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Re: Steps towards a patch to document disabling a daemon upon installation




Hello Sean Whitton,

Thanks for your work on this. Hopefully you'll find something in my
comments inlined below of any use...

On Sat, Sep 09, 2017 at 01:40:18PM -0700, Sean Whitton wrote:
> Hello,
> 
> This is what I have so far; it is certainly inadequate.  CCing -devel
> for help answering my technical questions about this patch.
> 
> > @@ -537,6 +537,21 @@ and in your ``postrm``
> >          update-rc.d package remove
> >      fi
> >  
> > +The default behaviour is to enable autostarting your package's daemon.
> > +If the daemon should not be autostarted unless the local administrator
> > +has explicitly requested this, use instead add to your ``postinst``
> > +script
> > +
> > +::
> > +
> > +    update-rc.d package defaults
> > +    update-rc.d package disable

I can't help myself but repeat that I'd prefer seeing more passive
wording eg. instead of "instead add to your postinst" use something
like "the postinst should contain" + a footnote about this normally
being added by dh_...
Manually written maintainer scripts should be avoided and I've seen
people being "fooled" by taking policy literally before. (Maybe this
deserves a section of its own?)

> > +
> > +An older practice, which should not be used, was to include a line
> > +like ``DISABLED=yes`` in the package's ``/etc/default`` file.  The
> > +package's init script would not start the service until the local
> > +system administrator changed this to ``DISABLED=no``, or similar.
> > +
> >  Note that if your package changes runlevels or priority, you may have to
> >  remove and recreate the links, since otherwise the old links may
> >  persist. Refer to the documentation of ``update-rc.d``.
> 
> 1. Is the 'should not' for the /etc/default practice too strong?

Not in my opinion, no.

>    I don't know an efficient way to find out how many packages this
>    would make buggy.  But given that we have very strong reasons
>    against the old practice, we might want to use a 'should not'
>    regardless.

Any maintainer being hit by policy extremists have two options:

1. Take the opportunity to fix the package to follow best pracises.
2. Postpone by saying "should not" is not "must not" (and lower severity),
   plus "patches welcome" ofcourse.

I think that's good enough.

> 
> 2. Do we need to include any text saying *why* the /etc/default practice
>    is a bad idea?  I couldn't come up with a succinct way to state it.
>    In general, I think we can err on the side of not including the text,
>    since we have policy bugs that document the reasons.

I don't think elaborating on all the ways something can be done
incorrectly is nessessary. Should not be too hard for anyone interested
in the reason to find out atleast one reason either by thinking it
through by themselves or by googling for past discussions.

If anything I'd rather see helpful suggestions (in footnotes?) on how
a proper cleanup should be done. (Convert admin changes on upgrades,
use debian/*.maintscript to rm_conffile)

> 
> 3. The maintscript snippet I have added is not right because it will
>    disable the daemon every time the package is updated.  Unfortunately,
>    the postinst doesn't know whether this is a new installation, or an
>    upgrade.
> 
>    An alternative is to require the package maintainer to set the
>    correct LSB headers and systemd unit file configuration values such
>    that the daemon is not autostarted (in the former case, setting the
>    daemon not to be started at any runlevel).  But I think this would
>    prevent the local system administrator from enabling the service with
>    a simple `update-rc.d package enable`, which is the whole point of
>    all this.
> 
>    I looked at dh_installinit(8) and update-rc.d(8) and I couldn't get
>    them to generate a postinst that does what I want.  It seems you're
>    expected to use all three of these:
> 
>        dh_systemd_enable --no-enable
>        dh_systemd_start --no-start
>        dh_installinit --no-start
> 
>    but then after a reboot, a sysvinit system will start the daemon,
>    AFAICT.

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=709384

Regards,
Andreas Henriksson