A live USB is a portable USB-attached external data storage device containing a full

operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs. Time-sharing operating systems schedule tasks for efficient use of the system and may also i ...

that can be booted from. The term is reminiscent of

USB flash drive Universal Serial Bus (USB) is an industry standard that establishes specifications for cables, connectors and protocols for connection, communication and power supply ( interfacing) between computers, peripherals and other computers. A bro ...

s but may encompass an external

hard disk drive A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating platters coated with magne ...

solid-state drive A solid-state drive (SSD) is a solid-state storage device that uses integrated circuit assemblies to store data persistently, typically using flash memory, and functioning as secondary storage in the hierarchy of computer storage. It is a ...

, though they may be referred to as "live HDD" and "live SSD" respectively. They are the evolutionary next step after

live CD 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 f ...

s, but with the added benefit of writable storage, allowing customizations to the booted operating system. Live USBs can be used in embedded systems for system administration,

data recovery In computing, data recovery is a process of retrieving deleted, inaccessible, lost, corrupted, damaged, or formatted data from secondary storage, removable media or files, when the data stored in them cannot be accessed in a usual way. The dat ...

, or test driving, and can persistently save settings and install software packages on the USB device. Many operating systems including , , Windows XP Embedded and a large portion of

Linux Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, w ...

and BSD distributions can run from a USB flash drive, and Windows 8 Enterprise has a feature titled Windows To Go for a similar purpose.

Background

To repair a computer with booting issues, technicians often use lightweight operating systems on bootable media and a command-line interface. The development of the first live CDs with graphical user interface made it feasible for non-technicians to repair malfunctioning computers. Most Live CDs are Linux-based, and in addition to repairing computers, these would occasionally be used in their own right as operating systems.

Personal computer A personal computer (PC) is a multi-purpose microcomputer whose size, capabilities, and price make it feasible for individual use. Personal computers are intended to be operated directly by an end user, rather than by a computer expert or tec ...

s introduced USB booting in the early 2000s, with the

Macintosh The Mac (known as Macintosh until 1999) is a family of personal computers designed and marketed by Apple Inc. Macs are known for their ease of use and minimalist designs, and are popular among students, creative professionals, and software en ...

computers introducing the functionality in 1999 beginning with the Power Mac G4 with AGP graphics and the slot-loading

iMac G3 The iMac G3, originally released as the iMac, is a series of Macintosh personal computers sold by Apple Computer from 1998 to 2003. The iMac was the first major new product release for Apple under Steve Jobs, Apple's interim CEO and cofounder ...

models. Intel-based Macs carried this functionality over with booting

macOS macOS (; previously OS X and originally Mac OS X) is a Unix operating system developed and marketed by Apple Inc. since 2001. It is the primary operating system for Apple's Mac computers. Within the market of desktop and lapt ...

from USB. Specialized USB-based booting was proposed by IBM in 2004 with ''Reincarnating PCs with Portable

SoulPad SoulPad is a mobile computing project developed by researchers at IBM. The project's aim is to provide a computer user with the ability to suspend their operating system and resume it on another computer using a USB data storage device. The Soul ...

s'' and ''Boot Linux from a FireWire device''.

Benefits and limitations

Live USBs share many of the benefits and limitations of live CDs, and also incorporate their own.

Benefits

* In contrast to live CDs, the data contained on the

booting device In computing, booting is the process of starting a computer as initiated via hardware such as a button or by a software command. After it is switched on, a computer's central processing unit (CPU) has no software in its main memory, so some ...

can be changed and additional data stored on the same device. A user can carry their preferred operating system, applications, configuration, and personal files with them, making it easy to share a single system between multiple users. * Live USBs provide the additional benefit of enhanced privacy because users can easily carry the USB device with them or store it in a secure location (e.g. a safe), reducing the opportunities for others to access their data. On the other hand, a USB device is easily lost or stolen, so data

encryption In cryptography, encryption is the process of encoding information. This process converts the original representation of the information, known as plaintext, into an alternative form known as ciphertext. Ideally, only authorized parties can de ...

and backup is even more important than with a typical desktop system. * The absence of moving parts in USB flash devices allows true random access, thereby avoiding the

rotational latency Higher performance in hard disk drives comes from devices which have better performance characteristics. These performance characteristics can be grouped into two categories: access time and data transfer time (or rate). Access time The ''access ...

and seek time of hard drives or

optical media In computing and optical disc recording technologies, an optical disc (OD) is a flat, usually circular disc that encodes binary data ( bits) in the form of pits and lands on a special material, often aluminum, on one of its flat surfaces ...

, meaning small programs will start faster from a USB flash drive than from a local hard disk or live CD. However, as USB devices typically achieve lower data transfer rates than internal hard drives, booting from older computers that lack support for USB 2.0 or newer can be very slow.

Limitations

* LiveUSB OSes like

Ubuntu Ubuntu ( ) is a Linux distribution based on Debian and composed mostly of free and open-source software. Ubuntu is officially released in three editions: '' Desktop'', ''Server'', and ''Core'' for Internet of things devices and robots. All ...

