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{{Short description|Complete, bootable computer installation that runs directly from a CD-ROM}}
{{for|musical recordings|Live album}}
{{other uses}}
A '''live CD''' or '''live distro''' is a computer ] that is executed upon ], without installation to a ]. Typically, the live distro is named after the bootable medium it is stored on, such as a ] or ] (live CD/DVD) or a ] (]).
{{Use dmy dates|date=August 2018}}
] 23.04 system running from a live DVD image, with the ] desktop environment]]


A '''live CD''' (also '''live DVD''', '''live disc''', or '''live operating system''') is a complete ] computer installation including ] which runs directly from a ] 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 ] for any purpose without installing it or making any changes to the computer's configuration. Live CDs can run on a computer without ], such as a hard disk drive, or with a corrupted hard disk drive or file system, allowing ].
The term "live" derives from the fact that these "distros", or ]s, each contain a complete, functioning and operational operating system on the distribution medium.


As CD and DVD drives have been steadily phased-out, live CDs have become less popular, being replaced by ]s, which are equivalent systems written onto ]s, which have the added benefit of having writeable storage. The functionality of a live CD is also available with an ] connected by USB. Many live CDs offer the option of ] by writing files to a hard drive or USB flash drive.
A live distro does not alter the operating system or files already installed on the computer hard drive unless instructed to do so. Live distros often include mechanisms and utilities for more permanent installation, including ] tools.


Many ]s make ]s available for burning to CD or DVD. While open source operating systems can be used for free, some commercial software, such as ] requires a license to use. Many live CDs are used for data recovery, ], ], ] and ] removal. The ] 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>
The default option, however, is to allow the user to return the computer to its previous state when the live distro is ejected and the computer is ]ed. It is able to run without permanent installation by placing the files that typically would be stored on a hard drive into ], typically in a ]. However, this does cut down on the RAM available to applications, reducing performance somewhat. As of 2007, certain live distros run a ] in as little as 32MB RAM.

In some live distros, the user can optionally install the OS from the removable media to the hard disk drive (they are called installable live distros).


== History == == History ==
]


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 ]s and hard disks were used as ].
On computers, optical discs were originally intended for storing video. Then the principles of storing information into the optical disc were changed to provide storing different types of information.


After the introduction of the ] ], 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.
In the case of operating systems those were mostly installation files, often packaged and archived in compressed formats.


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 ]. When operating systems came to be distributed on compact discs, either a ] 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 ],<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 ], 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>
Later, it became convenient and useful to boot the computer from compact disc, often with a minimal working system in order to install a full system onto a hard drive, and troubleshoot hardware.


=== Linux ===
The first Compact Disc drives on personal computers were generally much too slow for running complex operating systems such as Linux. Often, the computer could not even boot from ]s. When operating systems were distributed on discs, either a ] or the CD itself would boot specifically, and only, in order to install onto a hard drive. There was little reason not to install directly on a hard disk.
]


Although early developers and users of distributions built on top of the ] could take advantage of cheap optical disks and rapidly declining prices of CD drives for personal computers, the ] 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.
=== Origin of Linux Live CDs ===


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


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 ], a window manager and GUI applications directly from a CD without disturbing the OS on the hard disk.
However in the case of Linux, the free operating system was meeting resistance in the consumer market because of the difficulty and effort and risk involved with installing an additional partition on the hard disk, particularly the ] filesystem.


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 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, run X11, a window manager and GUI applications directly from a CD without disturbing the OS (generally Windows on FAT32 or NTFS) on the hard disk.


The first ]-based 'Live CD' was ] 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. ], released in 1998, was the first Linux distribution specially designed as a live CD. The ] ], 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}}, ] (first released in 2000) is the oldest Live CD still in production. ], a ]-derived Linux distribution, was released in 2003, and found popularity as both a ] system and as a primary distribution in its own right.
This was a new and different situation for Linux than other OSes, 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.


Since 2003, the popularity of live CDs has increased substantially, partly due to and ], which made it very easy to build customized live systems. Most of the popular ]s now include a live CD variant, which in some cases is also the preferred installation medium.
Copying Linux from the installation media was also encouraged instead of actively hindered and discouraged with such things as requiring the input of long and elaborate serial numbers and lengthy and complicated installation procedures.

