~mfisch/ubuntu/precise/live-manual/live-manual-fix-ftbfs-831392

:B~ Customizing run time behaviours

1~customizing-run-time-behaviours Customizing run time behaviours

All configuration that is done during run time is done by live-config. Here

are some most common options of live-config that users are interested in. A

full list of all possibilities can be found in the manpage of live-config.

2~ Customizing the live user

One important consideration is that the live user is created by live-boot at

boot time, not by live-build at build time. This not only influences where

materials relating to the live user are introduced in your build, as

discussed in {Live/chroot local includes}#live-chroot-local-includes, but

also any groups and permissions associated with the live user.

You can specify additional groups that the live user will belong to by

preseeding the #{passwd/user-default-groups}# debconf value. For example, to

add the live user to the #{fuse}# group, add the following to a file in the

#{config/chroot_local-preseed}# directory:

code{

 user-setup passwd/user-default-groups string audio cdrom dip floppy video plugdev netdev powerdev scanner bluetooth fuse

}code

2~customizing-locale-and-language Customizing locale and language

When the live system boots, language is involved in three steps:

_* the locale generation

_* setting the keyboard layout for the console

_* setting the keyboard layout for X

The default locale when building a Live system is "locales=en_US.UTF-8". To

define the locale that should be generated, use the #{locales}# parameter in

the #{--bootappend-live}# option of #{lb config}#, e.g.

code{

 $ lb config --bootappend-live "locales=de_CH.UTF-8"

}code

This parameter can also be used at the kernel command line. You can specify

a locale by a full #{language_country.encoding}# word.

Both the console and X keyboard configuration depend on the

#{keyboard-layouts}# parameter of the #{--bootappend-live}# option. Valid

options for X keyboard layouts can be found in

#{/usr/share/X11/xkb/rules/base.xml}# (rather limited to two-letters country

codes). To find the value (the two characters) corresponding to a language

try searching for the english name of the nation where the language is

spoken, e.g:

code{

 $ grep -i sweden -C3 /usr/share/X11/xkb/rules/base.xml | grep name

 <name>se</name>

}code

To get the locale files for German and Swiss German keyboard layout in X

use:

code{

 $ lb config --bootappend-live "locales=de_CH.UTF-8 keyboard-layouts=ch"

}code

A list of the valid values of the keyboards for the console can be figured

with the following command:

code{

 $ for i in $(find /usr/share/keymaps/ -iname "*kmap.gz"); \

     do basename $i | head -c -9; echo; done | sort | less

}code

Alternatively, you can use the #{console-setup}# package, a tool to let you

configure console layout using X (XKB) definitions; you can then set your

keyboard layout more precisely with #{keyboard-layouts}#,

#{keyboard-variant}#, #{keyboard-options}# and #{keyboard-model}# variables;

live-boot will use also these parameters for X configuration. For example,

to set up a French system with a French-Dvorak layout (called Bepo) on a

TypeMatrix keyboard, both in console and X11, use:

code{

 $ lb config --bootappend-live \

     "locales=fr_FR.UTF-8 keyboard-layouts=fr keyboard-variant=bepo keyboard-model=tm2030usb"

}code

2~persistence Persistence

A live cd paradigm is a pre-installed system which runs from read-only

media, like a cdrom, where writes and modifications do not survive reboots

of the host hardware which runs it.

A Debian Live system is a generalization of this paradigm and thus supports

other media in addition to CDs; but still, in its default behaviour, it

should be considered read-only and all the run-time evolutions of the system

are lost at shutdown.

Persistence is a common name for different kinds of solutions for saving

across reboots some, or all, of this run-time evolution of the system. To

understand how it could work it could be handy to know that even if the

system is booted and run from read-only media, modification to the files and

directories are written on writable media, typically a ram disk (tmpfs) and

ram disks' data do not survive reboots.

The data stored on this ramdisk should be saved on a writable persistent

medium like a Hard Disk, a USB key, a network share or even a session of a

multisession (re)writable CD/DVD. All these media are supported in Debian

Live in different ways, and all but the last one require a special boot

parameter to be specified at boot time: #{persistent}#.

3~ Full persistence

By 'full persistence' it is meant that instead of using a tmpfs for storing

modifications to the read-only media (with the copy-on-write, COW, system) a

writable partition is used. In order to use this feature a partition with a

clean writable supported filesystem on it labeled "live-rw" must be attached

on the system at boot time and the system must be started with the boot

parameter 'persistent'. This partition could be an ext2 partition on the

hard disk or on a usb key created with, e.g.:

code{

 # mkfs.ext2 -L live-rw /dev/sdb1

}code

If you already have a partition on your device, you could just change the

label with one of the following:

code{

 # tune2fs -L live-rw /dev/sdb1 # for ext2,3,4 filesystems

 # dosfslabel /dev/sdb1 live-rw # for a fat filesystem

}code

But since live system users cannot always use a hard drive partition, and

considering that most USB keys have poor write speeds, 'full' persistence

could be also used with just image files, so you could create a file

representing a partition and put this image file even on a NTFS partition of

a foreign OS, with something like:

code{

 $ dd if=/dev/null of=live-rw bs=1G seek=1 # for a 1GB sized image file

 $ /sbin/mkfs.ext2 -F live-rw

}code

Then copy the #{live-rw}# file to a writable partition and reboot with the

boot parameter 'persistent'.

3~ Home automounting

If during the boot a partition (filesystem) image file or a partition

labeled #{home-rw}# is discovered, this filesystem will be directly mounted

as #{/home}#, thus permitting persistence of files that belong to e.g. the

default user. It can be combined with full persistence.

3~ Snapshots

Snapshots are collections of files and directories which are not mounted

while running but which are copied from a persistent device to the system

(tmpfs) at boot and which are resynced at reboot/shutdown of the system. The

content of a snapshot could reside on a partition or an image file (like the

above mentioned types) labeled #{live-sn}#, but it defaults to a simple cpio

archive named #{live-sn.cpio.gz}#. As above, at boot time, the block devices

connected to the system are traversed to see if a partition or a file named

like that could be found. A power interruption during run time could lead to

data loss, hence a tool invoked #{live-snapshot --refresh}# could be called

to sync important changes. This type of persistence, since it does not write

continuously to the persistent media, is the most flash-based device

friendly and the fastest of all the persistence systems.

A /home version of snapshot exists too and its label is #{home-sn.*}#; it

works the same as the main snapshot but it is only applied to /home.

Snapshots cannot currently handle file deletion but full persistence and

home automounting can.

3~ Persistent SubText

If a user would need multiple persistent storage of the same type for

different locations or testing, such as #{live-rw-nonwork}# and

#{live-rw-work}#, the boot parameter #{persistent-subtext}# used in

conjuntion with the boot parameter #{persistent}# will allow for multiple

but unique persistent media. An example would be if a user wanted to use a

persistent partition labeled #{live-sn-subText}# they would use the boot

parameters of: #{persistent}# #{persistent-subtext=subText}#.

3~ Partial remastering

The run-time modification of the tmpfs could be collected using

live-snapshot in a squashfs and added to the cd by remastering the iso in

the case of cd-r or adding a session to multisession cd/dvd(rw); live-boot

mounts all /live filesystem in order or with the module boot parameter.