livecd-rootfs/live-build/ubuntu-cpc

TL;DR

In order to generate the hooks for a specific image target set, call the make-hooks script, located in hooks.d as

./make-hooks --hooks-dir ../hooks <image_set>

where image_set is the name of a series file (e.g. "vagrant") without leading path components. Do not check in the hooks folder, it is automatically generated by auto/config during Live Build runs.

Hook placement and ordering

Scripts live in subfolders below the hooks.d folder. Currently the folders chroot and base exist. The folder with the name extra is reserved for private scripts, which are not included in the source of livecd-rootfs. The scripts are not numbered, instead the order of their execution depends on the order in which they are listed in a series file.

Series files are placed in subfolders hooks.d/base/series or hooks.d/extra/series. Each series file contains a list of scripts to be executed. Empty lines and lines starting with a # are ignored.

Series files in extra/series override files in base/series with the same name. For example, if a series file base/series/cloudA exists and a series file extra/series/cloudA, then the latter will be preferred.

A series file in extra/series may also list scripts that are located in the chroot and base folders. In addition, series files can depend on other series files. For example, the series files for most custom images look similar to this:

depends disk-image
depends extra-settings
extra/cloudB.binary

Where disk-image and extra-settings may list scripts and dependencies which are to be processed before the script extra/cloudB.binary is called.

ACHTUNG: live build runs scripts with the suffix ".chroot" in a batch separate from scripts ending in ".binary". Even if you arrange them interleaved in your series files, the chroot scripts will be run before the binary scripts.

Image set selection for Live Build

During a Live Build, enumerated symbolic links are generated based on the contents of one or more series files. The series files are selected according to the contents of the IMAGE_TARGETS environment variable. For example, in order to trigger the build of squashfs and vagrant, list them in the IMAGE_TARGETS variable as squashfs,vagrant. The separator can be a comma, a semi-colon or whitespace.

The generation of the symbolic links is triggered from the auto/config script, from where the contents of the IMAGE_TARGETS environment variable are passed on to the make-hooks script.

Symlink generation

Since Live Build itself does not know about series files, a traditional hooks folder is generated using the make-hooks script. The script takes as arguments the names of the series files to be processed.

The script parses the series files and generates enumerated symbolic links for all entries. Per default, these are placed into a directory named hooks next to the hooks.d directory. This can be changed using the --hooks-dir parameter.