Create an Emergency OS for Your Computer on a USB Flash Drive

Having an emergency operating system on a keychain during moments when a computer crashes is an absolute life-saver. It makes it possible for you to still work with with files that normally wouldn't be accessible, and do things that would normally be impossible to do without a working OS. Best of all, you can do these things even without a working hard drive or cd-rom drive attached to your computer. You just need a bootable USB flash drive.

Although I could write an extensive article on how to create a bootable flash drive manually, I'm rather overjoyed at the fact that none of that will be necessary. Instead, you will be able to have a bootable linux OS in no more than an hour after you read this article. All it takes is one powerful program and a broadband internet connection. If you already have a linux or other OS that you wish to use as an ISO file, then you can create a bootable flash drive for it in about 10 minutes or less.

This should cover most versions of linux, a few versions of DOS, and some miscellaneous operating systems between. It won't cover the creation of Windows XP or other versions of Windows on a flash drive, due to the fact that Microsoft deliberately changed the way the installer works from a CD. Microsoft made it to where they limit XP, Vista, and Windows 7 to have usb devices work as an input device structure during OS installation rather than a block storage device. This CAN be modified by extracting out the USBSTOR_IN files from an XP or Vista installer, modifying them, and then adding them back to your ISO file...but that is beyond the scope of this article at present. Therefore, we're going to stick to the quick and easy method of bootable usb flash drives using the wonderful program called UNetBootIn. At the end of this article there is a pleasant surprise for people wanting Windows, though!

UNetBootIn (Universal Net-Boot Installer) is a free-source program available for several platforms which takes care of all the complexities and legwork of creating bootable USB flash drives from any predefined ISO file. It even lets you download a recent version of linux from the net and install it automatically with just the click of a button!

Here's how to do it:

Step 1: Plug in a usb flash drive you want to make bootable. If you have any data on it that you want to save, you should copy all of it off to a folder on your desktop or to another flash drive before continuing. Once the data is safely copied to another place, you can format the flash drive and prepare it for use.

Step 2: Download and run the UNetBootIn program. You can download it for Windows, Linux, or Mac OS X here: http://unetbootin.sourceforge.net/

Step 3: Please remove ALL other SD cards, MMC cards, usb flash drives, and any usb external hard drives you have connected to the system. Although you can select which drive you want exactly, for the sake of this article and such a vast user base, I want to ensure that the only flash drive connected to your system is the one that you intend to make bootable. Most of you already know this and know better, but I want to be extra cautious with anyone who might be new and eliminate any possibility for errors or mistakes as much as possible.

Step 4: After you have removed any and all other flash drives, usb cards, or sd-card memory that may be connected to your system, you can run the program. When the program starts, it will give you the option to create a bootable flash drive from a CD image (ISO file) or by downloading a setup image transparently from the net and installing it automatically. There is a radio button to the left of the selections that will let you choose which of the two methods you can do. For this article, we will assume that you have a good internet connection and want to download the latest distribution copy of a linux OS to install and create a bootable flash drive with.

Step 5: There are two drop-down menus at the top of this program. Select the type of Linux or other OS you want to download from the left box where it says "Distribution", and then select the version of it that you want from the menu next to it on the right. If there isn't a specific reason or need to have an older OS version, it's usually best to choose the most updated one on the list.

Step 5: At the bottom of the program window are a few extra options. By default, this program helps protect you from accidentally writing to any non-flash drives, such as the main hard drive on your computer. We want to keep it that way! Unless you are an experienced user and you know exactly what you are doing, please leave the box to show all drives unchecked. Directly under this, there is a box that that has which usb drive(s) UNetBootIn can install to, and has a selection box that you can use if you do have more than one usb flash drive connected to your system. Since we removed all flash and other drives from the system before running this program, the only available flash drive on this selection box should be the one that you plugged in and want to use with this program.

Step 6: You're ready to make your bootable usb. Just click the OK button! If all goes well, a progress bar will appear for the download of a linux image and then another for the installation of that image onto the usb drive. Once completed, the program will ask you to reboot the computer to test the usb drive. If you don't want to reboot now, you can just tell it no and boot from the drive when you restart your computer.

You're done! However, I wanted to share a few other important things in conclusion about booting off of usb devices:

There is usually a boot order pre-configured for every computer by the BIOS. Generally the order is to either boot off of your optical drive (cd-rom) or off of your hard drive first and not a usb flash or external drive. Although you can change this, it is safer to just use the bios hotkey that lets you boot from another device when you first start your computer. Before your operating system loads, you will see a logo or hardware test screen along with a quick message at the bottom of keys you can press, such as F10, F11, F2, etc. Look for the one that says "Boot Menu" or "Alternate Boot", "One time boot menu", or something similar and press the function key (i.e: F10 key) on your keyboard that is associated with that. You should get a quick text menu that shows you the bootable devices on your system, and lets you use the arrow keys on your keyboard to select which one you want to boot from. If your usb drive is plugged in when you power on your computer and press the function key to boot from another drive, you will be able to boot from the usb drive. If you plug the usb drive in after you hit that key, it won't appear on the menu due to the fact that the usb device (and all other storage devices) are pre-initialized when you first power on the computer before it loads anything from the drives. So if you want to be able to boot from it, make sure it is physically connected either before you restart your computer or before you power it on.

If you get the message "Boot Error", which may appear on some BIOS default setups, then you will have to change the way that usb and flash drives are booted from under the BIOS. The best way to fix this is to find the setting that asks how to see USB drives, and tell it to see and handle them by "Size", rather than block type or anything else. Unless you have an extremely large flash drive greater than 32GB, this will fix that error if it ever appears and ensure that your flash drive is bootable.

After you have made a usb flash drive bootable, if you have free space on the flash drive still (and usually you will), you can copy the contents that you copied off to another flash drive or elsewhere on your computer back to your flash drive safely. I strongly suggest that you create a separate folder for all of your data that you copy back though, just to make sure that none of the file names or directories from your old data conflict with the OS data we created on the flash drive to make it bootable.

One final note: Only systems after 2004 by majority include a standard system BIOS capable of booting successfully off of USB flash drives. There are a few older ones from 2003 that can, but not many. If your computer was manufactured after 2006, you will be fine. Otherwise, it may be difficult or impossible to boot from it even if you create one and your system bios is prior to 2004. Again, this isn't a problem for anyone whose computer is newer than 2005-2006, but may be an issue for just a few people who may be running older systems. If you are on an older system, the best way to fix this is to either update your bios, OR get a pci add-in card for usb 2.0 or usb 3.0 that should have a bios update disk and any system drivers you need to enable the pci card to perform a passthrough on the bios and boot your flash drive.

You can in some cases use UNetBootIn to create bootable flash drives on older systems using USB 1.1 connections...but I don't recommend it. Although I've been able to create a complete Ubuntu 10 installer on a flash drive and use it to set up a few systems, I had an issue with trying to do the same thing again on another flash drive from the same system while running just one small program in the background. Because USB 1.1 is so much slower than USB 2.0, it may not be able to keep up with what it needs to when installing the bootloader and data to a usb flash drive. As such, I recommend only using USB 2.0 or higher with UNetBootIn for a successful install without any worries.