The current stable version of DoudouLinux, Gondwana 1.x, requires to download a different file if you want to burn a CD or to write an USB key. Since Grub2 is now able to boot the kernel image that is contained into an ISO file, it is possible to boot a Live ISO written onto an USB key and then to only use the ISO file whatever the target support. This is of course very practical but doesn't work on Debian Squeeze Live images without a dedicated patch called findiso. We have included this patch in the latest development release, 2013-02, that will be turned into the next stable release Hyperborea 2.0 around April/May. Doing so provides several advantages:

  • Only one file to be downloaded, per language.
  • Easy system update on the USB key: just replace the ISO file with the newer one! (and update Grub parameters)
  • A single FAT partition can be preserved on the USB key, allowing the normal use of an USB key, especially on capricious systems that can only read FAT :p (do you really keep using these old-fashion systems???).
  • Ability to have several flavors of DoudouLinux on the same key, for example the stable release and the development one, or several languages.
  • Does not require to reformat the USB key and then should lead to better R/W access performances by preserving factory settings.

Of course it is better for DoudouLinux developers too since we don't need to test the USB image anymore. This also solves the issue we had with isohybrid images that don't run on every computer and also broke our persistence activation tool… So now let's see how to take benefit of this new feature :). Beware: the process to turn an ISO file into an USB live system is done from the command line! Ready?

Installing Grub2

NB: Here we are using Grub2 from a Debian system but, if you don't care about copying the kernel image and its ramdisk onto the USB key too, this should also be possible to use any other bootloader (no test ever achieved though).

You need to have Grub2 installed in your system. If not, install the corresponding package. A particularity of Grub2 is that it doesn't fit anymore on the very small 512 first bytes of a disk. It has then 2 alternatives:

  • If the first partition starts at the cylinder number 1 instead of number 0, there may be enough space after the first 512 bytes for Grub to copy all its files. As they are outside any partition, they should be preserved from any modification.
  • If there is not enough space before the first partition, Grub uses sectors in the first partition and records their position in the first 512 bytes. Of course the file system in the first partition may move these sectors without Grub knowing, this is then not 100% reliable.

If you are in the second situation and want to change to the first one, you have no other choice but reformatiing your USB disk. Grub displays a message during its installation when you are in the second situation.

So now let's install grub onto the USB key. We need to mount it and launch the Grub installation command:

$ sudo mount /dev/sdx1 /mnt/
$ sudo grub-install --force --no-floppy --root-directory=/mnt/ /dev/sdx

That's it! Take care of replacing the USB device path /dev/sdx by the actual path of your key ;).

Making the USB key bootable

(update of 2013/02/21)

Your USB key will probably not boot if you don't set its partition as active, the so-called boot flag. This operation can be quickly achieved with fdisk. First start fdisk onto your USB key:

$ sudo fdisk /dev/sdx

You should get a prompt. Type p to display information about your disk partitions:

Command (m for help): p

Disk /dev/sdh: 2 GB, 2070216704 bytes
64 heads, 62 sectors/track, 1019 cylinders
Units = cylinders of 3968 * 512 = 2031616 bytes

   Device Boot      Start         End      Blocks   Id  System 
/dev/sdh1               1        1019     2021665    b  FAT32
Command (m for help): 

As you can see, the boot flag (second column of the partition information table) is not set since there is no * sign in this column. So in the fdisk prompt, type a to activate the partition. fdisk will ask you to enter the partition number (ie. 1). You then just need to write the partition table by pressing w:

Command (m for help): a                                                   
Partition number (1-1): 1                                                 
Command (m for help): w                                                   

Copying files

You can now copy the ISO file – it takes few minutes, the Unicode font and the Grub background image:

$ sudo cp doudoulinux-2013-02-fr.iso /mnt/boot/
$ sudo cp /usr/share/grub/unicode.pf2 /mnt/boot/grub/
$ sudo mkdir /mnt/boot/grub/splash
$ wget http://doudoulinux.org/blog/public/screenshots/install/witch-knight-grub.png
$ sudo mv witch-knight-grub.png /mnt/boot/grub/splash/background.png
$ sudo sync

