Re: experimenting with dpkg: installing on a different system

[berenger.morel@neutralite.org]

Le 20.06.2014 18:43, Sven Joachim a écrit :
> On 2014-06-20 17:42 +0200, berenger.morel@neutralite.org wrote:
>
> > First, a warning: I am basically trying to reinvent a wheel, only 
> > for
> > my pleasure and knowledge.
>
> Good luck.  As you had already noticed, this wheel is going to have 
> some
> rough corners, and just using debootstrap is much easier.

Indeed. But I do this on my spare time, without any constraint or order 
from anyone, and since I consider this for pleasure, using debootstrap 
would be a little like using a cheat.
Of course, I know that I risk to generate noise here with that, but I 
think I was clear enough: I want fun and learn, not especially something 
which works out of the box.

> > Yesterday, I was experimenting with dpkg ( for my own fun, and to
> > learn things ), especially with the parameter "--root" which change
> > the targeted system. Or, to be more exact, to change the directories
> > where it tries to retrieve it's own informations ( /var/lib/dpkg ) 
> > and
> > where it tries to deploy stuff ( / ).
>
> You can do this, but the directory you pass as "--root" argument 
> better
> have some standard utilities on it, since dpkg requires them.

Now you mention it, it's true that dpkg's man says it uses a chroot. 
And indeed since the new root does not have anything, it can't run a 
script... did not thought about that.

> > * dpkg depends on various packages ( on my testing current system ),
> > namely: libc6, tar, libselinux1, liblzma5, libbz2-1.0, zlib1g.
>
> It also needs some programs from essential packages on which it does 
> not
> explicitly depend.  And the maintainer scripts will use those as 
> well.

I did not read the debootstrap script enough to notice those tools.

> > When it comes to libc6, dpkg report an error of being unable to find
> > various scripts, like IIRC "/var/lib/dpkg/tmp.ci/preinst" ( in the
> > chrooted environment, so /mnt/var/lib/dpkg/tmp.ci/preinst ).
>
> This could be because the interpreter for those scripts, typically
> /bin/sh, is missing.  Note that the exec(3) family of functions 
> return
> ENOENT in that case which often confuses users.
> Besides a shell for the maintainer scripts, dpkg needs some utilities
> like rm(1) for proper operation.  It checks for those at startup, but
> that does not work with the "--root" option.
>
> Maybe this gives you some idea why debootstrap has been invented in 
> the
> first place.

As I said, it's mostly for playing and fun. I understand why 
debootstrap was made (automated things which are painful otherwise). 
Trying to reinvent the wheel, or to be more precise, to reproduce it's 
behavior in my case, is not a good thing and I do not do it: at work. 
But for learning and understanding, it is a nice way imho. And I take 
some fun when tinkering around egg and chicken problems.

> Cheers,
>        Sven

Thanks for your reply.