Linux apply all filesystem writes to a casper filesystem overlay (casper-rw) that, once full or out of flash drive space, becomes unusable and the OS ceases to boot. * USB controllers on add-in cards (e.g. ISA, PCI, and PCI-E) are almost never capable of being booted from, so systems that do not have native USB controllers in their chipset (e.g. such as older ones before USB) likely will be unable to boot from USB even when USB is enabled via such an add-in card. * Some computers, particularly older ones, may not have a BIOS that supports USB booting. Many which do support USB booting may still be unable to boot the device in question. In these cases a computer can often be "redirected" to boot from a USB device through use of an initial bootable CD or floppy disk. * Some Intel-based Macintosh computers have limitations when booting from USB devices – while the

Extensible Firmware Interface UEFI (Unified Extensible Firmware Interface) is a set of specifications written by the UEFI Forum. They define the architecture of the platform firmware used for booting and its interface for interaction with the operating system. Examples of f ...

(EFI) firmware can recognize and boot from USB drives, it can do this only in EFI mode. When the firmware switches to "legacy" BIOS mode, it no longer recognizes USB drives. Non-Macintosh systems, notably Windows and Linux, may not be typically booted in EFI mode and thus USB booting may be limited to supported hardware and software combinations that can easily be booted via EFI. However, programs like Mac Linux USB Loader can alleviate the difficulties of the task of booting a Linux-live USB on a Mac. This limitation could be fixed by either changing the Apple firmware to include a USB driver in BIOS mode, or changing the operating systems to remove the dependency on the BIOS. * Due to the additional write cycles that occur on a full-blown installation, the life of the flash drive may be slightly reduced. This doesn't apply to systems particularly designed for live systems which keep all changes in

RAM Ram, ram, or RAM may refer to: Animals * A male sheep * Ram cichlid, a freshwater tropical fish People * Ram (given name) * Ram (surname) * Ram (director) (Ramsubramaniam), an Indian Tamil film director * RAM (musician) (born 1974), Dutch * ...

until the user logs off. A write-locked SD card (known as a Live SD, the solid-state counterpart to a live CD) in a USB flash card reader adapter is an effective way to avoid any duty cycles on the flash medium from writes and circumvent this problem. The SD card as a

WORM Worms are many different distantly related bilateral animals that typically have a long cylindrical tube-like body, no limbs, and no eyes (though not always). Worms vary in size from microscopic to over in length for marine polychaete wo ...

device has an essentially unlimited life. An OS such as Linux can then run from the live USB/SD card and use conventional media for writing, such as magnetic disks, to preserve system changes; .

Setup

Various applications exist to create live USBs; examples include Universal USB Installer,

Rufus Rufus is a masculine given name, a surname, an Ancient Roman cognomen and a nickname (from Latin '' rufus'', "red"). Notable people with the name include: Given name Politicians * Rufus Ada George (born 1940), Nigerian politician * Rufus ...

, Fedora Live USB Creator, and UNetbootin. There are also software applications available that can be used to create a Multiboot live USB; some examples includ
YUMI Multiboot Bootable USB Creator
and Ventoy. A few Linux distributions and live CDs have ready-made scripts which perform the steps below automatically. In addition, on Knoppix and Ubuntu extra applications can be installed, and a persistent file system can be used to store changes. A base install ranges between as little as 16 MiB (

Tiny Core Linux Tiny Core Linux (TCL) is a minimal Linux kernel based operating system focusing on providing a base system using BusyBox and FLTK. It was developed by Robert Shingledecker, who was previously the lead developer of Damn Small Linux. The distribut ...

) to a large DVD-sized install (4 gigabytes). To set up a live USB system for commodity PC hardware, the following steps must be taken: * A

needs to be connected to the system, and be detected by it * One or more partitions may need to be created on the USB flash drive * The "bootable" flag must be set on the primary partition on the USB flash drive * An MBR must be written to the primary partition of the USB flash drive * The partition must be formatted (most often in FAT32 format, but other file systems can be used too) * A bootloader must be installed to the partition (most often using syslinux when installing a Linux system) * A bootloader configuration file (if used) must be written * The necessary files of the operating system and default applications must be copied to the USB flash drive * Language and keyboard files (if used) must be written to the USB flash drive * USB support in the BIOS’s boot menu (although there are ways to get around this; actual use of a CD or DVD can allow the user to choose if the medium can later be written to.

Write Once Read Many Write once read many (WORM) describes a data storage device in which information, once written, cannot be modified. This write protection affords the assurance that the data cannot be tampered with once it is written to the device, excluding the p ...

discs allow certainty that the live system will be clean the next time it is rebooted.) Knoppix live CDs have a utility that, on boot, allows users to declare their intent to write the operating system's file structures either temporarily, to a RAM disk, or permanently, on disk or flash media to preserve any added configurations and security updates. This can be easier than recreating the USB system but may be moot since many live USB tools are simple to use.

Full installation

An alternative to a live solution is a traditional operating system installation with the elimination of swap partitions. This installation has the advantage of being efficient for the software, as a live installation would still contain software removed from the persistent file due to the operating system’s installer still being included with the media. However, a full installation is not without disadvantages; due to the additional write cycles that occur on a full installation, the life of the flash drive may be slightly reduced. To mitigate this, some live systems are designed to store changes in RAM until the user powers down the system, which then writes such changes. Another factor is if the speed of the storage device is poor; performance can be comparable to legacy computers even on machines with modern parts if the flash drive transfers such speeds. One way to solve this is to use a USB hard drive, as they generally give better performance than flash drives regardless of the connector.

Microsoft Windows

Although many live USBs rely on booting an open-source operating system such as Linux, it is possible to create live USBs for Microsoft Windows by using Diskpart or WinToUSB.

References

External links

The Differences Between Persistent Live USB and Full Linux Install on USB

Universal USB Installer

Tutorial – How to Set your BIOS to boot from CD or USB

HOW TO: Create a working Live USB

Debian Live project

How to create a Live USB in Ubuntu

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