The problem#

Last week, I talked about making bootable flash drives, but didn't go in depth about why you might want to do so.

The solution#

Bootable flash drives have a lot of different uses. The most common ones are simply dealing with an operating system that fails to boot or installing an operating system on a computer that doesn't have one. But there's also some cases where it's useful to not be using the main OS even if it is functional.

The details#

Diagnostics#

Certain diagnostics can't be run easily while an operating system is running. Memtest86+ is the most common one you'll want, which tries to have as small a memory footprint as possible so its tests can cover as much of your memory as possible. But it can also, for instance, be difficult to benchmark the performance of the drive your operating system is running off of while it's running. And if you're worried there's something wrong with that drive, you'll want to boot off something else to be using it as little as possible, which brings us to the next category.

Recovery#

If your operating system isn't working for software-related reasons, a bootable flash drive can provide you with a backup OS you can use to either fix the problem or at least get access to your data.

On Linux, you can use chroot after mounting your drives appropriately to get an environment that looks a lot like running the OS normally. This effectively lets you skip the normal boot process, so it can be useful to use your distribution's package manager tools to fix a broken boot setup which would normally prevent you from accessing those tools.

A notable special case is a forgotten password. Any bootable Linux will have passwd which you can use to change passwords. Hiren's BootCD includes tools to change Windows passwords or you can use chntpw. Of course, if the drive is encrypted, you'll only be able to modify it if you have the encryption key. And even if the password file is not encrypted, if you have any encryption system that uses the user's password to encrypt files, those files will be lost if you change the password.

Backups#

While the OS is working, you may want to make a complete backup of the disk it is installed on. Generally, while the computer is running, it will be writing to the drive it's running off of, so the simplest way to make a backup is to be running the OS. That generally means booting off a different device like a flash drive or somehow connecting the drive to a different computer (generally easiest with an external enclosure).

Portable OS/apps#

Some bootable Linux distros support "persistence": that is, your files and other changes will be saved to the flash drive and stick around for the next boot. Which might not even be on the same computer. That means you could, instead of carrying around a computer, carry around a flash drive and use it to boot whatever computer you have access to. Although, realistically, most places you find public computers might not be too happy with you booting them into a different OS.

Tails is a security-focused Linux distro intended for running off a flash drive with optional support for persistence. For a more generic Linux experience, the list of distros supported by YUMI includes notations of which ones support persistence.

A more lightweight version of this which doesn't require a bootable flash drive is portable applications where instead of an entire OS, the flash drive just has a few programs set up to save their settings and files back to the flash drive. Of course, the portable application could be virtual machine software, letting you run your own OS without booting into it.