Booting Linux from a USB-Pendrive

hertog

The 'Why'

Ever been in the situation where you wanted to flash your BIOS only to find out you ran all out of (working) floppy's, or you didn't have a windows bootdisk at hand, or even worse, you didn't have a (working) floppy drive?

Been there, done that, got the T-Shirt.

The (perceived) Solution

With the falling prices of the so called usb-pendrives and computers being able to boot from media connected to the machine via USB this problem is solved. At least, that is how simple I thought it would be.

Guess again.

The 'Bears on the road'

There seem to be no 'solid' standard as to how bios-makers implement this boot from USB-feature, so this might not work entirely as described, but with the hardware I have, things work. I can now boot a Windows 98SE bootdisk, a wide range of kernels and (but that's in the future) a whole linux system, all from my USB-stick.

The Lab
My hardware is as follows:
Epox EP-8RDA+ motherboard, this one is equipped with an Award bios (so maybe all systems with Award-biosses might operate in this manner)
A 512 MB USB Pendrive, which is detected by lsusb as a Apacer (this might be overkill, but as said, I want to do a full linux install on it)

In the BIOS I have enabled the support for USB-keyboards and USB-Mice (last one is also known as extended compatibility)
Boot-drive order is (first) set to USB-HDD, it also might work when set to USB-Floppy or USB-Zip.
So far the description of hardware. On to so more dry theory

Some dry theory

To be able to boot from a pendrive the partition that you are booting from (on the pendrive) needs to be FAT16. Since the bios has no knowledge about ext[2|3]/ntfs/filesystem-du-jour it MUST be FAT16.
This is not too bad, since you can put the bootdist of (e.g.) Win98SE in there, which might come in handy when you need to flash your bios (and as an added bonus, it gives the option to load the cd-drives for MS-DOS, you never know what that might be useful for).

The 'real' solution

So, enough theory, real work.

Plugin your USB-pendrive (I skip the kernel-configuration part, there are other howto's that describe what options need to be set for the kernel, see https://forums.gentoo.org/viewtopic.php?t=53537).
It probably get's detected as /dev/sda, you can always check dmesg for that.

taskara · Posted: Mon Feb 02, 2004 1:40 pm Post subject:

Hi,

thanks for your guide

I'm trying to get my usb pen drive to be /boot for my raid 0 array.

I have installed grub to the pen drive (sdc1), which is (hd2,0)

it has a 30mb bootable partition, which I mounted as /boot throughout my gentoo install

I emerged grub, and ran it with

Starkiller · n00b Joined: 22 Dec 2002 Posts: 4

I know from experiance that not all USB pendrives are bootable.
the two that I have , a dell braned 64mb drive, and a lexar jumpdrive something....

Anyway both are made by lexar, but only the lexar jumpdrive will boot.
I called them up and emailed them about it, and they simply said that some can some cant...(boot that is)

taskara · Posted: Thu Feb 05, 2004 10:45 pm Post subject:

raghu1111 · n00b Joined: 01 Mar 2004 Posts: 1

hertog,

Great explanation. I used it to get my cf card to boot.

I have one correction to grub.conf.

When we chain load XP from the first harddisk, we should 'map' hd1 to hd0 so that when XP boot loader is loaded, its hd0 points to the hard disk.

So the XP section above should be:

Gav · n00b Joined: 10 Oct 2002 Posts: 65 Location: Surrey, UK

I'm thinking about doing something like this...

Although rather than having a hard drive in the machine, use either the flash drive as /, or preferably mount a share on my server dedicated to this PC. Any thoughts?

I've only ever booted linux from a hard drive (and never used USB), so it'll be new teritory for me. I do have a spare 64MB Memory Stick that can be used without incurring extra costs, and a few spare hard drvives to get a working install while I try. Time isn't on my side, so I don't expect to get this up and running for a few weeks.

I could use network boot like foldings farms use, but it seems hard to do for just 1 PC.

nevynxxx · Posted: Tue Mar 09, 2004 3:46 pm Post subject:

@Gav If I remember correctly there are some distors availible that are aimed at firewalls that are specifically diskless, if you mount from a read only floppy its a little hard for an intruder to tamper with stuff. Looking at those and knoppix should be a good place to start
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satimis · Guru Joined: 21 Oct 2003 Posts: 365

Hi folks,

I have been searching around for solution to make BIOS detect and boot a pendrive using Grub bootloader.

