Re: Using python-apt's apt_pkg with a chroot

[Johannes Schauer Marin Rodrigues <josch@debian.org>]

Hi,

Quoting Sebastiaan Couwenberg (2025-12-02 18:36:00)
> Using python-apt's apt_pkg with a chroot turns out to be non-trivial unlike apt.cache.
> 
> I'm running a script [0] on a trixie system and need to interact with the cache in a testing chroot.
> 
> The chroot is created with mmdebstrap --mode=unshare, and the script is run via unshare as well.

maybe this is an XY problem.

Why do you need a full chroot for something that is as far as I get from the
script just a "I want apt to resolve the dependencies with my custom
sources.list"? This sounds like something like chdist is doing?

Maybe the mmdebstrap man page has an example which helps you. It is a snippet
which is the very bare-bones of what mmdebstrap does with a few thousand more
lines of code:


    mkdir -p "$2/etc/apt" "$2/var/cache" "$2/var/lib"
    cat << END > "$2/apt.conf"
    Apt::Architecture "$(dpkg --print-architecture)";
    Apt::Architectures "$(dpkg --print-architecture)";
    Dir "$(cd "$2" && pwd)";
    Dir::Etc::Trusted "$(eval "$(apt-config shell v Dir::Etc::Trusted/f)"; printf %s "$v")";
    Dir::Etc::TrustedParts "$(eval "$(apt-config shell v Dir::Etc::TrustedParts/d)"; printf %s "$v"

    END
    echo "deb http://deb.debian.org/debian/ $1 main" > "$2/etc/apt/sources.list"
    APT_CONFIG="$2/apt.conf" apt-get update
    APT_CONFIG="$2/apt.conf" apt-get --yes --download-only install '?essential'
    for f in "$2"/var/cache/apt/archives/*.deb; do dpkg-deb --extract "$f" "$2"; done
    chroot "$2" sh -c "dpkg --install --force-depends /var/cache/apt/archives/*.deb"


> Setting RootDir in the config does not result in the chroot paths to be used:

I think you need Dir.

>   apt_pkg.Error: E:Could not open lock file /var/lib/apt/lists/lock - open (13: Permission denied), E:Unable to lock directory /var/lib/apt/lists/

This sounds like you are trying to access something created for the unshared
user as the normal user?

Thanks!

cheers, josch

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