Live USB

A live USB or USB live distro is a USB flash drive or an external hard disk drive containing a full operating system which can be booted. Live USBs are closely related to live CDs, and are sometimes used interchangeably. Like live CDs, live USBs can be used in embedded systems system administration, data recovery, or the testing of operating system distributions without committing to a permanent installation on the local hard disk drive. Many operating systems including Microsoft Windows XP Embedded and many of the Linux distributions and BSDs can also be used from a USB flash drive.

Benefits and limitations

Live USBs share many of the benefits and limitations of live CDs.

Live USB distros can be run from the portable flash device in the same fashion (but much faster) than it would from the live CD. One important advantage over live CDs is the ability to conveniently change the data contained on the booting device. This allows for live USBs to be used as personal storage, as it allows a user to carry their preferred operating system, applications, and configuration as well as 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 the user 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, usually it is easy for an USB device to get 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 for faster seek time than is possible with 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 a computer lacking USB 2.0 support can be very slow.

Some computers, particularly older ones, may not have a BIOS that supports USB booting. In this case a computer can often be "redirected" to boot from a USB device through use of a bootable CD or floppy disk. [http://www.pendrivelinux.com/2007/11/21/use-a-floppy-to-boot-usb-pendrive-linux/ boot floppy for live USB]

Due to the additional read/write cycles that occur on a full blown install, the life of the flash drive may be slightly reduced.

Principle of installation

Various applications exist to create live USBs; examples include the Fedora Live USB Creator and UNetbootin, which works with a variety of distributions.

To install a live USB system on a memory stick 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
* A 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 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

In addition, on some Live distros, extra applications can be installed, and a persistent file system can be used to store changes.

History

*Proposed by IBM in 2004, in the papers "Reincarnating PCs with Portable SoulPads" ( [http://domino.watson.ibm.com/library/cyberdig.nsf/papers/577BB6B4F4A4BB7185256FF0004E578A/ PDF] & [http://www.research.ibm.com/WearableComputing/SoulPad/soulpad.html Summary] ) and [http://www-128.ibm.com/developerworks/linux/library/l-fireboot.html Boot Linux from a FireWire device]

Types of live USB

Live CD derived

The first type of live USB was created by simply taking the ISO image file from a live CD distribution and placing it on USB storage device and then making it bootable.

Sh (for linux) & bat (for windows) are scripts that make a usb storage device bootable (they are often used after extracting files to the formatted media)

See also

* Extensible Firmware Interface
* extlinux
* Live Distro
* Comparison of Linux Live Distros
* Disk cloning
* List of Live Distros
* Persistence (computer science)
* List of tools to create Live USB systems

External links

* [http://www.pendrivelinux.com/ pendrivelinux]

References