Setting up the logical volumes

Having decided how much space you want in the base, set up an LV for your base system (here I use 3 GiB in the volume group "vg", naming the resulting LV "/dev/vg/schroot"):

sudo lvcreate -L3G -nschroot vg

format it:

sudo mkfs.ext3 -Lschroot /dev/vg/schroot

and temporarily mount it somewhere so you can create the base systems:

sudo mount /dev/vg/schroot /mnt

Setting up Debian base systems with cdebootstrap

cdebootstrap is part of the Debian installer. Replace MIRROR with your local Debian mirror.

For use on a laptop with potentially wobbly networking, you probably want to cache installed packages with a local instance of approx, in which case replace MIRROR with localhost:9999.

cd /mnt
sudo cdebootstrap --flavour=build sarge sarge http://MIRROR/debian
sudo cdebootstrap --flavour=build etch etch http://MIRROR/debian
sudo cdebootstrap --flavour=build sid sid http://MIRROR/debian

Setting up Ubuntu or Debian base systems with debootstrap

debootstrap was the shell script that inspired cdebootstrap. It's likely to be more fragile, but the version shipped in Ubuntu supports making Ubuntu as well as Debian chroots, which cdebootstrap doesn't.

As an alternative to the cdebootstrap commands above, you could use:

cd /mnt
sudo debootstrap --variant=buildd sarge sarge http://MIRROR/debian
sudo debootstrap --variant=buildd etch etch http://MIRROR/debian
sudo debootstrap --variant=buildd sid sid http://MIRROR/debian

To get Ubuntu chroots on a Debian system, you'll have to fetch the debootstrap source tarball from <http://packages.ubuntu.com/debootstrap>. Untar it somewhere (I used ~/tmp) and use:

cd /mnt
sudo debootstrap dapper dapper http://MIRROR/ubuntu \
        ~/tmp/debootstrap-0.3.3.2ubuntu3/dapper
sudo debootstrap edgy edgy http://MIRROR/ubuntu \
        ~/tmp/debootstrap-0.3.3.2ubuntu3/edgy
sudo debootstrap feisty feisty http://MIRROR/ubuntu \
        ~/tmp/debootstrap-0.3.3.2ubuntu3/feisty

Very basic chroot configuration

At this point you want to set up the absolute basics in each schroot: /etc/resolv.conf, /etc/hosts and possibly /etc/sudoers.

In distributions where Recommends are installed by default, you probably also want to put this in /etc/apt/apt.conf:

APT::Install-Recommends "false";

If you'll be using the chroot for development rather than just builds, you'll probably want to add a deb-src line to /etc/apt/sources.list.

After that, unmount /mnt before continuing.

Configuring schroot

Here's what to put in /etc/schroot/schroot.conf for each chroot:

[sid]
# Optional. The chroot with alias 'default' is used if you just type
# 'schroot' without the -c option.
aliases=unstable,default
# Whatever you like
description=Debian sid
# Relative to what was /mnt until a moment ago
location=/sid
# Below here is standard for all the chroots
# Adjust according to the space available and size of builds you'll do
lvm-snapshot-options=--size 2G
device=/dev/vg/schroot
type=lvm-snapshot
priority=3
groups=sbuild,root
root-groups=sbuild,root
source-groups=sbuild,root
source-root-groups=root
run-setup-scripts=true
run-exec-scripts=true
# if you used XFS, you'll also need:
#mount-options=-o nouuid

If you want more than one chroot sharing a base system, make the name in square brackets different, but keep the location the same. For instance, my experimental chroot is headed [experimental] but uses location=/sid.

If most of your builds will be quite small, but you occasionally do one that needs more space, it may be worthwhile setting the snapshot size to be quite small, but then adding chroots like [sid-large] that use a larger snapshot for the same base system.

The schroot.conf from my laptop 'carbon' is available as an example.

