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:
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.
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.
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.
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.