LiveCD

A liveCD is a CD which contains a achievable Operating system without Installation, which launches out to the starting of the computer. By extension, liveCD indicates an operating system present on an external medium bootable. The typical memory supports are CD, DVD and the Clé USB.

Live is used in the televisual direction of “direct” (and not of “alive”).

Goal

A liveCD can have various goals:

demonstration of a Distribution Linux;
installation of an operating system;
itinerant operating system;
together of tools ready with employment for a given field (Information system security, Recovery of data, multi-media creation, education, etc).

Operation

When the liveCD is started, it copies the data necessary to its operation in Random access memory, one using a RAM disc for example. A liveCD does not require for the presence of an hard drive, although it can make use of it if the random access memory is full. Some liveCDs need only 32 Mo to function with a Graphical interface. A liveCD does not deteriorate the data present on the hard drive, although the user can have access to the data of the Hard drive starting from the liveCD. The system turns over in its preceding state when the liveCD is ejected and that the computer is started again.

History

The concept of liveCD was used in first by Slackware as of 1995, then was developed of 1999 to 2002 by DemoLinux. It is however only with the Knoppix (realized starting from Debian) that this type of system took its rise, in the neighborhoods of the year 2003. Other distributions liveCD quickly followed.

Types

A distribution on liveCD can or not make it possible to be installed on the hard drive.

The liveCDs which do not allow the installation are intended for a precise use. Multi-media reading for example, with GeeXboX, multi-media creation with Dynebolic, the recovery of systems or files with SystemRescueCd or education with many distributions.

Among the distributions which can be installed, one can note three tendencies:

distributions optimized before very for the use in liveCD. The permanent installation is possible but it is not the main objective. It is the case of Knoppix, and the large majority of its alternatives (of which the French Kaella).
the hybrid distributions, i.e. intended to be installed while remaining perfectly functional into live are a general tendency, but one can quote Mepis as being the first distribution to assert it and to put it into practice. These distributions are current today. Ubuntu for example is distributed by defect in liveCD. The liveCD can then be seen like an ergonomic procedure of installation of operating system.
the minidistribs being able to hold on a key USB of low capacity or CD small size like Damn Small Linux. There exist also liveCDs gathering several minidistribs liveCDs with the different orientations like Multidistro. They generally have the advantage of being fastest, and of being able to turn on an old system.

Positioning

Advantages

They make it possible to have a complete operating system (fenestrated environment, navigator Web, complete office automation continuation, programming tools, communication software, etc) on a small support, light and removable, without anything to modify machine where it is carried out. It does not touch indeed with the configuration of the machine host, nor generally with the disc (except in the particular case of liveCDs preserving a residential part). The operating system used in a system liveCD is mainly a distribution GNU/Linux, with which this kind of practice took its rise, but one also notes from now on the presence of *BSD and others.

Their ease of use, without passing by the constraining stage of installation, makes it possible to use them to show the capacities of the system (they are used thus by the promoters of the Free software like demonstration of GNU/Linux). They also often make it possible to test the system before installing it. Thus Canonical Ltd. distributes small pockets free including/understanding a liveCD allowing the installation of Ubuntu.

They make it possible to test by means of the interpreted languages (the distributions live do not comprise a compiler GCC in general) the increases in performances which one can hope for while passing in 64 bits if one usually turns in 32 bits. On a liveCD 64 bits are indeed at the same time a core 64 bits, libraries 64 bits and an interpreter Perl 64 bits also.

To start a computer on an operating system as the distribution Knoppix gives access in an elegant way the hard drive of a machine which does not want to start one operating system any more installed locally. Certain distributions are even specialized in the field of recovery (SystemRescueCd, for example).

Disadvantages

It is generally not possible to directly safeguard the modifications carried out in the course of session (choices of keyboard, personalizations, documents, new software…) but of many solutions exist:

the safeguard of these parameters on a Clé USB as initiated by the distribution Knoppix is generally present, to note that Knoppix MIB (and other distributions) makes it possible to safeguard the data in form encryptées on the key in order to reduce the chances to be made them conceal. It is the case of Mandriva, for example, which even makes it possible to launch all the distribution since key USB.
Certaines distributions (as KLA) makes it possible to create a backup file on the hard drive and by respecting the form of the system installed.
One can also find the possibility of storage by Internet.
Some allow also the use of the free part left on a CD-RW (like Puppy).

In the majority of the cases, the flow of reading CD, even the decompression of the data makes the version “live” definitely slower than the version installed, often by the occupation of the Random access memory to mitigate the problem. The use of virtual Memory starting from the hard drive (in the form of partition " Swap " or of temporary file) allows in certain cases to attenuate the problem. There however exist cases (like the liveCD of the Slax, minidistro) which can allow a speed of execution higher than that of a system installed on an hard drive thanks to its print reduced memory.

See too

list of the liveCDs

External bonds

heading liveCD of the site Framasoft
LiveCD List: list liveCDs which can be sorted according to various criteria

Random links: