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Manuale di Live Systems

Panoramica degli strumenti

5. Panoramica degli strumenti

This chapter contains an overview of the three main tools used in building live systems: live-build, live-boot and live-config.

5.1 Il pacchetto live-build

live-build is a collection of scripts to build live systems. These scripts are also referred to as "commands".

L'idea dietro live-build è di essere un'infrastruttura che utilizza una directory di configurazione per automatizzare totalmente e personalizzare tutti gli aspetti della creazione di un'immagine live.

Molti concetti sono simili a quelli applicati per creare pacchetti Debian con debhelper:

Unlike debhelper, live-build provides the tools to generate a skeleton configuration directory. This could be considered to be similar to tools such as dh-make. For more information about these tools, read on, since the remainder of this section discuses the four most important commands. Note that the preceding lb is a generic wrapper for live-build commands.

5.1.1 Il comando lb config

As discussed in live-build, the scripts that make up live-build read their configuration with the source command from a single directory named config/. As constructing this directory by hand would be time-consuming and error-prone, the lb config command can be used to create the initial skeleton configuration tree.

The lb config command creates the following directories inside config/: hooks/, includes/, several other includes subdirectories for each stage of the build process and package-lists/. The latter includes a list of several important live packages like live-boot, live-config and live-config-sysvinit.

Issuing lb config without any arguments completes the config/ subdirectory which it populates with some default settings in configuration files, and two skeleton trees named auto/ and local/.

$ lb config
[2014-04-25 17:14:34] lb config
P: Updating config tree for a debian/wheezy/i386 system

Using lb config without any arguments would be suitable for users who need a very basic image, or who intend to provide a more complete configuration via auto/config later (see Managing a configuration for details).

Normally, you will want to specify some options. For example, to specify which package manager to use while building the image:

$ lb config --apt aptitude

È possibile specificare molte opzioni, come:

$ lb config --binary-images netboot --bootappend-live "boot=live components hostname=live-host username=live-user" ...

Una lista completa delle opzioni è disponibile nel manuale di lb_config.

5.1.2 Il comando lb build

Il comando lb build legge la configurazione dalla directory config/ ed esegue a un livello inferiore i comandi necessari a costruire il sistema live.

5.1.3 Il comando lb clean

It is the job of the lb clean command to remove various parts of a build so subsequent builds can start from a clean state. By default, chroot, binary and source stages are cleaned, but the cache is left intact. Also, individual stages can be cleaned. For example, if you have made changes that only affect the binary stage, use lb clean --binary prior to building a new binary. If your changes invalidate the bootstrap and/or package caches, e.g. changes to --mode, --architecture, or --bootstrap, you must use lb clean --purge. See the lb_clean man page for a full list of options.

5.2 Il pacchetto live-boot

live-boot is a collection of scripts providing hooks for the initramfs-tools, used to generate an initramfs capable of booting live systems, such as those created by live-build. This includes the live system ISOs, netboot tarballs, and USB stick images.

All'avvio cercherà supporti in sola lettura che contengano una directory /live/ dove sia presente un filesystem root (spesso un'immagine compressa come squashfs). Se trovata, creerà un ambiente scrivibile usando aufs, per avviarsi da sistemi simili a Debian.

Si possono trovare maggiori informazioni sui ramfs iniziali nel capitolo su initramfs del Debian Linux Kernel Handbook all'indirizzo ‹http://kernel-handbook.alioth.debian.org/›.

5.3 Il pacchetto live-config

live-config è costituito da script eseguiti all'avvio dopo live-boot per configurare automaticamente il sistema live. Gestisce attività quali impostare l'hostname, localizzazione e fuso orario, creare l'utente live, inibire compiti automatizzati tramite cron ed eseguire il login automatico dell'utente live.


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