4.1. live-helper

live-helper is a collection of scripts to build Debian Live systems. These scripts are also referred to as "helpers".

The idea behind live-helper is to be a framework that uses a configuration directory to completely automate and customize all aspects of building a Live image.

Many concepts are similar to those in the debhelper Debian package tools written by Joey Hess:

  1. The scripts have a central location for configuring their operation.

    In debhelper, this is the debian subdirectory of a package tree. For example, dh_install will look for a file called debian/<packagename>.install to determine which files should exist in a particular binary package. In much the same way, live-helper stores its configuration entirely under a config/ subdirectory.

  2. The scripts are independent - that is to say, it is always safe to run each command.

Unlike debhelper, live-helper contains a tool to generate a skeleton configuration directory, lh config. This could be considered to be similar to tools such as dh-make. For more information about lh config, please see Section 4.1.1, “The lh config helper”.

Besides the common config/common, which is used by all live-helper helper commands, some additional files can be used to configure the behavior of specific helper commands. These files are typically named config/helper or config/stage (where "stage", of course, is replaced with the name of the stage that they belong to, and "helper" with the name of the helper).

For example, the lh bootstrap debootstrap helper command uses files named config/bootstrap and config/bootstrap_debootstrap to read the options it will use. Generally, these files contain variables with values assigned, one variable per line. Some programs in live-helper use pairs of values or slightly more complicated variable assignments.

live-helper respects environment variables which are present in the context of the shell it is running. If variables can be read from config files, then they override environment variables, and if command line options are used, they override values from config files. If no value for a given variable can be found (and is thus unset), live-helper will automatically set it to a default value.

All config files are shell scripts which are sourced by a live-helper program. That means they have to follow the normal shell syntax. You can also put comments in these files; lines beginning with "#" are ignored.

In some rare cases you may want to have different versions of these files for different architectures or distributions. If files named config/stage.arch or config/stage_helper.arch, and config/stage.dist or config/stage_helper.dist exist (where "arch" is the same as the output of dpkg --print-architecture and "dist" is the same as the codename of the target distribution), then they will be used in preference to the other, more general files.

Please see Chapter 2, Installation for information on how to install live-helper.

The remainder of this section discusses the three most important helpers:

lh config

Responsible for initialising a Live system configuration directory. See Section 4.1.1, “The lh config helper” for more information.

lh build

Responsible for starting a Live system build. See Section 4.1.2, “The lh build helper” for more information.

lh clean

Responsible for removing parts of a Live system build. See Section 4.1.3, “The lh clean helper” for more information.

4.1.1. The lh config helper

As discussed in Section 4.1, “live-helper, the scripts that make up live-helper source their configuration from a single directory named config/. As constructing this directory by hand would be time-consuming and error-prone, the lh config helper can be used to create skeleton configuration folders.

Issuing lh config without any arguments creates a config subdirectory which it populates with some default settings:

$ lh config
$ ls -l
total 4.1k
drwxr-xr-x 19 user group 4.1k 2008-05-09 21:37 config
$ ls -l config/
total 104
-rw-r--r-- 1 user group 4175 2010-04-11 12:16 binary
drwxr-xr-x 2 user group 4096 2010-04-11 12:16 binary_debian-installer
drwxr-xr-x 2 user group 4096 2010-04-11 12:16 binary_debian-installer-includes
drwxr-xr-x 2 user group 4096 2010-04-11 12:16 binary_grub
drwxr-xr-x 2 user group 4096 2010-04-11 12:16 binary_local-debs
drwxr-xr-x 2 user group 4096 2010-04-11 12:16 binary_local-hooks
drwxr-xr-x 2 user group 4096 2010-04-11 12:16 binary_local-includes
drwxr-xr-x 2 user group 4096 2010-04-11 12:16 binary_local-packageslists
drwxr-xr-x 2 user group 4096 2010-04-11 12:16 binary_local-udebs
drwxr-xr-x 2 user group 4096 2010-04-11 12:16 binary_rootfs
drwxr-xr-x 2 user group 4096 2010-04-11 12:16 binary_syslinux
-rw-r--r-- 1 user group 2205 2010-04-11 12:16 bootstrap
-rw-r--r-- 1 user group 1599 2010-04-11 12:16 chroot
drwxr-xr-x 2 user group 4096 2010-04-11 12:16 chroot_apt
drwxr-xr-x 2 user group 4096 2010-04-11 12:16 chroot_local-hooks
drwxr-xr-x 2 user group 4096 2010-04-11 12:16 chroot_local-includes
drwxr-xr-x 2 user group 4096 2010-04-11 12:16 chroot_local-packages
drwxr-xr-x 2 user group 4096 2010-04-11 12:16 chroot_local-packageslists
drwxr-xr-x 2 user group 4096 2010-04-11 12:16 chroot_local-patches
drwxr-xr-x 2 user group 4096 2010-04-11 12:16 chroot_local-preseed
drwxr-xr-x 2 user group 4096 2010-04-11 12:16 chroot_sources
-rw-r--r-- 1 user group 2938 2010-04-11 12:16 common
drwxr-xr-x 2 user group 4096 2010-04-11 12:16 includes
-rw-r--r-- 1 user group  206 2010-04-11 12:16 source
drwxr-xr-x 2 user group 4096 2010-04-11 12:16 templates

Using lh config without any arguments would be suitable for users who are either happy editing the generated files, or are simply happy with the defaults it creates.

You can ask lh config to generate a config/ directory "preseeded" with various options. This might be suitable if you do not require the default settings but do not need to change a large number of options. For example:

$ lh config -p gnome

will build a config/ directory configured to include the 'gnome' package list. It is possible to specify many options:

$ lh config --apt aptitude --binary-images net --hostname live-machine --username live-user ...

A full list of options is available in the lh_config man page. Most options have a parallel with an "LH_" prefixed variable.

4.1.2. The lh build helper

The lh build helper reads in your configuration from the config/ directory. It then runs the lower lower level commands needed to build your Live system.

4.1.3. The lh clean helper

It is the job of the lh clean helper to remove various parts of a Live helper build so subsequent builds can start from a clean state.