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Re: Bug#1012622: crontab gid became unreproducible



Hi Colin,

thank you for your quick reply!

Quoting Colin Watson (2022-06-13 12:27:59)
> On Mon, Jun 13, 2022 at 11:27:07AM +0200, Georges Khaznadar wrote:
> > I reassigned bug #1012622 to base-passwd, in order to make constant the
> > group id for crontab. I believe that the arguments provided by Johannes
> > Schauer Marin Rodrigues are strong enough to propose a change.
> 
> I'm afraid I am not very convinced by this line of argument; it seems
> very weak and circumstantial.  It leaves us in a position where every
> package with a user or group that might conceivably end up owning files
> in a system image will want to have a static ID, and there will be no
> particularly good way to draw distinctions between which ones should and
> which ones shouldn't.  The space of available static IDs is large
> (60000-64999), but not infinite; I would much rather push back on this
> proposal since otherwise there will be no incentive to come up with a more
> reasonably-scalable approach.
> 
> The cases where I allocate static IDs at present are typically those
> where it's important for interoperability that they be the same on all
> systems, often situations involving networked filesystems and such.
> 
> > > Excellent question! So in general, it would be great if there was a declarative
> > > way to allocate user and group ids at installation time, so that different
> > > installation ordering by apt would not lead to different user and group ids.
> > > Alas, we do not have such a mechanism and talking with developers of apt and
> > > dpkg revealed no easy way to create it.
> 
> Why would this be a matter for apt/dpkg, rather than for adduser?  Yes,
> there have been various conversations about doing declarative user/group
> creation in dpkg, but at present dynamic system users/groups are created
> by adduser.
> 
> Couldn't we fairly easily add a configuration file that adduser would
> read with preseeded user/group IDs for various names, and have it
> preferentially use those IDs if available rather than picking
> arbitrarily from the relevant ID namespace?  This certainly seems a lot
> easier than adding declarative user/group creation to dpkg.

I did not consider this way of solving this problem yet. Partly, because I'd
like to remove the adduser dependency from the apt maintainer script to create
the _apt user -- see #969631.

So you propose to introduce another registry of uid/gid <-> user/group mappings
but not maintained by the base-passwd package but by the adduser package? I
guess this should use the range 100-999, right?

Adding support for default uid/gid numbers to adduser would probably a "quick
fix" but I wonder whether this is the approach we want to use in the long term.
Since there is also https://wiki.debian.org/Teams/Dpkg/Spec/SysUser I'm adding
debian-dpkg@lists.debian.org to the CC.

Thanks!

cheers, josch

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