115 lines
4.6 KiB
Text
115 lines
4.6 KiB
Text
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Problems using cinit
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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 2007-04-24
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:Author Initials: NS
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Using a high-speed, true dependency aware, profile supporting
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logical acting and reliable init system like cinit is not
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completly problem free. This document describes some common
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problems you may have and their solutions.
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Possible problems
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-----------------
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Confused users
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~~~~~~~~~~~~~~
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Compared to traditional init systems like sys-v-init or bsd-init
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cinit introduces a complet new boot concept. This does not just
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mean that you have services instead of shell-scripts (which is
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one reason cinit is starting up faster), but also that the boot
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order may be changed dynamically at bootup:, if a service fails.
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And even if no service fails, the boot order may be different
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on each boot, because processes are started in parallel and
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may return earlier or later on each boot. To coordinate the
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parallel running processes, cinit uses depencies, which are pretty
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easy to understad when configurung, but may need some more
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detailled watching at boot to understand it.
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The 'confused users'-problem is perhaps also the biggest
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problem for introducing cinit as a replacement to current
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init systems.
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Configuration issues
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~~~~~~~~~~~~~~~~~~~~
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Not marking services as respawn
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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When cinit starts, it will wait for every service to exit.
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So if you have a dependency on a service
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that never exits, the whole init process may hang (dependending
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on the dependencies). If you have services that are intendet
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*not* to exit after start, you *have* to mark those with
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`respawn`: Those services are started and watched by cinit
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and will be restarted. This was a design choice to ensure
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that all 'always running' processes *are* restarted.
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I did not find any service that should not exit and not
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have a respawn flag. If you really really really have such
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a service and you can prove to me that the respawn flag
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would do harm to your system, I will think about implementing
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a flag that tells cinit not to wait for it, but mark it
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as successfully run after it has been started.
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User interaction
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~~~~~~~~~~~~~~~~
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User input
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~~~~~~~~~~
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There may be the situation that you have to press a key
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or enter some data when a service starts up (like entering
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the password for your crypto harddisks). With cinit, this
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will look like a mess, because other services may write to
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the same console the service wrote a user prompt.
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The best solution for this problem is in my humble
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opinion to create an user-input daemon that serialises
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the requests and displays one after another.
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This could look like this: Your daemon wants to ask for
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a passphrase for the SSL-certificate. You add aa needs
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to this daemon to the 'input-daemon'. When you
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start this service, it will contact the input-daemon
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running on another virtual console and displaying a text
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and an input field that is passed back to this service.
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After that the input daemon changes back to the initial
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console or asks for the next input, if there is another
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request available.
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This input daemon may also be run on a graphical (X11) display.
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.
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Output to the user
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~~~~~~~~~~~~~~~~~~
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When cinit starts up there may be many messages printed
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out that also may look like printed random order.
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To prevent your endusers from being confused you can create
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some kind of graphical interface (like a framebuffer
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or X11 display) that reads the output of cinit and converts
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it to flashing images. It could look like this:
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----------------------------------------------------------------------
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Your (graphical?) display:
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--------------------------------------------------------------
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| /-----------------\ |
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| | Red border, | |
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| | failed to start | |
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| \-----------------/ |
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| /------ |
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| | Green border, |
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| image van |
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--------------------------------------------------------------
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----------------------------------------------------------------------
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