Editing Live CD

{{Short description|Complete, bootable computer installation that runs directly from a CD-ROM}}
{{other uses}}
{{Use dmy dates|date=August 2018}}
[[File:Ubuntu 23.04 Lunar Lobster English.png|thumb|[[Ubuntu OS|Ubuntu]] 23.04 system running from a live DVD image, with the [[Gnome (desktop environment)|GNOME 40]] desktop environment]]

A '''live CD''' (also '''live DVD''', '''live disc''', or '''live operating system''') is a complete [[booting|bootable]] computer installation including [[operating system]] which runs directly from a [[CD-ROM]] or similar storage device into a computer's memory, rather than loading from a hard disk drive. A live CD allows users to run an [[computer operating system|operating system]] for any purpose without installing it or making any changes to the computer's configuration. Live CDs can run on a computer without [[Computer data storage|secondary storage]], such as a hard disk drive, or with a corrupted hard disk drive or file system, allowing [[data recovery]].

As CD and DVD drives have been steadily phased-out, live CDs have become less popular, being replaced by [[live USB]]s, which are equivalent systems written onto [[USB flash drive]]s, which have the added benefit of having writeable storage. The functionality of a live CD is also available with an [[Disk enclosure|external hard disk drive]] connected by USB. Many live CDs offer the option of [[Persistence (computer science)|persistence]] by writing files to a hard drive or USB flash drive.

Many [[Linux distribution]]s make [[ISO image]]s available for burning to CD or DVD. While open source operating systems can be used for free, some commercial software, such as [[Windows To Go]] requires a license to use. Many live CDs are used for data recovery, [[computer forensics]], [[disk imaging]], [[recovery disc|system recovery]] and [[malware]] removal. The [[Tails (operating system)|Tails operating system]] is aimed at preserving privacy and anonymity of its users, allowing them to work with sensitive documents without leaving a record on a computer's hard drive.<ref>{{cite web |url=https://pressfreedomfoundation.org/blog/2014/04/help-support-little-known-privacy-tool-has-been-critical-journalists-reporting-nsa |title=Help Support the Little-Known Privacy Tool That Has Been Critical to Journalists Reporting on the NSA |last=Timm |first=Trevor |date=2 April 2014 |website=Freedom of the Press Foundation |access-date=18 April 2014 |archive-date=20 July 2014 |archive-url=https://web.archive.org/web/20140720192050/https://pressfreedomfoundation.org/blog/2014/04/help-support-little-known-privacy-tool-has-been-critical-journalists-reporting-nsa |url-status=live }}</ref><ref>{{cite magazine |url=https://www.wired.com/2014/04/tails/ |title=Out in the Open: Inside the Operating System Edward Snowden Used to Evade the NSA |last=Finley |first=Klint |date=14 April 2014 |magazine=WIRED |access-date=18 April 2014 |archive-date=19 April 2014 |archive-url=https://web.archive.org/web/20140419003312/http://www.wired.com/2014/04/tails/ |url-status=live }}</ref>

== History ==
[[File:Ubuntu 23.04 install screen.png|thumb|Installation from Ubuntu 23.04 live CD]]

All computers except the earliest digital computers are built with some form of minimal built-in loader, which loads a program or succession of programs from a storage medium, which then operate the computer. Initially a read-only medium such as punched tape or punched cards was used for initial program load. With the introduction of inexpensive read-write storage, read-write [[floppy disk]]s and hard disks were used as [[boot disk|boot media]].

After the introduction of the [[Sound recording and reproduction|audio]] [[compact disc]], it was adapted for use as a medium for storing and distributing large amounts of computer data. This data may also include application and operating-system software, sometimes packaged and archived in compressed formats. Later, it was seen to be convenient and useful to boot the computer directly from compact disc, often with a minimal working system to install a full system onto a hard drive. While there are read-write optical discs, either mass-produced read-only discs or write-once discs were used for this purpose.