The first ]-based live CD was ] (went out of production in ]), though in practice it did not function well due to the low throughput of then-current CD-ROM drives. The ]-derived Linux distribution ] was released in ], and found popularity as both a ] system and as a primary distribution in its own right. Since 2003, the popularity of live CDs has increased substantially, partly due to and ] which made it very easy to build customized live systems.

Most of the popular ]s now include a live CD variant, which in some cases is also the preferred installation medium.


== Uses == == Uses ==
] 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 ] or ] 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 ] 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.
Some live distros are designed to "demo" or "test drive" a particular operating system (usually Linux or another ] or ] operating system).


A few additional uses include:
Although some live CDs can load into memory in order to free the optical drive for other uses, loading the data off 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 be highly practical. Loading the filesystem image into RAM can provide a significant performance boost as RAM is several orders of magnitude faster than a hard drive. Also, since RAM has no moving parts, a system running from a Live CD loaded into RAM can run with improved power efficiency.
* installing a ] to a hard drive

* ]
<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 | id = ISBN 059600754X }}</ref> Experienced users of the operating system may also use a live distro 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" /> Users may also use a live distro to troubleshoot hardware, especially when a hard drive fails. Some live CDs can save user-created files in a Windows partition, a USB drive, a network drive, or other accessible media.
* 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 ]
Live distros can be used for many purposes, including providing an environment for:
* optionally installing a ] to a hard drive
* testing new versions of software * 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>
* testing hardware
* ]s and public computers, which can be brought back to their original state by a reboot
* system repair and ]
* high security/non-invasive environment for a guest * high security/non-invasive environment for a guest
* cracking/stealing passwords * cracking, stealing, and changing passwords
* network security testing * network security testing
* being the primary or backup operating system for any computer
* as a fall back when a main drive fails.
* 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 ];
* Bypassing ] 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.
=== Live CD software appliances ===


=== Software appliances ===
Packaging a ] as an installable Live CD can often be
] 38]]
beneficial as a single image can run on real hardware in addition to
Packaging a ] 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.
most types of virtual machines.


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


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


=== Mounting without burning === === Mounting without burning ===
] machine configuration in ] with live image file (''6.3-Release-i386-bootonly.iso'')]]


The files on a live distro ] can be accessed in ] with a ] such as ], or in ] variants by ]. The files on a live CD ] can be accessed in ] with a ] such as ], or in ] variants by mounting a ]. 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 (I.e., without booting) by chrooting into the Live CD's mounted filesystem. After mounting the live CD's filesystem, software on the live CD can be run directly, without booting it, by ]ing into the mounted filesystem.


A live CD ISO image can also be mounted by ] software such as ] and ] or can be converted to a ] using ]. ] 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>
==Common traits==


== Features ==
Some live distros come with an installation utility launchable from a desktop icon that can optionally install the system on a ] or ]. Most live distros can access the information on internal and/or external hard drives, ]s and USB flash drives.
] 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 ]s.
Generally live distros are booted from ] media, requiring either copying to rewriteable media (i.e. a hard drive) or complete ] to install additional software; however, there are exceptions such as ] and ] which are one of the few Linux live CD distributions able to save files to the live CD itself or other ] medium, allowing users to carry data, and more importantly, added programs and customized settings, along with them on optical disc.


Some live CDs come with an installation utility launchable from a desktop icon that can optionally install the system on a ] or ]. Most live CDs can access the information on internal and/or external hard drives, ]s and USB flash drives.
Most live distros are based on Linux, as this was the operating system that had the most to gain by offering free trials and demonstrations without regard to sales or copyright. Now others are using the term ''live distro'' for other operating systems, such as ], ] and others based on ]. Other "live" operating systems include ], ], ], ], ], ], ] and ].


Live CDs are usually distributed on ] media, requiring either copying to rewriteable media (i.e. a hard drive or CD writer) or complete ] to install additional software; however, there are exceptions. If ] is recorded to an open ] 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.
Although ] and various ] releases can function as "live CDs" they are not referred to as such. This may be because these systems are only intended to be run from CD for troubleshooting, repair and installation. There are a growing number of Windows-based utilities like ], ] and ] that resemble and function as live distros, however.


