Quoting Antonio Russo (2023-03-18 07:49:00)

Hello,

I'm trying to perform a task during debian/package.config which
requires another package to be installed. I initially thought
pre-depends would be strong enough, because [1] describes it by:

This field is like Depends, except that it also forces dpkg to
complete installation of the packages named **before even starting
the installation of the package which declares the pre-dependency,**
as follows:

(my emphasis). However, reading the next paragraphs does not appear to indicate any requirements are attempted to be satisfied before debconf/ pre-configure questions are asked (only preinst, unpack, and configure
are explicitly mentioned).

Indeed, trying to install a package with a pre-depends on certbot that
has a debconf debian/config file does not have certbot installed by
the time the debconf script starts. This is on testing.

My question: is there a way to ensure a package is installed *before*
getting debconf input from the user? Alternatively, is there a way to
run debconf questions during a preinst script? Just doing

db_get package/template
db_go

doesn't seem to work (it does nothing?). Am I doing something wrong? Is
there a preferred way to do this?

Best,
Antonio

[1] https://www.debian.org/doc/debian-policy/ch-relationships.html

What confuses here is not package installation order, but that debconf
is a cache of answers to questions, and that cache may be (and is, for
normal uses of debconf together with apt) filled ahead of time.

Because debconf is a cache of answers to questions, insisting that
questions should be answered *without* caching is against the core
design of the tool, and you then better not use that tool. Beware
though, that there is a very good reason for the caching design: It was invented to allow asking all install questions once, not force the user
to sit next to their computer for the whole duration of a system
installation to wait for each question that might pop up and pause the
install process until answered. Therefore, since debconf got invented,
it has been added to Debian Policy that you should not ask questions
that cannot be cached (i.e. you really shouldn't bypass debconf).


- Jonas

--
* Jonas Smedegaard - idealist & Internet-arkitekt
* Tlf.: +45 40843136 Website: http://dr.jones.dk/
* Sponsorship: https://ko-fi.com/drjones

[x] quote me freely [ ] ask before reusing [ ] keep private

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Hello,

I'm trying to perform a task during debian/package.config which
requires another package to be installed. I initially thought
pre-depends would be strong enough, because [1] describes it by:

This field is like Depends, except that it also forces dpkg to
complete installation of the packages named **before even starting
the installation of the package which declares the pre-dependency,**
as follows:

(my emphasis). However, reading the next paragraphs does not appear to indicate any requirements are attempted to be satisfied before debconf/ pre-configure questions are asked (only preinst, unpack, and configure
are explicitly mentioned).

Indeed, trying to install a package with a pre-depends on certbot that
has a debconf debian/config file does not have certbot installed by
the time the debconf script starts. This is on testing.

My question: is there a way to ensure a package is installed *before*
getting debconf input from the user? Alternatively, is there a way to
run debconf questions during a preinst script? Just doing

db_get package/template
db_go

doesn't seem to work (it does nothing?). Am I doing something wrong? Is
there a preferred way to do this?

Best,
Antonio

[1] https://www.debian.org/doc/debian-policy/ch-relationships.html

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Antonio Russo <aerusso@aerusso.net> writes:

Indeed, trying to install a package with a pre-depends on certbot that
has a debconf debian/config file does not have certbot installed by the
time the debconf script starts. This is on testing.

See section 8 of the debconf specification:

The config-file contains a new element, which I call the
configmodule. This is a program that will determine the configuration
before the package is unpacked. This means it is usually run before
the preinst, and before the package is unpacked!

This could definitely be clearer (and easier to find), but yes, this is expected behavior.

My question: is there a way to ensure a package is installed *before*
getting debconf input from the user? Alternatively, is there a way to
run debconf questions during a preinst script?

The tripwire package prompts in preinst, so that worked at some point, but
it's for an old upgrade so I don't know if it's still working. I think
it's more common to prompt in postinst during configure. I know of
several packages that do that, although it's not considered ideal if you
can avoid it.

--
Russ Allbery (rra@debian.org) <https://www.eyrie.org/~eagle/>

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On 3/18/23 09:19, Russ Allbery wrote:

Antonio Russo <aerusso@aerusso.net> writes:

Indeed, trying to install a package with a pre-depends on certbot that
has a debconf debian/config file does not have certbot installed by the
time the debconf script starts. This is on testing.

See section 8 of the debconf specification:

The config-file contains a new element, which I call the
configmodule. This is a program that will determine the configuration
before the package is unpacked. This means it is usually run before
the preinst, and before the package is unpacked!

This could definitely be clearer (and easier to find), but yes, this is expected behavior.

My question: is there a way to ensure a package is installed *before*
getting debconf input from the user? Alternatively, is there a way to
run debconf questions during a preinst script?

The tripwire package prompts in preinst, so that worked at some point, but it's for an old upgrade so I don't know if it's still working. I think
it's more common to prompt in postinst during configure. I know of
several packages that do that, although it's not considered ideal if you
can avoid it.

I was using db_get instead of db_input in the preinst script (doh!).

Everything works fine if you just do the (correct) action in preinst or
(better still) in postinst. I.e., if you need any dependencies, do not
try to use them in the preconfigure scripts.

Thanks,
Antonio

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