The first Compact Disc drives on personal computers were generally much too slow to run complex operating systems; computers were not designed to boot from an [[optical disc]]. When operating systems came to be distributed on compact discs, either a [[boot floppy]] or the CD itself would boot specifically, and only, to install onto a hard drive. Early examples of operating systems which could be booted directly from CD-ROM are the [[Towns OS|FM Towns OS]],<ref>{{cite web|url=https://www.old-computers.com/museum/doc.asp?c=968|title=Fujitsu FM Towns|author=Jiro Kit|website=Old-Computers Museum|access-date=2022-03-26|archive-date=16 May 2022|archive-url=https://web.archive.org/web/20220516090420/https://old-computers.com/museum/doc.asp?c=968|url-status=live}}</ref> and the Desktop-VMS distribution of [[OpenVMS|VMS]], both of which were first released in 1989.<ref>{{cite web|url=http://home.iae.nl/users/pb0aia/vax/dsvs3100.html|title=DECUServe WORKSTATIONS Conference 8|access-date=2022-03-26|date=1989-01-11|author=Bob McCormick|website=home.iae.nl|archive-date=10 July 2022|archive-url=https://web.archive.org/web/20220710024529/http://home.iae.nl/users/pb0aia/vax/dsvs3100.html|url-status=live}}</ref><ref>{{cite web|url=http://www.digital.com/info/SP25F4/SP25F4PF.PDF|archive-url=https://web.archive.org/web/20000816181649/http://www.digital.com/info/SP25F4/SP25F4PF.PDF|title=Software Product Description - Desktop-VMS, Version 1.2|publisher=Digital|date=January 1991|archive-date=2000-08-16|access-date=2022-03-26}}</ref>

=== Linux ===
[[File:Lgx yggdrasil fall 1993.jpg|thumb|CD-ROM of the LGX Yggdrasil Linux distribution release "Fall 1993"]]

Although early developers and users of distributions built on top of the [[Linux kernel]] could take advantage of cheap optical disks and rapidly declining prices of CD drives for personal computers, the [[Linux distribution]] CDs or "distros" were generally treated as a collection of installation packages that would first need to be permanently installed to hard disks on the target machine.

However, in the case of these distributions built on top of the Linux kernel, the [[Free software|free]] operating system was meeting resistance in the consumer market because of the perceived difficulty, effort, and risk involved in installing an additional partition on the hard disk, in parallel with an existing operating system installation.

The term "live CD" was coined because, after typical PC RAM was large enough and 52x speed CD drives and CD burners were widespread among PC owners, it finally became convenient and practical to boot the kernel and run [[X11]], a window manager and GUI applications directly from a CD without disturbing the OS on the hard disk.

This was a new and different situation for Linux than other operating systems, because the updates/upgrades were being released so quickly, different distributions and versions were being offered online, and especially because users were burning their own CDs.

The first [[Linux]]-based 'Live CD' was [[Yggdrasil Linux]] first released in beta form 1992~1993 (ceased production in 1995), though in practice its functionality was hampered due to the low throughput of contemporary CD-ROM drives. [[DemoLinux]], released in 1998, was the first Linux distribution specially designed as a live CD. The [[Linuxcare]] [[bootable business card]], first released in 1999, was the first Live CD to focus on system administration, and the first to be distributed in the bootable business card form factor. {{As of|2023}}, [[Finnix]] (first released in spring 2000) is the oldest Live CD still in production. Shortly followed by [[Knoppix]], a [[Debian]]-derived Linux distribution, also still produced, it first released in fall 2000 and found popularity as both a [[data recovery|rescue disk]] system and as a primary distribution in its own right.

Since 2003, the popularity of live CDs has increased substantially, partly due to [http://www.linux-live.org/ Linux Live scripts] and [[remastersys]], which made it very easy to build customized live systems. Most of the popular [[Linux distribution]]s now include a live CD variant, which in some cases is also the preferred installation medium.

