Last week we saw how to get docker installed on your Debian-based system. If you haven’t installed docker by reading this article, take some minutes and follow the steps of Install Docker on Debian 6 (Squeeze) on a VPS. Don’t be confused about the VPS, the instructions are the same for your local machine.
If you’re using Arch Linux simply run
sudo pacman -S docker and start the service with
systemctl start docker
In the next section we’ll create a new Debian-based docker image which is no more than a tarball of a root file system.
Create the root file system
It’s fairly simple to install Debian’s base packages on your current machine and it doesn’t matter if you’re currently not on a Debian host system. There’s a tool called debootstrap which does all the work for you.
You can download it via your package manager.
# Arch Linux yaourt -S debootstrap # Debian/Ubuntu aptitude install debootstrap
As soon as the utility is available on your system you just need to tell it the suite, target and the mirror so basically, in that order, the name of the Debian version, the directory where to install the packages and the URL from which the packages are downloaded. Essentially the mirror is optional but we’ll specify it anyway here.
$ mkdir wheezy $ sudo debootstrap wheezy ./wheezy http://http.debian.net/debian/
This step can take a moment depending on your internet connection. You may have noticed that debootstrap requires root privileges to create a file system that belongs root.
Amongst the required suite and target Debian’s bootstrap utility also accepts options from which some are listed below.
SYNOPSIS debootstrap [OPTION...] SUITE TARGET [MIRROR [SCRIPT]] OPTIONS --include=alpha,beta Comma separated list of packages which will be added to download and extract lists. --exclude=alpha,beta Comma separated list of packages which will be removed from download and extract lists. WARNING: you can and probably will exclude essential packages, be careful using this option. --variant=minbase|buildd|fakechroot|scratchbox Name of the bootstrap script variant to use. Currently, the variants supported are minbase, which only includes essential packages and apt; buildd, which installs the build-essential packages into TARGET; and fakechroot, which installs the packages without root privileges. Finally there is variant scratchbox, which is for creating targets for scratchbox usage. The default, with no --variant=X argument, is to create a base Debian installation in TARGET. --make-tarball=FILE Instead of bootstrapping, make a tarball (written to FILE) of the downloaded packages. The resulting tarball may be passed to a later --unpack-tarball.
Assuming you want to install additional packages such as zsh or git you can do so by specifying them with the
Create the tarball
Docker supports both non-compressed but also compressed images so a .tar, .tar.gz, .tgz, .bzip, .tar.xz or .txz image will be totally fine. Here we create a non-compressed tarball. In a subsequent step we’ll fix the tarball’s owner so that further work with docker can be done by non-root users.
$ sudo tar -C wheezy -cf wheezy.tar . $ sudo chown you:you wheezy.tar
According debootstrap’s documentation one should be able to use its option –make-tarball to create the tarball during the bootstrap process by executing …
debootstrap --make-tarball=wheezy.tar wheezy ./wheezy http://http.debian.net/debian/
… but when doing so the image is some sort of corrupt and incomplete.
To share your image with the community you could upload the image and make it available for other docker users.
Next week you’ll be taught some basics to properly work with docker containers. Stay tuned.