:
 225           <ul><li>lecture d'un fichier (si le contenu n'est pas
 226               disponible, le processus passe de « prêt » à « en attente
 227               »)</li>
 228             <li>le processus attends volontairement pendant x
 229               secondes<br/>…</li>
 230           </ul>
 231         </li>
 232         <li>
 233           En fonction d'évènements externes au processus:
 234           <ul><li>un fichier devient disponible</li>
 235             <li>un <i>timer</i> arrive à 0</li>
 236             <li>le matériel déclenche une <em>interruption</em></li>
 237           </ul>
 238         </li>
 239       </ul>
 240     </div>
 241     <div class="sws-slide">
 242       <h1>États d'un processus</h1>
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 474     <div class="sws-slide">
 475       <h1>La commande <code><em>ps</em></code></h1>
 476       <p>Permet d'avoir des informations sur les processus en cours
 477         d'exécution (voir « <tt>man ps</tt> » pour les
 478         options):<br/>
 479         <code>$ ps -o user,pid,state,cmd x
 480           USER     PID   S CMD
 481           …
 482           kim      27030 Z [chrome] &lt;defunct&gt;
 483           kim      27072 S /opt/google/chrome/chrome --type=renderer
 484           kim      29146 S bash
 485           kim      29834 S evince
 486           kim      29858 S emacs cours.xhtml
 487           kim      29869 R ps -o user,pid,state,cmd x
 488         </code><br/>
 489       </p>
 490
 491     </div>
 492     <div class="sws-slide">
 493       <h1>États des processus (sous Linux)</h1>
 494       <table class="desc">
 495         <tr> <td>R</td> <td> <i>Running</i> (en cours d'exécution)</td> </tr>
 496         <tr> <td>S</td> <td> <i>Interruptible sleep</i> (en attente,
 497             interruptible) </td> </tr>
 498         <tr> <td>D</td> <td> <i>Uninterruptible sleep</i> (en attente,
 499             non-interruptible) </td> </tr>
 500         <tr> <td>T</td> <td> <i>Stopped</i> (interrompu)</td></tr>
 501         <tr> <td>Z</td> <td> <i>Zombie</i> (terminé mais toujours
 502             listé par le système)</td> </tr>
 503       </table>
 504     </div>
 505
 506     <div class="sws-slide">
 507       <h1>Signaux</h1>
 508       <p>L'OS peut envoyer des <em>signaux</em> à un processus. Sur réception
 509         d'un signal, un processus peut interrompre son comportement normal
 510         et exécuter son <em>gestionnaire de signal</em>. Quelques signaux:
 511       </p>
 512       <table class="simple">
 513         <tr><th>Nom</th> <th>Code</th> <th>Description</th> </tr>
 514         <tr><td>HUP</td> <td>1</td> <td>demande au processus de
 515             s'interrompre</td></tr>
 516         <tr><td>INT</td> <td>2</td> <td>demande au processus de se
 517             terminer</td></tr>
 518         <tr><td>ABRT</td> <td>2</td> <td>interrompt le processus et produit
 519             un <i>dump</i></td></tr>
 520         <tr><td>KILL</td> <td>9</td> <td>interrompt le processus immédiatement
 521         </td></tr>
 522         <tr><td>SEGV</td> <td>11</td> <td>signale au processus une erreur mémoire
 523         </td></tr>
 524         <tr><td>STOP</td> <td>24</td> <td>suspend l'exécution du processus
 525         </td></tr>
 526         <tr><td>CONT</td> <td>28</td> <td>reprend l'exécution d'un processus suspendu
 527         </td></tr>
 528       </table>
 529     </div>
 530     <div class="sws-slide">
 531       <h1>Processus et terminal</h1>
 532       <p >Un processus est lié au <em>terminal</em> dans lequel il est
 533         lancé. Si on exécute un programme dans un terminal et que le
 534         processus ne rend pas la main, le terminal est bloqué
 535 <code >
 536
 537  $ gedit
 538
 539 </code>
 540         On peut envoyer au processus le signal <em>STOP</em> en
 541         tapant <code>ctrl-Z</code> dans le terminal:
 542 <code>
 543
 544  $ gedit
 545  ^Z
 546  [1]+  Stopped            gedit
 547
 548 </code>
 549         Le processus est suspendu, la fenêtre est gelée (ne répond plus).
 550       </p>
 551     </div>
 552     <div class="sws-slide">
 553       <h1>Processus et terminal</h1>
 554       <p> <span>On peut reprendre l'exécution du programme de deux
 555           manières:<br/>
 556           <code> $ fg </code><br/>
 557           Reprend l'exécution du processus et le remet en avant plan (terminal
 558           bloqué)</span><br/>
 559         <span class="sws-pause"><code> $ bg </code><br/>
 560           Reprend l'exécution du processus et le remet en arrière plan (terminal
 561 libre)</span><br/>
 562         <span class="sws-pause">On peut lancer un programme
 563           directement en arrière plan en faisant:<br/>
 564 <code> $ gedit &amp; </code><br/></span>
 565         <span class="sws-pause">On peut envoyer un signal à un
 566           processus avec la commande «&nbsp;<tt>kill [-signal] pid</tt>&nbsp;»<br/>
 567 <code> $ kill -9 2345  </code></span>
 568         </p>
 569         </div>
 570     <div class="sws-slide">
 571       <h1>Processus et entrées/sorties</h1>
 572       <p>Le terminal et le processus sont liés par trois fichiers
 573       spéciaux:</p>
 574       <ol>
 575         <li> L'entrée standard (<tt><em>stdin</em></tt>), reliée
 576           au clavier</li>
 577         <li> La sortie standard (<tt><em>stdout</em></tt>), reliée
 578           à l'affichage</li>
 579         <li> La sortie d'erreur (<tt><em>stderr</em></tt>), reliée
 580           à l'affichage</li>
 581       </ol>
 582       <p>Dans le <i>shell</i>, on peut utiliser les
 583       opérateurs <tt><em>&lt;</em></tt>, <tt><em>&gt;</em></tt>
 584       et <tt><em>2&gt;</em></tt> pour récupérer le contenu
 585       de <tt><em>stdin</em></tt>, <tt><em>stdout</em></tt>
 586       et <tt><em>stderr</em></tt>:<br/>
 587 <code>
 588 $ sort &lt; toto.txt
 589 $ ls -l  &gt; liste_fichiers.txt
 590 $ ls -l * 2&gt; erreurs.txt
 591 </code>
 592 </p>
 593 </div>
 594     <div class="sws-slide">
 595       <h1>Processus et entrées/sorties</h1>
 596       <p>Dans le <i>shell</i>, l'opérateur <em>|</em> permet
 597       d'enchaîner la sortie d'un programme avec l'entrée d'un
 598       autre:<br/>
 599 <code> $ <span style="color:green;">ls -l *.txt</span> | <span style="color:blue">sort -n -r -k 5</span> | <span style="color:orange">head -n 1</span></code>
 600       </p>
 601       <ol>
 602         <li style="color:green;">affiche la liste détaillée des
 603         fichiers textes</li>
 604         <li style="color:blue;">trie (et affiche) l'entrée standard par ordre
 605         numérique décroissant selon le 5ème champ</li>
 606         <li style="color:orange;">affiche la première ligne de
 607         l'entrée standard</li>
 608       </ol>
 609       <div style="height:5em;position:relative;margin:0 0;padding:0 0;">
 610 <code class="sws-onframe-1" style="position:absolute;color:green;"> -rw-rw-r    1 kim kim 471 Sep 14 16:25 bd.txt
 611  -rw-rw-r    1 kim kim 234 Sep 15 17:46 foo.txt
 612  -rw-rw-r    1 kim kim 1048576 Sep 24 09:20 large.txt</code>
 613 <code class="sws-onframe-2" style="position:absolute;color:blue;"> -rw-rw-r    1 kim kim 1048576 Sep 24 09:20 large.txt
 614  -rw-rw-r    1 kim kim 471 Sep 14 16:25 bd.txt
 615  -rw-rw-r    1 kim kim 234 Sep 15 17:46 foo.txt
 616 </code>
 617 <code class="sws-onframe-3" style="position:absolute;color:orange;"> -rw-rw-r    1 kim kim 1048576 Sep 24 09:20 large.txt
 618 </code>
 619       </div>
 620
 621     </div>
 622
 623 <h1>Écriture de script <i>shell</i></h1>
 624 <div class="sws-slide">
 625   <h1>Script shell</h1>
 626   <p><a>Mentalité Unix</a> beaucoup de petits programmes spécifiques,
 627   que l'on combine au moyen de scripts pour réaliser des actions
 628   complexes. Exemple de fichier script:
 629   </p>
 630   <code style="background:white;">
 631     <s>#!/bin/bash</s>
 632
 633     <s>for</s> i <s>in</s>  img_*.jpg
 634     <s>do</s>
 635       base=$(echo "$i" | cut -f 2- -d '_')
 636       nouveau=photo_"$base"
 637       <s>if</s> test -f "$nouveau"
 638       <s>then</s>
 639          echo "Attention, le fichier $nouveau existe déjà"
 640          continue
 641       <s>else</s>
 642          echo "Renommage de $i en $nouveau"
 643          mv "$i" "$nouveau"
 644       <s>fi</s>
 645     <s>done</s>
 646   </code>
 647 </div>
 648 <div class="sws-slide">
 649 <h1>Rendre un script exécutable</h1>
 650 <p>Si un fichier <a>texte</a> (quel que soit son extension), commence
 651   par les caractères <tt>#!/chemin/vers/un/programme</tt>, on peut
 652   rendre ce fichier exécutable (<tt>chmod +x</tt>). Si on l'exécute,
 653   le contenu du fichier est passé comme argument à <tt>programme</tt>
 654   (qui est généralement un interpréteur)
 655 </p>
 656 <p><tt>#!/bin/bash</tt> signifie que le corps du fichier est passé au
 657   programme <tt>bash</tt> qui est l'interprète de commande
 658   (le <i>shell</i>).