== Uses ==
[[File:Trisquel 11 Live CD.png|thumb|230x230px|Live CD of [[Trisquel]] 11.0]]
Live CDs are made for many different uses. Some are designed to demonstrate or "test drive" a particular operating system (usually Linux or another [[Free software|free]] or [[Open-source license|open source]] operating system). Software can be tested, or run for a particular single use, without interfering with system setup. Data on a system which is not functioning normally due to operating system and software issues can be made available; for example, data can be recovered from a machine with an active virus infection without the virus process being active and causing more damage, and the virus can be removed with its defences against removal bypassed.

Although some live CDs can load into memory to free the optical drive for other uses, loading the data from a CD-ROM is still slower than a typical hard drive boot, so this is rarely the default with large live CD images, but for smaller live CD images loading the filesystem directly into RAM can provide a significant performance boost, as RAM is much faster than a hard drive, and uses less power.<ref name="Brickner000">{{cite book | title = Test Driving Linux: From Windows to Linux in 60 Seconds | first = David | last = Brickner | publisher = O'Reilly | year = 2005 | isbn = 0-596-00754-X | url-access = registration | url = https://archive.org/details/testdrivinglinux0000bric }}</ref> Experienced users of the operating system may also use a live CD to determine whether and to what extent a particular operating system or version is compatible with a particular hardware configuration and certain peripherals, or as a way to know beforehand which computer or peripheral will work before buying.<ref name="Brickner000" /> A live CD can be used to troubleshoot hardware, especially when a hard drive fails, and more generally as a [[recovery disc]] in case of problems. Some live CDs can save user-created files in a Windows partition, a USB drive, a network drive, or other accessible media. Live backup CDs can create an image of drives, and back up files, without problems due to open files and inconsistent sets.

A few additional uses include:
* installing a [[Linux distribution]] to a hard drive
* [[computer forensics]]
* Virus scanning and Malware removal<ref>{{cite web|url=https://www.howtogeek.com/howto/14434/scan-a-windows-pc-for-viruses-from-a-ubuntu-live-cd/|title=Scan a Windows PC for Viruses from a Ubuntu Live CD|website=howtogeek.com|access-date=19 March 2018|archive-date=19 March 2018|archive-url=https://web.archive.org/web/20180319214130/https://www.howtogeek.com/howto/14434/scan-a-windows-pc-for-viruses-from-a-ubuntu-live-cd/|url-status=live}}</ref>
* system repair and [[Data recovery|restoration]]
* testing new versions of software
* listing & testing hardware<ref>{{cite web|url=http://hdt-project.org/|title=Home - HDT Project|website=HDT Project|access-date=19 March 2018|archive-url=https://web.archive.org/web/20180725214325/http://www.hdt-project.org/|archive-date=25 July 2018|url-status=dead}}</ref>
* [[Internet kiosk]]s and public computers, which can be brought back to their original state by a reboot
* high security/non-invasive environment for a guest
* cracking, stealing, and changing passwords
* network security testing
* being the primary or backup operating system for any computer
* quick and simple clustering of computers<ref>{{cite web|url=http://www.flashmobcomputing.org/|title=FlashMob Computing – FlashMob Computing|website=flashmobcomputing.org|access-date=19 March 2018|archive-date=9 May 2008|archive-url=https://web.archive.org/web/20080509120957/http://www.flashmobcomputing.org/|url-status=live}}</ref>
* playing video games or running applications that require a different operating system
* providing a secure server platform where crucial files cannot be permanently altered
* providing a secure, reliable platform for the performance of high-vulnerability tasks such as [[internet banking]];
* Bypassing [[parental controls]] and other restrictions

Several live CDs are dedicated to specific type of applications according to the requirements of thematic user communities. These CDs are tailored to the needs of the applications in subject including general knowledge, tutorial, specifications and trial data too.