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 ], ], ], ], ], ], ], ] installation and repair discs, ], ], ], ], ], ], ], ], ] and others based on ]. There are maintenance versions of Microsoft Windows bootable from CD such as ], ], and ] (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 ], which could be booted from CD on an ] in 1990.{{Fact|date=November 2007}}. Earlier examples of live OS are of course the operating systems used from floppy, and most widely spread is ].


The first personal computer operating system on a CD to support "live" operations might have been the ], which could be booted from CD on an ] 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 ].
Unlike previous operating systems on optical media, though, Linux "live CDs" were specifically designed to run without installation onto other media like a hard disk drive. The live distro concept was meant to promote Linux and showcase the abilities of the free, ] operating system on conventional personal computers with Microsoft Windows already installed.


]]]
On a ], a bootable Compact Disc generally conforms to the ] specification. Many Linux based live distros use a compressed filesystem image, often with the ] compressed loopback driver, or ] compressed filesystem, generally doubling effective storage capacity, although slowing application start up.


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, ] operating system on conventional personal computers with Microsoft Windows already installed. {{Citation needed|date=November 2008}}
The resulting environment can be quite rich: typical ] systems include around 1,200 separate software packages. Live distros have a reputation for supporting advanced ] and ] functionality. This out of necessity 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.


On a ], a bootable Compact Disc generally conforms to the ] specification, introduced in 1994. Many Linux based live CDs use a compressed filesystem image, often with the ] compressed loopback driver, or ] compressed filesystem, generally doubling effective storage capacity, although slowing application start up{{Citation needed|date=November 2009}}.
== Technique ==


The resulting environment can be quite rich: typical ] systems include around 1,200 separate software packages. Live CDs have a reputation for supporting advanced ] and ] 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.
A read-only ], 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 ]. Often the default Linux ] "<code>/home</code>" (containing users' personal files and ]s) and "<code>/var</code>" (containing variable ]) are kept in ramdisk, because the system updates them frequently. Puppy linux has a savable layer so if you choose to, you can pick right back up again were you left off the next time you boot. Each time the CD boots, it looks for the file and then uses it if it has the right name.


== Creation ==
In modern live distros, a read-only file system is merged with ramdisk using ] techniques such as ] or ]. In MS-DOS systems, a DOS utility, ''ramdrive.sys'', can be loaded at boot for this purpose.


Live distros have to be able to detect a wide variety of hardware (including ]s, ]s etc.). This is easily achieved nowadays by ] or ], which is a common part of all distributions based on ] 2.6.


A read-only ], 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 ]. Often the default Linux ] "<code>/home</code>" (containing users' personal files and ]s) and "<code>/var</code>" (containing variable ]) 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.
=== Cheat code ===
During ] initialization, a user typically may resort to using one or more ]s 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 ]s.


In modern live CDs, a read-only file system is merged with a ] using ] techniques such as ], ] or ]. Boot loaders like syslinux can boot ISO files from USB memory devices.
== See also ==


Live CDs have to be able to detect and use a wide variety of hardware (including ]s, ]s etc.) in realtime, often using facilities such as ], ], hal, udisk etc.. which are a common part of all distributions based on ] 2.6.
* ]
* ]
* ]
* ]
* ]
* ], a simple tool to create a customized ubuntu live CD/DVD
* ]


==Screenshots== == See also ==
* ]
Here are some screenshots of live CDs:
* ]
<gallery>
* ]
Image:Mandriva Linux.png|Live CD of ] 2008 Spring
* ]
Image:Fedora.png|Live CD of ] 9
* ]
Image:ubuntu 8.04 Live CD.png|Live CD of ], running ], ] and ]
* ]
</gallery>
* ]
* ]
* ]


== References == == References ==


{{refs}} {{reflist}}


== External links == == External links ==

{{linkfarm|September 2007}}
*
*
*
* *
*
* : Extensive build/remaster howtos, tools and release announcements.
* - A BSD perspective on the concept of Live CDs
* : Howto remaster a ] live CD
*
* links & information on over 300 Live CDs
*
* Article published on Free Software Magazine about LiveDistros
*
*
* - A ] perspective on the concept of Live CDs
*
*


{{Operating System}}
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Latest revision as of 17:22, 28 October 2024

Complete, bootable computer installation that runs directly from a CD-ROM For other uses, see Live CD (disambiguation).