The story is as follow;

I tried copying the OS running on HD on a pendrive having 2 partitions. /boot was copied to /dev/sda1 running on FAT16 and the rest copied to /dev/sda2 running on ext2.

The motherboard can boot
-USB-FDD
-USB-HDD
-USB-ZIP
-SCSI
etc.

On booting the PC, the BIOS did not detect the pendrive.

I have no problem using syslinux bootloader to boot the pendrive then Linux distro running on it.

This is an experience to test whether a pendrive can be used as HD and whether Grub bootloader can used to boot a pendrive instead of syslinux.

Advice would be appreciated. TIA

B.R.
satimis

NeddySeagoon · Posted: Sun Mar 19, 2006 3:28 pm Post subject:

Hi guys,

This is no more than a few loose rocks in the pool.

1. The BIOS has no concept of filesystems at all. It reads raw disk blocks to locations in memory.
2. USB Pen drives come in two sorts, those that look like a floppy (with no partition table) and those that look like a HDD, with a partition table.
You may be able to swap them backwards and forwards, I only have the latter.

Much of the work here has been done before - Google flash linux Its Gentoo on a stick.
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rlittle · Apprentice Joined: 17 Dec 2003 Posts: 200

I thought of the same thing after I got a 1GB USB key, and I could not figure out how to but a bootable kernel on it, so I took the "easy" way out. I partitioned the USB key (just with fdisk) into 3 pieces something like:

slice 0: 255MB of free space (later formated to FAT32 for easy of portability)
slice 1: 717MB for bootable .iso image
slice 2: 15MB for /boot partition (just like in a normal Gentoo install)

I used dd to put the iso image into slice 1, and then I installed grub into slice2 (that was a little tricky, but nothing major. Just read the man page 10 times.

) I used the Knoppix live CD, (Gentoo Live CD wasn't out yet) and here's what my grub.conf file looked like to get Knoppix to work:

satimis · Guru Joined: 21 Oct 2003 Posts: 365

Hi rlittle,

Tks for your advice.

I'm on the same situration as yours, having a new 1G USB key bought recently. I want to make it as a HD with grub bootloader, booting on any 586 and/or above PC.

satimis · Guru Joined: 21 Oct 2003 Posts: 365

Hi NeddySeagoon,

satimis · Guru Joined: 21 Oct 2003 Posts: 365

Hi rlittle,

Further to my last posting, I made following test at WORK solely checking whether the bootable partition of the pendrive can be detected. On my WORK there was only a DSL on a partition to carry out this test.

Now I have 3 slices on the pendrive (1G)

# fdisk -l /dev/sda

satimis · Guru Joined: 21 Oct 2003 Posts: 365

Hi NeddySeagoon,

I got Flash Linux version 0.34, the latest release, download and burned on CD, playing it for about 2 hours. It is based on Gentoo with Gnome desktop but too slow. I can't setup broadband connection. "pppoe-setup" did not work. Neither I can find the setup process on desktop menu. The version is a little bid out of date, released on Feb, 2005.

I don't know what wil happen if burning it on pendrive. The discusion forum is not very active.

B.R.
satimis

rlittle · Apprentice Joined: 17 Dec 2003 Posts: 200

Sorry for being away so long.

Satimis! I think the main thing about about my method that you missed was that I took an already bootable iso image (it was around 700MB) and used dd to direct-dump it into slice 1 (/dev/sda2). dd-ing an already installed partition is not the same thing. Normally this trick wouldn't work at all, except that newer GRUB understands the iso filesystem and can read its contents.

Then, I configured the grub info in /dev/sda3,I pointed it at the kernel in /dev/sda2 (which is ONLY visible if you mount the iso image. Once you have used "dd" to put it on /dev/sda2, you can just mount /dev/sda2 to view the contents of your "boot disk").

Lastly, I ran grub-install which writes data to the Master Boot Record which is the first 1024(?) bytes on the device and is not visible as a "slice". It is before slice 0(/dev/sda1). When you try to boot from your USB key, your BIOS thinks your USB key is a SCSI drive and reads the MBR. The MBR will point to /dev/sda3 which has just enough brains to read the kernel INSIDE THE ISO IMAGE on /dev/sda2.

