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Old 02-08-2012, 07:03 PM
Roger Leigh
 
Default Comments on introducing a new Essential package: base-init?

This is regarding Bug #645540 ("Essential" package conflict between
sysvinit and systemd-sysv).

sysvinit is currently Essential. In order to permit the replacement
of sysvinit with an alternative init system, I'd like to propose the
creation of a new Essential package "base-init", with a Depends on
"sysvinit | init", where "init" is a virtual package provided by all
packages providing /sbin/init. This would be provided by sysvinit,
systemd, upstart, etc.

With this package in place, sysvinit could be removed from the
Essential set, but remain the default init system. This would
permit alternative init systems to entirely replace sysvinit.

An alternative would be for an existing Essential package such as
base-files to provide the Depends, which would save the need for
a separate base-init package. Is there any reason this would be
undesirable? (I note that it currently has no depends other than
a pre-depends on awk.)

Any comments?


Thanks,
Roger

--
.'`. Roger Leigh
: :' : Debian GNU/Linux http://people.debian.org/~rleigh/
`. `' Printing on GNU/Linux? http://gutenprint.sourceforge.net/
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Old 02-08-2012, 07:49 PM
Sven Joachim
 
Default Comments on introducing a new Essential package: base-init?

On 2012-02-08 21:03 +0100, Roger Leigh wrote:

> This is regarding Bug #645540 ("Essential" package conflict between
> sysvinit and systemd-sysv).
>
> sysvinit is currently Essential. In order to permit the replacement
> of sysvinit with an alternative init system, I'd like to propose the
> creation of a new Essential package "base-init", with a Depends on
> "sysvinit | init", where "init" is a virtual package provided by all
> packages providing /sbin/init. This would be provided by sysvinit,
> systemd, upstart, etc.

Assuming they all provide /sbin/init, they need to conflict with each
other, right? In that case, switching init systems has the dangerous
effect that apt will remove the current provider before unpacking the
replacement, leaving a window where /sbin/init does not exist. Sounds
rather dangerous to me.

Cheers,
Sven


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Old 02-08-2012, 08:09 PM
Roger Leigh
 
Default Comments on introducing a new Essential package: base-init?

On Wed, Feb 08, 2012 at 09:49:26PM +0100, Sven Joachim wrote:
> On 2012-02-08 21:03 +0100, Roger Leigh wrote:
>
> > This is regarding Bug #645540 ("Essential" package conflict between
> > sysvinit and systemd-sysv).
> >
> > sysvinit is currently Essential. In order to permit the replacement
> > of sysvinit with an alternative init system, I'd like to propose the
> > creation of a new Essential package "base-init", with a Depends on
> > "sysvinit | init", where "init" is a virtual package provided by all
> > packages providing /sbin/init. This would be provided by sysvinit,
> > systemd, upstart, etc.
>
> Assuming they all provide /sbin/init, they need to conflict with each
> other, right? In that case, switching init systems has the dangerous
> effect that apt will remove the current provider before unpacking the
> replacement, leaving a window where /sbin/init does not exist. Sounds
> rather dangerous to me.

This is a good point, but is there a safer alternative? Upstart
and systemd currently have a Replaces: sysvinit to replace it outright,
but it still requires sysvinit to be installed in the first place, and
it is still Essential. Any alternative init system is required to do
this, and it would be ideal to have a means of removing sysvinit
entirely. If there's a way which does not involve a virtual package,
we could do that--I guess it's not strictly necessary, but it does
avoid the need for init-providers to explicitly conflict/replace
each other. For example, upstart currently conflicts/replaces
sysvinit /anyway/, so it's not like the virtual package would
introduce a window of breakage which is not already present today.
Obviously, a perfectly safe and clean solution would be preferred!


Regards,
Roger

--
.'`. Roger Leigh
: :' : Debian GNU/Linux http://people.debian.org/~rleigh/
`. `' Printing on GNU/Linux? http://gutenprint.sourceforge.net/
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Old 02-08-2012, 10:53 PM
Colin Watson
 
Default Comments on introducing a new Essential package: base-init?

On Wed, Feb 08, 2012 at 08:03:27PM +0000, Roger Leigh wrote:
> An alternative would be for an existing Essential package such as
> base-files to provide the Depends, which would save the need for
> a separate base-init package. Is there any reason this would be
> undesirable? (I note that it currently has no depends other than
> a pre-depends on awk.)

