Live USB

Puppy Linux, an example of an operating system for live USBs.

Ubuntu 8.04 running Firefox, OpenOffice.org and Nautilus.

A live USB is a USB flash drive or external hard disk drive containing a full operating system that can be booted. Although they are closely related to live CDs in that they can be used in embedded systems for system administration, data recovery, or test driving, live USBs can persistently save settings and install software packages on the USB device. Many operating systems including Mac OS 9, macOS, Windows XP Embedded and a large portion of Linux 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

Personal computers introduced USB booting in the early 2000s, with the Macintosh computers introducing the functionality in 1999 beginning with the Power Mac G4 with AGP graphics and the slot-loading iMac G3 models.^[1] Intel-based Macs carried this functionality over with booting macOS from USB.^[2] Specialized USB-based booting was proposed by IBM in 2004 with Reincarnating PCs with Portable SoulPads and Boot GNU/Linux from a FireWire device.^[3][4]

Benefits and limitations

A USB flash drive.

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 can be changed and additional data stored on the same device. A user can carry his or her 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 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 avoiding the rotational latency and seek time (see mechanical latency) of hard drives or optical media, 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 USB 2.0 or newer can be very slow.

Limitations

• LiveUSB OSes like Ubuntu 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.^[5][6][7]
• Intel-based Macintosh computers have limitations when booting from USB devices – while the Extensible Firmware Interface (EFI) firmware can recognize and boot from USB drives, it can only do this in EFI mode. When the firmware switches to "legacy" BIOS mode, it no longer recognizes USB drives. Non-OS X systems may not be typically booted in EFI mode, notably Windows and Linux, and thus USB booting may be limited to supported hardware and software combinations, which can easily be booted via EFI,^[8] however, programs like Mac Linux USB Loader can alleviate 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 until the user logs off.^[9] 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 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; see persistence (computer science).

Setup

Various applications exist to create live USBs; examples include Rufus, Fedora Live USB Creator, UNetbootin WinToUSB, Win32DiskImager, and YUMI, which works with a variety of distributions. 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) to a large DVD-sized install (4 gigabytes).

To set up a live USB system for commodity PC hardware, the following steps need to be done:

• A USB flash drive 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' 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 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 and 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 systems 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 destitute; 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.

Windows

Although many live USBs rely on booting an open-source operating system such as Linux, it is possible to create live USBs for Windows by using Diskpart or WinToUSB.^[10]

Examples of Live USB operating systems

Bootable Windows To Go USB flash drive

• BeleniX: Customized OpenSolaris installs including live CD and live USB.^[11]
• Debian officially supports a Debian live project providing live images for its stable releases, with a choice of several desktop environments
• Fedora (with Fedora Live USB creator)
• Gentoo Gentoo USB Live
• Haiku: the Installer tool installs the operating system onto a hard disk or a USB Live indifferently.
• Knoppix, one of the first live Linux distributions
• Mac OS X (Intel): The Intel versions of Mac OS X can be booted off any USB file system including (but not limited to) USB flash drives.
• OpenBSD^[12]
• OpenSolaris: The Distribution Constructor project has tools allowing users to build an install image.
• OS-9 RTOS: The standard OS-9 Configuration Wizard for X86 creates bootable USB sticks. OS-9 5.0 for X86 will support the creation of bootable CDs.
• OSx86: some "hacked" Mac OS X images can be written to a USB flash drive and turn it into a bootable Mac OS X system.
• Pardus: by usb creator tools
• Puredyne: live CD/DVD/USB distribution for media artists and designers.
• PCLinuxOS: Version 2009.1 comes with a live USB creator tool, version 2008 "MiniMe" can be installed manually.^[13]
• Puppy Linux: Designed for easy install on USB. The Quirky 6.2 image even runs off F2FS storage.^[14]
• Sugar: Sugar on a Stick is a Live USB for children and learning.
• Tails: The Amnesic Incognito Live System, using Tor anonymisation, based on Debian
• Ubuntu Desktop (install media): can be running live-session from a USB drive, including programs, settings and documents.
• Windows To Go: Windows 8 feature that will allow the entire system to run from a USB drive, including programs, settings and documents
• Windows Preinstallation Environment: Freely available version of a live Windows installation, command-line only.

Comparison

Syslinux is a common program to make a bootable USB storage device.

See also

External links

Wikimedia Commons has media related to Live USB.

Wikibooks has a book on the topic of: Live distro and Full Linux Install

• The Differences Between Persistent Live USB and Full Linux Install on USB
• Universal USB Installer
• Partitionless Installation
• 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
• Casper

References