Re: /etc/init.d/ - add/remove services

From: Thomas Hood (jdthood_at_yahoo.co.uk)
Date: 02/01/04

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    To: debian-user@lists.debian.org
Date: Sun, 01 Feb 2004 17:17:15 +0100

    On Sat, 2004-01-31 at 22:10, I wrote:
    > Note that the expectation of the System V init system is
    > that every service have either an S or a K symlink in each
    > runlevel. If there is no symlink for a service in a particular
    > runlevel then the behavior of sysv's invoke-rc.d is undefined
    > for that service in that runlevel. Methods of shutting off
    > services must take that into account.

    This is true.

    > Suppose you have service foo that is S20 in runlevel 2 and
    > you want to shut it off. You should do something like:
    >
    > /etc/rc2.d/$ mv S20foo K80foo_originallyS20

    No.

    Further investigation has revealed to me that this won't work.
    The renamed symlink has to be K??foo or it won't be recognized
    as a foo script even though it links to foo.

    I conclude that the only correct way to disable a service is
    to do something like:

        /etc/rc2.d$ mv S20foo K80foo

    It is up to the administrator to keep a record of what the
    original symlink was called so that he can restore it to that
    name later if he wishes to do so.

    There are a couple of high-level utilities available that can
    automate this process for the administrator.

    "Miquel van Smoorenburg" <miquels () cistron ! nl> wrote in part:
    > A thought just hit me.
    > What if we added a "update-rc.d <name> enable|disable" command?

    This has already been wished for. See sysv-rc wish #214757 and
    sysvinit wish #67095.

    > That has never been done because the implementation would
    > be awkward and wouldn't fit into the sysv-rc design.
    > But what if we used the destination of the symlink ?

    Suppose you have a service foo enabled in runlevel 2 and disabled
    in runlevel 3. On moving from 2 to 3 you want foo to be stopped.
    However, if foo is disabled in runlevel 3 by having its S entry
    symlinked to /bin/true then it won't be stopped.

    The right thing to do is to write a simple runlevel editing tool
    and include it in the sysv-rc package. This tool would rename
    Snn symlinks to K(100-nn) symlinks and vice versa and would keep
    records of what it had done so that reversion was easy. The sysv
    update-rc.d program would be rewritten to work through the runlevel
    editing tool; commands coming from update-rc.d would determine what
    the tool considered to be the "default" setting.

    Other init systems would implement this tool differently, of course. 

    -- 
Thomas Hood <jdthood@yahoo.co.uk>
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