Created 20th October, 2013 02:32 (UTC), last edited 27th October, 2013 08:02 (UTC)

A simple script for making schroot environments from a JSON configuration file. The idea is to let you set up multiple schroot images simply and quickly and to be able to check in the configuration that makes this repeatable across many machines easily.

This first version isn't so smart. It assumes that you're using a 64 bit host machine, and doesn't check that you're on Debian as it should (it only uses debootstrap to build the chroot environment). It's probably also highly Ubuntu specific right now. To add to the fun it's not been very thoroughly tested yet either.

To use it you must install a couple of things:

apt-get install debootstrap schroot
pip install mkschroot

Using mkschroot

You just need to pass mkschroot a configuration file:

mkschroot ~/chroots/example.json

Don't run with root privileges. If root access is required then sudo rights will be requested.

If the schroot configuration has been changed then a new configuration file will be generated. If the image doesn't exist it will be created and have the packages installed on it, if it does exist it will be updated to the latest package list and package versions.

You really want to have a local apt-cacher if you're going to be making a lot of images.

Configuring mkschroot

The configuration file needs to be JSON. A configuration file might look like the below:

    "root": "/mnt/files2/chroot",
    "source": "",
    "http-proxy": "http://angelo:3142/",
    "base-packages": ["lsb-release", "openssh-client"],
    "defaults": {
        "sources": {
            "universe": {}
        "conf": {
            "root-users": ["kirit"],
            "users": ["kirit"]
    "schroot": {
        "build-lucid64": {
            "release": "lucid",
            "packages": [
                "g++", "libbz2-dev", "libssl-dev", "python-dev", "uuid-dev",
                "libboost-dev", "subversion", "git-core"
        "root-ca-kirit": {
            "release": "precise",
            "packages": ["openssl"],
            "conf": {
                "personality": "linux32"

The base options are:

  • base-packages: Packages that are to be installed in all chroots.
  • defaults: Default values for individual chroot configurations.
  • http-proxy: A HTTP proxy (probably an apt-cache) that should be used by debootstrap to fetch packages.
  • root: The directory where you want the chroots to be created in by default (override this using the directory setting within a chroot).
  • schroot: The schroot environments to be created.
  • source: Where the packages can be installed from. This is required.

A chroot configuration is described by a structure like the following:

    "release": "lucid",
    "variant": "buildd",
    "packages": ["g++"],
    "sources": {
        "universe": {}
    "conf": {
        "root-users": ["kirit'"],
        "users": ["kirit"]
  • release: The operating system version you wish to make use of.
  • variant: If specified then the variant is passed to debootstrap so that the right base image options are used. The variant name is also used in the schroot configuration file so that the right start up options are used when the chroot is started. Note that some schroot options (notably fstab for buildd) won't work until they're configured to match your system.
  • conf: The fields used for the schroot configuration file (in /etc/schroot/chroot.d/). All fields are optional. The fields root-users and users will have values created from the currently logged in user. The other fields that can be here are: description, type, personality, directory. Do read the part about common fields though (below).
  • sources: Extra sources that are to be added to the chroot. See sources below.
  • packages: Packages that need to be installed into the chroot using apt-get. These are combined with the base-packages.

Note that if you change the variant of an existing image no attempt is made to correct the packages that are installed.

Common configuration items

Generally many of the chroots that you want will share a good deal of configuration between machines. To help with this a default schroot configuration can be given which will then have values overridden by the specific schroots that you request be made.

This means that the values in the defaults key will be used, then any values in the specific schroots key will be added in, and finally a few defaults will be generated by mkschroot.

  • description: The release name together with personality name.
  • directory: The root global option will have the schroot name added to it.
  • type: Always directory.
  • personality: The same as the host personality (currently hard coded to 64 bits)
  • root-users: A list of user names. Defaults to the currently logged in user.
  • users: A list of user names. Defaults to the currently logged in user.


If the host environment has an /etc/apt/apt.conf file then it is assumed that this should also be in the schroot environments. If the file contents differ then the host file is copied into the schroot and apt-get update is run within the chroot.


If other sources are needed then they can be specified at either the defaults level or for an individual schroot. The name is used as the component name, and this will generate a file in /etc/apt/sources.list.d/ with the component pointing at the source. If a source field is given than that is used, otherwise the global source is used.

For example:

sources: {
    "universe": {},
    "private-example": {"source": ""}

Will generate two files, universe.list:

deb universe

And private-example.list:

deb private-example

Note that the value for a source component must be a JSON object, even if empty.