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This chapter discusses fine-tuning customization of the live system contents beyond merely choosing which packages to include. Includes allow you to add or replace arbitrary files in your live system image, hooks allow you to execute arbitrary commands at different stages of the build and at boot time, and preseeding allows you to configure packages when they are installed by supplying answers to debconf questions.
While ideally a live system would include files entirely provided by unmodified packages, it is sometimes convenient to provide or modify some content by means of files. Using includes, it is possible to add (or replace) arbitrary files in your live system image. live-build provides two mechanisms for using them:
Si consulti il Glossario per ulteriori informazioni sulla distinzione tra immagini "Live" e "binarie".
Chroot local includes can be used to add or replace files in the chroot/Live filesystem so that they may be used in the Live system. A typical use is to populate the skeleton user directory (/etc/skel) used by the Live system to create the live user's home directory. Another is to supply configuration files that can be simply added or replaced in the image without processing; see Chroot local hooks if processing is needed.
Per includere i file si aggiungano semplicemente alla directory config/includes.chroot. Questa corrisponde alla directory root / del sistema live. Per esempio, per aggiungere un file /var/www/index.html nel sistema live, si usi:
$ mkdir -p config/includes.chroot/var/www
$ cp /path/to/my/index.html config/includes.chroot/var/www
La configurazione avrà quindi il seguente schema:
-- config
[...]
|-- includes.chroot
| `-- var
| `-- www
| `-- index.html
[...]
Gli include locali del chroot vengono installati dopo l'installazione dei pacchetti in modo che tali file vengano in seguito sovrascitti.
Si possono utilizzare include locali binari per inserire sul filesystem del supporto materiale come documentazione o video affinché sia immediatamente accessibile dopo l'inserimento dello stesso senza avviare il sistema live. Ciò funziona in modo simile agli include locali del chroot; supponendo che i file ~/video_demo.* siano video dimostrativi del sistema descritti da e collegati a una pagina HTML indice, basta copiare il materiale in config/includes.binary/ come segue:
$ cp ~/video_demo.* config/includes.binary/
Questi file appariranno nella directory principale del supporto live.
Hooks allow commands to be run in the chroot and binary stages of the build in order to customize the image. Depending on whether you are building a live image or a regular system image you have to place your hooks in config/hooks/live or config/hooks/normal respectively. These are frequently referred to as local hooks because they are executed inside the build environment.
There are also boot-time hooks that allow you to run commands once the image has already been built, during the boot process.
To run commands in the chroot stage, create a hook script with a .hook.chroot suffix containing the commands either in the config/hooks/live or config/hooks/normal directories. The hook will run in the chroot after the rest of your chroot configuration has been applied, so remember to ensure your configuration includes all packages and files your hook needs in order to run. See the example chroot hook scripts for various common chroot customization tasks provided in /usr/share/doc/live-build/examples/hooks which you can copy or symlink to use them in your own configuration.
To run commands in the binary stage, create a hook script with a .hook.binary suffix containing the commands either in the config/hooks/live or config/hooks/normal directories. The hook will run after all other binary commands are run, but before binary_checksums, the very last binary command. The commands in your hook do not run in the chroot, so take care not to modify any files outside of the build tree, or you may damage your build system! See the example binary hook scripts for various common binary customization tasks provided in /usr/share/doc/live-build/examples/hooks which you can copy or symlink to use them in your own configuration.
Per eseguire comandi all'avvio, è possibile fornire degli hook a live-config come spiegato nella sezione "Customization" del suo manuale. Controllare gli hook di live-config in /lib/live/config/ e notare i numeri sequenziali; fornire quindi i propri hook con una sequenza numerica appropriata, sia come include locali del chroot in config/includes.chroot/lib/live/config/, sia come pacchetto personalizzato come discusso in Installare pacchetti modificati o di terze parti.
I file nella directory config/preseed/ con suffisso .cfg seguiti dalla fase (.chroot o .binary) sono considerati file di preconfigurazione di debconf e sono installati da live-build usando debconf-set-selections durante la fase corrispondente.
Per ulteriori informazioni su debconf, vedere debconf(7) nel pacchetto debconf.
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