Some of these topics covers sub topics, e.g. IT administration breaks down to firewall, rescue, security, etc. type of live CDs. In some cases a particular Live DVD covers more than one topic.

=== Software appliances ===
[[File:Fedora 38 live CD.png|thumb|Live CD of [[Fedora (operating system)|Fedora]] 38]]
Packaging a [[software appliance]] as an installable live CD, or live ISO, can often be beneficial as a single image can run on both real hardware and on most types of virtual machines.

This allows developers to avoid the complexities involved in supporting multiple incompatible [[virtual machine]] images formats and
focus on the lowest common denominator instead.

Typically after booting the machine from the live CD, the appliance either runs in non-persistent demo mode or installs itself, at the user's request, to an available storage device.

=== Mounting without burning ===
[[File:Vbox160debian.jpg|thumb|Virtual [[OpenBSD]] machine configuration in [[VirtualBox]] with live image file (''6.3-Release-i386-bootonly.iso'')]]

The files on a live CD [[ISO image]] can be accessed in [[Microsoft Windows]] with a [[disk image emulator]] such as [[Daemon Tools]], or in [[Unix]] variants by mounting a [[loop device]]. Later versions of Windows (i.e. Windows 8 and later), and software available for earlier versions, allow an ISO to be mounted as a volume.

After mounting the live CD's filesystem, software on the live CD can be run directly, without booting it, by [[chroot]]ing into the mounted filesystem.

A live CD ISO image can also be mounted by [[Virtual Machine]] software such as [[VirtualBox]] and [[VMware Workstation]] or can be converted to a [[Live USB]] using [[SYSLINUX]]. [[List of tools to create Live USB systems|Special tools]] can automate this process.<ref>{{cite web | url = https://help.ubuntu.com/community/USB%20Installation%20Media | title = USB Installation Media - UNetbootin | website = community.ubuntu.com | publisher = Ubuntu Community | access-date = 11 February 2014 | archive-date = 22 February 2014 | archive-url = https://web.archive.org/web/20140222030330/https://help.ubuntu.com/community/USB%20Installation%20Media | url-status = live }}</ref>

== Features ==
[[file:Mandriva2010eng.png|thumb|Live CD of [[Mandriva Linux|Mandriva]] 2010]]

During live CD initialization, a user typically may resort to using one or more boot codes to change the booting behavior. These vary from distribution to distribution but can most often be accessed upon first boot screen by one of the [[function key]]s.

Some live CDs come with an installation utility launchable from a desktop icon that can optionally install the system on a [[hard drive]] or [[USB flash drive]]. Most live CDs can access the information on internal and/or external hard drives, [[diskette]]s and USB flash drives.

Live CDs are usually distributed on [[read-only memory|read-only]] media, requiring either copying to rewriteable media (i.e. a hard drive or CD writer) or complete [[remaster (software)|remastering]] to install additional software; however, there are exceptions. If [[Puppy Linux]] is recorded to an open [[multisession]] medium, changes made during use (such as files created, programs installed, and preferences customised) are written in a new session to the boot medium<ref>{{cite web |url=http://puppylinux.org/wikka/MultiSessionLiveDVD |title=How to Create a Multi-session LiveDVD |date=26 April 2011 |website=Puppy Linux |access-date=1 August 2018 |archive-date=1 August 2018 |archive-url=https://web.archive.org/web/20180801155121/http://puppylinux.org/wikka/MultiSessionLiveDVD |url-status=dead }}</ref> persisting through subsequent boots.

