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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<title>Convergence and Forced Operations</title>
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<h1>Convergence and Forced Operations</h1>
Cfengine is about convergence to a stable state. The state of the system should
normally be at a fixed point, or else it should be returned to a fixed point.
Occasionally changes in dependencies lead us to force changes, e.g. kill and
restart a daemon.
<pre>
commands:
"Stop command";
"Start command";
</pre>
or
<pre>
processes:
"myprocess" signal => "term";
commands:
"start command";
</pre>
The problem with these commands is that they are not "guarded" (in the sense of Dijkstra's
guarded commands). Such a command is not a convergent change unless it is qualified by a
guarding class.
e.g.
<pre>
processes:
change_in_dependency::
"myprocess" signal => "term";
commands:
change_in_dependency::
"start command"
</pre>
or
<pre>
execution:
change_in_dependency::
"Stop command";
"Start command";
</pre>
or even
<pre>
processes:
change_in_dependency::
"myprocess"
signal => "term"
# define newclass ;
commands:
new_class::
"start command"
</pre>
<hr>
<address><a href="mailto:mark@atlas">Mark Burgess</a></address>
<!-- Created: Thu May 1 13:07:13 CEST 2008 -->
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Last modified: Sat Aug 2 09:58:12 CEST 2008
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