I think it would be better to avoid adding dependencies to base-files if
possible. base-files is one of the "super-Essential" packages with
special-case handling in debootstrap to install it very early indeed,
unpacked and configured while even dpkg has still only been extracted;
while that installation is done with --force-depends, I still think it
would be worth keeping its dependency tree as trivial as possible.

--
Colin Watson [cjwatson@debian.org]


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Old 02-09-2012, 09:50 AM
Bastian Blank
 
Default Comments on introducing a new Essential package: base-init?

On Wed, Feb 08, 2012 at 08:03:27PM +0000, Roger Leigh wrote:
> sysvinit is currently Essential.

Why do we need an init as essential anyway? It is used in all real
systems, but not chroots or other special systems. This makes it similar
to the kernel, which does not even have a high priority.

> where "init" is a virtual package provided by all
> packages providing /sbin/init.

The interface provided by sysvinit is much more then /sbin/init.

> (I note that it currently has no depends other than
> a pre-depends on awk.)

And awk is not even a real package.

Bastian

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Old 02-09-2012, 11:09 AM
Michael Biebl
 
Default Comments on introducing a new Essential package: base-init?

On 09.02.2012 11:50, Bastian Blank wrote:
> On Wed, Feb 08, 2012 at 08:03:27PM +0000, Roger Leigh wrote:
>> sysvinit is currently Essential.
>
> Why do we need an init as essential anyway? It is used in all real
> systems, but not chroots or other special systems. This makes it similar
> to the kernel, which does not even have a high priority.
>

I also think that simply dropping the Essential flag is how we should
address this. The priority of sysvinit would make sure that is installed
as the default init (similar to how we handle the default syslog daemon).

If it is a concern that people make accidentally uninstall their
/sbin/init and render their system un-booteable, we could add a warning
to postinst similar to how the kernel does it.

Or are there other reasons why sysvinit needs to be essential?

Michael


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Old 02-09-2012, 12:19 PM
Arno Töll
 
Default Comments on introducing a new Essential package: base-init?

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

Hi,

On 09.02.2012 13:09, Michael Biebl wrote:
> On 09.02.2012 11:50, Bastian Blank wrote:
>> On Wed, Feb 08, 2012 at 08:03:27PM +0000, Roger Leigh wrote:
>>> sysvinit is currently Essential.
>>
>> Why do we need an init as essential anyway? It is used in all
>> real systems, but not chroots or other special systems. This
>> makes it similar to the kernel, which does not even have a high
>> priority.

not objecting the idea by itself, please bear in mind this would turn
thousands of packages RC buggy immediately, as they all need to
declare a dependency against (an) init script given they rely on a
init script for functionality then.

- --
with kind regards,
Arno Töll
IRC: daemonkeeper on Freenode/OFTC
GnuPG Key-ID: 0x9D80F36D
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Old 02-09-2012, 12:58 PM
Michael Biebl
 
Default Comments on introducing a new Essential package: base-init?

On 09.02.2012 14:19, Arno Töll wrote:
> Hi,
>
> On 09.02.2012 13:09, Michael Biebl wrote:
>> On 09.02.2012 11:50, Bastian Blank wrote:
>>> On Wed, Feb 08, 2012 at 08:03:27PM +0000, Roger Leigh wrote:
>>>> sysvinit is currently Essential.
>>>
>>> Why do we need an init as essential anyway? It is used in all
>>> real systems, but not chroots or other special systems. This
>>> makes it similar to the kernel, which does not even have a high
>>> priority.
>
> not objecting the idea by itself, please bear in mind this would turn
> thousands of packages RC buggy immediately, as they all need to

We do have ~1200 init scripts belonging to ~1100 packages.

> declare a dependency against (an) init script given they rely on a
> init script for functionality then.

I guess you are referring to the fact that initscripts would no longer
by transitively-essential.
Most sysv initscripts do not directly depend on services from
initscripts, like mountall, mountkernfs, checkfs or checkroot. Actually,
those direct dependencies in the LSB header are very rare and generally
discouraged.

What most if not all init scripts have in their LSB header, is a
dependency on a virtual facility like $local_fs or $remote_fs.

And those virtual facilities are only really interesting for insserv to
calculate the start priorities. So maybe if insserv depends on
initscripts that would be all that is needed.

Michael
--
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