Adding hooks

Put this in /etc/schroot/setup.d/60append-apt-sources:

#!/bin/sh
# /etc/schroot/setup.d/60append-apt-sources
# Updated 2008-04-13 to support replacing /etc/apt/preferences

if [ "z$1" = "zsetup-start" ] || [ "z$1" = "zsetup-recover" ]; then

  NAME=$(echo "${CHROOT_NAME}" | sed -e 's/-[a-z0-9][a-z0-9][a-z0-9][a-z0-9][a-z0-9][a-z0-9][a-z0-9][a-z0-9]-[a-z0-9][a-z0-9][a-z0-9][a-z0-9]-[a-z0-9][a-z0-9][a-z0-9][a-z0-9]-[a-z0-9][a-z0-9][a-z0-9][a-z0-9]-[a-z0-9][a-z0-9][a-z0-9][a-z0-9][a-z0-9][a-z0-9][a-z0-9][a-z0-9][a-z0-9][a-z0-9][a-z0-9][a-z0-9]//g')

  EXTRA_APT_SOURCES="/etc/schroot/sources.list.d/${NAME}.sources.list"
  APT_PREFS="/etc/schroot/sources.list.d/${NAME}.preferences"

  if [ "$AUTH_VERBOSITY" = "verbose" ]; then
    echo "Checking for auxiliary apt sources in $EXTRA_APT_SOURCES"
  fi
  if [ -e "$EXTRA_APT_SOURCES" ]; then
    if [ "$AUTH_VERBOSITY" = "verbose" ]; then
      echo "... extra apt sources found"
    fi
    cat "$EXTRA_APT_SOURCES" >> "${CHROOT_PATH}/etc/apt/sources.list"
  fi

  if [ "$AUTH_VERBOSITY" = "verbose" ]; then
    echo "Checking for apt preferences in $APT_PREFS"
  fi
  if [ -e "$APT_PREFS" ]; then
    if [ "$AUTH_VERBOSITY" = "verbose" ]; then
      echo "... apt preferences found"
    fi
    install -m644 "$APT_PREFS" "${CHROOT_PATH}/etc/apt/preferences"
  fi
fi

and this in /etc/schroot/setup.d/80apt-get-update:

#!/bin/sh
# /etc/schroot/setup.d/80apt-get-update
# Updated 2008-04-13 to never output to stdout

if [ "z$1" = "zsetup-start" ]; then
    if [ "z$AUTH_VERBOSITY" = "zverbose" ]; then
        chroot "${CHROOT_PATH}" apt-get update >&2 || true
    else
        chroot "${CHROOT_PATH}" apt-get update >/dev/null || true
    fi
fi

chmod them both to be executable.

Using the sources.list hook

Create a directory /etc/schroot/sources.list.d and place files in it named after a chroot, with .sources.list appended. For instance, in /etc/schroot/sources.list.d/experimental.sources.list write:

# /etc/schroot/sources.list.d/experimental.sources.list
deb http://MIRROR/debian experimental main

with MIRROR replaced as above. Now that sources.list fragment will be appended to /etc/apt/sources.list in [experimental] chroots only. apt's default pinning behaviour means the experimental packages will only be used where selected by a versioned dependency.

If you want to force in experimental versions of particular packages, you can also do so with a file like this:

# /etc/schroot/sources.list.d/experimental.preferences
Package: libdbus-glib-1-dev
Pin: release a=experimental
Pin-Priority: 990

Package: libdbus-glib-1
Pin: release a=experimental
Pin-Priority: 990

Entering the source chroots

You can enter the source chroots with a command like:

schroot -c sid-source

Typically you'll want to do this as root, to perform updates or set up configuration. Some things you probably want to do on each chroot to start with:

outside% sudo schroot -c sid-source
inside# apt-get upgrade
inside# apt-get install devscripts vim-tiny sudo fakeroot aptitude \
        build-essential
inside# apt-get clean

Changes made here will be reflected in all subsequent snapshots.

For Sarge, or if you want a more capable editor in the chroot, install vim instead of vim-tiny.

Entering a snapshot

Enter a snapshot with a command like:

schroot -c sid

Any changes you make will be lost after the snapshot is closed.

Build a package in a single-use snapshot with:

sbuild foo-1.2.3.dsc

or to override the distribution in the .dsc file,

sbuild -d experimental foo-1.2.3.dsc

(Note that the distribution from sbuild -d will go into the .changes file. I've filed Debian bug #474160 asking for the ability to change the chroot independently.)

Create a persistent snapshot with:

schroot --begin-session -c sid > my-sid-session-id

You can then resume it with:

schroot --run-session -c `cat my-sid-session-id`

and end it with:

schroot --end-session -c `cat my-sid-session-id`