LiveDistro

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"Live CD" redirects here. For musical recordings, see Live album.

Gnoppix 0.8.1-beta5 running Epiphany 1.4.0 under GNOME, with Gaim connected to the freenode IRC Network

LiveDistro is a generic term for an operating system distribution that is executed upon boot, without installation on a hard drive. Typically, it is stored on bootable media such as a CD-ROM (Live CD), DVD (Live DVD), USB flash drive (Live USB), among others.

The term "live" derives from the fact that these distributions are a complete, runnable, i.e. "live" instance of the operating system residing on the distribution media, rather than the typical case of a collection of packages that must first be installed on the target machine prior to using the OS.

A LiveDistro does not alter the current operating system or files unless the user specifically requests it. The system returns to its previous state when the LiveDistro is ejected and the computer is rebooted. It does this by placing the files that typically would be stored on a hard drive into temporary memory, such as a ram disk. In fact, a hard drive is not needed at all. However, this does cut down on the RAM available to applications, reducing performance somewhat. At least 256 MB of RAM is recommended, but some LiveDistros do fine with less.

It is often said LiveDistros are a good way to demo or preview an operating system without having to install it to a hard drive.

1 Common traits
2 History
3 Technique
- 3.1 File system
- 3.2 Hardware detection
4 Emulation
5 See also
6 External links

[edit] Common traits

Some LiveDistros come with an installation utility launchable from a desktop icon that can optionally install the system on a hard drive or USB keydrive. Most LiveDistros can access the information on internal and/or external hard drives, diskettes and USB Flash drives. Generally LiveDistros are booted from read-only media, requiring either copying to rewriteable media (i.e. a hard drive) or complete remastering to install additional software; however, there are exceptions such as the Slackware ZipSlack distribution, which is designed to run off a Zip disk.

Most LiveDistros are based on Linux, but there are also LiveDistros based on other operating systems, such as Mac OS, Mac OS X, Solaris, BeOS, ReactOS, FreeBSD, Minix, NetBSD, Plan 9 from Bell Labs, MSDOS or Microsoft Windows. The first OS to support LiveDistro operations as they now exist appears to have been the AmigaOS, which could be booted from CD on an Amiga CDTV in 1990.

The syslinux utility is used to boot Linux based LiveDistros as well as Linux floppies. On a PC, a bootable CD generally conforms to the El Torito specification which treats a special file on the disc (possibly hidden) as a floppy diskette image. Many Linux based LiveDistros use a compressed filesystem image, often with the cloop compressed loopback driver, or squashfs compressed filesystem, generally doubling effective storage capacity, although slowing application start up. The resulting environment can be quite rich: typical Knoppix systems include around 1,200 separate software packages.

LiveDistros have a reputation for supporting advanced auto-configuration and plug-and-play functionality. This is necessary so as to avoid requiring the user to configure the system each time it boots, and to make them easily usable by those who are new to the operating system.

[edit] History

Originally, many disk-based microcomputer operating systems (including CP/M, early versions of MS-DOS, and Apple DOS) were effectively LiveDistros, since most (at least those that were not ROM-based like the CBM KERNAL) were distributed on floppy disk and there was generally no hard disk to transfer them to; without a hard drive, it was common practice to create a boot disk, often customized to run a specific application. The modern phenomenon of the LiveDistro began with the wide distribution of CD-ROM drives on computers already equipped with hard drives, allowing users to run an operating system not already installed without altering the installed configuration on the hard drive.

The first GNU/Linux-based LiveCD was Yggdrasil Linux (went out of production in 1995), though in practice it did not function well due to the low throughput of then-current CD-ROM drives. The first well-known LiveCD was the Debian-derived Knoppix (released in 2003), which has found wide usage as both a rescue disk system and as a primary distribution in its own right. Since 2003, the popularity of LiveCDs has increased substantially, partly due to Linux Live scripts which made it very easy to build customized live systems.

[edit] Technique

[edit] File system

Read-only file system is often merged with writable file system in ramdisk. Often /home directory (containing users' personal files and configuration files) and /var (containing variable data) are kept in ramdisk.

In modern LiveDistros read-only file system is merged with ramdisk using transparent techniques like UnionFS or aufs.

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[edit] Hardware detection

LiveDistros have to be able to detect a wide variety of hardware (including network cards, graphic cards etc.). This is easily achieved nowadays by udev or hotplug, which is common part of all distributions based on Linux kernel 2.6.

[edit] Emulation

There are number of emulators (the article virtual machine also contains a list of them) on the market that can be used to try a LiveDistro without the need to install it on a medium or burn it to a CD or boot it on the computer. The most widely supported i386 emulator is VMware. Others include QEMU and its accelerator Kemu, PearPC and Bochs which can all also emulate the x86 and/or PowerPC platforms, although due to their software emulation methods, they are slower than the hardware alternatives. VirtualBox is only a virtualization box, not an emulator which is far speedier than emulation and a good alternative. Both but VMware are free software under GPL license. Another emulator that has turned from commercial to freeware is Microsoft Virtual PC.