What the hell is a bootable ISO and a bootable USB-stick?
 

Hello forum,

maybe this will be a thread that will be read by many people in the future to definitely clear something up, something important occurring all the times for a million users. I have read through a hundred forums, through thousand of postings, all describing methods that too often just do not work.

Since 7 days I try to evaluate many Linux-distributions that I "burn" onto a USB-stick and which I downloaded from their homepages as .iso-files.

Sometimes it works, i.e., it boots from USB and I can go on to install the distro. More often it does not work (I get a message "Disk error" on boot or the computer just ignores the USB stick and boots from its hard drive.) And yes, I have enabled "boot from USB" as the first bootable device in the BIOS. I have tried several USB-sticks, each on several computers, the problem appearing everywhere.

Sometimes the old "dd"-way works:

# dd if=distro-blabla.iso of=/dev/sdb

or

# dd if=distro-blabla.iso of=/dev/sdb1

Sometimes it works with specialized programs such as unetbootin or HP-USB-Disk.

Now the questions:

1) What exactly is in an .iso-file and exactly when is it bootable?

2) What is required for the USB stick to boot from?

3) How do I get the .iso onto the USB stick such that I can boot from? What prerequisites does the stick have to fulfill?

4) When do I have to use

# dd if=distro-blabla.iso of=/dev/sdb

and when

# dd if=distro-blabla.iso of=/dev/sdb1

(Please note the "1" at the end to indicate that dd writes to the first partition.) Sometimes it works with /dev/sdb, sometimes with /dev/sdb1, and most of the time with neither of both.

5) What exactly do tools such as unebootin, and with what kind of .iso-files do they work? How can I find out that I have an "unetbootin-compliant" .iso? What do I have to do if it is not compliant?

6) When exactly is an .iso a "live"-ISO that I can burn onto a CD? In this case, can I also burn it onto a USB-Stick?

7) Is there a tool that makes my previous questions obsolete because it works with any .iso?

Please let us work out this thread and I promise to write a thorough, satisfactory tutorial for the millions out there who surely ask themselves the same questions as I do (how can it be that I find hundreds of tutorials?).

Greetings from Germany!
Duplex

Welcome to the forums!

I agree there are a lot of bad tutorials out there on the web, and it can be confusing knowing which ones to trust.

When in doubt I recommend you use tutorials from your distro's own website (as opposed to some random guy's blog).

For example if you are using Ubuntu: https://help.ubuntu.com/community/In...n/FromUSBStick
if you are using Fedora: http://fedoraproject.org/wiki/How_to...d_use_Live_USB

and so on.

First we must clear something: an iso file is an image of a cdrom file, it normally has an iso9660 filesystem, but some people create iso files of other FSs too.

you don't know if the iso it's booteable until you get it to boot (there are ways to know, but they require more knowledge from the user, so i'm simplificating this thing).
so we get to the point that not every iso file is necessarily an iso 9660 cd image; you need to trust on the advertising of the publisher.
not every iso file can be DD'ed to a pendrive, only those that have explicitly documented that.
normally, every iso file can be written and booted (if they are booteable) to a CD or DVD (depending the size).

in other situation, my experience shows me that the writing an iso to usb boot it's more prone to errors on some systems; this happened to me with my last notebook, it boots from usb with a pendrive of ubuntu that have been written with a special tool but it doesn't boot debian netinst writing the iso to the pendrive with dd; although the very same pendrive boots ok on another system; so i was limited to just burn a CD and install from it.

i'll suggest you that on every distribution you choose to test, read the documentation before trying your methods because there can be some caveats documented there.

i don't know of any "one method to rule'em all" in instalattion of any OS (not just Linux Distributions) other than "Read The Installation Manual before even download"

best regards

Thank you, snowpine and cpasqualini, to answer you both:

- Many more exotic distros such as eeebuntu have no installation instructions at all (at least I could not find any).
- Many distros such as Easypeasy have instructions the just do not work (at least for my hardware).

What to do?

Duplex

Lets start off with the basics.

ISO (International Organization for Standardization) is an organization that creates standards so that for example a CD that is burned in the US can be read by read by a computer/CDROM drive built in France. The CDROM standard for how data is written is ISO9660 which is the reason the filesystem designation for mounting a CD is iso9660. An ISO file is a binary file image of the CD and depending on how the CD was created it may or may not be bootable.

