53 lines
1.9 KiB
Text
53 lines
1.9 KiB
Text
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cinit - Respawning and sleeping
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===============================
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Nico Schottelius <nico-cinit__@__schottelius.org>
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0.1, for cinit 0.3, Initial Version from 2007-04-13
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:Author Initials: NS
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How cinit sleeps, before a service is respawned.
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Introduction
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------------
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When a service, that is configured to be respawning, exits cinit restarts it.
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Because services may be broken and thus cinit would try to restart it many
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times in a second, it is necessary to sleep between restarts.
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The big question: How to sleep?
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------------------------------------
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The first possibility is to sleep a fixed amount of time between restarts:
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For instance one second. This is not a good solution, because this waits
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one unecessary second if the process just crashed. It may be too less, if
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the service is really broken.
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The second possibility is to sleep a dynamic amount of time.
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The next big question: How long to sleep?
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-----------------------------------------
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I think that as long as a service is broken we should not investigate to much
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time into restarting it. So we can define a maximum amount of time to sleep
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(for instance 30 seconds). The minimum amount of time to sleep is zero seconds.
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When the service is first started, the sleep time defaults to the minimum
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amount of time. Each time the service is restarted, the sleep time is adjusted:
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sleep time (st) = Maximum sleep time (mst) / Time the process was running (tr)
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- If tr is < 1 it is adjusted to 1 and thus st is set to mst.
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- If tr is > mst, st is set to 0.
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How to force restart of a service?
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----------------------------------
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Use cvsc (to be implemented).
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Hom is it implemented?
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----------------------
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Everytime cinit has to respawn a service it has to fork() itself.
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The sleep call is implemented in the fork, so cinit itself does not have
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to care about it. After the sleep time is over or the fork() recieves
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SIGALARM it executes the real service. cinit itself records as start time
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the current time plus sleep time.
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