 659 </p>
 660 </div>
 661 <div class="sws-slide">
 662 <h1>Que mettre dans un script</h1>
 663 <ul>
 664   <li> des commandes (comme si on les entrait dans le terminal)</li>
 665   <li> des structures de contrôle (boucles <tt>for</tt>, <tt>if then
 666   else</tt>) </li>
 667   <li> des définitions de variables </li>
 668 </ul>
 669 </div>
 670 <div class="sws-slide">
 671 <h1>Définitions de variables</h1>
 672 <p>On peut définir des variables au moyen de la notation
 673 <code>VARIABLE=<i>contenu</i></code> et on peut utiliser la variable
 674 avec la notation <tt>$VARIABLE</tt> </p>
 675 <ul>
 676   <li>Attention, pas d'espace autour du <tt>=</tt></li>
 677   <li>nom de variable en majuscule ou minuscule</li>
 678   <li>contenu est une chaine de caractères. Si elle contient des
 679   espaces, utiliser <tt>" ... "</tt></li>
 680 </ul>
 681 <p>exemple de définition :</p>
 682 <code>    i=123
 683     j="Ma super chaine"
 684     TOTO=titi
 685     echo $TOTO
 686 </code>
 687 <p> exemple d'utilisation: <tt> echo $j $i $TOTO </tt><br/>
 688 affiche « <tt> Ma super chaine 123 titi</tt></p>
 689 </div>
 690 <div class="sws-slide">
 691 <h1>Boucles <tt>for</tt></h1>
 692 <p>Les boucles <tt> for </tt> ont la syntaxe:
 693 <code>
 694     for VARIABLE in elem<sub>1</sub> ... elem<sub>n</sub>
 695     do
 696         ....
 697     done
 698 </code>
 699 chaque <tt>elem<sub>i</sub></tt> est expansé (comme une ligne de
 700 commande) avant l'évaluation de la boucle:
 701 <code>
 702   for i in *.txt
 703   do
 704      echo $i est un fichier texte
 705   done
 706 </code>
 707 On peut quitter une boucle prématurément en utilisant <tt>break</tt>
 708 et passer directement au tour suivant avec <tt>continue</tt>
 709 </p>
 710 </div>
 711 <div class="sws-slide">
 712 <h1>Conditionnelle</h1>
 713 <p>La syntaxe est :
 714 <code>   if <i>commande</i>
 715    then
 716         ...
 717    else
 718         ...
 719    fi
 720 </code>
 721 <tt><i>commande</i></tt> est évaluée. Si elle se termine avec succès,
 722 la branche <tt>then</tt> est prise. Si elle se termine avec un code
 723 d'erreur, la branche <tt>else</tt> est prise. On peut utiliser la
 724 commande <tt>test</tt> qui permet de tester plusieurs conditions
 725 (existance d'un fichier, égalités de deux nombres, ...) et se termine
 726 par un succès si le teste est vrai et par un code d'erreur dans le
 727 cas contraire</p>
 728 </div>
 729 <div class="sws-slide">
 730 <h1>Conditionnelle (exemple)</h1>
 731 <p>On regarde tour à tour si fichier1.txt, fichier2.txt, ... existent :
 732 <code>
 733   for i in 1 2 3 4 5 6
 734   do
 735     if test -f "fichier$i".txt
 736    then
 737       echo le fichier "fichier$i".txt existe
 738    fi
 739   done
 740 </code>
 741 </p>
 742   </div>
 743 <div class="sws-slide">
 744 <h1>Sous-commandes et chaines</h1>
 745 <p>Il est pratique de pouvoir mettre <a>l'affichage d'une commande</a>
 746   dans une variable. On utilise <tt>$( commande ... )</tt>:
 747 <code>
 748   MESFICHIER=$(ls *.txt)
 749   for i in $MESFICHIER
 750   do
 751        echo Fichier: $i
 752   done
 753 </code>
 754 Attention à la présence de guillemets autour des variables. S'il y a
 755 f1.txt et f2.txt dans le répertoire courant:<br/>
 756 <code style="left:10%;position:relative;width:40%;float:left;">
 757   MESFICHIER=$(ls *.txt)
 758   for i in $MESFICHIER
 759   do
 760        echo Fichier: $i
 761   done
 762 <s>affiche:</s>
 763   Fichier: f1.txt
 764   Fichier: f2.txt
 765 </code>
 766 <code style="width:40%;float:left;left:10%;position:relative">
 767   MESFICHIER=$(ls *.txt)
 768   for i in "$MESFICHIER"
 769   do
 770        echo Fichier: $i
 771   done