Ouch. I think I remembered this better a week ago. I've lost a few brain cells since then, if you know what I mean. :lol:

To be honest, I can't remember the details for setting up GRUB, I just remeber having to keep a Live CD handy after I re-wrote the MBR on the wrong disk...

I know I didn't answer any questions directly, but I hope that clears up my other message a bit.
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satimis · Guru Joined: 21 Oct 2003 Posts: 365

Hi rlittle,

Tks for your advice.

rlittle · Apprentice Joined: 17 Dec 2003 Posts: 200

I'm at work right now so I can't poke around with Grub, but I think you have that correct. A few points.

- Yes, I just leave slice0 (/dev/sda1) blank. When I had completed all this, I formatted (mkfs -t vfat ) it with Win FAT32. That way I could use it on almost any system (M$ or Linux). The reason I did it is because some systems couldn't see anything besides the first parition, so if I wanted it to be useful, I had to put it first. The bootable stuff I could but anywhere.

- The MBR is always onthe beginning of the disk, not the partition. The MBR you write will POINT to /dev/sda3 where the configuration info that GRUB needs is stored (the first 1024 bytes of the disk is just not big enough). Once it reads the config info in /dev/sda3, it learnes enough to be able to read the kernel etc.. in /dev/sda2. You never actually "see" the MBR at any time. It is basically hidden unless the system is trying to boot from it.

In that snip of gub-kernel-boot stuff vga=79 should have 3 digits.
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satimis · Guru Joined: 21 Oct 2003 Posts: 365

Hi rlittle,

I have following points expected to clarify;

1. size of slice2 - 15M
Would it be suffient for installing grub?

2. Which slice needed to be tagged otherwise the BIOS can't find the pendrive? Slice2 ??? Then I need a boot floppy to boot the PC first which is not my target on this test. I don't expect to have a boot floppy.

3. About Gentoo Live CD.
On its officical sites I found;
livecd-i686-installer-2006.9.iso

I think this is an installer not the LIVE CD which can be booted and played on CDRom like Knoppix LiveCD.

Please advise. TIA

B.R.
satimis

rlittle · Apprentice Joined: 17 Dec 2003 Posts: 200

1. Not only is 15MB enough space, it's waaaay overkill space. The contents of my grub directory total up to 438KB which is all you will need. I guess I was being overcautios when I made mine 15MB. I'd recommend you only make it 1MB or 2MB. (hindsight is 20/20 as they say...)

2. I'm not sure if I understand Q #2 so I'll shotgun it:

-when the BIOS goes looking at the USB ports for something to boot, it will find your pendrive. When it does, it will look at Sector 0 (i.e. the Master Boot Record, which is not on any slice at all, it's at Sector 0 which is before all the slices). When it reads the MBR, the information put there when you ran "grub-install will tell grub to jump to /dev/sda3 and look for the grub-directory. When it finds that, it learns how to understand .iso filesystems and reads the kernel in the iso image in /dev/sda2 (grub.conf tells it /dev/sda2 and the kernel location).

Therefore, there is no need for a boot floppy, all the booting is done off the USB pendrive.

- if your question has anything to do with the "empty" /dev/sda1, the first time I set this up, I had my "empty space" in /dev/sda3. I found that when I plugged it into my Windoze machine, it couldn't find it. So I blew everything away and re-did it all, but put the "empty space" in /dev/sda1. Then my Windoze machine could find it etc.

I think that when you run grub-install, (with the proper flags, switches, etc), it writes the grub files (e2fs_stage1_5, stage2_eltorito, grub.conf.sample etc etc) to the partition you specify (/dev/sda3 in our case) and the updates the MBR with the info to go look in /dev/sda3 when booting.

One last thing. I finally went and re-read "man grub-install". If I remember right, I think I mount /dev/sda3 to a directory, then pointed grub-install at it:

satimis · Guru Joined: 21 Oct 2003 Posts: 365

Hi rlittle,

rlittle · Apprentice Joined: 17 Dec 2003 Posts: 200

Here is the output of "fdisk" on my USB key/pendrive (it shows as sdc becuase this machine has actual SCSI drives!) :

a1exus · n00b Joined: 25 Jan 2007 Posts: 9 Location: Brooklyn, NY

what about if you run that pen drive on few different scenarios

1) with IDE and no SATA or SCSI
2) with IDE and with SATA drives
3) with IDE and with SCSI drives

how would pendrive where to get root from?