We have chosen to put all the files into the /boot directory that Grub made, but you can choose any other directory on your USB key. The Unicode font is required if you want translated messages in the Grub splash screen. So now everything is ready to get DoudouLinux boot, except that Grub hasn't been configured…

Setting Grub2, quickly

The Grub configuration must be placed in the file “/mnt/boot/grub/grub.cfg” that does not exist yet. A very basic setting of Grub2, to start the ISO, is the following:

set timeout=5
set default=0

menuentry "DoudouLinux testing 2013-02" {
  set isofile=doudoulinux-2013-02-fr.iso
  loopback loop /boot/$isofile

  linux (loop)/live/vmlinuz findiso=boot/$isofile boot=live config locales=fr_FR.UTF-8 keyboard-layouts=fr keyboard-variant=oss keyboard-options=grp:alt_shift_toggle,terminate:ctrl_alt_bksp utc=yes timezone=Europe/Paris nox11autologin quiet splash nomodeset video=uvesafb:mode_option=640x480-16,mtrr=3,scroll=ywrap persistent persistent-subtext=doudoulinux username=tux hostname=doudoulinux
  
  initrd (loop)/live/initrd.img
}

Of course isofile is the name of the ISO you want to boot, change it to fit your needs! In these settings we tell Grub to mount the ISO file so that he can access the kernel image and the ramdisk image file into it. This feature is only needed to launch the kernel with the minimalistic system in the ramdisk. This minimalistic system will then use the boot parameter findiso to find the ISO file and mount it into the final Linux system, DoudouLinux.

If you wonder how we could have written so long a boot parameter line, well, that's just the LiveCD boot line with few arguments removed or added :). To retrieve it, mount the DoudouLinux CD and look in the file “isolinux/live.cfg”. Note that you may have to change the localization parameters of this boot command for your particular use:

  • locales → your language settings
  • keyboard-layouts → your keyboard layout
  • keyboard-variant → your keyboard variant
  • keyboard-options → your keyboard options
  • utc → whether your computer clock is UTC or local time
  • timezone → your timezone

Don't forget to unmount your key:

$ sudo sync
$ sudo umount /mnt/

So now you should have a booting USB key that launches DoudouLinux, except that the Grub screen is not very nice. Let's see how to improve this.

(update of 2013/02/21) NB: once you've launched DoudouLinux on your USB key, you can use its persistence tool to make a persistence file on the USB key so that your DoudouLinux system won't loose user's work :).

Setting Grub2 for real

In the following Grub configuration file we have added:

  • language settings, to get translated Grub messages
  • video modules to show the background image
  • colors and background image
  • classes to the DoudouLinux system entry, in case you want to graphically customize this entry

This is a bit more complicated but the result is as expected: a graphical boot as early as Grub! You now have no reason to not have DoudouLinux everywhere with you since it can also be on your USB stick of everyday use :).

set lang=fr

set timeout=5
set default=0

function load_video {
  insmod vbe
  insmod vga
  insmod video_bochs
  insmod video_cirrus
  insmod png
}

if loadfont /boot/grub/unicode.pf2 ; then
  set gfxmode=640x480
  load_video
  insmod gfxterm
fi
terminal_output gfxterm

set locale_dir=/boot/grub/locale
insmod gettext

if background_image /boot/grub/splash/background.png; then
  set color_normal=black/black
  set color_highlight=black/white
fi

#####################################
menuentry "DoudouLinux testing 2013-02" --class doudoulinux --class gnu-linux --class gnu --class os {
  set isofile=doudoulinux-2013-02-fr.iso
  loopback loop /boot/$isofile

  linux (loop)/live/vmlinuz findiso=boot/$isofile noeject boot=live config locales=fr_FR.UTF-8 keyboard-layouts=fr keyboard-variant=oss keyboard-options=grp:alt_shift_toggle,terminate:ctrl_alt_bksp utc=yes timezone=Europe/Paris nox11autologin quiet splash nomodeset video=uvesafb:mode_option=640x480-16,mtrr=3,scroll=ywrap persistent persistent-subtext=doudoulinux username=tux hostname=doudoulinux
  
  initrd (loop)/live/initrd.img
}
#####################################