 772 <s>affiche:</s>
 773   Fichier: f1.txt f2.txt
 774 </code>
 775 </p>
 776 </div>
 777 <div class="sws-slide">
 778 <h1>Commandes utiles</h1>
 779 <ul>
 780   <li><tt>seq <i>m</i> <i>n</i> </tt> : affiche la liste de tous les
 781   nombres entre <i>m</i> <i>n</i> </li>
 782 <li><tt>echo ... </tt> affiche ses arguments sur la sortie
 783   standard</li>
 784 <li><tt>printf "chaine" ... </tt> affiche ses arguments au moyen d'une
 785   chaine de format (comme le printf de C)</li>
 786 <li><tt>date</tt> : affiche la date courante </li>
 787 <li><tt>cut</tt> : découpe une chaine selon des caractères de
 788   séparations ou des positions</li>
 789 </ul>
 790 </div>
 791 <h1>Programmes non interactifs</h1>
 792 <div class="sws-slide">
 793   <h1>Processus de type <i>daemon</i></h1>
 794 <p>
 795   Un <i>daemon</i> (prononcé démon) est un processus
 796   qui <em>non-interactif</em> qui tourne en tâche de fond (pas
 797   d'entrée/sortie sur le terminal, pas d'interface graphique, …). On
 798   communique avec ce processus via des <em>signaux</em> ou en lisant
 799   ou écrivant dans des fichiers ou connexions réseau. Le plus souvent,
 800   leur but est de fournir un <em>service</em>
 801 </p>
 802 <p>Exemple de scénario: « <i> Les utilisateurs doivent interagir avec
 803     le matériel. L'accès au matériel demande des droits
 804     administrateur.</i> »
 805 </p>
 806 <ul class="empty">
 807   <li>Solution 1 : tout le monde est administrateur (DOS, Win XP,
 808   …)</li>
 809   <li>Solution 2 : on crée un programme particulier qui a les
 810   privilèges suffisants pour la tâche en question. Les utilisateurs
 811   communiquent avec ce programme</li>
 812 </ul>
 813 </div>
 814 <div class="sws-slide">
 815   <h1>Quelques <i>daemons</i> sous Linux</h1>
 816 <table class="simple">
 817 <tr><th>Nom</th> <th>Description</th> </tr>
 818 <tr><td>sshd</td> <td><i>shell</i> distant sécurisé</td> </tr>
 819 <tr><td>crond</td> <td>exécution périodique de programmes</td> </tr>
 820 <tr><td>cupsd</td> <td>serveur d'impressions</td> </tr>
 821 <tr><td>pulseaudio</td> <td>serveur de son (mixe les sons des
 822     différentes applications)</td> </tr>
 823 <tr><td>udevd</td> <td>détection de matériel <i>hotplug</i></td></tr>
 824 <tr><td>nfsd</td> <td>serveur de fichier réseau</td></tr>
 825 <tr><td>smtpd</td> <td>livraison des e-mail</td></tr>
 826 <tr class="sws-pause"><td><em>httpd</em></td> <td>serveur de pages Web</td></tr>
 827 </table>
 828 </div>
 829 <div class="sws-slide">
 830 <h1>Architecture client-serveur</h1>
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1250 <p>
1251   <br/><br/>
1252   Des processus <span style="color:blue;">clients</span> communiquent
1253   avec le <span style="color:orange;">serveur</span> à travers le
1254   réseau. Les clients sont indépendant et ne communiquent pas entre
1255   eux. <em>Attention</em> plusieurs clients peuvent se trouver su la
1256   même machine physique!
1257 </p>
1258 </div>
1259 <div class="sws-slide">
1260   <h1>Architecture client-serveur</h1>
1261 <ul>
1262   <li>Le serveur attend des connexions entrantes</li>
1263   <li>Les clients peuvent se connecter à tout moment</li>
1264   <li>L'application client est généralement légère, envoie une
1265   requête au serveur et attend un résultat</li>
1266   <li>Le serveur est une application plus lourde qui:
1267     <ul><li>effectue des calculs trop coûteux pour le client</li>
1268       <li>gère l'accès à une ressource distante partagée<br/>…</li>
1269     </ul>
1270   </li>
1271 </ul>
1272 <p>Exemples: serveur de bases de données, serveur mail, serveur Web,
1273   terminal de carte bancaire, …</p>
1274 </div>
1275   </body>
1276 </html>