postfix-master/backstage.html

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   5 <title>Postfix Anatomy - Behind the Scenes</title>
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  12 <h1><a href="big-picture.html"><img src="small-picture.gif" width="115" height="45"></a> Postfix
  13 Anatomy - Behind the Scenes</h1>
  14
  15 <hr>
  16
  17 <p> <strong> Note: this web page is no longer maintained. It exists
  18 only to avoid breaking links in web pages that describe earlier
  19 versions of the Postfix mail system. </strong> </p>
  20
  21 <a href="docs.html">Up one level</a> | <a
  22 href="receiving.html">Receiving Mail</a> | <a
  23 href="delivering.html">Delivering Mail</a> | Behind the Scenes |
  24 <a href="commands.html">Command-line Utilities</a>
  25
  26 <p>
  27
  28 The previous sections gave a simplified overview of how the Postfix
  29 system sends and receives mail. Several other things happen behind
  30 the scenes. Unfortunately, this is hard to visualize on a
  31 two-dimensional display, so this document has no illustration.
  32
  33 <ul>
  34
  35 <li>The <a href="master.8.html">master</a> daemon is the supervisor
  36 process that keeps an eye on the well-being of the mail system. It
  37 is typically started at system boot time by the <a
  38 href="postfix.1.html">postfix</a> command, and keeps running until
  39 the system goes down.  The <a href="master.8.html">master</a> daemon
  40 is responsible for starting all other Postfix daemon processes on
  41 demand, and for restarting daemons that terminated prematurely
  42 because of some problem. The <a href="master.8.html">master</a>
  43 daemon is also responsible for enforcing the daemon process count
  44 limits as specified in the <b>master.cf</b> configuration file.
  45
  46 <p>
  47
  48 <li>The <a href="bounce.8.html">bounce or defer</a> daemon is called
  49 upon left and right by other daemon processes, in order to maintain
  50 per-message log files with non-delivery status information.
  51
  52 <p>
  53
  54 <li>The <a href="trivial-rewrite.8.html">trivial-rewrite</a> daemon
  55 is called upon left and right by other daemon processes, in order
  56 to rewrite an address to <i>user@fully.qualified.domain</i> form,
  57 or in order to resolve a destination.
  58
  59 <p>
  60
  61 <li>The <a href="showq.8.html">showq</a> daemon lists the Postfix
  62 queue status. This is the program behind the <a
  63 href="mailq.1.html">mailq</a> command.
  64
  65 <p>
  66
  67 <li>The <a href="flush.8.html">flush</a> daemon improves the
  68 performance of the SMTP <b>ETRN</b> request, and of its command-line
  69 equivalent, <b>sendmail -qR</b><i>destination</i>, for selected
  70 destinations.
  71
  72 <p>
  73
  74 <li>The <a href="proxymap.8.html">proxymap</a> daemon provides
  75 read-only lookup service to Postfix client processes. The purpose
  76 is to overcome chroot restrictions, and to consolidate the number
  77 of open lookup tables by sharing one open table among multiple
  78 processes.
  79
  80 <p>
  81
  82 <li>The <a href="spawn.8.html">spawn</a> daemon listens on a TCP
  83 port, UNIX-domain socket or FIFO, and runs non-Postfix commands on
  84 request, with the socket or FIFO connected to the standard input,
  85 output and error streams.  It is currently used only in an example
  86 of the Postfix external content filtering system.
  87
  88 </ul>
  89
  90 <hr>
  91
  92 <a href="docs.html">Up one level</a> | <a
  93 href="receiving.html">Receiving Mail</a> | <a
  94 href="delivering.html">Delivering Mail</a> | Behind the Scenes |
  95 <a href="commands.html">Command-line Utilities</a>
  96
  97 </body>
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  99 </html>