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.
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, 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:
debconf passwd/user-default-groups string audio cdrom dialout floppy video plugdev netdev powerdev fuse
When the live system boots, language is involved in three steps:
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.
$ lb config --bootappend-live "locales=de_CH.UTF-8"
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:
$ grep -i sweden -C3 /usr/share/X11/xkb/rules/base.xml | grep name
To get the locale files for German and Swiss German keyboard layout in X use:
$ lb config --bootappend-live "locales=de_CH.UTF-8 keyboard-layouts=ch"
A list of the valid values of the keyboards for the console can be figured with the following command:
$ for i in $(find /usr/share/keymaps/ -iname "*kmap.gz"); \
do basename $i | head -c -9; echo; done | sort | less
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:
$ lb config --bootappend-live \
"locales=fr_FR.UTF-8 keyboard-layouts=fr keyboard-variant=bepo keyboard-model=tm2030usb"
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.
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.:
# mkfs.ext2 -L live-rw /dev/sdb1
If you already have a partition on your device, you could just change the label with one of the following:
# tune2fs -L live-rw /dev/sdb1 # for ext2,3,4 filesystems
# dosfslabel /dev/sdb1 live-rw # for a fat filesystem
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:
$ dd if=/dev/null of=live-rw bs=1G seek=1 # for a 1GB sized image file
$ /sbin/mkfs.ext2 -F live-rw
Then copy the live-rw file to a writable partition and reboot with the boot parameter 'persistent'.
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.
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.
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.
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.