The term "Live CD" came to be used for any CD containing operating system and software which could be run without installation on the host computer. Operating systems which can be used live include [[AmigaOS 4]], [[Amithlon]], [[AROS]], [[FreeBSD]], [[FreeDOS]], [[classic Mac OS]], [[macOS]], [[Microsoft Windows]] installation and repair discs, [[OS/2]], [[ReactOS]], [[NetBSD]], [[OpenBSD]], [[MINIX 3]], [[Plan 9 from Bell Labs]], [[MorphOS]], [[OpenSolaris]], [[BeleniX]] and others based on [[Solaris (operating system)|Solaris]]. There are maintenance versions of Microsoft Windows bootable from CD such as [[BartPE]], [[Windows Preinstallation Environment|Windows PE]], and [[Microsoft Diagnostics and Recovery Toolset]] (DaRT), previously known as Emergency Repair Disk Commander (ERD Commander).

The first personal computer operating system on a CD to support "live" operations might have been the [[AmigaOS]], which could be booted from CD on an [[Amiga CDTV]] in 1990.{{Citation needed|date=November 2007}}. Earlier examples of live OS are of course the operating systems used from floppy, and most widely spread is [[DOS]].

[[file:Gentoo-10.0-livedvd.png|thumb|Live CD of [[Gentoo Linux]]]]

Unlike previous operating systems on optical media, though, Linux and OS/2 "live CDs" were specifically designed to run without installation onto other media like a hard disk drive. The live CD concept was meant to promote Linux and showcase the abilities of the free, [[Open-source license|open source]] operating system on conventional personal computers with Microsoft Windows already installed. {{Citation needed|date=November 2008}}

On a [[personal computer|PC]], a bootable Compact Disc generally conforms to the [[El Torito (CD-ROM standard)|El Torito]] specification, introduced in 1994. Many Linux based live CDs 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{{Citation needed|date=November 2009}}.

The resulting environment can be quite rich: typical [[Knoppix]] systems include around 1,200 separate software packages. Live CDs have a reputation for supporting advanced [[auto-configuration]] and [[plug-and-play]] functionality. This came out of necessity to avoid requiring the user to configure the system each time it boots and to make it easily usable by those who are new to the operating system.

== Creation ==


A read-only [[file system]], such as on a CD-ROM has the drawback of being unable to save any current working data. For this reason, a read-only file system is often merged with a temporary writable file system in the form of a [[RAM disk]]. Often the default Linux [[file directory|directories]] "<code>/home</code>" (containing users' personal files and [[configuration file]]s) and "<code>/var</code>" (containing variable [[data (computing)|data]]) are kept in ramdisk, because the system updates them frequently. Puppy Linux and some other live CDs allow a configuration and added files to be written and used in later sessions.

In modern live CDs, a read-only file system is merged with a [[RAM drive]] using [[transparency (human-computer interaction)|transparent]] techniques such as [[UnionFS]], [[AuFS]] or [[Enhanced Write Filter|EWF]]. Boot loaders like syslinux can boot ISO files from USB memory devices.

Live CDs have to be able to detect and use a wide variety of hardware (including [[network card]]s, [[graphic card]]s etc.) in realtime, often using facilities such as [[udev]], [[hotplug (software)|hotplug]], hal, udisk etc.. which are a common part of all distributions based on [[Linux kernel]] 2.6.

== See also ==
* [[Boot disk]]
* [[Comparison of Linux distributions#Live media]]
* [[GIS Live DVD]]
* [[List of live CDs]]
* [[List of remastering software]]
* [[Live USB]]
* [[Self-booting diskette]]
* [[Software appliance]]
* [[Windows To Go]]

== References ==

{{reflist}}

== External links ==

* [http://www.tldp.org/HOWTO/Bootdisk-HOWTO/cd-roms.html Bootable CDROM HowTo]
* [http://www.linux-live.org/ Linux Live scripts]
* [http://www.netbsd.org/~jschauma/nblivecds.pdf Pondering Live CDs] - A BSD perspective on the concept of Live CDs
* [http://hirensbootcd.org Hiren's Boot CD]

{{Operating System}}

[[Category:Live CD| ]]
[[Category:Operating system distributions bootable from read-only media| ]]
[[Category:Software appliances]]