68 lines
2.4 KiB
Text
68 lines
2.4 KiB
Text
cinit - Dependencies
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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 2005-12-13
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:Author Initials: NS
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This document describes the different dependency types of cinit.
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Dependencies in general
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-----------------------
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Each service may have two types (non-exclusive) types of dependencies:
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The so called `needs` or `wants`. These are directories below the service
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directory and contain symbolic links to the dependencies.
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The name of the link can be freely chosen.
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An example:
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The service '/etc/cinit/svc/getty/2' needs the service
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'/etc/cinit/svc/local-tuning/keyboard-layout':
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--------------------------------------------------------------------------------
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[21:35] hydrogenium:needs# cd /etc/cinit/svc/getty/2/needs
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[21:35] hydrogenium:needs# ls -l
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insgesamt 0
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lrwxrwxrwx 1 root root 37 2006-10-26 17:51 keyboard-layout -> ../../../local-tuning/keyboard-layout
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[21:35] hydrogenium:needs# cd keyboard-layout/
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[21:35] hydrogenium:keyboard-layout# pwd -P
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/etc/cinit/svc/local-tuning/keyboard-layout
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--------------------------------------------------------------------------------
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(Warning: This is an incomplete example, it misses at least `mount/root`
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as dependency)
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This service could additionally want something else, too. It is also
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possible that a service only `wants` another service or that a service
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has no dependencies.
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Absolute versus relative links
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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cinit does not care whether a link is relative or absolute. And
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as far as I can see it does not make any difference to usability.
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In general, it seems to be a little bit 'easier' to use relative links
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when manually configuring cinit ('ln -s ../../../service' versus
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'ln -s /etc/cinit/svc/category/service'), but easier readable when
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analysing them (with `ls -l').
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The two types
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-------------
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needs
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~~~~~
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`Needs` are the 'hard dependencies': If a services fails to start that
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is linked in the `needs` directory, the service will not be started.
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wants
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~~~~~
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`Wants` are the 'soft dependencies': cinit will try to start the dependencies
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found in `wants` before the service, but the service will also be started,
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indenpendend of success of the dependencies.
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Circular dependency problem
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----------------------------
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If you manage to create circular dependencies cinit will fall into an
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endless loop. Use `cinit.check.config` to verify your configuration.
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