Ubuntu 23.04 system running from a live DVD image, with the GNOME 40 desktop environment

A live CD (also live DVD, live disc, or live operating system) is a complete 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 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 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 USBs, which are equivalent systems written onto USB flash drives, which have the added benefit of having writeable storage. The functionality of a live CD is also available with an external hard disk drive connected by USB. Many live CDs offer the option of persistence by writing files to a hard drive or USB flash drive.

Many Linux distributions make ISO images 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, system recovery and malware removal. The 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.

History

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 disks and hard disks were used as boot media.

After the introduction of the 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 FM Towns OS, and the Desktop-VMS distribution of VMS, both of which were first released in 1989.

Linux

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 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 2000) is the oldest Live CD still in production. Knoppix, a Debian-derived Linux distribution, was released in 2003, and found popularity as both a 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 Linux Live scripts and remastersys, which made it very easy to build customized live systems. Most of the popular Linux distributions now include a live CD variant, which in some cases is also the preferred installation medium.

Uses

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 or 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. 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. 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
  • system repair and restoration
  • testing new versions of software
  • listing & testing hardware
  • Internet kiosks 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
  • 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

Live CD of 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

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 chrooting 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. Special tools can automate this process.

Features

Live CD of 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 keys.

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, diskettes and USB flash drives.

Live CDs are usually distributed on read-only media, requiring either copying to rewriteable media (i.e. a hard drive or CD writer) or complete 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 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. There are maintenance versions of Microsoft Windows bootable from CD such as BartPE, 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.. Earlier examples of live OS are of course the operating systems used from floppy, and most widely spread is DOS.

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 operating system on conventional personal computers with Microsoft Windows already installed.

On a PC, a bootable Compact Disc generally conforms to the 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.

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 directories "/home" (containing users' personal files and configuration files) and "/var" (containing variable 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 transparent techniques such as UnionFS, AuFS or 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 cards, graphic cards etc.) in realtime, often using facilities such as udev, hotplug, hal, udisk etc.. which are a common part of all distributions based on Linux kernel 2.6.

See also

References

  1. Timm, Trevor (2 April 2014). "Help Support the Little-Known Privacy Tool That Has Been Critical to Journalists Reporting on the NSA". Freedom of the Press Foundation. Archived from the original on 20 July 2014. Retrieved 18 April 2014.
  2. Finley, Klint (14 April 2014). "Out in the Open: Inside the Operating System Edward Snowden Used to Evade the NSA". WIRED. Archived from the original on 19 April 2014. Retrieved 18 April 2014.
  3. Jiro Kit. "Fujitsu FM Towns". Old-Computers Museum. Archived from the original on 16 May 2022. Retrieved 26 March 2022.
  4. Bob McCormick (11 January 1989). "DECUServe WORKSTATIONS Conference 8". home.iae.nl. Archived from the original on 10 July 2022. Retrieved 26 March 2022.
  5. "Software Product Description - Desktop-VMS, Version 1.2" (PDF). Digital. January 1991. Archived from the original (PDF) on 16 August 2000. Retrieved 26 March 2022.
  6. ^ Brickner, David (2005). Test Driving Linux: From Windows to Linux in 60 Seconds. O'Reilly. ISBN 0-596-00754-X.
  7. "Scan a Windows PC for Viruses from a Ubuntu Live CD". howtogeek.com. Archived from the original on 19 March 2018. Retrieved 19 March 2018.
  8. "Home - HDT Project". HDT Project. Archived from the original on 25 July 2018. Retrieved 19 March 2018.
  9. "FlashMob Computing – FlashMob Computing". flashmobcomputing.org. Archived from the original on 9 May 2008. Retrieved 19 March 2018.
  10. "USB Installation Media - UNetbootin". community.ubuntu.com. Ubuntu Community. Archived from the original on 22 February 2014. Retrieved 11 February 2014.
  11. "How to Create a Multi-session LiveDVD". Puppy Linux. 26 April 2011. Archived from the original on 1 August 2018. Retrieved 1 August 2018.

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