Flash drive file images are a binary file of a hard drive or partition and typically use an img file extension. A flash drive is no different then a hard drive i.e. it has a partition table and master boot record etc. CDs and regular drives boot differently which is why you can not just copy an ISO file to the flash drive and the reason you need a tool like UNetbootin.

These days the iso extension is used for any type of image which can be confusing.

Yumi has a very good, built in list, of distros that are actually bootable off of a USB stick, and allows you to download and install them -- even going so far as to install multiple distros.

I have a flash-drive with about 30 distros that works fine. (Mostly fix-it and pentest distros, e.g -- backtrack, gparted, system rescue, etc..)

I have not had any failures to boot using this method of installation. But, without it, I had run into plenty of distros that were not USB friendly, such as Scientific Linux and the Dell Firmware Updating thing which seemed to be Centos.

Good luck

eeebuntu is abandonware their last release was 3 years ago and the project is dead!

EasyPeasy has instructions to make the USB stick right here (although that project isn't showing much signs of life either): http://www.geteasypeasy.com/get-easypeasy/

If a distribution is abandoned and has old/poor documentation then maybe you shouldn't use it? Stick to one of the major distros like Ubuntu/Mint/Fedora/Slackware and you will get good documentation and an active community. :)

And exactly these instructions do not work for me. I have tried it 10 times.

Yes, you're right of course. I was searching for a minimal distribution to install on an old Asus Eee 701 with 4GB of (disk) memory, where the most important desktop programs work out-of-the-box. That is the reason why i try out so many different distros.

I recommend you give Debian a try, with LXDE or Xfce desktop. Those old 701's are getting pretty dated, though.

I've followed your advices and worked with Yumi and the Debian-LXDE-Live-CD - and I now have a bootable USB-Stick!

BUT: When I start the Live-USB on my old Asus 701 and it comes to the point where the desktop is started and you see the icon "Desktop Installer" and I click on this icon, nothing happens. I've looked for what is behind this icon; it's a program called something like sudo-blabla-install. When I start it from a terminal, I see the error message "no initrd found", and I think this is because the 701 has only 4 GB of hard disk space. The normal Ubuntu-XFCE-CD even refused to install from the beginning because it wanted to have at least 4,7 GB of hard disk space.

That's why I went to EasyPeasy, which I successfully installed on the 701, then having 700 MB left on the drive :-) BTW, EasyPeasy is not as dead as you think. 2.0Alpha has been released in May. What I have to do is to evaluate this list:

http://en.wikipedia.org/wiki/Compari...ons#Comparison

But I am drifting away from the actual subject of this thread. Is it solved now with the hint to go for Yumi? I can hardly believe that.

Greetings from Germany,
Duplex

Always test your downloads with md5 or shal.

Just a note to the above posts on what an iso is. It is true that most distro's offer a bootable iso image. That doesn't mean it is a "live" bootable image rather an installer of some kind.

The newer way to create an iso image is by what they term a hybrid iso. Only those types are able to use dd to a real hard drive/usb drive. The creators of them need to do some special things to allow it to be used as a real hard drive. (to most linux, a usb is any real hard drive)

You may wish to consider a virtual machine for this testing.

If I have a hybrid image, do I have to use dd as

# dd if=blabla.iso of=/dev/sdb1

or

# dd if=blabla.iso of=/dev/sdb ?

How do I setup a virtual machine (what programs are good for)? I have a well-kept notebook with Windows XP and Debian on it. I guess that I just have to run the appropriate program to run a virtual machine.

Duplex

I'm very hazy on the details but ...

For a USB Flash Drive to be bootable it needs the same as a HDD does, that is something for the BIOS to load from the first 512 bytes (a master boot record, MBR) which can load a more capable boot loader which can (directly or indirectly) load an operating system.

In the case of .iso files which, when copied by dd to a UFD, create a bootable UFD, the start of the ISO 9660 image must be such an MBR.

ISO 9660 allows for this. From Wikipedia: "The first 32768 bytes of the disk are unused by ISO 9660 data structure, and therefore available for other use".

You dd to a device not a partition so (be sure of the device) it would be sda.

Actually I'd think of it as sdb or sdc but on a live cd boot it may be sda.

When I first installed BrowserLinux 501 it was from an .iso file, but I could use the same file with UNetBootin to install it on a bootable USB stick, or use my Windows Sonic DigitalMedia Plus software to burn the exact same .iso file to a CD and they both boot and work fine. From reading the explanations above I don't see how that could be?

When asking for help on a specific problem, it's important to give more details than does not work.

Adam