At work I need minimal Docker images. debootstrap is Debians default way to create chroot environments. By default they include all required and essential packages. For a hardware system this is okay, but too much for a container image.

Using a command line the following will print the binary packages, which are installed by default:

grep-dctrl -n -s Package -F Essential yes -o -F Priority required \
	/var/lib/apt/lists/deb.debian.org_debian_dists_buster_main_binary-amd64_Packages

As an alternative you can use debootstrap directly to get a list of packages. This also includes the resolved list of dependent packages:

debootstrap --print-debs \
	sid \
	"${TMPDIR:/tmp}/deb.sid" \
	http://deb.debian.org/debian/

This includes packages like:

• diffutils
• e2fsprogs
• fdisk
• login

The first two can be removed easily, but the last two are still pulled in as required dependencies.

So to build a minimize chroot environment (for pbuilder) I use the following command:

pbuilder create \
	--basetgz base-sid-amd64.tgz \
	--distribution sid \
	--mirror http://deb.debian.org/debian/ \
	--architecture amd64 \
	--debootstrapopts --variant=buildd \
	--debootstrapopts --exclude=e2fsprogs,diffutils \
	--extrapackages pbuilder

(I install pbuilder inside the chroot environment as I always use --pbuilder-internal to resolve dependencies inside the chroot environment.)

More less

This image is still quiet large. Please have a look at Debuerro which creates the official Slim Debian Docker Images. They use the following tricks to shrinkt the image even more compared to my naive approach:

• Setup /etc/dpkg/dpkg.cfg.d/ to exclude certain files during package installation:
  • All documentation below /usr/share/doc/ except the copyright files.
  • All locale related files below /usr/share/locale/ except for C.UTF-8`.
  • The unpacked Packages, Sources, Release files below /var/lib/apt/.